Fidji Berio

Allowen Evin

Nicolas Goudemand

Mélanie Debiais-Thibaud
email: melanie.debiais-thibaud@umontpellier.fr

The intraspecific diversity of tooth morphology in the large-spotted catshark Scyliorhinus stellaris: insights into the ontogenetic cues driving sexual dimorphism

Keywords: geometric morphometrics, gynandric heterodonty, monognathic heterodonty, ontogenetic trajectory, scyliorhinids

Nicolas Goudemand, ENS de Lyon, "Attractivité Nouveaux Professeurs" Teeth in sharks are shed and replaced throughout their lifetime. Morphological dental changes through ontogeny have been identified in several species, and have been correlated to shifts in diet and the acquisition of sexual maturity. However, these changes were rarely quantified in detail along multiple ontogenetic stages, which makes it difficult to infer the developmental processes responsible for the observed plasticity. In this work, we use micro-computed tomography and 3D geometric morphometrics to describe and analyze the tooth size and shape diversity across three ontogenetic stages (hatchling, juvenile, and sexually mature) in the large-spotted catshark Scyliorhinus stellaris (Linnaeus, 1758). We first describe the intraindividual variation of tooth form for each sex at each ontogenetic stage. We provide a tooth morphospace for palatoquadrate and Meckelian teeth and identify dental features, such as relative size and number of cusps, involved in the range of variation of the observed morphologies. We then use these shape data to draw developmental trajectories between ontogenetic stages and for each tooth position within the jaw to characterize ontogenetic patterns of sexual dimorphism. We highlight the emergence of gynandric heterodonty between the juvenile and mature ontogenetic stages, with mature females having tooth morphologies more similar to juveniles' than mature males that display regression in the number of accessory cusps. From these data, we speculate on the developmental processes that could account for such developmental plasticity in S. stellaris.

1963; [START_REF] Luer | Rate of tooth replacement in the nurse shark, Ginglymostoma cirratum[END_REF][START_REF] Correia | Tooth loss rate from two captive sandtiger sharks (Carcharias taurus)[END_REF][START_REF] Moyer | Tooth microstructure and replacement in the gulper shark, Centrophorus granulosus (Squaliformes: Centrophoridae)[END_REF][START_REF] Smith | Development and evolution of tooth renewal in neoselachian sharks as a model for transformation in chondrichthyan dentitions[END_REF]. Gynandric heterodonty (sexual dimorphism in teeth) is very common in elasmobranchs (Feduccia and Slaughter, 1974;[START_REF] Taniuchi | Dental sexual dimor-1235 phism and food habits in the stingray Dasyatis akajei 1236 from Tokyo Bay, Japan[END_REF][START_REF] Kajiura | Seasonal dynamics of dental sexual dimorphism in the Atlantic stingray Dasyatis sabina[END_REF]Geniz et al., 2007;Gutteridge and Bennett, 2014;[START_REF] Underwood | De-1247 velopment and evolution of dentition pattern and tooth 1248 Order in the skates And rays (Batoidea; Chondrichthyes)[END_REF]French et al., 2017) and affects specific tooth files (reported in Dasyatidae, Carcharhinidae, and Leptochariidae) to the whole dental set at various degrees during the sexually mature stage (Cappetta, 1986). The higher and sharper mature male teeth are indeed assumed to function in grasping females and consequently to facilitate clasper introduction during copulation [START_REF] Springer | A review of western Atlantic cat sharks, Scyliorhinidae, with descriptions of a new genus and five new species[END_REF][START_REF] Mceachran | Reply to "Sexual dimorphism in skates (Rajidae)[END_REF][START_REF] Mccourt | Mating behavior and sexual dimorphism in dentition in the stingray, Urolophus concentricus, from the Gulf of California[END_REF]Cappetta, 1986;[START_REF] Ellis | Ontogenic changes and sexual dimorphism in the head, mouth and teeth of the lesser spotted dogfish[END_REF][START_REF] Kajiura | Seasonal dynamics of dental sexual dimorphism in the Atlantic stingray Dasyatis sabina[END_REF][START_REF] Pratt | A Review of Elas-1140 mobranch Reproductive Behavior with a Case Study on 1141 the Nurse Shark, Ginglymostoma cirratum[END_REF][START_REF] Litvinov | Methods of investigations of shark heterodonty and dental formulae's variability with the blue shark, Prionace glauca taken as an example[END_REF]Gutteridge and Bennett, 2014). This feature has been recorded as a seasonal variation in the Atlantic stingray Dasyatis sabina [START_REF] Kajiura | Seasonal dynamics of dental sexual dimorphism in the Atlantic stingray Dasyatis sabina[END_REF], while it is assumed to be a fixed-in-time feature in other elasmobranch species for which it has been described (Gutteridge and Bennett, 2014;[START_REF] De Sousa Rangel | Dental sexual dimorphism and morphology of Urotrygon microphthalmum[END_REF]. Gynandric heterodonty has also been only described at sexually mature stages, suggesting that sex hormone signals triggering the reproductive activity may also be involved in the development of the observed dental sexual dimorphism [START_REF] Mceachran | Reply to "Sexual dimorphism in skates (Rajidae)[END_REF]Cappetta, 1986;[START_REF] Snelson | Serum concentrations of steroid hormones during reproduction in the Atlantic stingray, Dasyatis sabina[END_REF][START_REF] Powter | The in-1135 fluence of sex and maturity on the diet, mouth morphol-1136 ogy and dentition of the Port Jackson shark, Heterodon-1137 tus portusjacksoni[END_REF]. Shark tooth shapes have been mostly evaluated through semi-quantitative studies based on asymmetry, number, sharpness, and relative bending or size of cusps (Cappetta, 1986;Frazzetta, 1988). Moreover, studies that performed morphometrics on extant species mainly focused on tooth crown dimensions (height, width, and angle) of specific teeth (small-spotted catshark Scyliorhinus canicula (Linnaeus, 1758) [START_REF] Ellis | Ontogenic changes and sexual dimorphism in the head, mouth and teeth of the lesser spotted dogfish[END_REF], Lamniforms [START_REF] Shimada | Dental homologies in lamniform sharks 1176 (Chondrichthyes: Elasmobranchii)[END_REF], and Port Jackson shark Heterodontus portusjacksoni (Meyer, 1793) [START_REF] Powter | The in-1135 fluence of sex and maturity on the diet, mouth morphol-1136 ogy and dentition of the Port Jackson shark, Heterodon-1137 tus portusjacksoni[END_REF]). These approaches mainly base the tooth shape analysis on main cusp dimensions, which do not capture complex heterodonty patterns [START_REF] Whitenack | A morphomet-1262 ric approach for addressing tooth-based species delimi-1263 tation in fossil mako sharks, Isurus (Elasmobranchii: Lam-1264 niformes)[END_REF]. Recent publications, however, have fo-cused on quantitative tooth traits in sharks by using geometric morphometrics [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] Soda | Artificial neural networks and geometric morphometric methods as a means for classification: A case-study using teeth from Carcharhinus sp. (Carcharhinidae)[END_REF][START_REF] Cullen | Do sharks exhibit heterodonty by tooth position and over ontogeny? A comparison using elliptic Fourier analysis[END_REF], providing more subtle information on tooth size and shape quantitative variation. These comparative studies allow to infer developmental and phylogenetic hypotheses and refine our knowledge about the inter-and intraspecific tooth shape variation in several shark species. Overall, the authors highlight the benefits of a quantitative investigation of complete tooth shape patterns in sharks to understand ontogenetic and evolutionary shifts.

