Márcio José Silveira
email: s.marciojs@gmail.com

Gabrielle Thiébaut

Effect of density and neighbours on interactions between invasive plants of similar growth form. 1,2

Keywords: non-native species, clonal plants, morphological traits, Hydrocharitaceae

Effect of density and neighbours on interactions between invasive plants of similar growth form

Marcio Jose Silveira, Gabrielle

Introduction

Invasive aquatic plants constitute a major problem in many freshwater systems [START_REF] Dugdale | Survival of a submerged aquatic weed (Egeria densa) during lake drawdown within mounds of stranded vegetation[END_REF], being able to affect both biodiversity and ecosystem functioning [START_REF] Clayton | Aquatic plants as environmental indicators of ecological condition in New Zealand lakes[END_REF].

Although many studies have addressed the potential threats of invasion of aquatic ecosystems by exotic species (Spencer and Rejmanek 1989;Rahel and Olden 2008), few studies have considered the interactions (competition, facilitation, coexistence) between exotic aquatic plants with a similar growth form in invaded communities [START_REF] Barrat-Segretain | Experiments on growth interactions between two invasive macrophytes species[END_REF][START_REF] Mony | Competition between two invasive Hydrocharitaceae (Hydrilla verticillata (L.f.) Royle and Egeria densa Planch) as influenced by sediment fertility and season[END_REF][START_REF] Silveira | Abiotic factors, not herbivorous pressure, are primarily responsible for the performance of an invasive aquatic plant[END_REF].

There is some evidence that positive interactions (facilitation) can occur [START_REF] Thomaz | Using space-for-time substitution and time sequence approaches in invasion ecology[END_REF]. Exotic species may facilitate the successful establishment of other exotic species by creating suitable environmental conditions (e.g. increasing nitrogen availability). For example, [START_REF] Santos | Effects of invasive species on plant communities: an example using submersed aquatic plants at the regional scale[END_REF] found that invasion by Myriophyllum spicatum facilitated the spread of Egeria densa in California.

Conversely, competition is widely regarded as one of the most important mechanisms of species invasion and has been shown to play a large role in macrophyte communities [START_REF] Moen | Growth and competition between Potamogeton pectinatus L. and Myriophyllum exalbescens Fern. in experimental ecosystems[END_REF]Mc Creary 1991). This negative interaction is expected to occur mostly between species with a similar growth form and between closely related species, assuming that closely related species share similar niches and traits [START_REF] Violle | Phylogenetic limiting similarity and competitive exclusion[END_REF]. However, only a few studies have focused on the competition between aquatic plant species with such characteristics [START_REF] James | Competition between three submerged macrophytes, Elodea canadensis Michx, Elodea nuttallii (Planch) St John and Lagarosiphon major (Ridl ) Moss[END_REF][START_REF] Barrat-Segretain | Experiments on growth interactions between two invasive macrophytes species[END_REF][START_REF] Mony | Competition between two invasive Hydrocharitaceae (Hydrilla verticillata (L.f.) Royle and Egeria densa Planch) as influenced by sediment fertility and season[END_REF][START_REF] Sousa | Response of native Egeria najas Planch. and invasive Hydrilla verticillata (L.f.) Royle to altered hydroecological regime in a subtropical river[END_REF][START_REF] Gérard | Effect of water column phosphorus reduction on competitive outcome and traits of Ludwigia grandiflora and L. peploides, invasive species in Europe[END_REF]. The occurrence of invasive plant species in high densities may generate competition for resources [START_REF] Ren | The relative generality of plant invasion mechanisms and predicting future invasive plants[END_REF], which can inhibit the growth of other plants [START_REF] Wang | Above-and belowground competition between two submersed macrophytes[END_REF]. Thus, plant density manipulation is one of the main tools to study competition between plant species, as it can modify plant growth by influencing plant nutrient uptake [START_REF] Creed | Intraspecific competition in Fucus serratus germlings: the interaction of light, nutrient and density[END_REF][START_REF] Xie | Density-dependent root morphology and root distribution in the submerged plant Vallisneria natans[END_REF].

Elodea canadensis Michaux, Egeria densa Planchon, and Lagarosiphon major Rid. Moss ex Wager are considered to be the most troublesome submersed species in the world. They belong to the Hydrocharitaceae family and have an elodeid life form. The two submerged species E. densa and L. major form dense monospecific mats in their introduced range, whereas E. canadensis can co-exist with native submerged plants. However, E. densa and L. major can co-occur in freshwater ecosystems, for example, they co-exist in Lake Lacanau, a shallow lake located in the southwest of France [START_REF] Ribaudo | Invasive Aquatic Plants as Ecosystem Engineers in an Oligo-Mesotrophic Shallow Lake[END_REF]. The three species are dioecious clonal plants that mainly disperse vegetatively in their natural habitats, and even small fragments of all three species can establish and develop into new A c c e p t e d M a n u s c r i p t macrophyte beds (Howard-Williams 1994;[START_REF] Riis | Growth and morphology in relation to temperature and light availability during the establishment of three invasive aquatic plant species[END_REF]. Native from North America, only female plants of E. canadensis were introduced outside their native range [START_REF] Cook | A revision of the genus Elodea (Hydrocharitaceae)[END_REF].

Similarly to E. canadensis, E densa and L. major, coming from South-America and South-Africa respectively, were introduced into France, from where they have become widely distributed in many European countries [START_REF] James | Competition between three submerged macrophytes, Elodea canadensis Michx, Elodea nuttallii (Planch) St John and Lagarosiphon major (Ridl ) Moss[END_REF][START_REF] Cook | A revision of the genus Egeria (Hydrocharitaceae)[END_REF][START_REF] Mckee | Effects of simulated climate warming on macrophytes in freshwater microcosm communities[END_REF][START_REF] Silveira | Abiotic factors, not herbivorous pressure, are primarily responsible for the performance of an invasive aquatic plant[END_REF]. Despite their similarities, the distinctive nature of each genus is demonstrated by the fact that Elodea is unable to hybridize with Egeria (Cook and Urmi-Konig 1985). [START_REF] Les | A reappraisal of phylogenetic relationships in the monocotyledon family Hydrocharitaceae (Alismatidae)[END_REF] showed that the genus Lagarosiphon is not closely related to the genera Elodea and Egeria, but they recognized a clade containing Egeria, Elodea and Lagarosiphon at the rank of subfamily. Our aim was to investigate experimentally the effect of density in monospecific cultures and the effect of neighbour identity and plant density on the growth of focal species in mixed cultures during the early growth stage of these invaders. We used E. canadensis, E. densa and L. major as model species to test the following hypotheses: i) the performance of the invaders is reduced at high density both in monocultures and in mixtures; and ii) the presence of plants with a similar growth form may increase competition in mixed cultures.

Materials and methods

Material sampling

More than 280 fragments of each species (E. canadensis, E. densa and L. major) were collected randomly in the spring from three different ponds located in Brittany in western France (Table 1). Ramets, hereafter called "Plants", were derived from a single clone either of E. canadensis, E.densa or L. major.

Water was sampled close to the macrophyte beds where the plants were collected. Samples were kept refrigerated during transport to the laboratory and chemical analyses were carried out within 24h after sampling. Plants were collected from sites with alkaline water and a mean temperature of 15.3°C, with low oxygen content (mean value O2 = 31.5 %) and moderate conductivity (mean value conductivity = 308µS cm -1 ). All species grew in eutrophic waters (see Supplementary Material S1). In the laboratory, the apical shoots of E. canadensis (Ec), E. densa (Ed) and L. major (Lm) were washed to remove invertebrates, algae and debris. Plants were acclimatized for one week at ambient temperature (close to 20°C) in tap water which was slightly basic with a moderate nutrient A c c e p t e d M a n u s c r i p t concentration (mean annual values according to French Water Agency data: conductivity = 400 µS cm -1 ; pH= 8.10; [NO3 -N] = 1.44 mg L -1 ; [NH4 + N] = 0.03 mg L -1 ; [PO4 3-P] = 0.05 mg L -1 ).

Experimental design

Two experiments were conducted. In the first experiment, plants were cultivated as monocultures with two density levels. In the second experiment, the effects of both neighbour identity and density were tested in mixed cultures. The experiments were performed simultaneously.

Monoculture experiment

Each pot (L x W x H): 8cm x 8cm x 15cm was filled with 2 cm of substrate (loam) and 3cm of sand and tap water. Fertile fine-grained sediments, such as loam, contain high levels of organic matter with anaerobic conditions and are suitable for the growth of L. major [START_REF] Martin | Competition between two aquatic macrophytes, Lagarosiphon major (Ridley) Moss (Hydrocharitaceae) and Myriophyllum spicatum Linnaeus (Haloragaceae) as influenced by substrate sediment and nutrients[END_REF] and other macrophyte species. Individuals of each species were prepared by taking an apical shoot of 7 cm length, without buds or lateral stems. These ramets were planted 2 cm apart in the centre of each pot. The distance between ramets was the same for high (4 individuals) and low (2 individuals) densities. Pots were randomly distributed in the growth chamber (photoperiod: 12 h of light/12 h of darkness; light intensity 50% corresponding to 300-500 µmol m -² s -1 ) and at a temperature of 19°C.

Light intensity and temperature were chosen according to the growth optimum of the three invasive species in spring [START_REF] Riis | Growth and morphology in relation to temperature and light availability during the establishment of three invasive aquatic plant species[END_REF][START_REF] Silveira | Impact of climate warming on plant growth varied according to the season[END_REF].

After four weeks, four morphological traits were measured: length of the stem, leaf area, number of lateral shoots and number of roots. To measure leaf area, the surface of one leaf taken at 3 cm from each plant apex was scanned and thereafter measured using Scion Image software. Relative Growth Rate (RGR) and Leaf Area Growth Rate (LAGR) of the macrophytes were calculated using the following equation: RGR = (ln L2-ln L1)/(T2-T1), where L1 and L2 refer to plant length at times T1 and T2 (Barrat-Segretain and Elger 2004). LAGR was calculated using the same equation, where L1 and L2 refer to leaf area surface. LAGR was considered as a proxy of plant Photosynthetic ability (Weraduwage et al. 2015). This experiment also served as the control for calculating Relative Neighbour Effect (RNE) in the mixed culture experiment.

Mixed culture experiment

The same experimental design was applied to the mixed culture experiment. The effects of the experimental conditions were tested by combining different ratios of E. densa, E. canadensis and L.

major individuals for a total density of two or four individuals per pot. Individuals were planted 2 cm Each treatment had five replicates. The pots were placed randomly in the growth chamber under the same conditions as the monoculture experiment.

