Tarek Oueslati
email: tarek.oueslati@univ-lille.fr

Ben Gruwier

ON THE STATUS OF GREYLAG GEESE IN ROMAN PARIS: A LINEAR AND GEOMETRIC On the status of greylag geese in Roman Paris: A linear and 2D geometric morphometric approach

Keywords: domestication, greylag goose, domestic goose, linear morphometrics, geometric morphometrics, Roman, France

We investigate here the domestic status of goose remains from archaeological excavations of the Roman urban settlement of Paris Lutecia. Within the diet of the Parisii adult goose competes with chicken in importance, thus offering abundant material for exploring the question of the domesticity of this bird. We first use linear and geometric morphometrics on extant tarsometatarsi of wild and domestic greylag geese to investigate potential morphological differences between the two forms. Afterwards, we apply this model on a Roman sample from Lutecia. The extant domestic breed shows notable differences in length and gracility of the tarsometatarsus compared to the wild specimens. In domestic males, the tarsometatarsi appear significantly longer and more robust compared to females. In wild greylag geese, we do not observe significant differences between males and females. Geometric morphometric analysis shows a modification of the shape in the domestic form, with increased robusticity and a bend of the shaft towards the distal end. Following this analysis, we examine the metrical specificities of the archaeological sample that shows only an increase in robusticity and no modification of ON THE STATUS OF GREYLAG GEESE IN ROMAN PARIS: A LINEAR AND GEOMETRIC length and the shape relative to the wild form. Our linear and geometric morphometric models clearly indicates that the majority of the Roman geese are domestic. Nevertheless, a smaller number of wild greylag geese is also present and must be considered as being sourced from hunting activities in the surroundings of Lutecia.

Introduction

The Roman conquest of Northern Gaul influenced the composition of the diet of most consumers in the region. Eating meat goes beyond the large mammal consumption that characterized the pre-Roman diet [START_REF] Méniel | Les Gaulois et les animaux. Élevage, repas et sacrifice[END_REF], with the regular inclusion of chicken, goose, duck, pigeon, oysters, mussels and fish. In the case of Lutecia, the capital of the Parisii, we evidenced a clear diversification of the components of the meat-based diet, even though this varies according to the socio-economic status of each household [START_REF] Oueslati | Approche archéozoologique des modes d'acquisition, de transformation et de consommation des ressources animales dans le contexte urbain gallo-romain de Lutèce[END_REF]. At a wider scale, poultry emerges as a frequent ingredient within Roman cuisine, including on affluent rural settlements [START_REF] Oueslati | La consommation des ressources animales en milieu rural : quels indices pour quelle caractérisation de cet espace socio-économique? Actes du colloque Xe congrès de l'Association AGER, Consommer dans les campagnes de la Gaule romaine[END_REF]. The importance of goose and mallard consumption from the onset of the Roman period confronts zooarchaeologists with the need to clarify the status of these consumed birds. This is particularly important because of the marked difference in procurement strategies of reared and hunted animals. Moreover, in Northern France, hunting was often limited to high-status consumers during Antiquity and Medieval times [START_REF] Méniel | Les Gaulois et les animaux. Élevage, repas et sacrifice[END_REF][START_REF] Lepetz | L'animal dans la société gallo-romaine de la France du Nord[END_REF][START_REF] Lepetz | La consommation de viande dans les villes romaines d'Île-de-France au Ier siècle. Les cas de Meaux et de Paris (Seine-et-Marne et Seine)[END_REF][START_REF] Clavel | L'animal dans l'alimentation médiévale et moderne en France du Nord (XIIIe -XVIIe siècles)[END_REF][START_REF] Yvinec | Alimentation carnée au début du Moyen Âge[END_REF][START_REF] Yvinec | La part du gibier dans l'alimentation du haut Moyen Âge. Exploitation des animaux sauvages à travers le temps, XIIIe rencontres internationales d'Archéologie et[END_REF].

Zooarchaeologists working on sites from historical periods in Northern France and elsewhere often attribute a domestic status to goose, mallard and pigeon (e.g. Lepetz, 1997;[START_REF] Clavel | L'animal dans l'alimentation médiévale et moderne en France du Nord (XIIIe -XVIIe siècles)[END_REF]. This assumption relies primarily on the scarcity of other wild birds within such archaeological assemblages, shedding doubt on a provisioning strategy reliant on hunting. Furthermore, the lack of morphometric and morphological criteria poses challenges for species-level identification in the highly diverse family of Anatidae (but see [START_REF] Bacher | Vergleichend morphologische Untersuchungen an Einzel Knochen des postkranialen Skeletes in Mitteleuropa vorkommender schwane und Gänse[END_REF]. The subspecific differences between domestic and wild Anser anser are even more subtle.

In the case of Roman Paris, we initially assumed a domestic status for the geese, as they rival with chicken in number of fragments and because only adult individuals are present [START_REF] Oueslati | Approche archéozoologique des modes d'acquisition, de transformation et de consommation des ressources animales dans le contexte urbain gallo-romain de Lutèce[END_REF]. However, a preliminary morphometric comparison of the archaeological goose bones with extant wild and domestic Anser spp. specimens indicated a marked allometry in the archaeological specimens. Besides differences in the dimensions of the wing bones relative to those of the leg bones, we noted an increased robusticity of the limb bones, particularly in those of the hind leg 1 [START_REF] Oueslati | Approche archéozoologique des modes d'acquisition, de transformation et de consommation des ressources animales dans le contexte urbain gallo-romain de Lutèce[END_REF]. Other researchers have made similar observations on other sites 1 Number of probable wild geese in the Roman assemblages from Paris according to Oueslati 2006: 3 on a total of 34 coracoïds, 2 on a total of 66 ulnae, 1 on a total of 57 carpometacarpi and 1 on a total of 89 tibiotarsi. [START_REF] Reichstein | Untersuchungen an skelettresten von vogeln aus Haithaby[END_REF][START_REF] Prummel | Poultry and fowling at the Roman castellum Velsen I[END_REF] leading us to the conclusion that the geese from Lutecia were mostly domestic.

This paper attempts to evaluate the potential of 2D geometric morphometrics to improve this characterisation of the archaeological goose bones from Paris. Building on past studies on Paris, we target the tarsometatarsus, as it is a resistant and compact bone, which we often encounter in a more complete state, in comparison with other butchered elements of the carcass [START_REF] Oueslati | Approche archéozoologique des modes d'acquisition, de transformation et de consommation des ressources animales dans le contexte urbain gallo-romain de Lutèce[END_REF].

Theoretical framework

The domestication of the greylag goose was a complex phenomenon with a multiplicity of domestication centres [START_REF] Albarella | Alternate fortunes? The role of domestic ducks and geese from Roman to Medieval times in Britain[END_REF][START_REF] Crawford | Evolution of domesticated animals[END_REF][START_REF] Zeuner | A history of domesticated animals[END_REF]. Although, an early centre in China was recently suggested [START_REF] Eda | Multiple lines of evidence of early goose domestication in a 7000-y-old rice cultivation village in the lower Yangtze River, China[END_REF], it is commonly admitted that this process first occurred somewhere in the Eastern Mediterranean region [START_REF] Crawford | Evolution of domesticated animals[END_REF][START_REF] Zeuner | A history of domesticated animals[END_REF], possibly in Egypt, as early as the third or second millennium BC [START_REF] Albarella | Alternate fortunes? The role of domestic ducks and geese from Roman to Medieval times in Britain[END_REF]. Initial comparison of the tarsometatarsus of modern reference skeletons of the European domestic goose (Anser anser f. domestica) and its ancestor, the wild greylag goose (Anser anser), already shows striking visual differences, with the former longer and more robust. Domestication, including selective breeding of profitable meat-producing breeds can presumably explain the observed differences to an extent. These differences are not as obvious in archaeological material. Certain studies provide morphological criteria to distinguish between several species of Anatidae (e.g. [START_REF] Bacher | Vergleichend morphologische Untersuchungen an Einzel Knochen des postkranialen Skeletes in Mitteleuropa vorkommender schwane und Gänse[END_REF]Cohen & Serjeantson, 1996) but the differentiation between wild and domestic Anser anser can probably only be achieved using metric data. In fact, several authors have attempted this, using a combination of raw measurements and calculated indices on several skeletal elements [START_REF] Reichstein | Untersuchungen an skelettresten von vogeln aus Haithaby[END_REF][START_REF] Prummel | Poultry and fowling at the Roman castellum Velsen I[END_REF][START_REF] Macdonald | Domestic geese from Medieval Dublin[END_REF][START_REF] Oueslati | Approche archéozoologique des modes d'acquisition, de transformation et de consommation des ressources animales dans le contexte urbain gallo-romain de Lutèce[END_REF][START_REF] Poland | A methodological approach to the identification of duck and goose remains from archaeological sites with an application to Roman Britain[END_REF][START_REF] Duval | Les oies du site castral de Boves aux Xe siècle: tentative d'identification des individus domestiques[END_REF]. While wild and domestic geese do not necessarily vary in all dimensions, some studies found differences in the proportion of the wing bones relative to the size of the hind limb bones [START_REF] Reichstein | Untersuchungen an skelettresten von vogeln aus Haithaby[END_REF][START_REF] Oueslati | Approche archéozoologique des modes d'acquisition, de transformation et de consommation des ressources animales dans le contexte urbain gallo-romain de Lutèce[END_REF]. The tarsometatarsus, showing the most pronounced increase in robusticity, is presumably the most reliable bone to distinguish the wild from the domestic form [START_REF] Bramwell | Identification and interpretation of bird bones[END_REF][START_REF] Macdonald | Domestic geese from Medieval Dublin[END_REF][START_REF] Lepetz | La consommation de viande dans les villes romaines d'Île-de-France au Ier siècle. Les cas de Meaux et de Paris (Seine-et-Marne et Seine)[END_REF][START_REF] Duval | Les oies du site castral de Boves aux Xe siècle: tentative d'identification des individus domestiques[END_REF][START_REF] Poland | A methodological approach to the identification of duck and goose remains from archaeological sites with an application to Roman Britain[END_REF].

