Melanie Mcclure
email: mel_mcclure@hotmail.com

Louisa Mahrouche

Céline Houssin

Monica Monllor

Yann Le Poul

Brigitte B Frerot

Alexandra Furtos

Marianne Elias

Le Poul

Does divergent selection

Keywords: assortative mating, colour pattern, hybrids, mimicry, magic traits, reinforcement, sexual selection, speciation

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

A key aspect of evolutionary biology is determining the factors that promote population diversification and the processes that initiate progress towards speciation. Divergence in both mating preference and cues are expected to reduce mating between populations and increase reproductive isolation [START_REF] Boughman | Divergent sexual selection enhances reproductive isolation in sticklebacks[END_REF], and many studies have highlighted the importance of traits that are under divergent ecological selection that also contribute to assortative mating (e.g. [START_REF] Jiggins | Reproductive isolation caused by colour pattern mimicry[END_REF][START_REF] Servedio | Magic traits in speciation: 'magic' but not rare?[END_REF][START_REF] Maan | Magic cues versus magic preferences in speciation[END_REF][START_REF] Jiang | Assortative mating in animals[END_REF]. Because the trait subject to divergent selection can directly lead to assortative mating, gene flow is reduced, and these "magic traits" can be the first step in speciation [START_REF] Servedio | Magic traits in speciation: 'magic' but not rare?[END_REF].

However, assortative mating requires the evolution of both divergent cues and preferences, and divergence in one of these alone will not automatically lead to reproductive isolation [START_REF] Maan | Magic cues versus magic preferences in speciation[END_REF].

To understand how divergent selection affects reproductive isolation and hence speciation, we need to identify the mechanisms that generate mating assortment. What is currently needed are detailed studies of closely related taxa that span the speciation continuum, such as populations or species pairs, that are under divergent ecological selection and that vary strongly in their degree of reproductive isolation. A comparative approach based on natural replicates also offers a powerful means with which to study the conditions conducive for speciation. Mimetic organisms, whereby multiple co-occurring unpalatable species converge on the same warning signal and effectively share the cost of educating predators, are especially well suited for studies on speciation, as species often consist of multiple subspecies diverging for adaptive traits such as wing colour pattern, which can then cause reproductive isolation through sexual and natural selection against phenotypic intermediates [START_REF] Jiggins | Reproductive isolation caused by colour pattern mimicry[END_REF]Naisbit, Jiggins & Mallet 2001;[START_REF] Merrill | Disruptive ecological selection on a mating cue[END_REF][START_REF] Arias | Crossing fitness valleys: empirical estimation of a fitness landscape associated with polymorphic mimicry[END_REF].

The tribe Ithomiini (ca. 390 species) represents the largest radiation of mimetic butterflies in the Neotropics, where they numerically dominate forest butterfly communities, and have been instrumental in the discovery and description of Müllerian and Batesian mimicry in the 19 th century [START_REF] Bates | Contributions to an insect fauna of the Amazon valley: Lepidoptera: Heliconidae[END_REF][START_REF] Müller | Ituna and Thyridia; a remarkable case of mimicry in butterflies[END_REF]. Indeed, the tribe is thought to drive mimicry in many Lepidoptera [START_REF] Brown | Adaptive polymorphism associated with multiple Müllerian mimicry in Heliconius numata (Lepid. Nymph.)[END_REF][START_REF] Beccaloni | Ecology, natural history and behaviour of ithomiine butterflies and their mimics in Ecuador (Lepidoptera: Nymphalidae: Ithomiinae)[END_REF]. However, due to the difficulty in breeding and maintaining ithomiines in captivity, no study has, until now, investigated mate choice and mating behaviour in this tribe. Here we present the first experimental test of reproductive isolation in the tribe Ithomiini, using the genus Melinaea.

The genus Melinaea consists of at least 14 species and over 70 subspecies [START_REF] Lamas | Atlas of Neotropical Lepidoptera. Checklist: Part 4A. Hesperioidea-Papilionoidea[END_REF]; but see also [START_REF] Mcclure | Ecology, life history, and genetic differentiation in Neotropical Melinaea (Nymphalidae: Ithomiini) butterflies from north-eastern Peru[END_REF][START_REF] Mcclure | Heterozygosity and chain multivalents during meiosis illustrate ongoing evolution as a result of multiple holokinetic chromosome fusions in the genus Melinaea (Lepidoptera, Nymphalidae)[END_REF]) distributed across much of the Neotropics and is oligophagous on the plant subfamily Solandreae (Solanaceae; [START_REF] Willmott | Higher-level phylogeny of the Ithomiinae (Lepidoptera: Nymphalidae): classification, patterns of larval hostplant colonization and diversification[END_REF]. A recent assessment of diversification rates in the tribe revealed that a clade of eight species in the genus experienced an extremely rapid and recent radiation [START_REF] Chazot | Renewed diversification following Miocene landscape turnover in a Neotropical butterfly radiation[END_REF] in agreement with previous studies using mitochondrial and nuclear genes, and rapidly evolving microsatellite markers, that show little genetic differentiation among taxa of this clade [START_REF] Whinnett | Strikingly variable divergence times inferred across an Amazonian butterfly 'suture zone[END_REF][START_REF] Elias | Limited performance of DNA barcoding in a diverse community of tropical butterflies[END_REF][START_REF] Dasmahapatra | The anatomy of a "suture zone" in Amazonian butterflies: a coalescent-based test for vicariant geographic divergence and speciation[END_REF][START_REF] Mcclure | Ecology, life history, and genetic differentiation in Neotropical Melinaea (Nymphalidae: Ithomiini) butterflies from north-eastern Peru[END_REF]. The Melinaea of north-eastern Peru (San Martín and Loreto departments) are of particular interest for speciation studies, as multiple species, many consisting of different subspecies, are present and overlap in distribution.

Different subspecies are characterised by different wing colour patterns which are associated with distinct mimetic communities, including with the polymorphic Heliconius numata, whose different morphs are co-mimics to different Melinaea taxa [START_REF] Brown | Adaptive polymorphism associated with multiple Müllerian mimicry in Heliconius numata (Lepid. Nymph.)[END_REF][START_REF] Beccaloni | Ecology, natural history and behaviour of ithomiine butterflies and their mimics in Ecuador (Lepidoptera: Nymphalidae: Ithomiinae)[END_REF]). As a result, distribution is often parapatric, with a different dominant taxon in each locality, and a transition or contact zone where different taxa co-occur. Colour patterns are used in mate recognition in a range of mimetic organisms [START_REF] Jiggins | Reproductive isolation caused by colour pattern mimicry[END_REF][START_REF] Jiggins | The phylogenetic pattern of speciation and wing pattern change in Neotropical Ithomia butterflies (Lepidoptera: Nymphalidae)[END_REF][START_REF] Merrill | Disruptive ecological selection on a mating cue[END_REF], and this may also be the case in the genus Melinaea, although this has never before been investigated in Ithomiini. However, [START_REF] Jiggins | The phylogenetic pattern of speciation and wing pattern change in Neotropical Ithomia butterflies (Lepidoptera: Nymphalidae)[END_REF] have demonstrated a phylogenetic pattern of speciation that is correlated with changes in wing colour pattern in the genus Ithomia (Ithomiini), which strongly suggests that this may be the case. In addition to colour pattern, pheromones may also play an important role in mate recognition and reproductive isolation. Indeed, Ithomiini male butterflies collect pyrrolizidine alkaloids (PA) which are thought to provide toxicity and pheromone precursors (see Schulz et al. 2004 and references therein). Furthermore, as in other ithomiines, male butterflies have hairpencils on their posterior wings that are modified androconial scales used to diffuse these compounds (see e.g. [START_REF] Edgar | Isolation of a lactone, structurally related to the esterifying acids of pyrrolizidine alkaloids, from the costal fringes of male ithomiinae[END_REF].

Premating isolation is expected to be especially strong since females appear to mate only once (i.e. are monandrous; McClure & Elias 2017). Indeed, mistakes or mating with subpar males likely impose a high cost to females, and they are therefore expected to be choosy. This paper focuses on five Melinaea taxa thought to form a speciation continuum, from subspecies to fully recognized species [START_REF] Lamas | Atlas of Neotropical Lepidoptera. Checklist: Part 4A. Hesperioidea-Papilionoidea[END_REF] The main purpose of this study is to uncover the factors that drive reproductive isolation (and therefore, speciation) between different mimetic taxa, and what, if anything, promotes the evolution of mating preference and/or choosiness. Although most studies have focused on mating cues [START_REF] Servedio | Magic traits in speciation: 'magic' but not rare?[END_REF][START_REF] Maan | Magic cues versus magic preferences in speciation[END_REF], determining the evolutionary consequences of divergent selection on reproductive isolation requires studies of the variation that exist in both mating cues and preferences in diverging taxa. The types of isolation that exist between partially isolated taxa in nature are of great interest, as they can provide insight as to what mechanisms are important in the early stages and which processes are then important in driving reproductive isolation and speciation. Using genetic markers (microsatellites), wing colour pattern quantification and vision models for butterflies and their avian predators, male pheromone characterization and behavioural assays of mating preference, we characterize the extent of genetic and phenotypic differentiation for five Melinaea taxa, and compare it to the level of mate preference (as a measure of premating isolation). We then discuss the factors that best explain differential progress towards speciation in light of our results.