At the end of the experiment, the same four morphological traits were measured: Relative Growth Rate (RGR), Leaf Area Growth Rate (LAGR), number of lateral shoots and number of roots.

We also measured competition intensity. The relative competitive index (RCI) which compares the performance of a target plant grown in monoculture or mixed with neighbours, is one of the most widely used indices to quantify competition between plant species [START_REF] Wilson | Measuring the components of competition along productivity gradients[END_REF], whereas the Relative Neighbour Effect (RNE, Markham and Chanway 1996) is a a calculation of the neighbour effect relative to the plant with the greatest performance. The RNE is an improvement of the RCI index as it compares the performance of plants growing in monoculture and in the presence of neighbour species [START_REF] Weigelt | Indices of plant competition[END_REF]. The RNE index is symmetric around zero and constrained between +1

(competition) and -1 (facilitation), so it can be used to estimate facilitation interactions. We calculated the RNE index for each trait as follows:

RNE= (P control -P mixture)/x
where P control is the trait of the target species planted in monoculture ( = control) and P mixture is the trait of the same target species in the presence of a neighbour species.

Statistical analyses

To test for the effects of density and species identity on the morphological traits of the plant species in the monoculture experiment, we performed a two-way ANOVA. We applied Tukey's HSD test to test for pairwise differences between treatments. In the mixed culture experiment, to test the effect of neighbour identity, plant density and its interactions on the RNE of each trait and on each morphological trait, we used a two-way ANOVA. Permutation tests avoid the assumption of normality [START_REF] Anderson | Permutation tests for univariate or multivariate analysis of variance and regression[END_REF]. For this reason, the two-way ANOVA of both treatments (e.g. monoculture and mixed culture) was performed by permutation (α = 0.05; 9999 permutations). These analyses were done using software R Development Core Team (R Core Team 2016). The effects of neighbour identity, plant density and their interactions on the RNE of each trait and on each morphological trait were tested using a "post hoc" Tukey test. These analyses and graphics were performed using Statistica TM 10.0.

Results

Effect of plant density in monoculture

We found greater RGR and a higher number of shoots in E. canadensis than in E. densa and L. major (Table 1; Fig. 1 a andc). The LAGR did not differ between species (Table 1, Fig. 1b). Our test indicated a significant difference in the production of roots among species: E. densa produced a significantly lower number of roots compared to the other species at both low and high densities (Table 1; Fig. 1 d). The LAGR was lower for L. major at high density and for E. canadensis at low density (Table 1, Fig. 1b).

A c c e p t e d M a n u s c r i p t Effect of density and neighbour identity on RNE and morphological traits

The calculation of the RNE index for each morphological trait indicated that there was competition or facilitation between the three species depending on the different treatments (Fig. 2.A-M). However, at Mid-ratio (1), length of E. densa was slightly facilitated by the presence of E. canadensis (Fig. 2.B -treatment Mid-ratio (1)). Strong competition was established at high density for the production of lateral shoots of E. canadensis when it was outnumbered by L. major (Table 2, Fig.

2.D -treatment Low-ratio

). Higher competition intensities were shown for the formation of the number of roots of E. canadensis when the neighbour species was mainly L. major and E. densa (Fig. 3.Gtreatment Mid-ratio (2), Low-ratio and High-ratio), however root formation was stimulated in the presence L. major in the Mid-ratio (1) treatment. Leaf area growth of all species, RGR of E. canadensis and L. major, and the production of lateral shoots by E. densa and L. major were not impacted by the interactions between neighbour identity and plant density (Table 2; Fig. 2). Our results showed no effect of plant density and neighbour species on the RGR of L. major (Table 3, Fig. 3C), on the number of lateral shoots of E. densa and L. major (Table 3, Fig. 3,E,F) or on the LAGR of E. canadensis, E. densa and L. major (Table 3, Fig. 3 J,L,M).

However, they demonstrated significant effects of both plant density and neighbour species on the RGR and the number of lateral shoots of E. canadensis (Table 3, Fig. 3A,D). E. canadensis showed a lower RGR in the presence of L. major than in the presence of E. densa in the High-ratio treatment, whereas the presence of E. densa induced a reduction of the production of lateral shoots in the Mid-ratio (2) and Low-ratio (Fig. 3A, D) treatments. E. canadensis exhibited lower root production in the presence of L. major at high density (Fig. 3G -treatment High-ratio). The RGR of E. densa depended on plant density and neighbour identity (Table 3, Fig. 3B). E. canadensis stimulated the RGR of E. densa (Treatment Mid-ratio (1), Fig. 3B). L. major had high root production whether the neighbour was E. canadensis or E. densa in the Mid-ratio (1) treatment (Fig. 3I).

Discussion

Effect of density on morphological traits of invaders in monoculture and in mixtures.

Our results demonstrated that the performance of invasive submerged plants was density-dependent and that it could be influenced positively (facilitation) or negatively (competition) by the identity of neighbour species. Indeed, in high density, the LAGR of L. major and the root number of E. densa were reduced. A high density increased competition for resources by limiting light interception and nutrient uptake, and consequently reduced leaf growth and root production. However, However, other studies have reported equivalent or stronger interspecific effects [START_REF] Aguiar | Intensity of intra-and interspecific competition in coexisting shortgrass species[END_REF][START_REF] Mony | Competition between two invasive Hydrocharitaceae (Hydrilla verticillata (L.f.) Royle and Egeria densa Planch) as influenced by sediment fertility and season[END_REF][START_REF] Spencer | Competition between two submersed aquatic macrophytes, Potamogeton pectinatus and Potamogeton gramineus, across a light gradient[END_REF]Rejmánek 2010, Yu et al. 2018). For example, Yu et al. ( 2018) found higher interspecific competition than intraspecific competition for E. densa. Our results also showed an interspecific competition for root production between the three invaders. Moreover, an increase in density significantly stimulated competition intensity, although the effect of density on the performance of the invader also depended on neighbour identity. Our results in mixed culture were broadly similar to the findings in monoculture, demonstrating that a high density had a strong impact on the interspecific competition for all three species. From this, we can infer that the results obtained in monoculture and mixed cultures are probably due to the fact that the plants are morphologically similar, that the mechanisms driving intraspecific and interspecific competition are very similar for these submerged plants and that the performance of invaders was density-dependent. Thus, our results partially corroborate our first hypothesis for E. canadensis, E. densa and L. major.

The presence of plants with similar growth form may increase competition in mixed cultures.

Although the morphological development of E. canadensis was mainly influenced by plant density, the numbers of lateral shoots (= lateral growth) and roots of this species were slightly related to the identity of the neighbour species. The lowest apical growth and root and lateral shoot production of E. canadensis when this species grew with L. major could be consequences of competition for nutrient uptake and space between E. canadensis and L. major. It is well known that the presence of plants with similar growth form and architecture can negatively affect nutrient concentrations in the sediment and solar radiation available for the plant community which may increase competition, thus

A c c e p t e d M a n u s c r i p t inhibiting plant growth. Other authors have demonstrated similar results, for example, [START_REF] Riis | Growth and morphology in relation to temperature and light availability during the establishment of three invasive aquatic plant species[END_REF] also showed that L. major and E. canadensis differ in their branching and stem length under similar experimental conditions (i.e. at temperatures close to 20°C and 50% light). Under these conditions, E. canadensis is the most competitive species regarding morphological characteristics at 20 °C especially due to its high degree of branching [START_REF] Riis | Growth and morphology in relation to temperature and light availability during the establishment of three invasive aquatic plant species[END_REF], on the other hand, L. major has a highest stem length. Our results showed low competition intensity for branching and root production at high intensities. Surprisingly, the response of E. canadensis differed in the presence of E. densa and L.

major. Furthermore, a facilitative effect of E. canadensis on the RGR (apical growth) of E. densa was established. The presence of E. canadensis stimulated the RGR of E. densa (RGR in the presence of Ec = 0.028 ± 0.004 cm per day, in presence of Lm = 0.015 ± 0.009 cm per day). Conversely, the presence of E. densa did not influence the RGR of E. canadensis. Thus, interactions between E. canadensis and E. densa were distinctly asymmetrical. Plant density did not influence L. major traits, except for root production in mixtures, indicating that species coexistence is favoured instead of competitive exclusion [START_REF] Stiers | Competitive abilities of invasive Lagarasiphon major and native Ceratophyllum dermersum in monocultures and mixed cultures in relation to experimental sediment dredging[END_REF]). Thus our hypothesis, that the presence of plants with similar growth form may increase competition in mixed cultures was partially validated.

Neighbour identity had no impact on L. major. The RGR of L. major at high density was on average 0.014 cm per day in the presence of E. canadensis, whereas the RGR of E. canadensis was around 0.030 cm per day at high density in mixtures. Moreover, the leaf area growth of L. major, a proxy for photosynthetic ability, was not affected by density or neighbour identity. The apical growth ability of E.

canadensis may enable it to shade out neighbouring species and outpace the establishment of other species such as L. major. These results are not consistent with the literature. For example L. major may be successful in out-competing Elodea spp. as a result of its ability to photosynthesize and consequently grow, particularly under very stressful conditions of high pH and low free CO2, perhaps through more efficient bicarbonate utilization than the other species [START_REF] James | Competition between three submerged macrophytes, Elodea canadensis Michx, Elodea nuttallii (Planch) St John and Lagarosiphon major (Ridl ) Moss[END_REF]. Competition intensity for root production of L. major increased slightly with density, whatever the neighbour species. Therefore the outcome of competition between species of the same family, having similar architecture and competition ability, is not the same. For example, [START_REF] Mony | Competition between two invasive Hydrocharitaceae (Hydrilla verticillata (L.f.) Royle and Egeria densa Planch) as influenced by sediment fertility and season[END_REF] showed that H.

verticillata may out-compete E. densa in many situations and [START_REF] Hofstra | Competitive performance of Hydrilla verticillata in New Zealand[END_REF] [START_REF] James | Responses of three invasive aquatic macrophytes to nutrient enrichment do not explain their observed field displacements[END_REF]. Furthermore, E. canadensis was not considered as an aggressive species in Polish lakes (Kolada and Kutyla 2016). Similarly, a clear difference was obtained between experimental conditions and field observations in the study of [START_REF] Hofstra | Competitive performance of Hydrilla verticillata in New Zealand[END_REF]. These authors established that H. verticillata, a world-wide invasive species belonging to the Hydrocharitaceae family, had little apparent impact on the competitor species biomass (E. densa, L.

major, E. canadensis), whereas H. verticillata out-competed these species in Lakes in New Zealand.