Despite these observations, we know little about the underlying mechanisms that drive these morphological changes. Some authors have suggested that the increase in robusticity relates to the greater weight and a higher reliance on terrestrial locomotion in domestic breeds [START_REF] Bramwell | Identification and interpretation of bird bones[END_REF][START_REF] Macdonald | Domestic geese from Medieval Dublin[END_REF]. However, even if such a scenario is accepted, it remains unclear whether these accommodations for increased weight have a genetic component, or if they result directly from environmental factors in the life history of an individual. While artificial selection for heavier geese is well documented [START_REF] Serjeantson | Goose husbandry in medieval England, and the problem of ageing goose bones[END_REF], an increase in limb bone robusticity could potentially also signify changes in the ontogenetic trajectory of an individual. During the early stages of their life, Anatidae invest more energetic resources in the development of the hind limb, at the cost of developing the wings [START_REF] Dial | Precocial hindlimbs and altricial forelimbs: partitioning ontogenetic strategies in mallards (Anas platyrhynchos)[END_REF][START_REF] Duggan | Differences in hindlimb morphology of ducks and chickens: effects of domestication and selection[END_REF]. This is advantageous, as ducklings mainly evade predators by running and swimming, thus quickly developing robust leg bones with sufficient musculature [START_REF] Dial | Precocial hindlimbs and altricial forelimbs: partitioning ontogenetic strategies in mallards (Anas platyrhynchos)[END_REF]. Halfway through their ontogenetic trajectory, this strategy reverses and energetic resources divert to the development of the wings, as flight becomes the main predator evasion strategy [START_REF] Dial | Precocial hindlimbs and altricial forelimbs: partitioning ontogenetic strategies in mallards (Anas platyrhynchos)[END_REF]. It is conceivable that domestic geese, having been subject to a reduction in natural selective pressures, have retained their precocial growth pattern -with emphasis on hind leg developmentuntil the adult stage. As changes in the developmental trajectory (e.g. paedomorphosis) exist for other domestic animals [START_REF] Zeder | Pathways to animal domestication[END_REF], this is plausible for geese.

Materials

This work relies on the archaeological material from Paris and reference specimens of domestic and wild geese. The latter consist of 39 complete goose tarsometatarsi measured in the collections of the Muséum National d'Histoire Naturelle (Paris, France) and the Laboratoire de Bioarchéologie Animale de Lille (University of Lille, France) (Figure 1). The wild specimens are all of the western subspecies Anser anser anser, while the domestic specimens are of the Maxipalm strain of the grey Toulouse breed (collected at Farm Andrevias, Sorges, France). We combined these measurements with a morphometric dataset of 43 specimens of modern domestic and wild geese from the literature [START_REF] Poland | A methodological approach to the identification of duck and goose remains from archaeological sites with an application to Roman Britain[END_REF]. All extant specimens were included in the linear morphometric analysis (N=82). Our geometric morphometric analysis required photos of the reference specimens which were not available in Poland's dataset not to mention the impossibility to verify for identical photo shooting technique, thus restricting this approach to the specimens from the Muséum National d'Histoire Naturelle and the Laboratoire de Bioarchéologie Animale de Lille (n=39).

We incorporated only adult tarsometatarsi in our study. We excluded individuals that were clearly pathological. We systematically collected data on the left tarsometatarsus. When not possible we used the right tarsometatarsus and virtually mirrored the right specimens in TPSdig 2.16 [START_REF] Rohlf | TpsDig 1.40-Thin Plate Spline Digitizer 1.40[END_REF] for the geometric morphometric analysis. Of this sample, a subsample of 12 specimens had a preservation that was adequate for geometric morphometric analysis (Figure 2a). In many cases, the proximal articulation or one of the condyles of the distal articulation was absent (Figure 2b, c andd). Table S1 provides the raw measurements of all the archaeological and extant goose tarsometatarsi.

Wild Domestic m f m + f m f m + f Muséum National d'Histoire Naturelle - - 10

Methods

In this study, we used a combined linear and geometric morphometric approach to assess morphological variation in wild and domestic Anser anser. For our linear morphometric approach, we measured the greatest length (GL) and the smallest breadth of the corpus (SC) of the tarsometatarsus following von den [START_REF] Driesch | A Guide to the Measurement of Animal Bones from Archaeological sites[END_REF] and expressed in millimetres. As relatively simple ratios have been successfully applied to discriminate taxa in other zooarchaeological studies (e.g. [START_REF] Castaños | Estudio osteometrico preliminar de los restos de ciervo (Cervus elaphus) del yacimiento paleontologico del Pleistoceno Superior de Kiputz IX (Mutriku, Gipuzkoa)[END_REF][START_REF] Zeder | Pathways to animal domestication[END_REF][START_REF] Iwaniuk | Extraordinary cranial specialization in a new genus of extinct duck (Aves: Anseriformes) from Kauai, Hawaiian Islands[END_REF][START_REF] Lister | Metric analysis of ungulate mammals in the early Middle Pleistocene of Britain in relation to taxonomy and biostratigraphy II: Cervidae, Equidae and Suidae[END_REF], we calculated a gracility index (GL/SC) based on similar morphometric studies on mammalian bones [START_REF] Oueslati | Approche archéozoologique des modes d'acquisition, de transformation et de consommation des ressources animales dans le contexte urbain gallo-romain de Lutèce[END_REF][START_REF] Albarella | Size and shape of the Eurasian wild boar (Sus scrofa), with a view to the reconstruction of its Holocene history[END_REF].We plotted the resulting data on an XY-graph and in a series of boxplots. Statistical significance (p < 0.05) of between group differences was tested using ANOVA in PAST 2.17 [START_REF] Hammer | PAST: Paleontological statistics software package for education and data analysis[END_REF].

Alongside our traditional morphometric approach, a number of tarsometatarsi were also analysed using geometric morphometrics (GMM). Previous research has shown that digital image analysis can be used to track phenotypic diversity in vertebrates (e.g. [START_REF] Cucchi | New insights into pig taxonomy, domestication and human dispersal in Island South East Asia: molar shape analysis of Sus remains from Niah caves, Sarawak[END_REF]2011;[START_REF] De Mendoza | Ecomorphology of the tarsometatarsus of waterfowl (Anseriformes) based on geometric morphometrics and its application to fossils[END_REF][START_REF] Foster | Identifying chicken breeds in the archaeological record: a geometric and linear morphometric approach[END_REF][START_REF] Gruwier | Exploration of the taxonomy of some Pleistocene Cervini (Mammalia, Artiodactyla, Cervidae) from Java and Sumatra (Indonesia): a geometric-and linear morphometric approach[END_REF][START_REF] Jeantet | Investigating past and present carpometacarpus morphology in Mimidae: A multi-methods approach to evidence from the Guadeloupe Islands[END_REF]. An advantage of this approach is that geometric morphometrics allow for size and shape to be analysed separately [START_REF] Viscosi | Leafmorphology, taxonomy and geometric morphometrics: a simplified protocol for beginners[END_REF] and that anatomical elements can be analysed as whole units instead of a series of separate measurements [START_REF] Zelditch | Geometric Morphometrics for biologists: A primer[END_REF]. As such, the results of our GMM analysis function as a test to validate potential patterns found in the linear morphometric analysis and optimally control for size effects.

In our GMM analysis we quantitatively assed morphological variation using a series of homologous landmarks, placed at discrete anatomical loci on a series of goose tarsometatarsi [START_REF] Zelditch | Geometric Morphometrics for biologists: A primer[END_REF]. Specimens were systematically fixed to a platform with plasticine, after which digital photographs were taken of the anterior side of the bone with a Nikon D750 camera mounted with a AF micro Nikkor 60mm 1:2.8 D lens. We placed a total number of 28 landmarks on the standardized photos of the tarsometatarsus using TPSdig 2.16 [START_REF] Rohlf | TpsDig 1.40-Thin Plate Spline Digitizer 1.40[END_REF]. Our model consisted of a combination of different landmark types: type I landmarks, placed at the juxtaposition of anatomical features, type II landmarks, found at the maximal curvature of an anatomical feature and type III landmarks, that are placed along an outline which is homologous at the level of the wider structure [START_REF] Baab | The shape of human evolution: a geometric morphometrics perspective[END_REF][START_REF] Ghislanzoni | Measuring 3D shape in orthodontics through geometric morphometrics[END_REF]. In this case, only landmark 5 could be classified as a type I landmark, while landmarks 1, 2, 3, 4, 6, 7 and 8 were type II landmarks (Figure 3). Landmarks 9 to 18 and 19 to 28 were two series of type III landmarks that we slid along the homologous outlines of the diaphysis using TPSrelw 1.49 [START_REF] Rohlf | TpsRelw 1.41-Thin Plate Spline Relative Warp[END_REF].