Material and Methods

Butterfly sampling. Butterflies were collected in north-eastern Peru from 2011 to 2016.

Collection localities consisted of premontane forest habitats near Tarapoto (Rio Shilcayo basin: 6°27'30''S, 76°21'00''W), Shapaja (6°36'56''S, 76°09'61''W) and Chazuta (6°57'05''S, 76°13'75''W), and lowland forest on Pongo-Baranquita road (6°17'53''S, 76°14'38"W) and Shucushyacu (5°57'20''S, 75°53'06''W). Various sites a few kilometres apart were sampled within each locality. The number of individuals of each taxon used to measure genetic differentiation, pheromone characterization and colour pattern quantification are found in Table 1.

Individuals that were phenotypically intermediate between M. mar. phasiana and M. mar. rileyi were considered to be putative hybrids. To test if the occurrence of putative hybrids deviated from expectations if mating were random, a Pearson's χ 2 test was done on the observed frequencies obtained from the data and by calculating expected frequencies based on Hardy-Weinberg equilibrium (Table S1). This was done both for the entire distribution (i.e. all localities were pooled) and for the contact zone, where hybridization may be more common.

Rearing conditions. Gravid wild caught females were kept in 2x2x2 m outdoor insectaries under ambient conditions in Tarapoto, San Martín, where all rearing was carried out (see [START_REF] Mcclure | Unravelling the role of host plant expansion in the diversification of a Neotropical butterfly genus[END_REF] for further information). Butterflies were provided with nourishment in the form of sugar water solution and bee pollen. All species in this study use J. parasitica as a host plant [START_REF] Mcclure | Unravelling the role of host plant expansion in the diversification of a Neotropical butterfly genus[END_REF][START_REF] Mcclure | Ecology, life history, and genetic differentiation in Neotropical Melinaea (Nymphalidae: Ithomiini) butterflies from north-eastern Peru[END_REF], and as such, potted J. parasitica plants were used for oviposition, and larvae collected in the cages were reared individually in transparent plastic containers in the shade behind a nearby building under ambient conditions. Larvae were checked daily for food replacement and cleaning, and leaves were offered ad libitum.

Newly emerged butterflies were kept segregated by sex in outdoor insectaries until use, with sugar water solution and bee pollen for nourishment, and pyrrolizidine alkaloid sources in the form of withered Heliotropium sp. (Boraginaceae) and Eupatorieae (Asteraceae).

No-choice mating experiments. To test for reproductive isolation, no-choice experiments were used as they examine whether mating can occur, when no alternatives are present (a situation more likely to reflect what happens in nature). Strict preference in a choice situation does not preclude the possibility of accepting a mate when no alternative is present. Trials were carried out with four males and four females, unrelated, and of either the same or different taxa. Trials lasted for four days or until a mating event occurred and 12 replicates were done for each combination. For trials between different taxa, half of the replicates were done using each reciprocal cross so as to control for potentially different mating probabilities. For trials between the closely related species M. satevis cydon and M. marsaeus, half of the replicates were done using each of the M. marsaeus subspecies. However, the results of these reciprocal crosses were not found to be statistically different (M. menophilus: χ 2 =1.2, df=1, p=0.273; M. marsaeus: no mating was observed; M. marsaeus x M. satevis cydon: no mating was observed; see Table 2), and were therefore pooled.

Melinaea marsaeus was used with M. satevis cydon to test assortative mating between closely related species as McClure & Elias (2017) have shown, using microsatellite markers, that M. menophilus clusters separately from M. marsaeus and M. satevis cydon. The latter two species are therefore more closely related, and provide a relevant comparison after reproductive isolation is complete.

McClure & Elias (2017) reported that copula lasted anywhere between a little over an hour up to 24 h. As such, cages were checked hourly between 6 AM and 6 PM (hours during which there is daylight) every day for mating events. To further ensure that no mating events took place unnoticed, the presence of a spermatophore was ascertained by palping the females' abdomen at the end of the experiment. Males, regardless of whether they were mated, and females that did not mate, were occasionally re-used, but only after 7-10 days had elapsed to prevent habituation and no more than once. Females that mated were not re-used.

Mating probabilities Pij between i-type females and j-type males relative to the probability of mating within types were estimated using likelihood in order to test between hypotheses [START_REF] Mcmillan | What initiates speciation in passion-vine butterflies[END_REF]Naisbit, Jiggins & Mallet 2001). The probability of mating occurring can be calculated by maximizing the loge-likelihood expression:

L(Pij) =mij loge(Pij) + (Nij-mij)loge(1-Pij)
N and m are the total number of trials and the number of trials where mating occurred, respectively.

Fitting models with different numbers of parameters (i.e., same versus different mating probabilities for different types of crosses) enabled to test for differences in the mating probability across trials using a likelihood ratio test with G=2ΔlogeL, which asymptotically follows a χ2distribution [START_REF] Edwards | Likelihood[END_REF]. As such, we were able to test whether individuals of different taxa mate less frequently than those of the same taxon, or if all crosses are either equal or all significantly different from one another. [START_REF] Coyne | Patterns of speciation in Drosophila[END_REF] was also calculated using the expression:

An index of premating isolation similar to what was used by

1-This index ranges from -∞ (complete disassortative mating) through 0 (no mating isolation) to 1 (complete mating isolation).

Genetic differentiation.

Samples used in this study were preserved in either ethanol or in saltsaturated 20% dimethylsulphoxide (DMSO) with ethylenediaminetetraacetic acid (EDTA).

Individuals were genotyped at 12 microsatellite markers developed for Melinaea, using primers and PCR conditions from [START_REF] Mcclure | The development and characterization of polymorphic microsatellite loci for the genus Melinaea (Nymphalidae, Ithomiini)[END_REF]. The extent of genetic differentiation and admixture, and the number of possible genetic clusters (or distinct groups), was assessed in three ways. First, STRUCTURE version 2.3.4 [START_REF] Pritchard | Inference of population structure using multilocus genotype data[END_REF] was used on the data, run with 500 000 updates of the Markov chain after an initial 'burn-in' of 50 000 updates for one to five genetic clusters (K=1-5), with five replicates at each value of K. The method described by [START_REF] Evanno | Detecting the number of clusters of individuals using the software STRUCTURE: a simulation study[END_REF], based on the second-order rate of change of the log likelihood and implemented in STRUCTURE HARVESTER [START_REF] Earl | STRUCTURE HARVESTER: a website and program for visualizing STRUCTURE output and implementing the Evanno method[END_REF], was used to determine the number of clusters that best describe the data. A factorial correspondence analysis was also used on the data using GENETIX [START_REF] Belkhir | GENETIX 4.0.4, Logiciel sous Windows TM pour la génétique des populations. Laboratoire Génome, Populations, Interactions[END_REF]. Finally, Fst values for each pair of taxa were calculated using GENEPOP version 4.2 [START_REF] Raymond | An exact test for population differentiation[END_REF].

Differentiation of colour pattern. Differentiation in colour pattern was quantified using Colour

Pattern Modelling (CPM) described by [START_REF] Poul | Evolution of dominance mechanisms at a butterfly mimicry supergene[END_REF]. Photographs, taken under standardized conditions (see Le [START_REF] Poul | Evolution of dominance mechanisms at a butterfly mimicry supergene[END_REF] for details), of the dorsal and ventral sides of forewings and hindwings of each specimen were used. The CPM automatically detects and eliminates the background in the pictures and each pixel of the butterfly wing image is automatically attributed a colour, which is then categorized into one of three major colours present in the wing patterns (that is, black, orange or yellow). Hind and forewings are aligned separately using a rigid transformation, and similarity (accounting both for wing shape and pattern) with a wing model that averages all wing images is maximized recursively. After alignment, the position of each pixel in the wing image is considered homologous among all individuals, enabling a pixelby-pixel analysis of pattern variation.