This study experimentally demonstrated that despite the fact that the three invasive species were morphologically similar, the positive (facilitation) or negative (competition) effects of density on performance of each species depend on the identity of the neighbour species and on the degree of density. This finding implies that the presence of one invasive species (focal species) can be inhibited or facilitated by the introduction of other exotic species (neighbour species). Our study demonstrated that the species least affected by neighbour species was the invasive L. major, whereas E. canadensis and E. densa, were affected by the presence of other neighbour species. These results suggest that L.

major can be considered as the most aggressive species.

However, we emphasize that these observations were recorded in the early stages of fragment regeneration, and whether they also pertain to later life stages is a matter for further investigation.

Figure captions

  centre of each pot. The distance between ramets was the same for high and low densities.Experimental conditions consisted of planting individuals of E. canadensis, E. densa and L. major to give two plant densities (2 or 4 individuals) and using different species ratios (i.e. Mid-ratio = 1/1 or 2/2; High-ratio = 3/1 and Low-ratio = 1/3). The first number is the focal species and the second number the neighbour. The treatments consisted of pots (containing two or four individuals), with the following ratios: Mid-ratio pots: pots including two individuals, one focal species and one neighbour species -1/1, or pots including four individuals, two focal species and two neighbour species -2/2 .These treatments are shown in Figures2 and 3as: Mid-ratio (1) = 1/1; and Mid-ratio (2) = 2/2. High-ratio pots: including four individuals with a ratio of three individuals of the focal species to one neighbour species -3/1. Low-ratio pots: including four individuals with a ratio of one individual of the focal species to three neighbour species -1/3. The combinations of focal species and neighbours were: focal E. canadensis with L. major and E. densa as neighbour species; focal E. densa with L. major and E. canadensis as neighbour species; and focal species L. major with E. densa and E. canadensis as neighbour species.

Figure 1 :

 1 Figure 1: Means and standard errors of each morphological trait (Relative growth rate = RGR, lateral shoot number, root number and Leaf area growth rate = LAGR) of E. canadensis, E. densa and L. major in monocultures at two plant densities. Empty symbols = low density; Black symbols = high density. Circle: E. canadensis, Square: E. densa, Triangle: L. major. Different small letters above columns are used to indicate a significant difference between species and densities.

Figure 2 :

 2 Figure 2: Means and standard errors of the RNE of each morphological trait (Relative Growth Rate = RGR), lateral shoot number, root number and leaf area growth rate = LAGR) of E. canadensis, E. densa and L. major at two plant densities and different ratios (Mid-ratio (1) = 1/1; Mid-ratio (2) = 2/2; Low-ratio =1/3 and High-ratio = 3/1). The first number is the focal species and the second number the neighour. Empty Circle: E. canadensis, Empty Square: E. densa, Black Triangle: L. major. Different small letters above columns are used to indicate a significant difference between species and densities.

Figure 3 :

 3 Figure 3: Means and standard errors of each morphological trait (relative Growth Rate = RGR), lateral shoot number, root number and leaf area growth rate = LAGR) of E. canadensis, E. densa and L. major at two plant densities and different ratios (Mid-ratio (1) = 1/1; Mid-ratio (2) = 2/2; Low-ratio =1/3 and High-ratio = 3/1). The first number is the focal species and the second number the neighour. Empty Circle: E. canadensis, Empty Square: E. densa, Black Triangle: L. major. Different small letters above columns are used to indicate a significant difference between species and densities.

  of E. canadensis was stimulated at high density in monoculture, suggesting an investment in photosynthetic capacity as a strategy to overcompensate for stress. No intraspecific competition for initial growth (apical and lateral growth) was seen in monocultures independently of treatments with low or high densities. The latter results were surprising, because two individuals of the same species have exactly the same ecological requirements, and competition may occur rapidly when one factor is limited in the environment[START_REF] Barrat-Segretain | Experiments on growth interactions between two invasive macrophytes species[END_REF]. The short period of the experiment may not have been long enough to induce nutrient stress and this could explain the weak competitiveness between individuals, as longer experiments have shown strong intraspecific competition effects and niche differentiation[START_REF] Barrat-Segretain | Experiments on growth interactions between two invasive macrophytes species[END_REF][START_REF] Stiers | Competitive abilities of invasive Lagarasiphon major and native Ceratophyllum dermersum in monocultures and mixed cultures in relation to experimental sediment dredging[END_REF]).

Figure 1 :

 1 Figure 1: Means and standard errors of each morphological trait (Relative growth rate = RGR, lateral shoot number, root number and Leaf area growth rate = LAGR) of E. canadensis, E. densa and L. major in monocultures at two plant densities. Empty symbols = low density; Black symbols = high density. Circle: E. canadensis, Square: E. densa, Triangle: L. major. Different small letters above columns are used to indicate a significant difference between species and densities.

Figure 2 :

 2 Figure 2: Means and standard errors of the RNE of each morphological trait (Relative Growth Rate = RGR), lateral shoot number, root number and leaf area growth rate = LAGR) of E. canadensis, E.densa and L. major at two plant densities and different ratios (Mid-ratio (1) = 1/1; Mid-ratio (2) = 2/2; Low-ratio =1/3 and High-ratio = 3/1). The first number is the focal species and the second number the neighour. Empty Circle: E. canadensis, Empty Square: E. densa, Black Triangle: L. major. Different small letters above columns are used to indicate a significant difference between species and densities.

Figure 3 :

 3 Figure 3: Means and standard errors of each morphological trait (relative Growth Rate = RGR), lateralshoot number, root number and leaf area growth rate = LAGR) of E. canadensis, E. densa and L. major at two plant densities and different ratios (Mid-ratio (1) = 1/1; Mid-ratio (2) = 2/2; Low-ratio =1/3 and High-ratio = 3/1). The first number is the focal species and the second number the neighour. Empty Circle: E. canadensis, Empty Square: E. densa, Black Triangle: L. major. Different small letters above columns are used to indicate a significant difference between species and densities.

  traits used were: RGR, number of shoots, number of roots and leaf area of each individual planted in monoculture or mixed culture.

	M a n u s c r i p t
	A c c e p t e d

The term x depends on which value of P is greater. If P control > P mixture, then x= P control; however, if P mixture > P control, then x= P mixture. The

Table 1 .

 1 Results of a two-way ANOVA for each morphological trait of monoculture treatments of E. canadensis, E. densa and L. major at two plant densities (low= 2:0 and high=4:0). Significant results are in bold type.

	Morphological traits Relative growth rate (cm d -1 ) Plant density Species Plant density X Species Number of lateral shoots Plant density Species Plant densities X Species Number of roots Plant density Species Plant density X Species Leaf	df 1 2 2 1 2 2 1 2 2	F 2.06 67.58 2.10 0.62 99.08 2.36 7.63 49.70 1.05	p 0.163 0.000 1.44 0.437 0.000 1.15 0.010 0.000 0.364

area growth rate (cm 2 d -1 )

	Plant density Species Plant density X Species	1 2 2	0.19 0.40 3.57	0.662 0.673 0.043

Table 2 :

 2 Results of a two-way ANOVA on the Relative Neighbour Effect (RNE) index calculated for each morphological traits of E. canadensis, E. densa and L. major. Significant results are in bold type.

	E. canadensis F 1.87 0.164 p 3.62 0.051 0.24 0.865 8.76 0.000 0.06 0.806 3.11 0.039 8.93 0.000 1.31 0.260 2.13 0.114 1.02 0.392 0.05 0.810 0.39 0.758 A c c e p t e d Morphological traits df Plant density 3 Neighbour species 1 Plant density X Neighbour species 3 RNE of lateral shoots Plant density 3 Neighbour species 1 Plant density X Neighbour species 3 RNE of roots Plant density 3 Neighbour species 1 Plant density X Neighbour species 3 RNE of Leaf area Plant density 3 Neighbour species 1 Plant density X Neighbour species 3 RNE of length M a n u s c r i p t E. densa df F p df F 3 4.35 0.050 3 0.86 0.469 1 0.85 0.361 1 0.19 0.660 3 5.51 0.003 3 1.09 0.365 2 0.46 0.711 3 0.95 0.424 2 1.01 0.320 1 0.005 0.941 4 0.56 0.639 3 1.58 0.211 3 2.68 0.051 3 5.88 0.002 1 0.001 1.000 1 0.004 0.983 3 1.16 0.337 3 0.56 0.640 3 0.56 0.644 3 0.65 0.577 1 0.67 0.417 1 0.001 1.000 3 0.43 0.730 3 0.51 0.687 p L. major

Table 3 :

 3 Results of a two-way ANOVA for each morphological trait of E. canadensis, E. densa and L. major in mixed cultures. Significant results are in bold type.

	Morphological traits Relative growth rate (cm d -1 ) Plant density Neighbour species Plant density X Neighbour species Number of lateral shoots Plant density Neighbour species Plant density X Neighbour species Number of roots Plant density Neighbour species Plant density X Neighbour species Leaf area growth rate (cm 2 d -1 ) Plant density Neighbour species Plant density X Neighbour species	df 3 1 3 3 1 3 3 1 3 3 1 3	E. canadensis F 3.66 0.022 p 6.78 0.013 0.46 0.706 9.92 0.000 11.77 0.001 1.98 0.135 10.48 0.000 1.23 0.274 3.77 0.019 0.58 0.624 0.54 0.464 1.31 0.285	df 3 1 3 3 1 3 3 1 3 3 1 3	E. densa F 3.36 1.40 6.77 0.37 0.768 p 0.030 0.244 0.001 0.06 0.803 0.44 0.724 2.92 0.048 0.000 1.000 1.36 0.271 1.55 0.218 1.30 0.262 1.62 0.202	df 3 1 3 3 1 3 3 1 3 3 1 3	L. major F 0.79 0.00 1.39 1.54 0.10 0.75 6.57 0.07 0.43 1.40 0.00 0.40	p 0.507 0.976 0.263 0.222 0.744 0.524 0.001 0.783 0.729 0.259 0.954 0.753

  dominate some habitats. Our results are original because they also suggested that the interactions between invaders depended on the identity of the neighbour in mixed cultures.Our experimental study indicated that E. canadensis was characterized by the highest RGR and number of roots and lateral shoots in both treatments (monoculture and mixed culture), suggesting that E. canadensis is a stronger competitor than E. densa and L. major[START_REF] Riis | Growth and morphology in relation to temperature and light availability during the establishment of three invasive aquatic plant species[END_REF][START_REF] Silveira | Impact of climate warming on plant growth varied according to the season[END_REF]. Furthermore,[START_REF] Redekop | Elodea canadensis shows a higher dispersal capacity via fragmentation than Egeria densa and Lagarasiphon major[END_REF] demonstrated that E. canadensis shows a higher dispersal capacity via fragmentation than E. densa and L. major. This capacity increases its potential invasiveness. However, the highest dispersal ability of E. canadensis does not explain its low abundance in the field, where it has been shown that E. canadensis was displaced by Elodea nuttallii and E. nuttallii by L. major

	M a n u s c r i p t
	A c c e p t e d

established that the growth of H. verticillata appeared to be impeded by the dense E. densa canopy and that under particular environmental conditions E. canadensis may still coexist with H. verticillata or even

Table 1 .