Figure 3 Anterior side of a left tarsometatarsus of a wild greylag goose with positioning of type I, II (black dots) and III landmarks (crossed dots).

Consequently, we conducted a generalized Procrustes analysis (GPA) on the data matrix in PAST 2.17, where the objects were scaled, rotated and translated to exclude all information irrelevant to differences in shape [START_REF] Goodall | Procrustes methods in the statistical analysis of shape[END_REF][START_REF] Walker | The ability of geometric morphometric methods to estimate a known covariance matrix[END_REF]. As the GPA procedure involves projecting coordinate data in a euclidean space tangent to the Procrustes shape space [START_REF] Viscosi | Leafmorphology, taxonomy and geometric morphometrics: a simplified protocol for beginners[END_REF], we used TPSsmall 1.20 [START_REF] Rohlf | TpsSmall 1.20[END_REF] to test if this approximation was adequate for further statistical analysis.

We conducted all further statistical analyses in PAST 2.17. Principal Component Analysis (PCA) served as a dimensionality reduction method and as the primary analysis to explore morphological variation in the Procrustes transformed shape data. All shape variables were included to identify the greatest axes of variation in the dataset [START_REF] Cucchi | Early Neolithic pig domestication at Jiahu, Henan Province, China: clues from molar shape analyses using geometric morphometric approaches[END_REF]. To identify the number of principal components to retain for further analysis, we plotted the eigenvalue distribution against a broken stick model [START_REF] Jackson | Stopping rules in principal components analysis: A comparison of heuristical and statistical approaches[END_REF]. According to this model, only components with an eigenvalue above the broken stick are relevant. Thin plate spline deformation grids visualized the shape changes along the different axes of the relevant principal components.

To assess statistical significance (p < 0.05) of between group differences in the PCA, we took an approach that involved conducting a nonparametric MANOVA (npMANOVA) on the relevant principal components [START_REF] Hou | Soft tissue facial changes among adult females during alignment stage of orthodontic treatment: A geometric morphometric study[END_REF][START_REF] Marramà | Principal component and discriminant analyses as powerful tools to support taxonomic identification and their use for functional and phylogenetic signal detection of isolated fossil shark teeth[END_REF][START_REF] Polly | Phenotypic variation across chromosomal hybrid zones of the common shrew (Sorex araneus) indicates reduced gene flow[END_REF][START_REF] Schutz | Differential sexual dimorphism: Size and shape in the cranium and pelvis of grey foxes (Urocyon)[END_REF].We chose a permutation test because the required assumptions for parametric testing, including normal distribution and across-group homogeneity of variance, are not necessarily met by GMM data [START_REF] Cardini | How many specimens do I need? Sampling error in geometric morphometrics. Testing the sensitivity of means and variances in simple randomized selection experiments[END_REF][START_REF] Lopez-Lazaro | Sexual dimorphism of the first deciduous molar: A geometric morphometric approach[END_REF][START_REF] Gruwier | Ecomorphology of the cervid calcaneus as a proxy for paleoenvironmental reconstruction[END_REF].When overall differences were significant, we conducted post hoc tests in the form of pairwise npMANOVAs between all pairs of groups, to test which populations differed significantly.

Even though the GPA procedure excludes isometric size differences, it does not rule out possible allometric effects [START_REF] Curran | Hominin Paleoecology and Cervid Ecomorphology[END_REF]. To account for this factor, we regressed PC-scores against natural log of centroid size [START_REF] Cucchi | Early Neolithic pig domestication at Jiahu, Henan Province, China: clues from molar shape analyses using geometric morphometric approaches[END_REF][START_REF] Owen | Morphological variation in wild and domestic suids[END_REF]. In case of a significant correlation between size and shape, we interpreted this as indicative for an allometric effect [START_REF] Zelditch | Geometric Morphometrics for biologists: A primer[END_REF][START_REF] Gruwier | Ecomorphology of the cervid calcaneus as a proxy for paleoenvironmental reconstruction[END_REF].

Results

Linear morphometrics

The results of our linear morphometric analysis show that when maximal length (GL) is plotted against a gracility index (GL/SC), the wild population separates well from the domestic population (Figure 4). In wild greylag geese, the overall length (GL) of the tarsometatarsus is smaller than in the domestic form (Figures 4 and5). This separation is confirmed by an ANOVA, resulting in significant differences between the two populations (F = 116.3; p < 0.001). When considering males and females separately, there is more intra-group overlap. Nevertheless, in the domestic population sexual dimorphism is clear, with males having significantly (F = 10.6; p = 0.004) longer tarsometatarsi than females (Figure 4). In the wild population sexual size dimorphism is much less pronounced, with males being of similar size as females (F = 0.1; p = 0.8).

Looking at the gracility index, wild specimens visually give higher scores than the domestic specimens (Figures 4 and5). Based on this index, the ANOVA confirms that wild greylag geese have significantly more gracile tarsometatarsi than the domestic form (F = 55; p < 0.001). Although no significant differences are noted between male and female wild geese (F = 0.2; p = 0.639), there is significant sexual dimorphism in gracility between the two sexes in domestic geese (F = 6.5; p = 0.019).

Figure 4 Plot of the greatest length (GL) and gracility index (GL/SC) of extant male (m) and female (f) Anser anser (open squares) and Anser anser f. domestica (filled squares) and archaeological specimens from Paris (crosses).

Figure 5 Boxplots of greatest length (GL) and gracility index (GL/SC) in male (m.) and female (f.) wild (wi.) and domestic (do.) Anser anser. The categories Wi. and Do. group all wild and domestic specimens of known and unknown sex together.

As a group, the archaeological specimens give different scores in the scatterplot than either the wild or the domestic population. As far as the length of the tarsometatarsus is concerned, all of the Roman specimens fell at the lower end of the spectrum. With the exception of two specimens from P634, all bones fall within the size range measured for wild Anser anser. 13 specimens also fall within the size range of the domestic form, but 10 are smaller in total length than the smallest modern domestic specimen. As a group, the specimens from Paris are significantly different in length from the domestic population (F = 73.1; p < 0.001), but not from the wild population (F = 73.1; p < 0.721).

Most archaeological tarsometatarsi yielded low gracility scores that were similar to the to the domestic population (Figures 3 and4). All specimens fall within the range of modern domestic geese, except one specimen from P634 that even exceeds the maximum robusticity measured in extant domestic geese. Nine specimens also overlap with the more robust specimens of the wild Anser anser population. The ANOVA indicates that, as a group, the Roman geese are significantly different from the modern wild population (F = 42.1; p <.0.001), but not from the domestic population (F = 42.1; p = 0.218).

Geometric morphometrics

The PCA on the Procrustes-transformed GMM data gives visual separation between wild and domestic geese when the first two axes are plotted (Figure 6). The thin plate spline deformation grids indicate that the first axis mainly summarizes a difference in robusticity (Figure 6). This is primarily expressed in domestic individuals showing a wider shaft relative to the articulations than wild geese. Furthermore, in (domestic) specimens with a lower score on PC1, there appears to be a more pronounced curvature of the shaft near the distal articulation. Along PC2, the main shape difference summarized by this axis is a variation in the position of the most proximal point of the eminentia intercotylaris and the most medial point of the trochlea metatarsi II. In specimens with a low score, the eminentia intercotylaris is positioned more towards the cotyla medialis and the trochlea metatarsi II gradually extends at the same level as the shaft. In specimens with a high score, the eminentia intercotylaris is positioned in the middle and the trochlea metatarsi II protrudes further towards the medial side.

Although PC2 explains 21.9% of the variation, between-group separations appear to be almost exclusively driven by the first component (32.3% of the variation). Despite limited overlap, wild specimens give an overall higher score on PC1 than domestic specimens, indicating that the latter population has a substantially more robust morphology than the wild population. An npMANOVA on the relevant components (PC1 to PC6), as indicated by a scree plot of the eigenvalue distribution [START_REF] Jackson | Stopping rules in principal components analysis: A comparison of heuristical and statistical approaches[END_REF], shows that the observed differences between the wild and domestic form are significant (p<0,001).

When considering specimens by sex, there is no clear visual pattern in the PCA scatterplot (Figure 6). Female specimens do not score higher or lower than males in either the wild or the domestic population. This is confirmed by an npMANOVA on the relevant components (PC1 to PC6) (p < 0.001), with associated pairwise comparisons (Figure 6). Differences are significant between all wild and domestic groups, but not between respectively domestic males and females (p = 0.7487) and between wild males and females (p = 0.6487). Although the GPA procedure removes the effects of isometric size differences, we conducted a regression of the first component (giving the best separation) against the natural log of centroid size (Figure 8) to account for potential allometric effects. When PC1 is regressed against log centroid size, a weak but significant correlation is found between the two variables (R 2 =0,051, p < 0.001). A regression of PC2 against centroid size also resulted in a significant, but somewhat stronger correlation (R 2 = 0.306, p < 0.001).

Figure 8 Results of regressions of PC1 and PC2 against natural log of centroid size for all geese tarsometatarsi.

As far as the position of the Roman geese is concerned, all of the 12 archaeological specimens from Paris fall within the range of variation of the modern geese on the first axis of the PCA (Figure 6). This indicates that all tarsometatarsi have a gracility typical of either wild or domestic Anser anser. Along the second axis, three specimens from p634 give unusually high scores. In terms of morphology, this means that the three specimens have an eminentia intercotylaris that is positioned more in the middle and a trochlea metatarsi II that protrudes further towards the medial side, than is the case in the modern Anser anser populations. However, this axis was considered less relevant, as it does not give substantial visual separation between extant wild and domestic geese.