In order to link divergence in colour pattern to reproductive isolation (specifically, prezygotic isolation driven by mate choice, and postzygotic isolation driven by predation), the value of each pixel was re-calculated by incorporating models of animal vision (see [START_REF] Arias | Crossing fitness valleys: empirical estimation of a fitness landscape associated with polymorphic mimicry[END_REF] for details) and by using the precise colour spectrum of each colour (see [START_REF] Llaurens | Cryptic differences in colour among Müllerian mimics: how can the visual capacities of predators and prey shape the evolution of wing colours?[END_REF]. Models of animal vision, based on the sensitivities of photoreceptors present in their eyes, allow inferences about the colour contrasts and the conspicuousness of the different colours that can be perceived by different animals. As such, two avian vision systems that vary in their sensitivity to ultra-violets (i.e. wavelengths below 400nm) and one butterfly vision system were performed. All vision systems consist of four photoreceptors. Specifically, the quantum catches, which is the relative amount of light captured by each photoreceptor when observing a given colour [START_REF] Iriel | Implications of reflectance and fluorescence of Rhododendron indicum flowers in biosignaling[END_REF], was applied using the method described in [START_REF] Vorobyev | Tetrachromacy, oil droplets and bird plumage colours[END_REF] and assuming a Weber fraction of 0.05 for all vision systems. A light environment corresponding to both small and large gaps in a forest canopy (computed as in Llaurens, Joron & Théry 2014) was used. As the photoreceptor sensitivities of the birds composing the predator community in this study system are not known, the calculations were based on the two main vision systems found in birds. The blue tit (Parus caeruleus) was used for vision with ultra-violet sensitive pigments (UVS), with cone proportion and sensitivity as described by [START_REF] Hart | Visual pigments, oil droplets, ocular media and cone photoreceptor distribution in two species of passerine bird: the blue tit (Parus caeruleus L.) and the blackbird (Turdus merula L.)[END_REF], and the shearwater (Puffinus pacificus) was used for vision with violet sensitive pigments (VS), as described by [START_REF] Hart | Microspectrophotometry of visual pigments and oil droplets in a marine bird, the wedge-tailed shearwater Puffinus pacificus: topographic variations in photoreceptor spectral characteristics[END_REF]. To model butterfly vision, the photoreceptors sensitivity was computed using the visual sensitivity peaks reported for Danaus plexippus (the monarch, the closest relative of Melinaea for which sensitivity peaks are known) in [START_REF] Stalleicken | Physiological characterization of the compound eye in monarch butterflies with focus on the dorsal rim area[END_REF] and [START_REF] Blackiston | Color vision and learning in the monarch butterfly, Danaus plexippus (Nymphalidae)[END_REF], applying Stavenga (2010)'s equations. Since [START_REF] Blackiston | Color vision and learning in the monarch butterfly, Danaus plexippus (Nymphalidae)[END_REF] reported the existence of a dark orange filter in the long wavelength receptor, which effectively gives rise to a fourth type of receptor, we also modelled this filtered photoreceptor by digitizing the spectrum reported in [START_REF] Mcculloch | Sexual dimorphism in the compound eye of Heliconius erato: a nymphalid butterfly with at least five spectral classes of photoreceptor[END_REF] for Heliconius erato (the closest butterfly species -also a Nymphalidae -for which the spectrum has been characterized, and whose long wavelength photoreceptor peaks at the same value as D. plexippus) using the software Graph Grabber 2.0 (www.quintessa.org/). The vision model for D. plexippus is available in ESM. The precise colour spectrum of each colour detected by CPM (black, orange and yellow) were those taken on Melinaea by [START_REF] Llaurens | Cryptic differences in colour among Müllerian mimics: how can the visual capacities of predators and prey shape the evolution of wing colours?[END_REF]. Quantum catches for each photoreceptor in birds and butterflies were estimated using AVICOL (Gomez 2006), under large light gap and small light gap light conditions. The phenotypic variation (variation among all pixels common between all wings) after accounting for animal vision was summarized using a principle component analysis (PCA). Differences between groups were tested using ADONIS (PERMANOVA) in the R package Vegan [START_REF] Oksanen | Vegan: Community ecology package. R package version 2[END_REF], followed by a pairwise comparison (i.e. post hoc test) with Bonferroni correction (pairwiseAdonis: Martinez Arbizu 2017). Finally, differentiation between taxa was measured as Euclidean distances between centroids in PCA space.

Chemical analysis. Preliminary tests of female wing extracts failed to reveal any compounds, so all further tests focused on males. The hairpencils (i.e. androconial scales) of 6-10 males per taxa were dissected and extracted individually in 100 μl of ultrapure dichloromethane (Sigma-Aldrich®) shortly after capture. Samples were kept at -20°C until analysis in Montreal, Canada, by gas chromatography/mass spectrometry (GC/MS) with an Agilent 7890A-5975C. Using pulsed splitless injection, 2 µL of each extract was injected on an Agilent HP-5MS column (30 m x 250 µm x 0.25 µm) with the inlet maintained at 250°C. Helium was used as a carrier gas and flow rate was of 1.5411 mL/min. Temperature gradient was programmed from 50°C to 300°C at a rate of 8°C/min for a total run time of 39min. Kovats' retention indices (RIs) were computed using nalkanes from C8 to C20 that were eluted under the same conditions as the samples (external standards). Compounds were identified by comparison of mass spectra and gas chromatographic retention indices to those in the literature and the NIST library. A data matrix of all the compounds for each individual was aligned using GCAligner 1.0 [START_REF] Dellicour | GCALIGNER 1.0: an alignment program to compute a multiple sample comparison data matrix from large eco-chemical datasets obtained by GC[END_REF]. Relative concentrations were determined by peak area analysis and differences between groups were visualized using nonmetric multidimensional scaling (NMDS) ordination based on Bray-Curtis similarity matrix, using the function metaMDS in the R package Vegan [START_REF] Oksanen | Vegan: Community ecology package. R package version 2[END_REF].

Differences between groups were tested using ADONIS (PERMANOVA) in the R package Vegan, followed by a pairwise comparison (i.e. Post hoc test) with Bonferroni correction (pairwiseAdonis: Martinez Arbizu 2017). If differences within species (i.e. between subspecies) were found to be significant, this was followed with a non-parametric Mann-Whitney U test so as to test for differences in the amount of each compound. Finally, differentiation between taxa was measured as Euclidean distances between centroids.

Results

Distribution. Partial geographical isolation is observed between the subspecies of both M. marsaeus and M. menophilus, with uneven abundance at the different localities. Distribution and relative frequency of the five different taxa in each region is shown in Fig. S1. The general pattern of distribution for these subspecies pairs consists in one subspecies being present in premontane forest (M. men. ssp. nov. 1 and M. mar. phasiana) and the other in lowland forest (M. men. hicetas and M. mar. rileyi). The different subspecies are considered parapatric, and both species have a transition or contact zone in the lowlands near Pongo, a known suture and hybrid zone [START_REF] Whinnett | Strikingly variable divergence times inferred across an Amazonian butterfly 'suture zone[END_REF][START_REF] Dasmahapatra | The anatomy of a "suture zone" in Amazonian butterflies: a coalescent-based test for vicariant geographic divergence and speciation[END_REF]. Finally, the third species, M. satevis cydon, is a lowland species.

Overall, the number of potential M. marsaeus hybrids (based on intermediate phenotypes) is much lower than expected under random mating (4.4% observed vs. 45.8% expected; see Table S1). This is also true in the contact zone where a strong hybrid deficit is observed (12.5% observed vs. 42.97% expected; see Table S1). Of 34 phenotypically "pure" females that were collected in the field and used to produce broods, two produced offspring of intermediate "hybrid" phenotypes (i.e. 5.9% of females). This is putatively the result of mating between M. mar. phasiana and M.

mar. rileyi.

No putative M. menophilus hybrids were observed. This is consistent with [START_REF] Mcclure | Ecology, life history, and genetic differentiation in Neotropical Melinaea (Nymphalidae: Ithomiini) butterflies from north-eastern Peru[END_REF] who reported that progeny of crosses between M. men. hicetas and M. men. ssp. nov. 1 possess either of the parental phenotypes.

No-choice mating experiments. Mating events were much more prevalent within taxa for both the closely related species M. satevis cydon and M. marsaeus (p<0.01), and within the M. marsaeus subspecies (p<0.01). However, this was not true for M. menophilus (p>0.05). Table 2 shows mating probabilities both within and between subspecies, and between closely related species. Both the closely related species M. marsaeus and M. satevis cydon showed strong premating isolation, as did the M. marsaeus subspecies (index of premating isolation=1). By contrast, the subspecies of M. menophilus showed no assortative mating (index of premating isolation=0).

Genetic differentiation.

Both STRUCTURE (Fig. S2) and the factorial correspondence analyses (GENETIX; Fig. 1) detected low levels of structuring (K=3; Delta K peak=7.5), with the three groups corresponding to the three species (M. menophilus, M. marsaeus and M. satevis cydon).

Subspecies clustered together and presented high levels of admixture, as also evidenced by low Fst values (Fst within M. menophilus = 0.01 and M. marsaeus < 0.01; Table 3). The species M. marsaeus and M. satevis cydon were also found to be closely related (Fst = 0.02-0.04; Table 3).

Differentiation of colour pattern. Fig. S3 shows the average wing colour patterns, calculated by the CPM, for each Melinaea taxon (Fig. S3a) and the heatmaps (Fig. S3b) generated to visualize how each of the three colours (black, orange and yellow) vary (from blue to red) across the wings.

Because results were identical for animal visions under both light conditions (large and small light gaps), only models based on small light gaps, which likely replicate conditions in primary forest where natural populations of Melinaea occur, are shown. Similarly, results for both avian vision (VS and UVS vision) were the same, and as such, only results for UVS vision (i.e. the blue tit) are discussed here, although results for VS vision are shown in Fig. S4. Differentiation in colour pattern was significant for all taxa and putative hybrids, both under butterfly (PERMANOVA ADONIS: F = 79.39; df = 5; p = 0.001; Fig. 2a) and avian (PERMANOVA ADONIS: F = 73.30; df = 5; p = 0.001; Fig. 2b) vision. A pairwise post hoc test with Bonferroni correction shows all groups as being significantly different from each other (p = 0.001). However, differentiation of the two subspecies of M. menophilus, which differ for a single yellow band, appears greater under the butterfly vision model than under the avian vision model.