 1 Results of a two-way ANOVA for each morphological trait of monoculture treatments of E.canadensis, E. densa and L. major at two plant densities (low= 2:0 and high=4:0). Significant results are in bold type.

Table 2 :

 2 Results of a two-way ANOVA on the Relative Neighbour Effect (RNE) index calculated for each morphological trait of E. canadensis, E. densa and L. major. Significant results are in bold type.

Table 3 :

 3 Results of a two-way ANOVA for each morphological trait of E. canadensis, E. densa and L. major in mixed cultures. Significant results are in bold type.

Table S1 :

 S1 Chemical composition of the water from sampling sites in the spring.

Acknowledgements

The authors thank Dra. Vanessa C. Harthman (Universidade Estadual de Maringá) for fruitful discussion, Msc. Dieson André by help with quality of the figures and the two anonymous reviewers for suggestions that have improved our manuscript a lot. We also thank Bertrand Coupé and Marc Hervé for their help in the field and Nathalie Josselin-Le Bris for assistance with water analyses. M.J.

 S1: Chemical composition of the water from sampling sites in the spring.


F Guiho

F Alizard

J.-Ch Robinet

Global Instability in Shock Wave Laminar Boundary-Layer Interaction

The linear global stability of an interaction between an oblique shock wave and a laminar boundary layer is carried out for various oblique shock angles. It is illustrated that such a flow acts as a noise amplifier. The least temporally damped global modes are classified into three main categories, low, medium and high frequencies. The high frequencies are localized into the attached boundary layer, the medium frequencies are associated with Kelvin-Helmholtz like structures along the shear layer and convective waves in the separated flow downstream whereas the low frequencies are driven by the interaction zone. In particular, a low frequency mode emerges which is scaled by the interaction length and the freestream velocity.

Introduction

Shock-wave/boundary-layer interactions (SWBLI) have important applications in a wide range of industrial problems, such as high speed flight occurring on aircraft, space/launch vehicles and projectiles. In particular, these interaction phenomena is a prior interest for supersonic/hypersonic flows where aerodynamic heating is a major factor [START_REF] Délery | Shock-wave boundary layer interactions[END_REF]. The generation of shock waves by various surfaces of a vehicle or aircraft engine and the impingement of those shocks on other surfaces can greatly amplify the local heat transfer. When shock wave interacts with a laminar boundary layer, the experiments have shown that, for a sufficiently large pressure gradient amplitude, the boundary-layer becomes turbulent. It strongly modifies the interaction zone as well as its dynamics yielding to a reduced separated zone. Transition mechanisms are poorly known. However, in the presence of a low environmental noise or low upstream disturbances, linear stability analysis can provide a good approximation of the position of laminar-turbulent transition (see for instance the e N method) [START_REF] Tullio | Transitional shock-wave/boundary layer interaction behind a roughness element[END_REF]. In addition, when the interaction zone is higher, one may also trigger self-sustained low-frequency oscillations or three-dimensionality [START_REF] Robinet | Bifurcations in shock wave / laminar boundary layer interaction: global instability approach[END_REF]. This specific dynamics can not be captured by a local linear stability analysis, a global analysis is thus required.

In this paper, the linear global stability of a two-dimensional interaction between an oblique shock wave and a laminar boundary-layer on a flat plate is carried out. In particular, it will be further examine whether such a flow may act as a resonator or a noise amplifier when it is subjected to two-dimensional perturbations. In addition, the global modes which are involved in the space-time dynamics will be highlighted.

Governing Equations and Numerical Methods

The present approaches are based on the standard small perturbation technique. The instantaneous flow is decomposed into base flow and unsteady perturbations:

q(x, y, t) = Q b (x, y) + q (x, y, t) (1)
where 1) is introduced into compressible Navier-Stokes equations. The base flow Q b is supposed to be an equilibrium solution of the 2-D compressible Navier-Stokes equations. The resulting equations are further simplified by considering that the perturbation is infinitesimal, i.e. the nonlinear fluctuating terms are neglected. Finally, compressible Navier-Stokes equations are transformed into a linear partial differential equations ∂q /∂t = A q where q represents the conservative variables for the perturbation. Let-us introduce the following decomposition q = qˆk (x) e -iΩ k t where the couple qˆk,Ω k is the so-called global mode and is a solution of large eigenvalue problem. The space and time behaviour of each global mode are governed by qˆk (the eigenfunction) and Ω k (the complex circular frequency) respectively. The numerical method implemented in CFD DynFluid Phoenix solver is based on the finite-volume approach and on a cell centered discretization. Roe flux difference splitting scheme are employed to obtain advective fluxes at the cell interface. The MUSCL approach extends the spatial accuracy to third order. For viscous terms, a central difference method is used. For unsteady computations, the dual time stepping method is used, the derivative with respect to the physical time is discretized by a second-order formula. For more details about the numerical methods, see [4].

Q b = (ρ b ,ρ b U b ,ρ b V b ,ρ b E b ) T . The decomposition (
To obtain an equilibrium state of the compressible Navier-Stokes equations, the dual-time is turned off with a large CFL number with respect to the fully implicit method. To perform a global stability analysis, the eigenvalues of the Jacobian matrix A are computed with a time-stepper approach, see [START_REF] Bagheri | Matrix-free methods for the stability and control of boundary layer[END_REF]. The Arnoldi algorithm implemented into the temporal loop of Phoenix code is used to obtain the most unstable modes, see [4].

Base Flow

The configuration studied is similar as the case of Degrez et al. described in [START_REF] Degrez | The interaction of an oblique shock wave with a laminar boundary layer revisited. an experimental and numerical study[END_REF]. An oblique shock wave, whose the angle of the shock relative to the horizontal axis is referred as θ hereafter, is made to impinge on the flat plate laminar boundary layer at M ∞ = 2.15 by enforcing at the inlet boundary discontinuous conditions that satisfy the Rankine-Hugoniot relations. In addition, the stagnation pressure is fixed at 12,300 Pa. Nonreflecting boundary conditions are enforced at the freestream and downstream boundaries. Finally, Dirichlet boundary conditions for both the velocity components and the temperature are prescribed at the adiabatic wall.

A preliminary computation is performed by considering a laminar boundary layer without impinging shock. Hence, δ * is the displacement thickness taken at the theoretical location where the shock impinges the boundary layer, U ∞ , ρ ∞ and μ ∞ , are the velocity, the density and the molecular viscosity at the freestream.In the next, the Reynolds number based on the previous quantities is fixed to Re δ * = 886. After having reached a stationary state for the laminar boundary layer, the shock is introduced at the inflow condition. Hereafter, we consider four-different values for θ = 30.8 o , 31.2 o , 31.6 o and 32 o while holding the Reynolds number and the Mach number constants. Finally, we note L sep and L int the separation and the interaction length respectively.

The computational domain D extends from x 0 /δ ; x n /δ × y 0 /δ ; y n /δ = [0; 400] × [0; 250] in the streamwise and wall-normal directions respectively. Figure 1a,b show comparisons between the base flow obtained by the Phoenix code and data from the experiments of Degrez et al. [START_REF] Degrez | The interaction of an oblique shock wave with a laminar boundary layer revisited. an experimental and numerical study[END_REF]for θ = 30.8 o . Both the wall pressure distribution (Fig. 1a) and the friction coefficient (Fig. 1b) exhibit a good agreement with the experimental results. As an example, we plot the streamwise velocity for θ = 30.8in Fig. 2.

Global Stability Analysis

Stability for the Shock Wave Angle θ = 30.8

As shown in Fig. 3, all the global modes are damped temporally which is consistent with the experiment of Degrez et al. [START_REF] Degrez | The interaction of an oblique shock wave with a laminar boundary layer revisited. an experimental and numerical study[END_REF] where none global unsteadiness is observed. Such a flow acts therefore as a noise amplifier. The modes labelled 1, 2, 3, medium, low and high frequencies respectively, are showninFig. 4a, b and c. All these modes are associated with convective waves which are travelling along the shear layer in the separated zone and the attached boundary One may precise that the convergence of our results have been carefully checked by carrying out the global stability analysis with a large computational box which extends up to 400δ and a coarse mesh, where 20 grid points per wavelength are used for the mode labelled 3 for instance.

Influence of the Shock Wave Angle

When the incident angle increases, the interaction becomes stronger, causing an increase in the recirculation zone (not shown here for the sake of conciseness). The spectrum for θ = 30.8, 31.2, 31.6 and 32 are shown in Fig. 5. Because all the modes are damped temporally for all the shock angles which are considered, the present shock wave-laminar boundary layer interaction is clearly identified as a noise amplifier. Hence, our global stability analysis further confirms the DNS results of Pagella et al. [START_REF] Pagella | Numerical investigations of small-amplitude disturbances in a boundary layer impinging shock wave at ma = 4.8[END_REF]. In addition, it is interesting to remark that a low frequency mode emerges for all equilibrium states (labelled as 2 in Fig. 3). When rescaled by the interaction length L int and the freestream velocity U ∞ , the corresponding frequency is seen to be almost constant around S t ≈ 0.05.

Conclusion

The linear global stability analysis of the interaction between an oblique shock wave and a laminar boundary-layer confirms that such a flow acts as a noise amplifier, even for large shock wave angles. The global modes exhibit a Kelvin-Helmholtz like structure developing in the shear-layer. The lower frequency modes are mainly localized in the interaction zone. Finally, a low frequency mode strongly localized in the interaction zone and scaled by the interaction length and the freestream velocity emerges which may provides new insight about the low frequencies unsteadiness observed in the turbulent regime.