Five specimens from P634 visually give low scores on the first axis and only fall within the measured range of domestic goose. One particularly gracile specimen from P634 gives high scores on PC1 and falls exclusively within the range of wild greylag goose. The other four specimens from P634 and the two specimens from P553 are of intermediate gracility and give scores that fall within the range of both wild and domestic goose.

6. Discussion

Extant specimens

The results of our linear morphometric analysis of the extant reference material confirmed the notion that robusticity in the tarsometatarsus can be used to differentiate wild and domestic geese.

As previous studies have already suggested, the relative width of the shaft increases in domestic populations [START_REF] Bramwell | Identification and interpretation of bird bones[END_REF][START_REF] Reichstein | Untersuchungen an skelettresten von vogeln aus Haithaby[END_REF][START_REF] Macdonald | Domestic geese from Medieval Dublin[END_REF][START_REF] Oueslati | Approche archéozoologique des modes d'acquisition, de transformation et de consommation des ressources animales dans le contexte urbain gallo-romain de Lutèce[END_REF][START_REF] Duval | Les oies du site castral de Boves aux Xe siècle: tentative d'identification des individus domestiques[END_REF][START_REF] Poland | A methodological approach to the identification of duck and goose remains from archaeological sites with an application to Roman Britain[END_REF]. Although a large portion of the population of domestic geese was substantially larger than wild greylag geese, even in cases where the two extant populations overlapped in size, the domestic form had a more robust shape on average. When considering sexes, there were no clear differences in robusticity or length between male and female wild greylag geese. In the domestic form, sexual size dimorphism was clear, with males being larger on average than females. This was in line with Rensch's rule, which states that populations with a larger body size exhibit higher male to female body size ratio's [START_REF] Rensch | Die abhangigkeit der relative sexualdifferenz von der korpergrosse[END_REF]. This contradicts studies on sexual size dimorphism in cattle [START_REF] Polák | Patterns of sexual size dimorphism in cattle breeds support Rensch's rule[END_REF], sheep [START_REF] Polák | Sexual size dimorphism in domestic goats, sheep, and their wild relatives[END_REF], goat, [START_REF] Polák | Sexual size dimorphism in domestic goats, sheep, and their wild relatives[END_REF] and chicken [START_REF] Remeš | Domestic chickens defy Rensch's rule: sexual size dimorphism in chicken breeds[END_REF], where sexual dimorphism is reduced in domestic forms [START_REF] Polák | Sexual size dimorphism in domestic goats, sheep, and their wild relatives[END_REF], 2010;[START_REF] Remeš | Domestic chickens defy Rensch's rule: sexual size dimorphism in chicken breeds[END_REF].

At least for the ungulates, the authors explain this by the presence of strong male-male competition and sexual selection for a large body size in wild forms, a condition that is relaxed in the controlled settings associated with domestication [START_REF] Schaller | Mountain monarchs. Wild sheep and goats of the himalaya[END_REF]Polák &[START_REF] Polák | Sexual size dimorphism in domestic goats, sheep, and their wild relatives[END_REF]2010). Our results, in line with those of an earlier study on Anatidae [START_REF] Pares-Casanova | Is sexual size dimorphism similar irrespective of the origin of the goose breed?[END_REF], demonstrate that this is not the case for geese. As domestic geese have to be kept in mixed male-female groups [START_REF] Serjeantson | Goose husbandry in medieval England, and the problem of ageing goose bones[END_REF], it is likely that male-male competition is not reduced in captive settings (Pares-Casanova, 2013). In the wild, sexual selective pressures are still confounded by other, natural selective pressures, counterbalancing the development of very large phenotypes [START_REF] Pares-Casanova | Is sexual size dimorphism similar irrespective of the origin of the goose breed?[END_REF].Under captive conditions, the combination of reduced natural selection and heavy male competition may in fact lead to an increase in sexual size dimorphism [START_REF] Pares-Casanova | Is sexual size dimorphism similar irrespective of the origin of the goose breed?[END_REF].

The results of our GMM analysis were in line with those of the linear morphometric analysis. Despite some overlap, the PCA was able to differentiate between wild and domestic specimens on the first axis. The thin plate spline deformation grids confirmed that the main shape variation between the two groups was a difference in gracility of the shaft. This was, moreover, not an effect of isometric size differences, as the GPA procedure removed these effects from the dataset. The regressions against centroid size, however, indicated the presence of a weak allometric effect in the dataset. We expected this correlation because the domestic specimens, with their more robust morphology, were in most cases also larger than the wild specimens. The reason that the correlation was only weak, was probably because most of the archaeological specimens were small in size but had a similar shape as the domestic population.

In addition to a more robust shape, domestic Anser anser possibly also had a more pronounced curvature of the shaft near the distal articulation. Previous studies have proposed a relationship between increased curvature and a more rapid growth rate in the leg bones of mallard and chicken [START_REF] Duggan | Differences in hindlimb morphology of ducks and chickens: effects of domestication and selection[END_REF]. It is possible that, in geese, this morphological trait is also the result of artificial selection for individuals with a faster growth rate, although it should be noted that there is disagreement whether sexual maturity (2-3 years) is reached earlier in domestic than in wild geese [START_REF] Serjeantson | Goose husbandry in medieval England, and the problem of ageing goose bones[END_REF]Kozák 2019).

Our shape analysis did not confirm the sexual size dimorphism suggested by the linear morphometric analysis for the domestic population. We observed no significant shape differences between males and females within either the wild or the domestic population. This result may indicate that the underlying mechanisms that drive more robust hind leg morphology in domestic populations are different from those that give rise to increased size disparity between sexes. Although we did not explicitly test for changes in locomotion and function in the hind limb, the ontogenetic trajectory could play a role in the increased curvature [START_REF] Dial | Precocial hindlimbs and altricial forelimbs: partitioning ontogenetic strategies in mallards (Anas platyrhynchos)[END_REF][START_REF] Duggan | Differences in hindlimb morphology of ducks and chickens: effects of domestication and selection[END_REF].

The archaeological sample

The Roman specimens from Paris gave somewhat ambiguous results in the linear morphometric analysis. On average, the specimens within this group were of the size of wild greylag geese, but with a robust morphology typical of domestic geese. This suggested that most of the archaeological specimens were of a small, domestic form, a notion confirmed by our GMM analysis. After the removal of isometric size effects, our shape analysis placed most specimens within the range of domestic geese. There is, however, no reason to assume our archaeological population was homogenous and composed of a single form. Indeed, seven specimens from P634 and one from P538, fall well into the range of wild geese as far as the gracility index is concerned. Moreover, in the GMM analysis one specimen from P634 falls exclusively within the range of wild greylag geese, while an additional four from P634 and two from P538 could be either wild or domestic. The reasons for this were not entirely clear, but it is conceivable that in the modern domesticated specimens that dominated our sample, a stricter artificial selection led to an increased robusticity of the tarsometatarsus. We also cannot rule out a degree of introgression between wild and domestic forms in Antiquity, a well-known phenomenon in the Anatidae [START_REF] Heikkinen | Long-Term reciprocal gene flow in wild and domestic geese reveals complex domestication history[END_REF].

In terms of archaeological application, it appears from our results that geese tarsometatarsi with a gracility index of more than 11.8 can be interpreted as wild. Specimens with a gracility index of less than 10.7 may be interpreted as domestic goose. This was confirmed by the GMM analysis which successfully classified specimens that met those criteria in the respective domestic and wild populations. Using univariate size variables in isolation proved insufficient to make the distinction between the two forms, as the substantial size increase seen in modern domestic geese had

apparently not yet set in during Roman times. When this evolution took place remains unknown, but a particular moment where such changes may have happened, is from the onset of intensive culling of immature geese in the post-medieval time [START_REF] Serjeantson | Goose husbandry in medieval England, and the problem of ageing goose bones[END_REF][START_REF] Clavel | L'animal dans l'alimentation médiévale et moderne en France du Nord (XIIIe -XVIIe siècles)[END_REF], which relates to a more meat oriented production and an emphasis on increasing meat-yield.

Conclusions

The investigation of the status of the Roman geese from Paris relied on the acquisition and analysis of a comparative sample of male and female domestic and wild greylag geese. The analysis of the extant domestic and wild forms highlights the degree of divergence we observe today between the domestic Maxipalm strain of the grey Toulouse breed and the wild greylag. This translates in greater size and robusticity but also in a significantly stronger sexual dimorphism in comparison with the wild form. Although the long-term selection of profitable breeds, notably for meat production, has probably affected the modern domestic goose skeleton in a more profound way than that of Roman domestic flock from Paris, our results showed that the modern and ancient domesticates share a similar morphotype. This demonstrates that a combination of linear and geometric morphometrics are an appropriate set of techniques to differentiate between wild and domestic goose populations. Especially our GMM model, which allowed us to describe subtle morphological differences and adequately account for size effects, proved particularly effective. It corroborates the results of our linear analysis, which in itself equips zooarchaeologists with an easily accessible tool for identification.

Furthermore, 23

 23 Roman specimens from 3 sites from Paris (P634 Rue Pierre et Marie Curie, P538 Rue Gay-Lussac and P553 Hôtel-Dieu) were included from the collections of the Pôle Archéologique du Département d'Histoire, de l'Architecture et d'Archéologie de Paris (DHAAP).