Euclidean distances between centroids of pairs of taxa are presented in Table 3. Chemical analysis. A total of six compounds (Table 4) were identified, four of which were common to all taxa, albeit at different ratios (Fig. 3), and two were unique to M. menophilus. A comparison of the different chemical extracts was found to be significantly different (PERMANOVA ADONIS: F=27.60; df=4; p=0.001) and the NMDS ordinal plot shows the three species as being completely separate, but the subspecies as clustering together (Fig. 4). A pairwise post hoc test with Bonferroni correction confirmed that the closely related species M. marsaeus and M. satevis cydon are significantly different from each other (p = 0.015). The subspecies of M. menophilus (p = 1.0) were not found to be significantly different, but the subspecies of M. marsaeus were (p = 0.02). This difference appears to be the result of a difference in the ratio between the ΔC21 acid (U = 7; p = 0.002) and the C21 acid (U = 4; p < 0.01; Fig. 3). However, most individuals of both subspecies, in addition to the potential hybrid, possess the same intermediate ratio of the two compounds (Figs 3 & 4). Euclidean distances between centroids of pairs of taxa are presented in Table 3 and show increasing levels of differentiation with increasing reproductive isolation.

Discussion

Synchrony between assortative mating and divergent selection can trigger rapid speciation. Indeed, when mate choice is based on an ecologically important trait, divergence in that trait can facilitate reproductive isolation and speciation, even with gene flow [START_REF] Servedio | Magic traits in speciation: 'magic' but not rare?[END_REF][START_REF] Kopp | Mechanisms of assortative mating in speciation with gene flow: connecting theory and empirical research[END_REF] and references therein). Mimicry is a good example of a trait under strong ecological divergent selection that can also be used as a mating cue, and this has been shown for many different organisms, including fish (Hypoplectrus coral reef fishes: [START_REF] Puebla | Colour pattern as a single trait driving speciation in Hypoplectrus coral reef fiches[END_REF], frogs (Dendrobates:

Reynolds & Fitzpatrick 2007) and butterflies (Heliconius: Jiggins et al. 2001;[START_REF] Merrill | Disruptive ecological selection on a mating cue[END_REF].

Because the evolution of mate choice is thought to be an important process generating and maintaining biological diversity, determining which traits and corresponding selective pressures initiate differentiation is important, but understanding the causes of speciation also requires studies associated with diverging preference and/or increased choosiness [START_REF] Maan | Magic cues versus magic preferences in speciation[END_REF]). In the poison frog Ranitomeya imitator, [START_REF] Twomey | Mimetic divergence and the speciation continuum in the the mimic poison frog Ranitomeya imitator[END_REF] found that although colour pattern diverges repeatedly, genome-wide divergence occurs only when there is mate preference, resulting in assortative mating. Similarly, in the mimetic Heliconius butterflies, [START_REF] Chouteau | Polymorphism at a mimicry supergene maintained by opposing frequency-dependent selection pressures[END_REF] showed that H. numata is a panmictic population despite the presence of polymorphism as a result of disassortative mating, an unusual feature in Müllerian mimetic organisms.

To understand how divergent selection affects speciation, we need to know how it affects the evolution of reproductive isolation. [START_REF] Servedio | The role of sexual selection in local adaptation and speciation[END_REF] suggested that the ideal empirical evidence to evaluate how the evolution of choosiness affects speciation would result from testing whether evolutionary changes in choosiness are associated with changes in assortative mating among species and reduction in gene flow, preferably by comparing early to late stages of speciation. The genus Melinaea is therefore especially pertinent in furthering our understanding of the evolution of reproductive isolation and speciation as the genus has undergone a rapid and recent diversification, and consists of pairs of taxa that differ in their degree of differentiation and assortative mating, with some in the very early stages of speciation.

Our results show strong premating isolation between the closely related species M. satevis cydon and M. marsaeus, in addition to genetic and phenotypic differentiation, both for the colour pattern and pheromones. This is consistent with [START_REF] Mcclure | Ecology, life history, and genetic differentiation in Neotropical Melinaea (Nymphalidae: Ithomiini) butterflies from north-eastern Peru[END_REF] who observed that mating between sympatric species were extremely rare, including between these two closely related species, and that these crosses never produced any eggs. Reproductive isolation may not be as strong between allopatric species, however, and [START_REF] Mcclure | Heterozygosity and chain multivalents during meiosis illustrate ongoing evolution as a result of multiple holokinetic chromosome fusions in the genus Melinaea (Lepidoptera, Nymphalidae)[END_REF] reported having successfully crossed the allopatric species M. satevis cydon and M. tarapotensis (formerly M. satevis tarapotensis: see [START_REF] Mcclure | Heterozygosity and chain multivalents during meiosis illustrate ongoing evolution as a result of multiple holokinetic chromosome fusions in the genus Melinaea (Lepidoptera, Nymphalidae)[END_REF]. These crosses successfully produced viable hybrid offspring, and although most of the gametes of these hybrids had an unbalanced genome and a degenerative appearance, some hybrids produced a small proportion (4%) of viable offspring in backcrosses [START_REF] Mcclure | Heterozygosity and chain multivalents during meiosis illustrate ongoing evolution as a result of multiple holokinetic chromosome fusions in the genus Melinaea (Lepidoptera, Nymphalidae)[END_REF]. In regards to the sympatric species M. satevis cydon and M. marsaeus, strong pre-and post-mating isolation may prevent the costly production of hybrids with possible genetic incompatibilities.

Premating isolation was also observed between the subspecies of M. marsaeus, but not those of M. menophilus, despite the absence of genetic differentiation between subspecies of both these species. [START_REF] Mcclure | Ecology, life history, and genetic differentiation in Neotropical Melinaea (Nymphalidae: Ithomiini) butterflies from north-eastern Peru[END_REF] observed mating pairs of M. menophilus, and reported that these crosses were fertile and resulted in viable progeny. Chemical differentiation was not significantly different between the subspecies of M. menophilus, but was significantly different between the subspecies of M. marsaeus. This difference appears to be driven by a difference in the ratio between the ΔC21 acid and the C21 acid. However, whether this difference can be perceived by the butterflies and whether it is biologically significant remains unknown. Furthermore, this difference was not present in all individuals, with many individuals of both subspecies and the potential hybrid possessing the same ratio. This suggests that even if this difference is biologically significant, it is not the sole trait used for mate recognition. As such, colour pattern is likely the first trait to diversify and be used in mate recognition. Chemical differentiation may only occur subsequently, reinforcing mate recognition and premating isolation. Differentiation of colour pattern was significantly different between subspecies of both species, but this differentiation was found to be more pronounced between the subspecies of M. marsaeus. This was especially true when differentiation was modelled on bird vision, thought to be the main predators. A study by [START_REF] Llaurens | Cryptic differences in colour among Müllerian mimics: how can the visual capacities of predators and prey shape the evolution of wing colours?[END_REF] that compared the colour pattern of Heliconius numata with that of their Müllerian co-mimics Melinaea found that the colour contrast of yellow against a black background was greater for butterflies than for birds. The authors suggested that this variation in colour, likely undetectable to birds, might be used by butterflies to distinguish between mating partners without losing the benefits of mimicry. As such, migrants between populations of M. marsaeus are likely to suffer higher levels of predator attacks because they are strongly non-mimetic outside their habitat [START_REF] Chouteau | Warning signals are under positive frequencydependent selection in nature[END_REF], which can directly reduce gene flow between populations by lowering the rate of heterospecific encounters.

Differences in the distribution of the two species may also be due to differences in the strength of disruptive selection in the form of predation. In M. menophilus, where both phenotypes differ in the presence or absence of a single yellow band, the overlap in distribution is wide and both phenotypes occur to some extent throughout their range. In M. marsaeus, where both phenotypes differ more considerably, area of contact is narrow and each phenotype is almost exclusively present at either end of the distribution. Furthermore, putative hybrids between M. mar. phasiana and M. mar. rileyi possess intermediate non-mimetic colour patterns and likely suffer intense frequency-dependent predation similar to what is observed in the perfect co-mimic Heliconius numata [START_REF] Arias | Crossing fitness valleys: empirical estimation of a fitness landscape associated with polymorphic mimicry[END_REF], which can further decrease gene flow and drive the spread of alleles for enhanced mate preference and/or choosiness in a reinforcement-like process. In Heliconius butterflies, [START_REF] Merrill | Disruptive ecological selection on a mating cue[END_REF] suggested that selection against hybrids was as strong as selection against migrants (in this case, a non-mimetic control species). Progeny of crosses between M. men. hicetas and M. men. ssp. nov. 1 do not produce phenotypic intermediates, but rather possess either of the parental phenotypes, with the hicetas phenotype appearing to be at least partly dominant [START_REF] Mcclure | Ecology, life history, and genetic differentiation in Neotropical Melinaea (Nymphalidae: Ithomiini) butterflies from north-eastern Peru[END_REF].

Although currently untested, differences in colour pattern within M. menophilus may be the result of a single locus with dominance, and this genetic architecture may differ from other Melinaea species, including M. marsaeus. Nevertheless, as there are no intermediate phenotypes produced in M. menophilus, selective pressure against mating between taxa is likely reduced and rampant gene flow can be expected, thereby inhibiting the fixation of preference or increased choosiness alleles. Yukilevich (2012) demonstrated that, in Drosophila, asymmetries in the strength of premating isolation between species pairs matches the cost of producing hybrids. As such, at least in M. marsaeus, mating preference may have directly evolved in response to selection against maladaptive offspring of intermediate phenotypes.