Fig. 1

 1 Fig. 1 Base flow characteristics for θ = 30.8 o , Re δ = 886. Comparison between numerical solution and Degrez's experiment a P (x) /P ∞ b C f (x)

Fig. 2 Fig. 3

 23 Fig. 2 Base flow characteristics for θ = 30.8 o , Re δ = 886. Iso-lines of streamwise velocity U (x, y), streamlines and some characteristic phenomena: 1 incident shockwave; 2 separated waves; 3 expansion waves; 4 reattachment waves Fig. 3 Eigenspectrum for Degrez's case, θ = 30.8 o and Re δ = 886. St = r L int /(2πU ∞ )

( a )Fig. 4

 a4 Fig. 4 Eigenfunctions for θ = 30.8 o , Re δ = 886. The streamwise component is shown

Fig. 5

 5 Fig. 5 Eigenspectrum for various shock angles θ(30.8 o (+), 31.2 o (×), 31.6 o (•), 32.0 o ( )].Re δ = 886


Khuder Alagha

Arnaud Bourdin

Charlotte Vernisse

Céline Garulli

Céline Tummino

Jérémy Charriot

Isabelle Vachier

Carey Suehs

Pascal Chanez

Delphine Gras

Goblet Cell Hyperplasia as a feature of neutrophilic asthma


Digital Libraries and Crowdsourcing: A Review

Cataloguing, indexing and correcting the OCR of digitized documents, libraries have often externalized certain activities to service providers with recourse to a low-price workforce in developing countries like Madagascar, India, or Vietnam. From now on, though, they could instead call on the masses of Internet users, that is, crowdsourcing, to realize tasks their own staff cannot handle.

The development of crowdsourcing in libraries is particularly important in the domain of OCR correction. In fact, character recognition software that converts photos of digitized book pages into texts do not provide 100% reliable results and, depending on the quality of the original document, its digitization, its typography and the possible presence of handwritten notes, it may be necessary to correct the texts produced with the help of dictionaries. OCR correction is necessary to enable more efficient whole-text searches of the digitized texts, better referencing of the contents by search engines, the production of eBook in EPUB or MOBI formats so they can be read on Chapter written by Mathieu ANDRO and Imad SALEH.

eReaders, data extraction through text mining technologies, or even scientific exploitations related to culturomics. 1 This question of recourse to crowdsourcing is being asked more and more today of libraries, from the very largest of them to the very smallest. In order to bring them part of the solution and bring about an original conceptual contribution to crowdsourcing in libraries, we have written this state of the art, which comes from thesis work.

It will offer conceptual elements to understand this phenomenon, a taxonomy and panorama of the initiatives, and analyses from library and information science points of view.

The concept of crowdsourcing in libraries

Definition of crowdsourcing

Crowdsourcing literally means outsourcing to Internet users, according to Jeff Howe's expression proposed in Wired Magazine in June 2006. According to an authoritative definition, Crowdsourcing is a type of participative online activity in which an individual, organization, or company with enough means proposes to a group of individuals of varying knowledge, heterogeneity, and number, via a flexible open call, the voluntary undertaking of a task. The undertaking of the task, of variable complexity and modularity, entails mutual benefit. The user will receive the satisfaction of a given type of need, be it economic, social recognition, self-esteem, or the development of individual skills, while the crowdsourcer will obtain and utilize to their advantage that what the user has brought to the venture, whose form will depend on the type of activity undertaken. (from Estellés-Arolas, Towards an integrated crowdsourcing definition. Journal of Information Science, 2012. [EST 12]) Contrary to these authors, we think crowdsourcing can also exist as participation that is not necessarily and strictly voluntary, as is the case with projects where Internet users contribute by playing games, which are qualified as gamification. We even think crowdsourcing can also call on the 1 Culturomics could be defined as the quantitative analysis of culture through large volumes of digitized texts.

involuntary or unconscious participation of Internet users, as is the case, for example, with the reCAPTCHA project. The millions of books digitized by Google Books are OCRized. The words not occurring in dictionaries are then sent to Internet users who, for security reasons, are forced to reassemble jumbled words to prove that they are not robots. In doing this, by creating their accounts on websites, they involuntarily contribute to OCR correction for Google Books and Google Maps. We qualify this involuntary participation of Internet users as implicit crowdsourcing.

Having defined crowdsourcing, all that remains is to explain what it is not. Crowdsourcing must not be confused with outsourcing, for there is indeed a sort of call for bids in the form of a call for contributions; the relationship with the contributor, however, is not contractual. It also must not be confused with "user innovation", as the undertaking remains at the project's initiative, not with the open source since the contribution method is not necessarily collaborative, but can, quite the opposite, appeal to competition.

Historic origins of crowdsourcing

This economic model finds its source in -government appeals to the people to solve scientific problems for recompense starting in the 18th Century; -competitions and public offerings; -free service and free access that allowed the consumer to take over part of the producer's work, then the "on-demand" model that allowed him to take over the production decision itself.

Below, we propose a chronology of the historic origins of crowdsourcing and citizen science. This chronology is the result of analyses done on the literature on this subject. It was created using a collection of the most important events at the core of crowdsourcing (call for participation, recompense, collective work, microtasks, outsourcing, wisdom of crowds). The events assembled here are also the most representative of the taxonomy that we propose later in the chapter.

The English government launches a call for scientists to find a solution to determine maritime longitude from a boat. John Harrison, a carpenter and clockmaker, wins the 20,000 pound reward over more than 100 competitors, including Cassini, Huygens, Halley and Newton A ruling by the King of France, Louis XV, requests that ship captains bring plants and seeds back from foreign countries that they visit British astronomer Nevil Maskelyne calculates the position of the moon for navigation at sea, thanks to the calculations of two astronomers who made their calculations twice each, and then were verified by a third Mathematician Alexis Clairaut manages to calculate the orbit of Halley's comet by dividing the calculation tasks among three astronomers French engineer Gaspard de Prony organizes addition and subtraction microtasks for 24 unemployed barbers in order to develop detailed logarithmic and trigonometric tables With his new methods of food preservation that will lead to canned food, Nicolas Appert receives 12,000 francs from the French government after a call for contributions

The store "Au bon marché" is the first self-service store. From then on, consumers directly access merchandise without going through the intermediary of a merchant and thus take on part of the producer's work After a call for volunteer contributions, the Oxford English Dictionary benefits from more than 6 million documents containing word proposals and citations of use The Statue of Liberty is financed by public donations During a competition on the livestock market to guess the weight of the cow, Francis Galton notices that the average of a crowd's estimates is closer to the truth than experts' estimates, implying the existence of the "wisdom of crowds" The National Audubon Society (USA and Canada) organizes a "Christmas bird count" Librarian James Duff Brown invents free access in libraries. Readers of the Clerkenwell Public Library from then on have direct access to part of the collections

18??

In the field of editing, public offerings multiply to finance the publication of books Toyota gathers 27,000 people and chooses the best proposed design for its brand logo

In the United States, the Mathematical Tables Project employs 450 out-of-work victims of the economic depression, led by a group of mathematicians and physicists, to tabulate mathematical functions, long before the invention of the computer

195?

A Toyota industrial engineer, Taiichi Ōno, invents the "just-in-time" model, predecessor of the "on-demand" model, which would allow production without reserves or unsold articles, just-in-time manufacturing as a function of demand.

In a way, it is a matter of outsourcing the production decision itself to the consumer. This model is at the root of on-demand digitization through crowdfunding and on-demand printing The first telethon in the United States allows fundraising to fight cerebral palsy The Sydney Opera House is designed and built after a public competition that encouraged ordinary people from 32 countries to contribute to this design project The Zagat survey (restaurant guide) bases its ratings on a large number of testers.

Conceptual origins of crowdsourcing

Crowdsourcing finds its conceptual origin in as diametrically opposed ideologies as socialism, libertarianism, humanism or liberalism [AND 14a], where the Californian Ideology would accomplish the most propitious synthesis for the development of crowdsourcing.

Socialist and Marxist ideologies

"From each according to his ability, to each according to his needs" production and abolition of the law of value, money is no longer the main motive, free products, spirit of sacrifice, work to serve humanity, socialist emulation, abolition of the fundamental separation of necessary labor and surplus labor, reconsideration of wage labor and social classes, each person able to be employer or employee in turn, overcoming private property through shared use, "collaborative communities", participatory, peer-to-peer contribution economy

Libertarian and anarchist ideologies

Critical of the authority of the dominating classes and totalitarianism, direct democracy, equal contribution from the hobbyist and the expert, disappearance of the boundary between producers and consumers, work becomes leisure, weisure (work + leisure) or playbor (play + labor)

Humanism

Digital humanities, Internet rehumanization and restitution of humans from a central place on the Web as origin and end, trust in man's abilities superior to those of algorithms, altruism and love of neighbor, concern for the weaker in the face of the strong

Liberalism

Outsourcing, integration of the consumer in production, meritocracy, increase in individual freedoms, defense of the freedom of expression, spirit of initiative and enterprise, "fun at work", universalism, internationalism, democracy, invisible hand, spontaneous order (Friedrich Hayek) of Wikipedia, which works through the autonomous action of individuals with no planning, trust in the market, selfemployment, reconsideration of monopolies, "uberization" Californian Ideology: libertarian liberal philosophy, libertarian philosophy of hippie meritocratic entrepreneurs and philosophy of digerati (digital literati)

Table 5.2. The conceptual origins of crowdsourcing

Critiques of crowdsourcing. Towards the uberization of libraries?

Crowdsourcing applied to libraries could also be considered a form of library uberization. Uberization could be defined as challenging established societies and professions through the emergence of web platforms allowing non-professionals to offer competing services. In the library domain, it could take the form of replacing the professional, authoritative data producer with a volunteer working for free or even an underpaid worker producing lowquality data outside any legal framework [FOR 11]. This exploitation of the invisible work of the Web's proletariat is sometimes considered "servuction". It is accused of unfair competition by traditional service providers. It would bring about disengagement on the part of workers, like those who employ this interchangeable workforce. It would create impersonal relations and fraud.

As a result, some thinkers, like Bernard Stiegler, talk about creating a "contributory revenue" [STI 15]; others speak of taxing data to return to citizens part of the value that they have created through their invisible data production work; and still others discuss making data produced by the masses joint property.

As for libraries, they sometimes remain too focused on the constitution of collections as a means in and of itself rather than on satisfying the needs of readers. Before mass digitization, they enjoyed a sort of monopoly on access to information, and their administration, forming a corporation with a relative ideological homogeneity, benefitted from prestigious titles of curators. Under these conditions, outsourcing expert work to hobbyists, opening up to the private as a renewed public/private partnership, risks being seen as questioning, losing control, disloyal competition, an attack against social benefits and, finally, an uberization of libraries.