Figure 2

 2 Figure 2 Goose tarsometatarsi from Lutecia showing different states of preservation with (a) complete specimen integrated in the geometric morphometric study P634/1008 and specimens with altered proximal or distal articulations only used in linear morphometrics (b) P634/2293 (c) P553/1006 and (d) P553/1006.

Figure 6 Figure 7

 67 Figure 6 PCA on Procrustes residuals of extant wild and domestic geese (m=male, f=female) and archaeological specimens from Paris (P634 and P553), with scree plot of the eigenvalue distribution and thin plate spline deformation grids showing hypothetical extreme values at the end of the first two axes.

Acknowledgments

The authors wish to thank Jérôme Fuchs and the collection management service of the Muséum National d'Histoire Naturelle of Paris (France) for permitting us to study their reference material of wild greylag geese. Hans Klaassen and Albin Meynard from the Andrévias Farm are thanked for providing extant wild and domestic geese used in our morphometric analyses.


Lola Serée
email: lolaserée@hotmail.fr

Aude Barbottin

François Chiron

Muriel Valantin-Morison

Antoine Gardarin

Within-field floral resources have the potential to increase parasitism rates in winter oilseed rape pests more than resources at field margins

Keywords: Pollen beetle, stem flea beetle, conservation biological control, accessible nectar, parasitism

Pollen beetles (Brassicogethes spp.) and stem flea beetles (Psylliodes chrysocephala) are among the main pests of oilseed rape crops in Europe, causing high yield losses. Increasing insecticide resistance and environmental concerns have highlighted the need for alternatives to chemical control, such as conservation biological control. Conservation biological control can be enhanced by providing resources to beneficial organisms in and around crop fields. Flower strips are a promising tool to provide nectar resources for parasitoids. In addition, the planting of such resources in field margins should be reinforced by the absence of insecticide application. However, the presence and the amount of weeds within the field could mitigate the effect of flower strips and needs to be explored. We surveyed 25 oilseed rape fields in 2019 and 2020. Ten of these fields were adjacent to a sown wildflower strip. We compared an eco-friendly strategy (wildflower strip without insecticide in spring) to a conventional approach (no wildflower strip and chemical control of pests). We assessed the parasitism of stem flea beetle and pollen beetle larvae in the spring, at distances of 5 m and 30 m from the wildflower strip or the natural field margin. We performed botanical surveys in wildflower strips and natural field margins and within the field, to assess the availability of accessible nectar resources to parasitoids. Stem flea beetle parasitism rates were not affected by the strategy used, but the eco-friendly strategy had a weak positive effect on pollen beetle parasitism. Unexpectedly, the amount of accessible nectar did not differ significantly between wildflower strips in the eco-friendly strategy and natural herbaceous field margins in the conventional strategy. The amount of accessible nectar provided by weeds in the field was positively related only to pollen beetle parasitism rates. By contrast, the amount of accessible nectar for both spontaneous field margin and flower strips had no effect on the rates of parasitism of either species. Parasitism rate decreased significantly with decreasing distance to the field edge, for both species. Our results suggest that further studies are required: (i) to improve the composition of wildflower strips, so as to provide more accessible nectar resources at the start of spring and (ii) to explore more management strategy options, notably on in-field resources management such as unsown patches or intercropping.

Introduction

Winter oilseed rape is a crop of considerable economic and agronomic value that is grown on 8.5 % of all European arable land (FAO 2016[START_REF] Ruser | Nitrous oxide emissions from winter oilseed rape cultivation[END_REF]. However, it is also subject to high pest pressure from insects such as pollen beetle (Brassicogethes aeneus, Coleoptera: Nitidulidae, Fabricius, 1775), stem flea beetle (Psylliodes chrysocephala, Coleoptera: Chrysomelidae, Linnaeus, 1758) and stem weevils (Ceutorhynchus spp., Coleoptera: Curculionidae) [START_REF] Williams | Integrating parasitoids into management of pollen beetle on oilseed rape[END_REF]. The management of these pests has become more difficult with the move towards organic cropping systems and other types of cropping system without insecticides [START_REF] Valantin-Morison | Diagnosis of limiting factors of organic oilseed rape yield. A survey of farmers' fields[END_REF]. For instance, the abundance of stem flea beetle populations has increased in Sweden following the introduction of a neonicotinoid ban [START_REF] Lundin | Consequences of the neonicotinoid seed treatment ban on oilseed rape production -what can be learnt from the Swedish experience?[END_REF]. Oilseed rape pests have also become a key issue in conventional cropping systems. Indeed, stem flea beetle and pollen beetle are increasingly resistant to pyrethroids, one of the last families of chemical substances authorized for their control since the ban on neonicotinoids in the European Union [START_REF] Robert | Pyrethroids resistance monitoring in French cabbage stem flea beetle (Psylliodes chrysocephala) and rape winter stem weevil (Ceutorhynchus picitarsis) populations in oilseed rape. Écologie Chimique: nouvelles contributions à la protection des cultures contre les ravageurs et 11e Conférence Internationale sur les Ravageurs et Auxiliaires en Agriculture[END_REF][START_REF] Slater | Pyrethroid resistance monitoring in European populations of pollen beetle (Meligethes spp.): A coordinated approach through the Insecticide Resistance Action Committee (IRAC)[END_REF][START_REF] Willis | Investigating the status of pyrethroid resistance in UK populations of the cabbage stem flea beetle (Psylliodes chrysocephala)[END_REF]. In addition, oilseed rape is a mass-flowering crop very attractive to pollinators, where insecticide applications caused deleterious effects particularly when they are applied during flowering to control inflorescence insects such as pollen beetle [START_REF] Mänd | Oilseed Rape, Bees and Integrated Pest Management[END_REF]. It is therefore necessary to provide efficient and biodiversity-friendly crop protection strategies against insects considered as pests, such as through conservation biological control.

Most oilseed rape pests can be regulated by generalist predators (from insects to birds) or more specialist parasitoids [START_REF] Gagnon | Caractérisation de la guilde des ennemis naturels du méligèthe des crucifères (Brassicogethes viridescens, Coleoptera: Nitidulidae) dans la culture du canola dans la région néarctique[END_REF][START_REF] Riggi | Pollen beetle mortality is increased by ground-dwelling generalist predators but not landscape complexity[END_REF]. Parasitoids are important biocontrol agents that target oilseed rape pests [START_REF] Ulber | Parasitoids of Oilseed Rape Pests in Europe: Key Species for Conservation Biocontrol[END_REF]. In Europe, the main parasitoid of pollen beetle is Tersilochus heterocerus (Hymenoptera: Ichneumonidae, Thomson, 1889) and the main parasitoid of stem flea beetle is Tersilochus microgaster (Hymenoptera: Ichneumonidae, Szépligeti, 1899 ; [START_REF] Ulber | Parasitoids of Oilseed Rape Pests in Europe: Key Species for Conservation Biocontrol[END_REF]. These parasitoids are sufficiently widespread and abundant across Europe to be of potential importance for the conservation biological control of these target pests [START_REF] Ulber | Parasitoids of Oilseed Rape Pests in Europe: Key Species for Conservation Biocontrol[END_REF].

Across Europe, the larval parasitism rates of pollen beetle generally lie within the 25-50% range in unsprayed crops, but they may occasionally exceed 80% [START_REF] Ulber | Parasitoids of Oilseed Rape Pests in Europe: Key Species for Conservation Biocontrol[END_REF], highlighting the potential of parasitoids for the effective biological control of oilseed rape pests. However, stem flea beetle parasitism rates vary considerably between years and geographic contexts (Ulber and Wedemeyer, 2004;[START_REF] Ferguson | Distributions and interactions of the stem miners Psylliodes chrysocephala and Ceutorhynchus pallidactylus and their parasitoids in a crop of winter oilseed rape (Brassica napus)[END_REF].

Once Tersilochus spp. larvae have completed their development, they pupate and overwinter in the soil. The adults then emerge in early spring and disperse to colonize oilseed rape crops. At the landscape scale, higher rates of parasitism by T. heterocerus are often associated with more complex landscapes, with a low proportion of arable land [START_REF] Scheid | Enhancing rape pollen beetle parasitism within sown flower fields along a landscape complexity gradient[END_REF] or a high proportion of semi-natural habitats (Schmidt, Thies, and Tscharntke, 2004;[START_REF] Rusch | Local and landscape determinants of pollen beetle abundance in overwintering habitats[END_REF]. Semi-natural habitats adjacent or close to agricultural fields could provide nectar and pollen resources for parasitoids depending on their plant composition and vegetation structure [START_REF] Rusch | Integrating Crop and Landscape Management into New Crop Protection Strategies to Enhance Biological Control of Oilseed Rape Insect Pests[END_REF]. Indeed, in most parasitoid species, adult survival is dependent on the availability of plant-derived sugar-rich foods, such as nectar [START_REF] Vollhardt | Spatial distribution of flower vs. Honeydew resources in cereal fields may affect aphid parasitism[END_REF]. These resources enhance longevity and fecundity, which can translate into higher reproductive success and parasitism rates [START_REF] Gillespie | Beyond nectar provision: The other resource requirements of parasitoid biological control agents[END_REF][START_REF] Tylianakis | Improved Fitness of Aphid Parasitoids Receiving Resource Subsidies[END_REF].