In this study we show that the absence of ecological adaptations other than colour pattern (see [START_REF] Mcclure | Unravelling the role of host plant expansion in the diversification of a Neotropical butterfly genus[END_REF] does not preclude the evolution of mating isolation. In fact, through the maintenance of a spatial mosaic of mimetic colour patterns, predation on Müllerian mimics constrains geographical distribution and allows for different species or subspecies, even those with similar ecological niches, to exist in different regions [START_REF] Aubier | Mimicry among unequally defended prey should be mutualistic when predators sample optimally[END_REF]. This study also suggests that mate preference and assortative mating evolve adaptively in response to divergent selection, and that even in the early stages of speciation, reproductive isolation can be nearly complete due to mating preferences, as seen in M. marsaeus. But perhaps surprisingly, we also show that changes in traits used for mate recognition, such as colour pattern, does not invariably lead to reproductive isolation, as demonstrated by the equal hetero-and conspecific mating probabilities observed in M. menophilus. Nevertheless, populations of M. menophilus remain partly segregated by colour pattern, likely as a result of selection against immigrants. [START_REF] Mallet | Strong natural selection in a warning-color hybrid zone[END_REF] showed selection against immigrants across a hybrid zone to be of 52% where two races of H. erato meet, sufficient to maintain a cline in colour pattern, despite random mating. But because M. menophilus does not produce any phenotypic hybrids, it is presently difficult to evaluate the true occurrence of heterospecific mating in the field.

In conclusion, we find that premating isolation in Melinaea arises early and quickly, with apparently no intermediate levels of premating isolation, despite a continuum of genetic and phenotypic differentiation. Our results suggest that colour patterns adapted to different mimicry rings may be used in mate recognition. However, reproductive isolation, as a result of mate preference and/or increased choosiness, and variable progress towards speciation is consistent with selection against maladaptive hybrids rather than a change in colour pattern per se. Uncovering the evolutionary cause of assortative mating requires the comparative analyses of the strength of assortative mating across different taxa subject to different selective pressures or genetic architectures [START_REF] Jiang | Assortative mating in animals[END_REF]. The exceptional conditions present in the region of Tarapoto, north-eastern Peru, where multiple species form concordant contact or hybrid zones between taxa of lowland and premontane forests [START_REF] Dasmahapatra | The anatomy of a "suture zone" in Amazonian butterflies: a coalescent-based test for vicariant geographic divergence and speciation[END_REF] offer an optimal natural setting to investigate the evolution of assortative mating across a large range of taxa.

  : M. menophilus ssp. nov. 1 and M. men. hicetas, M. marsaeus phasiana and M. mar. rileyi, and finally M. satevis cydon. Previous studies have shown that these taxa utilize the same hostplant, Juanulloa parasitica (McClure & Elias 2016; McClure & Elias 2017). As such, McClure & Elias (2016) suggested that diversification in these taxa was likely driven by shifts in colour pattern linked to co-occurring Müllerian mimics and the resulting predation pressure rather than hostplant shifts. Using artificial models of the polymorphic and Müllerian co-mimic Heliconius numata, Chouteau et al. (2016) and Arias et al. (2016) have shown that migrants and intermediate phenotypes respectively, possess locally unrecognized warning signals and suffer greater predator attack frequencies. As the Müllerian comimics Heliconius numata and Melinaea are undistinguishable to predators (Llaurens, Joron & Théry 2014), the results of these studies can be extrapolated to the genus Melinaea.

Figure 2 :Figure 3 :Figure 4 :

 234 Figure 2: Principal component analysis showing the variation in the colour pattern of five Melinaea taxa and putative hybrids between subspecies of M. marsaeus as quantified by Colour Pattern Modelling and modelled on a) butterfly vision and b) UVS bird vision

Table 1 .

 1 The number of individuals of each Melinaea taxon used to measure genetic differentiation, pheromone characterization and colour pattern quantification

				Colour
		Genetic	Pheromone	pattern
		differentiation	characterization	quantification
	M. menophilus ssp. nov. 1	37	9	20
	M. menophilus hicetas	18	6	17
	M. marsaeus rileyi	18	10	20
	M. marsaeus putative hybrid	3	1	6
	M. marsaeus phasiana	37	8	19
	M. satevis cydon	19	9	22

Table 2 .

 2 Observed mating probabilities within and between different Melinaea taxa and the resulting best fitting model for each (i.e. whether different taxa mate less frequently than those of the same taxon, or if all crosses are either equal or all significantly different from one another). Different lower-case letters indicate significant differences of p<0.05 for each cross, based on the best fitting model obtained.

		Number of	Number of	Mating	Best fitting
	No-choice mating experiments	trials	mating	probability	model
	M. menophilus ssp. nov. 1 x M. menophilus ssp. nov. 1	12	9	0.75 a	Pii=Pjj=Pij=Pji
	M. menophilus ssp. nov. 1 x M. menophilus hicetas	12	8	0.67 a
	M. menophilus hicetas x M. menophilus hicetas	12	7	0.58 a
	M. marsaeus rileyi x M. marsaeus rileyi	12	8	0.67 a	Pii=Pjj≠Pij=Pji
	M. marsaeus rileyi x M. marsaeus phasiana	12	0	0 b
	M. marsaeus phasiana x M. marsaeus phasiana	12	6	0.5 a
	M. marsaeus x M. marsaeus	24	14	0.58 a	Pii≠Pjj≠Pij=Pji
	M. marsaeus x M. satevis cydon	12	0	0 b
	M. satevis cydon x M. satevis cydon	12	11	0.92 c

Table 3 .

 3 Measures of genetic differentiation (Fst), colour pattern differentiation as perceived by butterflies and birds (Euclidean 690 distances between group centroids), pheromone differentiation and the index of premating isolation (where 0=no mating isolation, 691 1=complete mating isolation) for different pairs of Melinaea taxa. For clarity and ease of comparison, a relative value ranging from 0 to 692 1, calculated as the absolute Euclidean distance value divided by the maximum value observed in the dataset, is included in brackets for 693 colour pattern and pheromones.

	694
	Pairs of taxa

Acknowledgements. We thank the Peruvian authorities and Dr Gerardo Lamas (Museo de Historia Natural, Universidad Mayor de San Marcos) for research permits (236-2012-AG-DGFFS-DGEFFS, 201-2013-MINA-GRI-DGFFS/DGEFFS and 002-2015-SERFOR-DGGSPFFS). We also thank Mario Tuanama, Ronald Mori-Pezo and Javier Bacigalupo for their precious help in the field. Molecular work was carried out at the Service de Systématique Moléculaire du Muséum National d'Histoire Naturelle (CNRS-UMR 2700). We thank Violaine Llaurens, Doris Gomez and Monica Arias for providing spectra for Melinaea taxa, ambient light files and quantum catches for birds to perform the vision modelling. We thank Doris Gomez and Adriana Briscoe for advice on butterfly vision modelling.

Data

accessibility. Data available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.008b59c (McClure et al. 2019) Funding. This research was funded by a CNRS ATIP grant and ANR grant (SPECREP) awarded to ME and by the Fonds Québecois de la Recherche sur la Nature et les Technologies (FQRNT) as a PDF award to MMc.

List of Figures

Figure 1: Factorial correspondence analysis for five Melinaea taxa and putative hybrids between subspecies of M. marsaeus on 12 microsatellite loci computed using the program GENETIX


Teenagers' information practices in academic settings: What relevance for a transliteracy-based approach?

Karine Aillerie

Introduction

We will not dwell here on the digital transformation discussed by many researchers but we would like to emphasize that the means of obtaining information have been radically restructured, rather than being replaced, by connected technologies. As Jenkins argues, the current media landscape is being shaped by individual everyday-life uses and by an expected direct interaction for users with knowledge and contents [START_REF] Jenkins | Convergence Culture: Where Old and New Media Collide[END_REF]. Other points we are interested in are the social dimension of current practices, especially via social networking sites (SNS), and the fact that daily digital uses could blur the borders between contexts [START_REF] Broadbent | Intimacy at Work: How Digital Media Bring Private Life to the Workplace[END_REF]. Moreover we keep in mind that the required "21st century skills" level has considerably increased or become more complex [START_REF] Voogt | A comparative analysis of international frame-works for 21st century competences: Implications for national curriculum policies[END_REF]. Teenagers are the first group affected by these requirements while their individual information habits are "complex and fascinating" (boyd, 2014) and deeply heterogeneous. We examine here the possible relevance of a transliteracy-based approach to better understand high school students' information uses and the way they produce content within academic situations.

Teenagers' media and information practices have been extensively studied by researchers, especially in the context of personal context, perhaps less so in the school environment. Their media uses are multifaceted, mixing social and recreational activities with educational obligations, etc. What is important here is to broaden the focus, to understand these practices at school and at home rather than at school or at home, especially when the schools' requirements increase the need to work out of school. Moreover, these uses have until now been considered mainly from a digital perspective. But we consider it important to describe the richness of everyday life uses taking into account the current plethora of information means, media and tools, available online and offline. "Holistic in nature" [START_REF] Megwalu | Transliteracy: A Holistic and Purposeful Learning[END_REF], an approach based on transliteracy, as originally defined by Sue Thomas and colleagues and then theoretically developed by many scholars, seems intrinsically relevant. Even though it originally came from a study of literacy as such which was outside the field of library and information science (LIS) itself, transliteracy, that we will define more precisely in this paper, has joined the ongoing studies into Information Literacy (IL), the overhaul of education guidelines and the possible introduction of new or different perspectives required by the current socio-technological context [START_REF] Aillerie | Vers une orientation translittératique des modèles d'Information Literacy ?[END_REF].