The question of the quality of contributions, the costs connected with monitoring the quality, the individual appropriation of the collective heritage by uneducated laypeople, and the possible malevolence of Internet users will thus be pointed out against crowdsourcing projects that will not be able to develop without significant change initiatives.

Taxonomy and panorama of crowdsourcing in libraries

Most of the actors establish a typology of crowdsourcing projects as a function of the public's degree of engagement. In this way, with participatory or contributory crowdsourcing, Internet users are happy to produce data for institutions that come up with projects, pilot their development and frame the public's participation, which remains limited to microtasks only requiring a small individual investment. With collaborative crowdsourcing, Internet users can also interact with one another. Through co-creation, this individual investment is even stronger, as Internet users can actively weigh in on the policy and definition of projects' goals and premises, and sometimes even be the source of the projects themselves.

Beyond this quantitative distinction, we were led to propose a more qualitative taxonomy of crowdsourcing projects in libraries. We distinguish among the following large types: All of these forms of crowdsourcing shown synthetically and introductorily in the above tables are the object of an analysis developed in the section that follows and returns to this taxonomy's structuration.

Explicit crowdsourcing

Volunteer crowdsourcing

This is the most obvious and classic form of crowdsourcing, but recourse to volunteers could quickly reach its limits faced with the proliferation of projects. Furthermore, nothing indicates that future generations of pensioners, who are sometimes a significant portion of contributors, will have the same interests. to receive work from them (gamification) or make them work without their knowing it (implicit crowdsourcing).

Gamification

Gamification consists in making Internet users work through games with a useful and productive end ("games with a purpose"). It could be defined as the act of applying design, psychology and video game elements in other contexts [DET 11].

The simple act of giving points for Internet users' participation therefore must not be confused with gamification, but rather results in a sort of "pointification". Gamification is also different from "serious games" because it does not aim to educate for personal development, but rather to achieve goals outside oneself like correcting OCR or indexing digitized photographs [AND 15b].

Unlike explicit crowdsourcing, doing randomly performed, out-ofcontext microtasks in a game is generally less favorable to personal development and the acquisition of knowledge, but it could allow work that is sometimes rather thankless to be done more easily.

Implicit crowdsourcing

The notion of implicit crowdsourcing was conceptualized by [HAR 13], but the term is still not very widespread in the literature. The Internet users who participate do it involuntarily or unconsciously. Implicit crowdsourcing could thus be considered less ethical than explicit, voluntary crowdsourcing by unpaid workers on the Web, an intrusion of eCommerce seeking to instrumentalize Internet users.

The most emblematic project of this kind of crowdsourcing in the domain of digital libraries is reCAPTCHA. In order to create an account on a website and avoid any attack by robots, the websites require Internet users to reassemble jumbled words, thereby proving that they are not malicious bots. The programs Google Books and Google Maps have thus cleverly used this system to have untreated OCR from their campaigns of digitization by masses of Internet users corrected by comparing their input. Thus, 200 million words would be compared each day, 12,000 h of volunteer work collected and, according to our calculations, 146 million euros per year saved by Google through text correction services [AND 15a].

Crowdfunding

Sometimes considered institutional begging [AYR 13], crowdfunding is indeed a form of crowdsourcing that calls not on the work of Internet users, but on their financial resources. In libraries, it can be used to acquire documents or to finance digitization.

On-demand digitization

On-demand digitization allows libraries to offer digital reproduction services by having Internet users support the costs, outsourcing part of the costly, thankless task of selecting documents that still deserve to be digitized and obviously completing their digitization programs. The user thus finds himself placed at the center of library policy [GST 11], whereas in the past, libraries sometimes tended to neglect them by principally focusing on their collections. The documentary policy of the digital library thereby becomes a co-construction between the librarians and the general public since the acquisition policy is from then on shared. For Internet users, on-demand digitization gives them access to a digital reproduction service. For potential patrons and investors, on-demand digitization could be the chance to finance the digitization of books that may interest such and such audience, and eventually to collect a return on investments through web traffic created by these books on the advertisement model Google Adwords. This economic model could allow public funds, which have become more rare, to be concentrated on the digitization of documents with patrimonial, historic and scientific interest but not interesting private sector and to allow private funds from individuals or patrons finance the digitization of works interesting the general public or communities of scholars. In doing this, libraries would have a chance to better refocus on their own areas of expertise and better value the skills of curators in the patrimonial, historic and scientific domain.

On-demand digitization by crowdfunding is a new form of public subscription allowing new life to be given to a work. It is particularly well adapted to the current situation, where only leftovers still need to be digitized after large mass-digitization programs pass through.

The main difficulty of on-demand digitization projects consists in automatically evaluating the costs of document digitization. In fact, it is claimed that for these projects, a cost estimate is necessary for each demand. This estimate serves to evaluate the cost of digitization. Producing this estimate requires verifying the presence of the document, its state, its actual page count, its format and how wide it opens, all of which will determine how many pages must be digitized and the type of scanner to be used, thus the cost of digitization. Unfortunately, after the Internet user receives the estimate, he only very rarely proceeds with his demand through an order, as his desire to purchase has been surpassed and he may be surprised by the cost to be paid. At the end of the day, the work time spent producing estimates costs as much as the money collected from Internet users, and in the absence of an automatic calculation for digitization costs or a subsidy through public funds, on-demand digitization projects are hardly ever viable [AND 14b].

On-demand printing and libraries

Although it is not a matter of crowdsourcing, the economic model is identical to that of on-demand digitization, from which is it often indistinguishable. Here we are dealing with the revival of a print through the digitized document. This model, more and more often used in publishing to produce just in time, without reserves or unsold articles, has been applied to library digitization programs [AND 15c].

As we have seen with on-demand digitization, the documentary policy of digital libraries and the constitution of digital collections are henceforth more of a co-construction; furthermore, they are henceforth partly the work of Internet users. With on-demand printing, we could even go so far as to imagine a physical library directly made up of prints demanded by its readers, printed in a few minutes through an Espresso Book Machine and, after being returned by the reader, constituting a collection built by the user and made up of works having all been consulted at least once [LEW 10]. This way of functioning would be radically different from the acquisition of libraries, which currently depends essentially on the anticipation of needs and the purchase of books in case they one day interest a reader, a policy that is thus not exclusively focused on the user. In this way, it extends the possibility already offered by libraries to their readers to suggest acquisitions. Beyond this taxonomy, there are forms of crowdsourcing that have probably not yet been invented, such as gamification paid according to the results obtained through playing, the resource to citizens, possibly paid, for themselves digitizing documents within libraries, or even the application of a reCAPTCHA benefitting public libraries or a reCAPTCHA charging for the OCR corrected and sharing its profits with the sites that accepted to implement it.

Analyses of crowdsourcing in libraries from an information and communication perspective

Why do libraries have recourse to crowdsourcing and what are the necessary conditions?

Clay Shirky thought that if Americans spent their time on projects like Wikipedia instead of watching television, they could create 2,000 projects on the same scale as the famous participatory encyclopedia [SHI 10]. As for Luis Von Ahn, he claimed that the 425 million images on Google Images could have been indexed in just 31 days by 5,000 Internet users playing the ESP Game [VON 08]. Whatever it is, there would be a significant reserve of good will that libraries could benefit from, especially as they already have experience in motivating communities, the setting of these good wills; they have a good image with the public to whom they seem worthy of trust and they seem to serve general interests and whom they could, consequently, more easily recruit.

They could therefore have recourse to crowdsourcing, that is, to outsourcing microtasks to masses of Internet users to reduce their costs or to multiply their human resources and realize a painstaking, tedious task that they do not have the means to take on, or even to complete, undertake, or make possible projects that until now were unachievable, impossible or even unimaginable [HOL 10]. By taking advantage of the collaboration of Internet users, libraries could benefit from limitless knowledge and skills, far beyond that of their limited teams, all despite the excellent general education of their directors. Crowdsourcing therefore challenges the borders of the organization, as it allows value to be created beyond its borders [REN 14]. Libraries could thus tap into the greater strength lying beyond their organizations and recruit such and such scholar or specialist to identify a location or person in a photograph, recognize a book cover, date an object in a curio cabinet, etc. Libraries could thus get engaged in a participatory redocumentarization process and see their collections revisited and reinvented. Beyond these incentives, libraries could also seek to deeply engage the user in their collections, to democratize heritage conservation in the form of an "empowerment", an emancipation, and a change in relations between heritage and society in the name of a right to information and participation, to improve their image, to seek to innovate or, unfortunately, also to start institutional communication around a trendy subject.

Although it is absolutely possible to talk about an authentic use of data produced by users, there seem to be two different conceptions in libraries. One thinks that libraries need Internet users, while the other thinks that Internet users need libraries. The first is utilitarian and economical. It humbly recognizes its need for reinforcements and is truly seeking to produce a result, thanks to collaboration between heritage and society. The second is more strongly tied to democratic considerations and seeks instead to practice crowdsourcing for the sake of practicing crowdsourcing, publicizing the process and increasing public participation as an end in itself.

While this second conception holds sway, the work produced by Internet users is barely valued or used and the metadata that they seize will only rarely be integrated into library information systems, which may discourage and be seen as a betrayal by volunteers, as we will see in a later chapter.

Whatever the case may be, libraries will only be able to get engaged in the crowdsourcing path under the condition that the tasks concerned can be performed online as microtasks, that they do not involve confidential data, that they can be undertaken independently and requiring little interaction, education and communication, and, finally, that they can be accomplished by non-specialized amateurs.

There is a growing interest for crowdsourcing in libraries in the world literature, as illustrated in Figure 5.6. Moreover, a state-of-the-art from the OCLC forming a definitive work on the subject and indexing the crowdsourcing projects in libraries [SMI 11a, SMI 11b] never mentions France in 350 pages, and it will have to wait until February 2013 for the first study on the subject to be published in France [MOI 13], in the scope of a project by the National Library of France.

Why do Internet users contribute? Taxonomy of Internet users' motivations

Among the many motivations that lead Internet users to contribute to crowdsourcing projects in libraries are mainly seen intrinsic motivations pushing the individual to act selflessly and for the pure joy that the work brings him and the extrinsic motivations pushing him to work for the effects and results obtained, thanks to this work, like recognition, recompense or remuneration. We have identified and organized the motivations shown in Figure 5.8 from the literature. The kinds of motivations can be very diverse as a function of the types of crowdsourcing types of individuals and cultures, so if volunteer crowdsourcing encourages Internet users to seek personal development, gamification is rather appealing to the need for useful entertainment. The emergence of extrinsic motivations and particularly symbolic recompense, real or virtual, can sometimes take place to the detriment of the quality of data produced and of intrinsic values, that is, those that lead them to act out of pure interest in the job itself. Starting in 1975, an experiment by Edward L. Deci showed that if people were remunerated for doing puzzles, they lost all interest in these activities if they no longer saw rewards for doing it.