Like flower fields [START_REF] Krimmer | Flower fields and pesticide use interactively shape pollen beetle infestation and parasitism in oilseed rape fields[END_REF], flower strips may be a useful management option for providing trophic resources at the edge of the crop, to promote biological control by parasitoids. [START_REF] Büchi | Mortality of pollen beetle (Meligethes spp.) larvae due to predators and parasitoids in rape fields and the effect of conservation strips[END_REF] found significantly higher rates of pollen beetle parasitism in oilseed rape fields adjacent to wildflower strips than in an extensively managed meadow, a finding that may be explained by higher levels of nectar resources close to flower strips. Parasitism has been much less investigated in stem flea beetles than in pollen beetles. The parasitoids of stem flea beetles are active from February to March [START_REF] Ulber | Parasitoids of Oilseed Rape Pests in Europe: Key Species for Conservation Biocontrol[END_REF], at least one month before those of pollen beetles, when nectar resources may be even more limited than later in the spring, due to the very small number of plants flowering during this period. In a recent field experiment, perennial wildflower strips increased the parasitism of P. chrysocephala, B. aeneus and of Ceutorhynchus pallidactylus, the magnitude of this effect depending on the amount of nectar available and accessible to parasitoids [START_REF] Gardarin | The hump-shaped effect of plant functional diversity on the biological control of a multi-species pest community[END_REF]. However, the importance of the nectar resources provided by wildflower strips covering a small area at the edge of the field relative to those provided by weeds over the whole field area have not been investigated. Indeed, weeds growing spontaneously in fields may also be beneficial to parasitoids, through the provision of nectar and pollen resources [START_REF] Norris | Interactions between weeds, arthropod pests, and their natural enemies in managed ecosystems[END_REF]. These resources can act as a 'relay' in the field, as parasitism rates generally decline exponentially with increasing distance from floral patches [START_REF] Tylianakis | Improved Fitness of Aphid Parasitoids Receiving Resource Subsidies[END_REF].

In this study, we investigated the extent to which a pest management strategy based on a wildflower strip with no spring insecticide treatment, as an alternative to conventional approaches based exclusively on insecticides, could promote the parasitism of two main pests of oilseed rape: stem flea beetle and pollen beetle. We compared parasitism rates in fields close to a wildflower strip without insecticide treatment (referred to hereafter as the 'eco-friendly strategy') to a reference situation consisting of fields with no flower strip that were treated with insecticide in the spring (hereafter referred to as the 'conventional strategy').

We expected (i) a positive effect of eco-friendly management on the rates of stem flea beetle and pollen beetle parasitism, with (ii) a decrease in efficacy with increasing distance from the flower strip. We also expected that (iii) the effect of wildflower strips would depend on the amount of accessible nectar available at the field margin and in the field (weeds), and that this effect might be strengthened when no insecticide is used.

Methods

Study sites

The northern half of France is dominated by the cultivation of arable crops (mostly cereals and oilseed rape) in open field landscapes. We followed 12 and 13 fields in 2019 and 2020 respectively, 10 of which were adjacent to a sown wildflower strip, the others being bordered by a natural, spontaneously growing herbaceous field margin. Each flower strip (approximately 4 m x 500 m) was sown in autumn 2018 with a mixture of 42 native, mostly perennial species (Table S1) The plant species were selected to provide arthropods with physical habitats and diverse trophic resources throughout the year [START_REF] Gardarin | Understanding plant-arthropod interactions in multitrophic communities to improve conservation biological control: Useful traits and metrics[END_REF]. We asked farmers to leave a 50 m buffer zone not treated with insecticide between the wildflower strip and the central part of the field, to increase the positive effects on biological control [START_REF] Geiger | Persistent negative effects of pesticides on biodiversity and biological control potential on European farmland[END_REF]. Removing insecticide treatments on the whole field was considered too risky by a majority of farmers. In fields treated in spring, farmers mainly applied insecticide once, sometimes twice. Treatments occurred in March and April at full dose with pyrethrinoids (e.g. Trebon 30 EC, Karate Zeon, Sentinel Pro) or less often with neonicotinoids (e.g. Mavrik Flo) or organophosphorous insecticides (e.g. Boravi WG).

In the years studied, over a network of 41 oilseed rape fields farmed conventionally and monitored by agricultural extension services within the study region (DRIAAF, 2020), the rate of oilseed rape plant infestation with stem flea beetle larvae ranged from 0 to over 30 individuals per plant, with a mean of four larvae per plant in 2019 and 2.5 larvae per plant in 2020. This level of infestation is among the highest recorded over the last decade. In the same network, pollen beetle pressure was also the highest in a decade, with a mean of 6 (2019) to 10 (2020) individuals per flowering stem at the sensitive stage, just before flowering.

We digitized the land cover types of cropped and non-cropped areas within a 500 m radius around each field (the landscape buffer), based on an intensive land survey, with QGIS software (version 3.12; www.qgis.org). We calculated the proportion of semi-natural habitats (including woods, fallow, hedges, and wildflower strips) within this radius. The proportion of semi-natural habitats within a radius of 500 m ranged from 0.18 to 63.72% (median=7.48%) of the landscape buffer areas. The proportion of oilseed rape ranged from 4.75 to 37.79% (median=18.68%). Our sampled fields were mostly located in open landscapes and the proportions of semi-natural habitats and oilseed rape tested in the first model did not significantly explain the rates of parasitism in the two species (Table S2). We did not, therefore, introduce landscape variables into the statistical models, to prevent overparametrisation.

Assessment of parasitism rates in pollen beetle and stem flea beetle larvae

Stem flea beetle

In April 2019 and 2020, we collected 100 last-instar larvae from the petioles of basal leaves of oilseed rape. The larvae were samples at random along a transect of 50 m, at 5 m and 30 m from the wildflower strip, or from the natural herbaceous field margin. We excluded one and four fields from the analysis of stem flea beetle parasitism in 2019 and 2020, respectively, due to the presence of too few stem flea beetle larvae in the plants. We reared the larvae to the adult stage for the determination of parasitism rates. The larvae were placed in hermetic plastic boxes (9.5 cm in diameter, 7 cm high), filled to two thirds of their total volume with moist sieved soil. The soil used consisted of a sand and soil mixture (50:50), which was sterilized before use.

The rearing boxes were placed at room temperature (about 20°C) for six months. We recorded the number of the emerging adults of P. chrysocephala (developing from non-parasitized larvae) during the first two months after collection in the field. Rearing boxes were then stored at 4°C for a further three months, to simulate winter temperatures, and were then returned to room temperature. Parasitoids emerged after the release from low temperatures and were recorded over a period of two months, until no further emergence occurred. The parasitoids species was morphologically similar to Tersilochus microgaster and T. obscurator (Hymenoptera: Ichneumonidae, Aubert, 1959) according to published identification tools [START_REF] Barari | The separation of two hymenopteran parasitoids, Tersilochus obscurator and Tersilochus microgaster (Ichneumonidae), of stem-mining pests of winter oilseed rape using DNA, morphometric and ecological data[END_REF], and could not be assigned to either species with certainty. For simplicity, we named them Tersilochus sp. for the purposes of this study.

Parasitism rate was calculated as the number of emerging parasitoids divided by the sum of the number of emerging stem flea beetles and the number of emerging parasitoids, expressed as a percentage.

Pollen beetle

At the end of blooming periods (BBCH stage 66: [START_REF] Lancashire | A uniform decimal code for growth stages of crops and weeds[END_REF][START_REF] Weber | Explanations of the BBCH decimal codes for the growth stages of maize, rape, field beans, sunflower and peas -with illustrations[END_REF] i.e. in early May 2019 and late April 2020), we collected a minimum of 100 last-instar larvae of more than 3 mm in length from oilseed rape flowers. The larvae were sampled randomly along a transect of 50 m parallel to the field edge, at 5 m and 30 m from the wildflower strip and from the natural herbaceous field margin. The collected larvae were stored in 70° alcohol. Under a binocular microscope, we recorded the presence of eggs in the larvae. They were identified as eggs of T. heterocerus due to their black colour [START_REF] Osborne | Observations on the natural enemies of Meligethes aeneus (F.) and M. viridescens (F.)[Coleoptera: Nitidulidae][END_REF]. This species is the principal parasitoid of B. aeneus in the area [START_REF] Rusch | Multi-scale effects of landscape complexity and crop management on pollen beetle parasitism rate[END_REF]. Parasitism rates were calculated as the number of larvae containing at least one parasitoid egg divided by the total number of hosts, expressed as a percentage.

Nectar resources at the field margin and within the field

Standardized botanical surveys were carried out during the sampling of each oilseed rape pest, to assess the nectar resources provided to parasitoids by sown wildflower strips, by the natural vegetation growing spontaneously at the field margin (always herbaceous) and within fields.

We performed three transects: at the field edge, and at distances of 5 m and 30 m from the edge of the field. Every 2 m, over a distance of 40 m (20 plots of 1 m 2 ), we attributed a cover class to each dicotyledonous species present (as a putative nectar-producing resource) according to its percent cover (Class 1: 1% or less; Class 2: 2-10%; Class 3: 11-30%: Class 4: 31-75%; Class 5: 76-100%). We noted the phenological stage of each species (vegetative, flowering, fruiting). We then calculated the cover of plants (%) providing floral and extrafloral nectar for parasitoids as the sum of the plant species cover producing available and accessible nectar (Supplementary Materials Appendix A). Nectar was considered to be available if it was produced during the period of parasitoid activity. Floral nectar accessibility depends on the morphological match between the plant and parasitoid, and was determined by measuring traits for each parasitoid and plant within the assemblage [START_REF] Gardarin | The hump-shaped effect of plant functional diversity on the biological control of a multi-species pest community[END_REF]. For the calculation of floral nectar accessibility, we adapted the geometric model proposed by [START_REF] Van Rijn | Nectar accessibility determines fitness, flower choice and abundance of hoverflies that provide natural pest control[END_REF]. We considered the ability of the insect to penetrate the flower and its ability to reach the nectar, which depended on corolla shape, nectar depth, insect head size and the size of the mouthparts.