Proceeding from a program funded by the French national research agency (ANR Translit1 ), our research questions are:

-What can a transliteracy based approach tell us about the observed information uses? -How could a transliteracy-based approach be constructive for research into teenagers' information uses?

We begin with a definition of transliteracy compared with multimodal media literacy and metaliteracy, prior to giving the reasons why we have chosen transliteracy as the basis of our investigation. Based on an ethnographic methodology including observations of existing situations at school and interviews, our findings will then focus on the possible aspects of transliteracy in action, i.e. how students manage information with all the media and tools at their disposal, individually as well as collectively, in order to produce the required outputs.

What is transliteracy?

The idea of transliteracy comes from academic work undertaken in the early 2000s in the fields of communication and cultural studies. Initially, researchers aimed to shed light on the relationship between digital media and reading and writing practices. The article "Transliteracy: Crossing divides" by Sue Thomas and colleagues, set out the operational definition of transliteracy as "the ability to read, write and interact across a range of platforms, tools and media from signing and orality through handwriting, print, TV, radio and films, to digital social networks" [START_REF] Thomas | Transliteracy: Crossing divides[END_REF]. Transliteracy does not come directly from the field of LIS but extends and broadens the notion of IL. It emphasizes the need to encompass different literacies, not only those related to recent new technologies but all means of information and communication currently available, on-and off-line [START_REF] Ipri | Introducing Transliteracy: What does it mean to academic libraries?[END_REF][START_REF] Sukovic | Transliteracy in Complex Information Environments[END_REF]. Thus, transliteracy, initially understood as a field of expertise, is currently contributing to the development of a theoretical approach which matches the fast-changing information world and real users' practices. We here specifically choose to base our investigation on this perspective and will explain below the epistemological and methodological reasons that lead us to this choice. However, let us consider transliteracy with regard to other similar approaches in order to better understand what makes it specific.

From digital literacy to transliteracy

We focus here firstly on digital literacy, as transliteracy can be misunderstood to refer to digital media and online information uses only. Initially, the concept of "literacy" basically refers to the "ability to understand and employ printed information in daily activities, at home, at work and in the community -to achieve one's goals, and to develop one's knowledge and potential" (OECD, 2000). Developed in the context of the pre-eminence of printed and textual formats, this concept is nevertheless fundamentally linked to the medium to which it relates and to the social contexts in which it develops. Over the last few decades, capabilities and behaviors have become increasingly important in an era of media, technological, economic and cultural convergence. Thus, the concept of "digital literacy" has become established since the late 1990s, initially introduced by Gilster as "the ability to understand and use information in multiple formats from a wide range of sources when it is presented via computers" [START_REF] Gilster | Digital Literacy[END_REF]. The most important elements of digital literacy are the ability to understand and use information from various digital sources; the basic ability to read and write in a technological world, and above all, the ability to use critical thinking. In line with this definition, Peters and Gervais describe three main principles of digital literacy: the use of computers, software programs and the Web; the understanding and critical thinking the user is able to have on the retrieved information; and creativity [START_REF] Peters | Littératies et créacollage numérique[END_REF]. Therefore, digital literacy is really specific. However, while there is a close relationship between information and digital literacies, they are not entirely the same thing (ALA, 2013). One reads, writes, gets information, and produces content with digital tools, but not only those. Information uses are therefore likely to be considered relevant to every media or information channel currently available, from books and websites to SNS and even word of mouth. To manage this complexity, authors therefore proposed overarching approaches: namely multimodal media literacy and metaliteracy, which are both similar to transliteracy. Distinct from cumulative or hierarchical approaches, these initiatives work within a revised theoretical paradigm and toward its incorporation into the field of education.

Transliteracy and similar approaches

Multimodal media literacy (MML) is a concept inherited from the concept of multiliteracies [START_REF] Cazden | A pedagogy of multiliteracies: Designing social futures[END_REF] which highlighted the diversity of communication means in globalized societies and the need for a suitable pedagogy. The current media landscape requires skills able to combine different modes (linguistic, visual, and auditive) usually within the same medium and the same content (Lacelle, [START_REF] Lebrun | Genèse et essor du concept de littératie médiatique multimodale[END_REF]. MML defines the specific skills relating to the reading, analysis and evaluation of the various media, both printed and electronic, which gradually bring to an end the boundary between the reader and the writer.

Three basic domains of MML are presented in the literature: information proficiency, aiming to define effective seeking strategies and to analyze, organize and review information sources especially on the Internet; technological proficiency, centered on the adoption of tools; and multimodal proficiency, relating to the ability to read and communicate effectively by combining writing, image and audio in a variety of media [START_REF] Lebrun | Genèse et essor du concept de littératie médiatique multimodale[END_REF].

For its part, the metaliteracy model was developed within the field of LIS [START_REF] Mackey | Metaliteracy: Reinventing Information Literacy to Empower Learners[END_REF]. The challenge was not to add other literacies but rather to propose a theoretical and practical overarching framework able to unify the many aspects of IL. The model aims to train students not only to search effectively for information but also to understand and modify their own information habits. This model is thus intended to be part of a complete institutional training project, to be incorporated into the curriculum and to close the gap between daily habits or abilities and information-communication skills. To effectively apply metaliteracy in practice, the model is presented through a visual diagram that outlines IL basics enriched by four skill areas: collaboration, sharing, participation, use, incorporation and production.

Transliteracy and why we choose this approach

The word "transliterate" etymologically originates from the passage from one alphabet to another. Liquète highlighted three main domains of meaning for the prefix "trans" [START_REF] Liquète | Can one speak of an "Information Transliteracy[END_REF]. In the first place, the most explicit aspect mirrors a deep interaction among literacies as Ipri already demonstrated: "Transliteracy is concerned with mapping meaning across different media and not with developing particular literacies about various media" (Ipri, 2010, p. 532).

Transliteracy is not only a matter of being aware of one media in a particular situation, but of being able to shift from one to another. It is this flexibility and openness, a kind of informational or media eclecticism, which gives transliteracy its uniqueness.

Furthermore, according to Liquète's analysis, the prefix "trans" also refers to the possible links between different settings. Uses mature in different contexts but also in the connections as well as in the gaps between them. Indeed, research findings have already showed that, far from the "digital natives" myth, a strong heterogeneity characterizes individual teenagers' information uses. Some students make their daily digital uses scholastically profitable whereas others could have personal practices competing with the demands of school [START_REF] Robinson | Digital inequalities and why they matter[END_REF]. Sukovic precisely describes the essence of transliteracy as a fluid "movement across" a range of contexts [START_REF] Sukovic | Transliteracy in Complex Information Environments[END_REF]. But this question of possibly connected settings must be seen within the context of individual practices and not be valued only as a theoretical idea: this is about moving physically but also and above all symbolically, allowing the possible transfer of uses and knowledge from one context to another, either from personal environments to school situations, or vice versa, re-using skills acquired at school for personal purposes. This mobility refers to a set of abilities that are likely to be unequal and dividing [START_REF] Cailly | Capital spatial, stratégies résidentielles et processus d'individualisation[END_REF].

The prefix "trans" can also highlight the collective nature of existing information uses.

Original information-seeking models, such as the ELIS (everyday-life information-seeking) model have already identified "others" as a privileged source of information [START_REF] Savolainen | Everyday life information seeking: Approaching information seeking in the context of "way of life[END_REF]. Other authors have stressed that information can be found through "others", especially for teenagers [START_REF] De | Toward a Model of the Everyday Life Information Needs of Urban Teenagers, Part 1: Theoretical Model[END_REF][START_REF] Shah | Collaborative information seeking[END_REF]. Today the social nature of information uses is substantial: to seek and access but also to validate or characterize information (comments, tags etc.). It is also crucial to include here the organizational dimension of information seeking and processing which can be done collectively, especially at school [START_REF] Leeder | Strategies, obstacles, and attitudes: student collaboration in information seeking and synthesis projects[END_REF].

It is because of these aspects and their heuristic potentialities that we choose transliteracy as the basis of our inquiry. The common challenge in the proposals presented (multimodal media literacy, metaliteracy and transliteracy) is to think holistically about the complexity the term literacy encompasses today and to challenge it with what research results tell us about information uses. We anticipate that transliteracy, the broadest of these three approaches, could be the most valuable to describe and understand youth information practices and the possible symmetry with scholastic requirements they must meet.

Methodology

This work is based on 13 in situ observations (a session of 3 hours every week over a semester) and 7 semi-structured interviews, conducted by an LIS researcher and included in a The observations were based on an ethnographic methodology using the "situated" and "distributed" cognition approach [START_REF] Conein | Action située et cognition : le savoir en place[END_REF]. Relying on an observation and analysis grid common to the 4 Translit project's fields of investigation, we collected as much evidence as possible: audio capture and photos of the classes, pupils' drafts, organizational documents and outputs, guidelines provided by teachers, discussions on Facebook, online collaborative documents, etc.