From symbolic recompense to concrete remuneration

As the preceding concept map of motivations shows, crowdsourcing projects are necessarily carried out for the mutual benefit of the institution and the Internet user. In addition to the intrinsic movements, the rewards can range from symbolic rewards (ranking, grades, medals) to very real rewards, from gifts even to remuneration. As such, volunteers with the Foldit project were publicly thanked in an article in the celebrated academic journal Natural Structural & Molecular Biology vol. 18, 2011 for having made the discovery of a very important enzyme's structure possible. Other volunteers with other projects were mentioned in newsletters and invited to talk about their work at conferences, and they were rewarded training courses, subscriptions, books, T-shirts, MP3 players, gift certificates, tours or trips.

Communication for recruiting contributors

Cultural institutions benefit from a good public image and seem worthy of trust and to serve public interests. As a result, they have solid advantages for recruiting volunteers. Among the communication means used for crowdsourcing projects, we could mention campaigns in the associative, local, national and trade press, the publication of articles and posters, the distribution of leaflets, putting up stickers and posters particularly for conferences and symposia, the organization of public meetings or specific events, and radio and television presence, but also the production of videos, the use of social networks, forums, mailing lists, direct mail campaigns, institutional websites, and, finally, the purchase of specific words in the Google Adwords campaign.

A crowdsourcing site must always have a homepage that describes the project simply and clearly explains its end goal and progress, and immediately invites volunteer participation by showing them how their participation will be useful and how they will be guided and recognized [MCK 15].

Community management for keeping contributors

The majority of the data produced in the framework of crowdsourcing projects has been produced by a well-determined minority of participants and not by anonymous masses.

As seen in the previous diagram where each square corresponds to the contributions of a single person and where the size of each square is proportionate to quantity of contributions, all volunteer crowdsourcing projects also show us that the largest part of contributions is the result of a minority and that it is thus not really a matter of anonymous crowds, but rather of a well-defined community of volunteers [OWE 13]. Under these conditions, it would therefore be more judicious to speak of communitysourcing [CAU 12] or even nichesourcing and to seek to recruit well-targeted people rather than addressing faceless crowds. Whatever the case may be, there are numerous studies that show that data produced by those who consult a digitized document online can be of the highest quality, as the person consulting the document is generally someone who knows the subject covered in the consulted document well. Furthermore, as expected by followers of the "wisdom of crowds", the diversity of profiles constituted by a crowd of Internet users and the "law of large numbers" would have the effect of neutralizing individual errors in the mass of accurate data [BOE 12] and sometimes even providing better results than those obtained by experts. This seems to be confirmed by several comparative studies [ROR 10, OOM 11].

However, the data produced by Internet users are not always reintegrated by institutions sometimes aiming more towards democratization of heritage or even institutional communication on a trendy subject than real Internet user participation. When they are reused, these data born of free, volunteer contributions should always be distributed under legal conditions authorizing the largest possible reuse.

The evaluation of crowdsourcing projects

Although it has proven difficult to collect figures in the literature except for [CAU 12], it seems that crowdsourcing projects are far from all being profitable in the sense that the profits in data harvested are not always on the level of the costs for project management, platform development, administration, maintenance, hosting, communication, community management and reintegration of produced data.

In a previous study [AND 15a], we had estimated that the California Digital Newspaper Collection project gathered more than 1,500 € of OCR correction work per month, the Digitalkoot project more than 2,000 € per month, the TROVE project nearly 35,000 € per month and the reCAPTCHA more than 12 million euros per month.

The projects that seem to work the best are those that have clear ends goals, lead an efficient communication campaign, and have managed and motivated communities at their disposal. Those that fail generally call on overly complex tasks, overly specialized knowledge requiring too great an investment in training, do not communicate sufficiently with the volunteers [RID 13], and sometimes neglected internal change management.

Conclusions on collective intelligence and the wisdom of crowds

If we average the individual estimates of a crowd concerning the weight of a cow, the number of marbles in a jar, the temperature in a room or the response to a general culture question on a game show like "Who Wants To Be A Millionaire?", it will become clear that this average is closer to the truth. This phenomenon was identified long ago as "vox populi vox dei" and well understood by Machiavelli, who wrote: "I say that the people are more prudent and stable, and have better judgment than a prince; and it is not without good reason that it is said, 'The voice of the people is the voice of God'; for we see popular opinion prognosticate events in such a wonderful manner that it would almost seem as if the people had some occult virtue, which enables them to foresee the good and the evil. As to the people's capacity of judging things, it is exceedingly rare that, when they hear two orators of equal talents advocate different measures, they do not decide in favor of the best of the two, which proves their ability to discern the truth of what they hear." [MAC 37] Today, this phenomenon is known as the "wisdom of crowds" [SUR 04]. Many crowdsourcing projects rely on this phenomenon to obtain quality data or sometimes even true expertise. As such, an American intelligence agency, the "Good Judgment Project", relies on the geopolitical forecasts of crowds of Internet users quantitatively estimating the probability or improbability of such and such event. In the same way, big data and the analysis of geographic locations occurring alongside the name "Ben Laden" in the international press using text-mining technologies has shown that those locations were near where he was hiding. When data form crowds, they could therefore also form science, and thanks to crowdsourcing, human brains could be connected like high-powered processors contributing to a calculation much more massive than that of algorithms. We could thus speak of "Human computation" [VON 06].

However, in history, crowds are not always distinguished by their wisdom, but sometimes rather by the criminal irresponsibility of the individuals making up the masses, as Gustave Le Bon brought up in his The Crowd: A Study of the Popular Mind, particularly in light of the events tied to terror in the French Revolution, and this long before the totalitarian experiences of the 20th Century. On the Web today, while the madness of the masses does not have the same breadth, the rumors, conspiracy theories and collective paranoia sometimes also seem to disprove the existence of any wisdom of the crowds.

But beyond the simple production of data, recourse to crowds of amateurs with diverse profiles not seeking to reproduce the established models with which professionals have been educated can also be a source of happy coincidences (serendipity), "unexpected readers", accidental discoveries or even innovative breakthroughs. In any case, it encourages the development of an ecosystem of innovation. Thus, according to Eric Von Hippel, "user innovation" theorist, 46% of American companies in innovating sectors find their origins in a simple do-it-yourself consumer [VON 05].

Figure 5 . 1 .

 51 Figure 5.1. Page from an old thesis saved at the National Veterinary School of Toulouse for which OCR correction is proposed via Wikisource

  Figure 5Windisc

Figure 5 . 3 .

 53 Figure 5.3. Screenshot of the Digitalkoot OCR correction game [CHR 11]

Figure 5 . 4 .

 54 Figure 5.4. Diagram explaining how reCAPTCHA works according to https://www.google.com/recaptcha

Figure 5 . 5 .

 55 Figure 5.5. The Espresso Book Machine according to http://ondemandbooks.com

Figure 5 . 6 .

 56 Figure 5.6. Number of publications indexed in Google Scholar as a function of their years of publication and responding to the search "crowdsourcing AND library AND digitization"

Figure 5 . 7 .

 57 Figure 5.7. Relative influence of different countries in the thesis bibliography (216 publications). For a color version of the figure, see www.iste.co.uk/szoniecky/collective.zip

  Figure 5.8. Taxonomy of the motivations of Internet users who participate in crowdsourcing projects in libraries

Table 5 .

 5

1. Chronology of crowdsourcing in libraries

  Participatory uploading and curation: Oxford's great war archive, Europeana 1914-1918, Internet Archive, Commons Wikimedia, Wir waren so frei, Open Call -Brooklyn Museum, Pin-a-tale, Make history, Click! A Crowd-Curated Exhibition, The Changing Faces of Brooklyn, ExtravaSCANza Flickr, The Commons, steve.museum, GLAM Wikimedia, Glashelder!, VeleHanden, 1001 Stories Denmark, Historical Maps Pilot, Mtagger, PennTags, Social OAC, Describe me, Tag! You're It!, Freeze tag!, Your Paintings Tagger, Operation war diary

	Implicit
	crowdsourcing and	Definition	Identified projects
	gamification
		recourse to
	Implicit crowdsourcing	involuntary work by	OCR correction: reCAPTCHA
		Internet users
	Explicit crowdsourcing Gamification "human computation" "games with a purpose"	Definition recourse to Internet users' work in game form	Identified projects OCT correction: Digitalkoot, COoperative eNgine for Correction of ExtRacted Text, TypeAttack, Word Soup Game, Smorball, Beabstalk Indexing: Art Collector, Google Image Labeler, ESP Game, GWAP, Peekaboom, KissKissBan, PexAce, museumgam.es, Metadata Games, SaveMyHeritage, Picaguess, Wasida
			On-demand digitization: eBook on demand (EOD),
			books à la carte, Éditions du Phoenix, Chapitre.com, les
			amis de la BnF, Numalire, revealdigital, Lyrasis,
	Crowdfunding	Recourse to recourse to Internet users' financial contributions	Participatory OCR correction: TROVE, Distributed Proofreader, Wikisource, California Digital Newspaper Collection, Correct, Franscriptor FeniXX, unglue.it, Maine Shared Collections Strategy, International Amateur Scanning League, "Sauvez nos reliures" Participatory manuscript transcription: Transcribe On-demand printing: Espresso Book Machine,
	Volunteer	voluntary work	Bentham, What's on the Menu?, Ancient lives, Electronic Library, Higher Education Resources ON
	crowdsourcing	from voluntary Internet users	ArcHIVE, What's the score, Transkribus, les Demand, Amazon Book Surge, CreateSpace, Jouve, Herbonautes, Do it yourself History, Monasterium lulu.com, Lightning source, Virtual Bookworm,
			Collaborative Archive, Citizen Archivist Dashboard, Wingspan press, iUniverse, Xlibris
			National Archives Transcription Pilot Project, Field
		Table 5.3. Taxonomy of crowdsourcing and Notes of Laurence M. Klauber, Notes from Nature, Transcribe Bushman, Smithsonian Digital Volunteers panorama of the projects for digital libraries
			Transcription Center
	Recourse to the Folksonomy: Paid All kinds of work: Amazon Mechanical Turk Marketplace, 99design, CloudCrowd, Cloud-Flower, CrowdFlower, Upwork, Foule Factory, Freelancer, work of paid Guru, Innocentive, ManPower, Mob4hire, crowdsourcing Internet users MobileWorks, oDesk, Postmates, quora.com,
			Samacource, sparked.com, TaskRabbit, Topcoder,
			Trada, Turkit, uTest

Comment [U1]:Please check the year '18??' in Table5.1.