Statistical analyses

We ran generalized linear mixed models (GLMM), assuming a binomial distribution, with the 'glmer' function (nlme package, Pinheiro et al., 2017). We used the 'cbind' function with the number of parasitized larvae as 'successes' and the number of larvae without parasitism as 'failures'.

We generated two models for each species, for (i) the type of strategy (eco-friendly vs. conventional) and (ii) for the gradient of accessible nectar resources at each distance. In the first type of model, we introduced strategy, distance to the field margin (5 or 30 m) and year as explanatory fixed-effects variables, together with the first-order interaction between strategy and distance. In the second type of model, we introduced strategy, distance, year, and mean cover of plants providing accessible nectar at the edge of the field (natural vegetation or wildflower strip) and in the field (weeds) as explanatory fixed-effect variables. We tested the first-order interactions between the cover of plants providing accessible nectar in the fields and (a) strategy and (b) distance.

We accounted for the spatial dependence of observations between distances in the same field, by introducing field name as a random-effect variable. All variables were standardized (i.e. by subtracting the mean and dividing by the standard deviation). Correlations between covariates in full models were assessed with variance inflation factors (all VIF < 5; [START_REF] James | An Introduction to Statistical Learning[END_REF]. Diagnostic residual plots were generated with DHARMa (Hartig and Hartig, 2017) and confirmed a good fit for all models. Spatial correlation in the residuals was evaluated with the 'bubble' function from the 'sp' package and with Correlogram (package 'ncf'); no spatial correlation was detected. All analyses were performed with a significance threshold of 5% in R statistical software version 3.5. 2 (2018-12-20).

Results

Availability of floral resources

Availability of field margin resources during stem flea beetle sampling

During stem flea beetle sampling, 29 dicotyledonous plant species were found in the natural field margins (18 species with nectar accessible to stem flea beetle parasitoids) and 18 were found in wildflower strips (11 species with accessible nectar, Fig. S2). A complete list of the plant species providing accessible nectar for each parasitoid studied is provided in Table S4. There was some overlap (61%) in flower species composition with accessible nectar between natural field margins and wildflower strips at the start of the season.

In spontaneous field margins, Veronica persica, Taraxacum officinale and Sinapis arvensis were the main species providing accessible nectar (Fig. S2). In the wildflower strips, nectar was mainly provided by Vicia sativa, Lamium purpureum, L. hybridum, and Veronica hederifolia (Fig. S2) During stem flea beetle sampling, the average percentage of plant coverage providing accessible nectar at field margins was 9.8 % (min-max = 0.1-60.5 %). The mean cover of plants at the field edge providing nectar accessible to parasitoid of stem flea beetle did not significantly differ between the two management strategies: conventional vs. eco-friendly (Fig. 1).

Availability of weeds resources during stem flea beetle sampling

During stem flea beetle sampling, 12 dicotyledonous weed plant species with accessible nectar to parasitoids were found in oilseed rape field (Table S5). Stellaria media, Vicia sativa, Lamium hybridum and Veronica persica were the main weed species providing accessible nectar over the two distances (Table S5). The average percentage of weed cover within the field providing nectar accessible to parasitoids of stem flea beetle was 6.2 % (min-max = 0.2-14.2 %) and 2.1 % (min-Mmax = 0.1-12.9 %) in the eco-friendly or in the conventional strategy, respectively. There was a 50% overlap in weed species communities found in conventional and eco-friendly strategy fields (50% of the species were found in both strategies; Fig. S4).

We detected no difference in weeds cover between the two management strategies (Wilcoxon test: W=172, P=1).

Availability of field margin resources during pollen beetle sampling

During pollen beetle sampling, 44 dicotyledonous plant species were found in the natural field margins (21 species with accessible nectar) and 33 were found in wildflower strips (24 species with accessible nectar, Fig. S2). A complete list of the plant species providing accessible nectar for each parasitoid studied is provided in Table S4. There was a 52% overlap in the flower species composition with accessible nectar between the natural field margin and wildflower strips. The differences in composition between the natural field margin and flower strips were more marked later in the season, i.e. during pollen beetle sampling than during stem flea beetle (Fig. S3). In spontaneous field margins, Veronica persica, Geranium spp. and Taraxacum officinale were the main species providing accessible nectar (Fig. S2). In the wildflower strips, nectar was mainly provided by Vicia sativa, Leucanthemum vulgare, Lamium purpureum, and Barbarea vulgaris (Fig. S2). During pollen beetle sampling, the average percentage of plant coverage providing accessible nectar at field margins was 13.4 % (min-max = 0.0-52.2 %). The mean cover of plants at the field edge providing nectar accessible to parasitoid of pollen beetle did not significantly differ between the two management strategies: conventional vs. eco-friendly (Fig. 1).

Availability of weeds resources during pollen beetle sampling

During pollen beetle sampling, 19 dicotyledonous weed plant species with accessible nectar to parasitoids were found in oilseed rape field (Table S5). Vicia sativa, Stellaria media, Lamium hybridum and Veronica persica were the main weed species providing accessible nectar over the two distances (Table. S5). The average percent of weed cover within the field providing nectar accessible to parasitoids of pollen beetle) was 5.4 % (min-max = 0.1-12.3 %) and 3.7 % (min-max = 0.1-52.5 %) in the eco-friendly or in the conventional strategy, respectively. There was a 60% overlap in the weed species found in conventional and eco-friendly strategy fields (60% of the species were found in both strategies; Fig. S4). We detected no difference in weeds cover between the two management strategies (Wilcoxon test: W=359, P=0.244).

Effect of strategy and of distance to the edge of the field on parasitism rate

The mean parasitism rates for stem flea beetle (mean=29.55% ± 21.78) and pollen beetle (mean=13.12% ± 18.59) varied considerably between fields, ranging from 0 to 90% and 0 to 43.75%, respectively. Study year had no effect on parasitism rate for either of the species (Table 1, Fig. 2). Stem flea beetle parasitism rates decreased significantly with increasing distance from the field edge and were not influenced by the type of strategy tested (Table 1, Fig. 2). Parasitism rates also decreased with increasing distance from the field edge in pollen beetle. Parasitism rates were significantly higher at 5 m than at 30 m from the edge of the field, in both stem flea beetles and pollen beetles (Table 1, Fig. 2). In pollen beetle, a trend towards a positive effect of the eco-friendly strategy was observed (Table 1, Fig. 2).

Table 1. Effect of management strategy on the rates of parasitism of stem flea beetle and pollen beetle in oilseed rape fields managed with an 'eco-friendly' (wildflower strip without insecticides in spring) or a conventional (natural herbaceous field margin plus insecticides) strategy. Reference levels for factors: Distance = 30 m; Strategy = conventional; Year = 2019. Significant results are indicated in bold. *P < 0.05, **P < 0.01, ***P < 0.001.

Response

Effect of accessible nectar on parasitism rates

The nectar resources at the margin of the field did not influence the parasitism rates of stem flea beetles and pollen beetles (Table 2). However, within-field resources enhanced parasitism rates, regardless of distance from the field margin for pollen beetles, and particularly at 5 m from the field margin for stem flea beetle (Table 2; Fig. 3). An interaction between management strategy and within-field nectar resources was observed only for pollen beetle. For this species, the nectar resources provided by weeds had a stronger positive effect in fields managed with the conventional strategy than in fields managed with the eco-friendly strategy (Table 2; Fig. 3). The interaction between the percentage of semi-natural habitat and the strategy was not significant for both species (Table S2).

Discussion

Effect of eco-friendly oilseed rape management on parasitism rates

We compared the effects of perennial wildflower strips without spring insecticide spraying of the crop (eco-friendly management) with a conventional strategy (no flower strips plus insecticide) on the parasitism rates of two major pests of the oilseed rape: stem flea beetle and pollen beetle. The eco-friendly strategy did not significantly increase the rate of stem flea beetle parasitism, but tended to increase the rate of pollen beetle parasitism. For both species, parasitism rates were higher 5 m from the field margin than at 30 m from the field margin, but the eco-friendly strategy did not have the expected strengthening effect on this relationship.

In our study, most farmers who managed their fields conventionally sprayed insecticides between mid-March and mid-April, essentially after the period during which the adults of T. microgaster would be flying around in the crop (during February to March). This may account for the very small differences, if any in parasitism rates for stem flea beetle observed between the two crop management strategies. Parasitoids, such as T. heterocerus, are active later in the season (from late March to late April, according to our observations) and prefer to oviposit in L2-stage pollen beetle larvae [START_REF] Ulber | Parasitoids of Oilseed Rape Pests in Europe: Key Species for Conservation Biocontrol[END_REF]. According to the treatment calendar of conventional farmers, the trend of a positive effect of the eco-friendly strategy on pollen beetle parasitism may be linked to the absence of insecticide treatment in spring. Indeed, the trend of a positive effect of flower strips on parasitism rates is known to be greater when no pesticide is applied [START_REF] Krimmer | Flower fields and pesticide use interactively shape pollen beetle infestation and parasitism in oilseed rape fields[END_REF], highlighting the need to combine a reduction of pesticide use with flower strips to maintain parasitism rates in oilseed rape pests. In addition, the amount of available nectar in wildflower strips and natural field margins was similar, but the difference in species composition in May (Figure S3) could explain this trend.