Findings

First of all, let us note that the point here is obviously not to demonstrate again previous findings about students' digital uses or information-seeking behavior or collaboration in the school context as such. What makes our approach significant is the transliteracy angle we choose to have on the observed situations, and what this perspective is able to shed light on. We focus therefore on the possible diversity of media and tools employed, on the ways of and reasons for switching from one to another, on how these different media and tools are distributed within contexts, according to the academic requirements and tasks individually and collectively performed by the students.

Transliteracy at school

Observed situations took place not only in the information center, in a classroom and in a computer room but also in the high school's building more widely (when pupils had, for instance, to film their videos). Generally, we should point out the high multi media dimension of these situations. Despite the great emphasis placed on digital technology in this school, multiple media and resources are still present both physically and symbolically. Students' desks are cluttered with notes taken on sheets of paper (often snapped with smartphones), books, newspapers and magazines, side by side with websites added to bookmarks and organization documents on Google Docs and Facebook, etc. Blackboards, books and textbooks coexist with the high school's computers and school and/or personal mobile devices (tablets, phones, music players). Symbolically this variety is also very apparent in the requirements formulated by teachers. Indeed, the interviewed teachers insisted on the importance of using multiple media rather than giving priority to digital resources. This strong learning goal is then presented as a habit that students do not yet have, a skill they must gain.

Teachers insist on the requirement that pupils' work should be based on as wide a range of resources as possible. This is included in the evaluation criteria in order that students "(…) do not focus on a single media type… because, quite simply, it's too easy. Otherwise they all tend just to choose the Internet and I really think that this is not the solution. Our role is also to broaden their vision at this level so that they can try a bit of everything". Thus, during the observed situations, the teachers continually checked and reminded the pupils to be aware of the sources they were using, not only regarding their documentary quality but also regarding their diversity.

The practical dimension of transliteracy

Teachers and pupils describe the materials and resources of all kinds used to carry out their work in terms of its accumulation in which both digital and other media intertwine. From that perspective, our approach highlights the strong physical, temporal and spatial nature of the observed teaching and learning situations and the management skills that this multiplicity requires for both pupils and teachers.

The teachers' interviews show a recurrence of the very real necessity to manage the students' movements in time and space as well as resources and documents. As a teacher comments: "In this respect, freedom, in terms of time, action, movement ... in space ... that's what really changed". This logistical dimension applies to class space and lesson time but also to what happens outside the class. In this respect, teachers emphasize the freedom of organization left to the pupils at the same time as the management effort that they have to use to monitor and complete the work. This is often described in logistical and "trial and error" terms: "We know that it is not right but we do it anyway because it works, but afterwards we adjust using the evaluation grids". Here, we see a physical and symbolic mix which is not always obvious between the pedagogical tools promoted by the institution and teachers, integrated into the evaluation criteria, and the real day-to-day practices of both pupils and teachers. Indeed, the high school makes available everything necessary to store the work: the computer network is organized in such a way that files are sharable between the pupils themselves and between pupils and teachers. These files are organized according to the progress with the work: draft files, validation files, archives and so on. But students and teachers still use Google, Dropbox and Facebook, as well as physical media (usb, cd etc.). It is in fact efficient and technically compatible with their omnipresent mobile devices. Above all, it is in line with their daily social practices combined with the need felt by the pupils to work outside school time. Pupils are however always required to organize themselves, to "figure it out on their own", so that their work is always available on the high school network's files. This organizational point is a core part of the evaluation criteria. Apart from this obligation to use the school network, teachers do not give particular instructions on the tools to be used. The students thus demonstrate very real difficulties (loss of files, insufficient connectivity, compatibility problems, etc.). Less tangible difficulties might delay the collective organization and the progress of the work such as the choice of one tool rather than another and the transition from one tool, especially personal, to another.

Regarding the physical organization of space, we observe that it can sometimes be obstructed by the presence of multiple documents and devices (space occupied by a computer on a narrow desktop, layout of computers in blocks, for instance). They can also hinder the interactions between students. They must work in groups but the spatial organization observed is often individually designed. In that respect, a teacher mentions the need to organize learning spaces according to the diversity of resources used by the students. She talks about a "lack of perspective to see how one can organize the space with all that". This teacher regrets that because of material constraints, students are obliged to choose one media rather than another, but not in an "investigative approach": "The lack of space prevents the use of magazines, books and paper... so we will use the tablet because it takes up less space".

Collective outputs

Two aspects remain to be considered, incorporating the MID as this pedagogical activity had been designed: the collective search for information and the production of the required outputs.

The observed situations show a monitoring of group activity by the teachers formulated in terms of injunction and referring to the spontaneity of the students at the same time: "You must be organized within the group"; "Organization counts"; "Here you should share your work". Students form their own groups and decide amongst themselves on the spaces and tools that will allow them to work together. Thus a teacher recounts: "They are left free, because I think it is up to them to organize and ... well, we can sometimes give them some recommendations but overall, it is they who created their spaces, they sorted them out".

Regarding the organization within the groups, SNS and collaborative tools play a central role, face-to-face and remotely, as a student explains: "We are there all the time (...) We can answer directly, discuss, etc, so ... (...) As soon as there is any high school project, where we are in small groups, we're straight onto Facebook". Collaborative documents are also created (especially with Google Docs) to organize group ideas, share the work, and memorize useful resources. During observations as well as within the interviews, we notice that some teachers' instructions insist on the necessity for students to distribute the tasks mainly according to the different media or searching tools during the information-seeking stage (one pupil searching the Web, another searching the library database, yet another reading a novel related to the topic, for instance). Likewise, students without this kind of advice divide the work according to the media and searching tool types.

From the teachers' point of view, the focus is very strongly on the final output. The requested level is relatively high but in line with the national expectations regarding this level of schooling. Regarding the production itself, one of the specific features of this high school is that pupils are provided once a week with Information and Communication Technologies in Education and Media (TICEM) courses. Focusing on digital culture (e.g. critical thinking and intellectual property) as well as technical training (e.g. how to edit a video, create a blog), these courses directly support pedagogical activities such as MID. Teachers who are not in charge of these courses seem to have totally based the technical part of the expected outputs on TICEM lessons. During the interviews, they report their incompetence in the matter. Even if they regularly mention the "technical" difficulties of many pupils, they consider at the same time the pupils in general to be very independent and proficient. If the order to produce, in a thoughtful or even creative way is strong, pupils'statements contradict explicitly these representations: they highlight numerous problems they have to struggle with. They are likely to report modest information and digital proficiencies. Describing the difficulties they have had to overcome, they refer frequently to their daily habits, the skills they say they have acquired by themselves, the equipment available at home, and the ability of their parents or friends to help them.

Students sort things out

Students are aware of the freedom they are given and the challenging requirements that go with it. For students, "sorting things out" is an integral part of high school life, differing quite radically from what they were used to in middle school: "(…) here it is really... (...) it requires... it is more complicated, it requires organization (...) there is much more freedom and it is up to us, ourselves, to set limits, for ourselves, to organize ourselves, to set the timetable (…)". Observations and interviews show that the time allowed for production was not sufficient for most groups. It is the production itself and also the logistical and collective organization that are affected by this work outside school time and the mobilization of adequate resources and tools. Teachers claim that they plan in such a way that students do not have to work outside the appointed time. However, they are aware of these heavy demands:

"We asked a lot in a very short time...". For the interviewed teachers, having to work outside the stipulated hours is either a problem of organization within the group or something inevitable that students must eventually learn to handle.

Organizing collectively, especially outside classes and school, during breaks, personal time or even holidays, can be complicated for some groups. The lack of time and the constraints of organization are related to the expected requirements but also to the number of tools they use and the time needed for reflection. During interviews students state explicitly that it is indeed not enough to have an effective means at their disposal for the organization of the group to be achieved efficiently. The fundamental need for this unavoidable and prerequisite reflective dimension was underlined by a pupil: "In fact digital tools take time to set up; once they are it goes much faster, but the setting up is very long and in fact, there, we did not really have enough time to reflect, to think about what means we will use". The wide range of media and tools and how they articulate with each other, the choice of a particular tool for a particular task and the distribution of work within the group refer to expert and crucial skills which remain quite implicit. Thus the comment from a teacher that echoes the last student's comment: "(...) they have to get to work but neither we nor they have considered what can be used, how one can use it and why. It means that sometimes the documents are too abundant and we do not use them or we always use the same resources".

The real work of organization can be done internally within the group. The students hand in only what they decide to put in the files that they make accessible to their teacher: "The server is where the teachers have to go to watch while Hangout is really just for the setting up". All the drafts, the documents shared between them and the discussions, while not secret or intentionally hidden remain in the domain of their internal organization, of no interest, according to them, for teachers.

Discussion

It has been already theoretically demonstrated that transliteracy can make it possible to consider holistically the three fields of information literacy, media literacy and computing literacy [START_REF] Delamotte | La translittératie, à la convergence des cultures de l'information : supports, contexte et modalités[END_REF]. But Thomas and colleagues pointed out that the nature of transliteracy as such remains to be clarified: "we have not decided whether it is a practice, or a way of analyzing practice, or both" [START_REF] Thomas | Transliteracy: Crossing divides[END_REF]. The authors call for the notion to be put into practice in empirical studies. Here, we deal with transliteracy as a horizon, a way of seeing, a clearly exploratory inductive approach likely to "give meaning" to raw data [START_REF] Blais | L'analyse inductive générale : description d'une démarche visant à donner un sens à des données brutes[END_REF]. The participants of our study obviously do not speak of "Transliteracy". This term does not appear as such, either in the instructions or in the pedagogical documents. Moreover, the high school where our investigation took place does not completely correspond to the norm in France. However, this distinctiveness does not totally prevent our results from questioning what happens more widely at school. Our investigation took place in an innovative high school during specific educational activities.