Comment [U2]:Please check the year '195?' in Table5.1.

Comment [U3]:Please check the term 'masses joint property'.Comment [U4]:Please check the sentence 'Under these conditions, outsourcing expert work to hobbyists…' for clarity.

Comment [DBD5]:Reference "[SHI 10]" is cited in the text but not provided in the list. Please provide its complete details.

Comment [DBD9]:Reference "[SHI 08] " is provided in the list but not cited in the text. Please provide its citation details in the text.


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Use of a skin perforator flap pedicled by the intercostal muscle for reconstruction of a posterior cervical defect

Use of a skin perforator flap pedicled

Introduction

The use of a flap to cover a posterior cervical defect featuring exposed spinal and occipital bone is difficult. Flaps used for this purpose may be locoregional or free. An "ideal" flap should be a pedicled locoregional flap that can be harvested quickly and easily without A c c e p t e d M a n u s c r i p t muscular sequelae and with minimal morbidity; the flap should reach the occiput. Adjuvant radiation therapy may reduce the available options; free flaps are frequently used [START_REF] Goh | Outcome predictors in elderly head and neck free flap reconstruction: A retrospective study and systemic review of the current evidence[END_REF][START_REF] O'connell | Head and neck reconstruction with free flaps based on the thoracodorsal system[END_REF] . Three principal types of pedicled flap are available: the trapezius myocutaneous, latissimus dorsi, and dorsal intercostal artery propeller perforator flaps. We present a case in which none of these flaps was suitable. We created a skin perforator flap pedicled by the intercostal muscle; we previously used this flap to cover tracheoesophageal fislulae [START_REF] Bertheuil | Skin perforator flap pedicled by intercostal muscle for repair of a tracheobronchoesophageal fistula[END_REF][START_REF] Bertheuil | Skin perforator flap pedicled with intercostal muscle: Additional data[END_REF] that developed after surgery to treat esophageal carcinoma. The flap afforded satisfactory esthetic and functional results. To our knowledge, this report is the first to describe the use of this flap to cover a posterior cervical defect.

Case report

A 62-year-old man with a history of asthma, osteoporosis, and disc herniation at L1-S5 treated by laminectomy and osteosynthesis, and who was being weaned from a smoking addiction and alcoholism, was admitted to Rennes University Hospital for treatment of severe metastatic C2 osteolysis including the odontoid (Fig. 1). The primary tumor was an inoperable TxN3M1b squamous cell carcinoma of the lung that was first treated by six injections of carboplatin (TEVA, Petah Tikva, Israel) and Taxol (Bristol Myers Squibb, New York, NY, USA) over a period of 4 months. Opdivo (Bristol Myers Squibb) was then introduced as a second-line treatment; the patient had recently received his 32 nd injection. At the last followup, the patient's lung disease had been found to be controlled by the immunotherapy. The C2 metastasis was initially treated via two occipitocervical arthrodeses; the postoperative course was uneventful. Adjuvant external-beam radiation therapy (37.5 Gray) was then delivered. Three months postoperatively, wound dehiscence was evident on top of the scar. The patient was then lost to follow-up. He reconnected with his neurosurgeon 20 months after surgery, with a 1.5-cm-diameter occipitocervical defect featuring exposure of material. Computed tomography of the cervical region revealed complete bone remodeling and consolidation, allowing removal of the material without any further need for immobilization. Two years after the initial surgery, a re-operation was performed with the patient in the left lateral decubitus position under general anesthesia. Radiodermatitis (LENT-SOMA score = 4) was apparent; we debrided the wound (Figure 1), removed the material, and took several bone samples for bacteriological testing. The cavity created by the loss of substance was 9 cm in height, 10 cm in width, and 5 cm in depth; bone was exposed from the occiput to C5. We harvested a skin Briefly, three perforators were preoperatively identified in the fifth intercostal space using an 8-MHz handheld Doppler ultrasonographic device. After incision, we created a 14 × 7-cm elliptical skin flap to allow primary closure of the donor site. Two perforators were visualized under the fascia, dissected, and skeletonized. The flap was next harvested subfascially in the distal to proximal direction. The fifth and sixth costal planes were exposed, and the periostea of the two ribs were incised and separated from the bone along the intercostal muscle. The subcostal pedicle was ligated anteriorly to the perforator vessels. With the aid of finger dissection, the parietal pleura was incised, but not detached from the intercostal muscle (Figure 2A&B). The flap was then dissected beyond the latissimus dorsi muscle (which was preserved). After harvesting, the flap was moved to the neck defect (Figure 3) via a submuscular and subcutaneous tunnel (beneath the trapezius muscle).

Cervical and chest drains were placed, and the skin flap was sutured around the cervical cavity using interrupted, non-absorbable 3-0 sutures; the thoracotomy was then closed.

The bone samples were positive for methicillin-sensitive Staphylococcus aureus.

Antibiotic treatment (intravenous tazocillin; Pfizer, New York, NY, USA) was commenced perioperatively; oral Rifadine (Sanofi Aventis, Paris, France) and Ciflox (Bayer, Leverkusen, Germany) were then added for a total of 42 days. The postoperative period was marked by venous congestion of the flap, probably attributable to constriction of the pedicle under the trapezius muscle. This complication was resolved via leech therapy. We removed the chest drain without complications on postoperative day 7 and discharged the patient to home on day 15. He remains alive 18 months postoperatively (Figure 4A &B).

Discussion

We here describe an innovative surgical technique; we used a skin perforator flap pedicled by the intercostal muscle to cover a posterior cervical defect. Only a few pedicled locoregional flaps can be created. The use of a propeller perforator flap [START_REF] Kneser | Transverse cervical artery perforator propeller flap for reconstruction of supraclavicular defects[END_REF] or a flap pedicled by another muscle might have been an option. This report is the first to describe the use of our flap for head-and-neck reconstruction. Of value, propeller perforator flaps are not associated with muscular sequelae. In the head-and-neck region, such a flap can be harvested if the dorsal intercostal artery perforator is present. We found no vessel close to the defect, probably because of the radiation therapy and prior surgery. Flaps fed by the transverse cervical A c c e p t e d M a n u s c r i p t arteries are often used to cover head-and-neck defects; the flaps include myocutaneous trapezius [START_REF] Lynch | The lower trapezius musculocutaneous flap revisited: versatile coverage for complicated wounds to the posterior cervical and occipital regions based on the deep branch[END_REF] , muscle-sparing trapezius [START_REF] Nascimento | Trapezius perforator flap for reconstruction of a posterior cervical defect[END_REF] , propeller [START_REF] Okada | A propeller flap based on the thoracoacromial artery for reconstruction of a skin defect in the cervical region: A case report[END_REF] , and island perforator flaps [START_REF] Giordano | Supraclavicular artery island flap (SCAIF): a rising opportunity for head and neck reconstruction[END_REF][START_REF] Chen | Extended vertical lower trapezius island myocutaneous flap for reconstruction of cranio-maxillofacial defects[END_REF] . We did not choose any of these options because the pedicles lay in the irradiated area and we did not want to risk placement of a poorly vascularized flap. The trapezius musculocutaneous flap is reliable and robust when head-and-neck reconstruction is required, affording a large arc of rotation in the absence of any major functional deficit. However, the flap is vascularized by the suprascapular artery (a branch of the transverse cervical artery), which may have been damaged by the radiation therapy. Another possibility was a muscular latissimus dorsi flap, which is well vascularized by the thoracodorsal artery, quick to harvest, and affords robust coverage. Its preparation is simple and reliable, associated with the removal of a large area of skin. We did not favor this option as a first-line treatment because postoperative muscle sequelae were likely. The preservation of latissimus dorsi muscle function was essential because the two arthrodeses had been associated with major functional limitations. Otherwise, this flap would have been a good alternative.

We have used skin perforator flaps pedicled by the intercostal muscle eight times [START_REF] Grimminger | Diagnosis, assessment, and management of surgical complications following esophagectomy[END_REF][START_REF] Bertheuil | Thoracotomy and esophageal surgery: Key points to preserve the possibilities of flaps[END_REF] to treat tracheobronchial fistulae developing after esophageal carcinoma resections. The flap affords several advantages. First, the pedicle is long (up to 30 cm), thus allowing access to remote (e.g., intrathoracic) defects, but also extrathoracic defects that include the occiput. The flap is easily and safely harvested with primary closure of the donor site if the skin paddle is not too wide (not >8 cm). In the present case, the pedicle had not been damaged by the radiation therapy. The flap is rather thick, permitting good bone coverage and yielding a pleasing esthetic result. A disadvantage is that the chest cavity must be opened and, therefore, a chest drain must be placed. This procedure can be painful, but was not so in our patient. We encountered flap venous congestion that resolved after leech therapy [START_REF] Herlin | Leech therapy in flap salvage: Systematic review and practical recommendations[END_REF] . The congestion may be attributable to the tunneling of the flap along the costal plane under the trapezius muscle, which may have compressed the flap. It might have been better to have passed the flap over the muscle.

In conclusion, to our knowledge, this report is the first to describe the use of this flap to cover the posterior cervical area; the outcome was good. Our approach is feasible and safe, and is a useful new option for head-and-neck reconstruction.

COMPLIANCE WITH ETHICAL STANDARDS

A c c e p t e d M a n u s c r i p t

A

  c c e p t e d M a n u s c r i p t perforator flap pedicled by the intercostal muscle and translated it subcutaneously; we thus used a mini-invasive technique to cover the defect.

Fig 1 :

 1 Fig 1: The cervical defect after wound debridement. The irradiated skin was removed. The

Fig 2 :

 2 Fig 2: The skin perforator flap (LICAP) pedicled by intercostal muscle harvesting. Anterior

  A c c e p t e d M a n u s c r i p t

Fig 3 :

 3 Fig 3: The flap at the end of surgery. Posterior cervical and chest view in left lateral

Conflict of Interest statement : authors declare that they have no conflicts of interest to disclose.

Statement of human and animal rights, or ethical approval : This article does not contain any studies with human participants or animals performed by any of the authors.

Informed consent : For this type of study informed consent is not required.