Effect of nectar resources and management on parasitism rates

We expected that the effect of wildflower strips on pest parasitism, relative to that of natural spontaneously growing herbaceous field margins, would depend on the trophic resources provided to parasitoids. In a previous factorial field experiment, the percent cover of plants providing accessible nectar in wildflower strips to parasitoids was positively related to stem flea beetle and pollen beetle parasitism [START_REF] Gardarin | The hump-shaped effect of plant functional diversity on the biological control of a multi-species pest community[END_REF]. Here, parasitism rates were highly variable but, contrary to our hypothesis, did not seem to be related to the amounts of accessible nectar available at the edge of the fields. The trend towards a weak positive effect of the eco-friendly strategy on pollen beetle parasitism rates was, therefore probably more closely linked to the absence of insecticide treatment than to flower strip resources. However, the absence of wildflower strip was confounded with the absence of treatment in our study, making a more detailed interpretation of the mechanisms difficult. In general, very few plants in the flower strips were flowering in March and April in our study. The amount of available nectar provided by the flower strips was essentially similar to that of natural herbaceous margins, but they exhibit different species composition in May, as shown in figure S3. Differences in their effect could be explained by traits not taken into account here, such as the amount and quality of nectar, flower attractivity toward parasitoids as well as possible preferences toward specific plant species. In addition, despite a choice of species to ensure the provision of food resources throughout the entire season, the nectar of sown species, such as Bellis perennis, was not accessible to parasitoids (as shown by morphometric models) whereas other widespread wild species, such as Taraxacum officinale or Veronica spp., provided accessible resources. These wild species grew spontaneously in the natural field margins, and their presence therefore decreased the expected difference in the efficacy of flower strips relative to natural field margins. Although the nectar of the majority of species was accessible to stem flea beetle and pollen beetle parasitoids, we estimated the resource by the ground cover of these plants, without counting the flowers or taking into account the amount of nectar produced (see for example [START_REF] Baude | Historical nectar assessment reveals the fall and rise of floral resources in Britain[END_REF]. The high presence of low nectar-producing species could explain the lack of relationship between the amount of resources observed (in terms of cover of nectarproducing species) at the field margins and parasitism rates of oilseed rape pests.

The very small effect of wildflower strips may also be due to their young age (established for less than two years) and their relatively small size (<1 ha). [START_REF] Krimmer | Flower fields and pesticide use interactively shape pollen beetle infestation and parasitism in oilseed rape fields[END_REF] recently showed that newly established flowering fields (sown the previous year) did not greatly improve pollen beetle parasitism rates, whereas older flower fields (5-6 years old) and calcareous grasslands did. They also showed that flower fields with an area greater than 1.5 ha promoted parasitism more effectively than smaller flower fields.

The presence of weeds offering floral resources within the field influenced the parasitism rates.

A greater abundance of weed resources at 5 m resulted in higher stem flea beetle parasitism rates. Pollen beetle parasitism rates also increased with the abundance of weed resources. This effect was greater in conventionally managed fields than in fields under eco-friendly management, indicating that the field resources were more effective without wildflower strip and with insecticide application. Parasitism rates declines exponentially with increasing distance from floral patches [START_REF] Albrecht | The effectiveness of flower strips and hedgerows on pest control, pollination services and crop yield: A quantitative synthesis[END_REF][START_REF] Tylianakis | Improved Fitness of Aphid Parasitoids Receiving Resource Subsidies[END_REF]. Within-field resources, close to the hosts, may, therefore, increase parasitism rates at field scale more effectively than resources at the margin of the field. Also, considering the 48% difference in species field margin composition between the ecofriendly and conventional strategies, the effect of weeds in the conventional strategy could originate from traits and processes not taken into account to relate plant species composition and parasitoid activity. At similar levels of available and accessible nectar, all plant species may not have similar effects. For instance, the chemical characteristics of nectar which can affect their attractivity, nutritional quality and preferences toward parasitoids [START_REF] Belz | Olfactory attractiveness of flowering plants to the parasitoid Microplitis mediator: potential implications for biological control[END_REF].

Maintaining desirable target levels of weeds in the crop is difficult for farmers, particularly in terms of preventing competition with the crop, but our results highlight the importance of managing the resources available to natural enemies at whole-field level, rather than just at the edge of the field. One recent study highlighted increases in species richness and parasitoid abundances in the presence of within-field unsown patches in oilseed rape fields [START_REF] González | Artificial temporary non-crop habitats support parasitoids on arable land[END_REF]. Further studies of the effects of unsown patches on parasitism rates could lead to the formulation of guidelines for farmers. Otherwise, intercropping or undersowing are also two agricultural practices that could decrease pest pressure and enhance within field resources for parasitoids (e.g. extra-floral nectar secreted by leguminous plant) while allowing to reduce herbicide applications by competition with undesirable weeds for farmers. In oilseed rape, intercropped service plants modify the architecture of the crop canopy by increasing its structural heterogeneity, and they make it more difficult for pests to find their hosts [START_REF] Finch | Host-plant selection by insects-a theory based on 'appropriate/inappropriate landings' by pest insects of cruciferous plants[END_REF], leading to a decrease of pest oviposition rates (Âsman et al., 2001). This resulted in a reduction of the abundance and damage of several oilseed rape pests (Breintenmoser et al., 2022;[START_REF] Cadoux | Intercropping frost-sensitive legume crops with winter oilseed rape reduces weed competition, insect damage, and improves nitrogen use efficiency[END_REF]. Although promising, some studies are required to assess their effect on parasitism rate.

Conclusion

This study shows that a pest management strategy based on a wildflower strip combined with an absence of spring insecticide treatment, as an alternative to conventional methods based on insecticides, tended to promote the parasitism of pollen beetle, but not that of stem flea beetle. The eco-friendly strategy alone is therefore not enough sufficient to significantly improve parasitism rates. The effect of the flower strip did not depend on distance or on the amount of resources provided. Conversely, the presence of weeds within the field seemed to have a good potential for promoting parasitism.

These results open up new perspectives for promoting the conservation biological control of oilseed rape pests. Further studies are required to improve the composition of wildflower strips, to provide more accessible nectar resources at the start of spring.

The implementation of this strategy should also be accompanied by a reflection on the management of other factors influencing the quality of crop habitats, including weed management, in particular. We would argue for the exploration of more management strategy options, trying to achieve a balance between competitive ability and the ability to sustain conservation biological control, for example. Furthermore, it will only be possible to do without insecticides if other technical levers, such as those related to bottom-up control via autumn intercropping with legumes to deal with stem flea beetles or with early flowering varieties to deal with pollen beetles, are implemented.

Figure 1 .

 1 Figure 1. Percent cover of nectar resources accessible to a) Tersilochus heterocerus (parasitoids of pollen beetle) and b) Tersilochus sp. (parasitoids of stem flea beetle) in field margins, according to management strategy. Conventional = natural herbaceous field margin plus insecticides. Eco-friendly = wildflower strip without insecticides in spring. Boxplots show medians, and the 1 st and 3 rd quartiles.

Figure 2 .

 2 Figure 2. Mean parasitism level of pollen beetle and stem flea beetle according to a) sampling year and b) distance to the edge of the field and management strategy. Boxplots show medians, and the 1 st and 3 rd quartiles. Conventional = the natural spontaneously growing herbaceous field margin plus insecticide treatment. Eco-friendly = wildflower strip without insecticide application in spring.

Figure 3 .

 3 Figure 3. Rates of parasitism of (a) stem flea beetle and (b) pollen beetle as a function of the percentage of accessible nectar resources within the field in interaction with the distance to the field edge for (a) stem flea beetle, or according to management strategy for (b) pollen beetle. Conventional = natural, spontaneously growing herbaceous field margin plus insecticides. Eco-friendly = wildflower strip without insecticide application in spring. The figures show the predictions of the models, with confidence intervals.

Table 2 .

 2 Effect of oilseed rape management strategy (eco-friendly vs. conventional), distance to the edge of the field and of nectar resources accessible to parasitoids on rates of parasitism in stem flea beetle and pollen beetle larvae. Reference levels for factors: Distance = 30 m; Strategy = conventional; Year= 2019.

	Significant results are shown in bold: *p < 0.05, **p < 0.01, ***p < 0.001.

Acknowledgements

This work was funded by INRAE (metaprogram EcoServ), the François Sommer Foundation, AgroParisTech, the Office Français de la Biodiversité, the Fondation pour la Recherche sur la Biodiversité, and Labex BASC.

We would like to thank Eleonore Courteau, Arnaud Butier, Alexandre Morisseau, Dominique Le Floch, Emmanuel Frankenreiter and Solene Morelle for technical assistance in the collection of field data and larval dissection. We thank all the farmers involved in the study.

Author Contributions

LS, AB, MVM, FC and AG conceived the ideas and designed the methodology; LS, AG and AB collected the data; LS analyzed the data and wrote the first draft of the manuscript. All authors contributed critically to the drafts and approved the final version for publication.