This study field is largely in line with the ambitions of public policies in digital equipment and media education. It is for this reason that it seems interesting to question these kinds of situations and to draw useful lessons for the observation of more standard circumstances (Aillerie, 2017). Our conclusions are in fact complementary with those established by researchers who have analyzed average high schools. In particular the recent work coordinated by Cottier and Burban (Cottier & Burban, 2016), which underscores that core information requirements in terms of organization of work and project management are not equally mastered by the students nor taught as such at school. Our presented findings relate to the three dimensions of transliteracy explained above [START_REF] Liquète | Can one speak of an "Information Transliteracy[END_REF]. (1) We stressed the variety of media used by pupils and required by teachers, and the coexistence of these different media in the uses and changeovers from one medium, or tool, to another. We have also highlighted the very real difficulties that this multiplicity entails on a daily basis, and the educational challenges it implies for pupils and for teachers.

(2) Our results showed how this "agility" is linked to the continuation of school work outside the timetable and to the locations available to do it. (3) This diversity of contexts, as well as the challenging transitions from one to another, are also closely linked to the collective dimension of the information uses presented here.

Digital tools are ubiquitous in this school and integrated into the overall educational school project, but they do not replace traditional media. This is a useful point to keep in mind when observing average situations. From a transliteracy basis, analysis of the collected research material illustrates the complex and permanent links between digital tools and media and traditional media and resources in school work, in the smallest details of the creative process, in the distribution of work beyond what is visible, and in the collective dimension of the executed work. Thus we have observed learning and teaching situations that both in practice and symbolically refer to transliteracy, that is the ability to use different media being considered here as a key learning goal and an assessable ability. In the areas of information seeking, collective organization and production, students spontaneously use a multitude of media, resources and tools, in both school and personal contexts. On the other hand, these transliteracy-related uses are also the subject of a requirement formulated by teachers in terms of instructions and evaluation criteria. We must therefore clearly distinguish between transliteracy as a potentially achievable and observable requirement and the everyday life transliteracy into action, hard to see, uncertain and ubiquitous. This observation (using multiple media on a daily basis, some specifically designed for education, others not) can also be done for high school students in general. This has been demonstrated with respect to SNS for they play a great role in youth sociability but can also include academic purposes (Lamp et al., 2011;[START_REF] Aillerie | Are Social Networking Sites information sources: Informational purposes of high-school students in using SNS?[END_REF]. It is an important part of school time as well as everyday life that should be included in education.

Transliteracy considers digital media along with other existing media. Regarding France, this position seems quite relevant and truly useful from an educational point of view. It can actually help to reduce the supremacy of digital material within the debate about the role that technologies should have in education today. Furthermore, assuming that technology is able to impact positively or negatively on learning and teaching practices is still very common.

Plantard uses the expression "magical tablet effect" to refer to the massive provision of French schools with the latest technology as a response to educational problems which go beyond even the question of technologies [START_REF] Plantard | Contre la « fracture numérique », pas de coup de tablette magique ![END_REF]. This idea fails to take into account the many factors, including the technological environment, which together contribute to the transformation or not of teaching practices and learning [START_REF] Amadieu | Digital literacy, libraries, and public policy: Report of the Office for Information Technology Policy's Digital Literacy Task Force[END_REF]. A transliteracy-based approach contributes then to the consideration of digital media in both historical (intellectual technologies) and social (role of interactions, matching between digital and social divides) perspectives. Moreover, a strong dichotomy between digital and traditional media prevents the perception of the abundance and the complexity of real uses that are mixed and built both online and offline. In this sense, methodological and epistemological initiatives critiqued how Internet and digital tools had been understood as only distinctly specific [START_REF] Leander | Tracing the Everyday 'Sitings' of Adolescents on the Internet: a strategic adaptation of ethnography across online and offline spaces[END_REF][START_REF] Pastinelli | Pour en finir avec l'ethnographie du virtuel ! Des enjeux méthodologiques de l'enquête de terrain en ligne[END_REF]. Likewise, our perspective contributes to show that teenagers' information uses are not to be understood solely from the point of view of their digital habits but in a continuum of interwoven uses. This has been demonstrated regarding their social uses by boyd's findings about the correlation between friendships at school and interactions on SNS (boyd, 2014). Digital technology does not determine practices, interactions or ways of working on its own. This kind of analysis is far from being entirely new but a transliteracy-based approach can help to take into account this complexity. In this perspective, transliteracy meets other proposals such as the emerging socio-critical approach of digital technology in education (Nelwyn, 2010;[START_REF] Collin | Une approche sociocritique des usages numériques en éducation[END_REF].

Thomas and colleagues depict transliteracy by means of a picture of Al Gore in his office surrounded by a mountain of media. They thus demonstrate the omnipresence of information devices and the intellectual virtuosity required to master simultaneously their multiple affordances. Far from the idea of immediacy and facilitation being associated with connected technologies, a transliteracy-based approach contributes to describe the very real and material nature of such uses: the time-consuming necessity for pupils and teachers to deal with different materials, different formats and several tools at their disposal. It also highlights that the required and demanding time for reflection, planning and metacognition is not fully included in the working time provided within school and hence tends to transfer to the personal part of the students' life. And what transliteracy is all about is also precisely what is outside the frame: the sound of a possible radio channel, those with whom Gore interacts remotely, what he will continue to work on when he leaves his office etc. From a methodological point of view, one of the main issues of an ethnographic observation is this difficulty of perceiving what happens before and after the observed situation. Methodological solutions have been suggested, for instance in the field of organizational communication such as Grosjean's work [START_REF] Grosjean | Une approche microethnographique et multi-située en organisation : Double mouvement de « zoom avant/arrière » sur l'activité d'arpentage[END_REF]. We state that online and offline practices are interlinked and school uses are not just those that are observed in the classroom. Learning dimensions, very directly linked to IL such as collective organization or information processing, remain still very implicit here. More generally, our approach makes it possible to bring to light the implicit part of the work that pupils undertake to meet academic demands, that is the activities that take place behind the scenes of their individual and collective organizations. Within these can be found the aspects which they do not show to their teachers, specifically the difficulties they encounter and the strategies they develop, to find, process and store information, to choose and use tools, to go from one to the other, etc. This is where we can perceive the gap between what is required at school and the production of work in these "intermediate spaces" (Cottier & Burban, 2016) between school and personal life. That is to say, even in a privileged situation such as the one we observed, pupils encounter difficulties and it is necessary to shape them explicitly to the demands of the current media and technological world.

It is especially in these blind spots that the educational stakes of transliteracy, as well as the mediation that they imply, are played out. In this way, in the students' and their teachers' practices and in what they say about those practices, we can perceive a real tension between expertise as a goal and everyday life tactics. At the core of the academic demands as well as pupils' endeavor, we discern this willingness to investigate the media and information field, to build an individual and collective learning path and to become aware of it: to genuinely choose this or that media, a particular tool, a particular resource according to specific objectives and motivations, to be able to acknowledge their complementarity and not only merely multiply them. Our results also illustrate the collective dimension of information practices in school situations and, more broadly, the collective dimension of learning in the current media landscape. Founding models of IL such as those elaborated by Kuhlthau have tended to think of IL as an individual and collective inquiry process [START_REF] Kuhlthau | Guided Inquiry Design: A Framework for Inquiry in Your School[END_REF]. Our findings suggest that this collective dimension of information uses has still largely yet to be described for young people of school age. This implies that the design of workspaces also needs to tangibly incorporate this multiplicity of media and collective work.

Conclusion

In light of our findings, transliteracy is valuable as a means to capture teenagers' daily uses in different contexts, to grasp the observable but also the hidden part of their uses and of academic requirements. Our results contribute in turn to enrich the notion of transliteracy itself. Information literacy, known as the internationally recognized Information and Media Literacy (Moscow declaration, 2012), is now at the heart of the requirements defined by educational systems. At the same time, according to 21st century skills, there is an

  broader research program (ANR Translit). The interviews were carried out with 4 individual teachers and with 3 groups of students. The observations took place between November 2013 and March 2015, in a French high school during specific activities called MID (Inter Disciplinary Modules) organized for tenth grade (15-16 years old) students (2 classes of around 30 pupils each). The high school is located on the outskirts of an average French city (about 600 pupils and 90 teachers). Since 2013, a school-level digital project has been developed: teachers and pupils are provided with personal digital devices. Based on projectbased teaching, MIDs are similar to "supervised personal works" (TPE 2 ), a compulsory education in the French eleventh and twelfth grades. Students must collectively (in teams of 3 or 4 members) search and collect information in order to produce several types of outputs during the two MIDs they follow in a school year: a radio clip, a slide show, a blog and a video.

http://www.agence-nationale-recherche.fr/?Projet=ANR-12-CULT-0004