Scyliorhinids are emerging models for shark studies [START_REF] Coolen | The dogfish Scyliorhinus canicula: A reference in jawed vertebrates[END_REF] and among them, S. canicula tooth morphologies have been the most studied. Mature S. canicula specimens display gynandric heterodonty that has been qualitatively described (Brough, 1937;[START_REF] Ellis | Ontogenic changes and sexual dimorphism in the head, mouth and teeth of the lesser spotted dogfish[END_REF]Erdogan et al., 2004;[START_REF] Debiais-Thibaud | Tooth and scale morphogenesis in shark: an alternative process to the mammalian enamel knot system[END_REF][START_REF] Soares | The catshark genus Scyliorhinus (Chondrichthyes: Carcharhiniformes: Scyliorhinidae): taxonomy, morphology and distribution[END_REF] but quantification of scyliorhinids dental variation is still fragmentary. In particular, the nursehound Scyliorhinus stellaris (Linnaeus, 1758) is a phylogenetically close relative of S. canicula [START_REF] Iglésias | Extensive paraphylies within sharks of the order Carcharhiniformes inferred from nuclear and mitochondrial genes[END_REF][START_REF] Vélez-Zuazo | Shark tales: A 1255 molecular species-level phylogeny of sharks (Selachi-1256 morpha, Chondrichthyes)[END_REF] and has mostly been studied for physiological aspects [START_REF] Piiper | Respiration and circulation during swimming activity in the dogfish Scyliorhinus stellaris[END_REF][START_REF] Heisler | The role of physicochemical buffering and of bicarbonate transfer processes in intracellular pH regulation in response to changes of temperature in the larger spotted dogfish (Scyliorhinus stellaris)[END_REF].

To our knowledge, the study of [START_REF] Soldo | Contribution to the study of the morphology of the teeth of the nursehound Scyliorhinus stellaris (Chondrichthyes: Scyliorhinidae)[END_REF] is the only one focusing on S. stellaris tooth shape patterns.

However, this study did not test the impact of ontogeny on tooth morphology and did not detect sexual dimorphism although gynandric heterodonty is known to be a common feature to Scyliorhinidae (Cappetta, 1986;[START_REF] Soldo | Contribution to the study of the morphology of the teeth of the nursehound Scyliorhinus stellaris (Chondrichthyes: Scyliorhinidae)[END_REF][START_REF] Soares | The catshark genus Scyliorhinus (Chondrichthyes: Carcharhiniformes: Scyliorhinidae): taxonomy, morphology and distribution[END_REF].

Here, we provide the first detailed description of S. stellaris tooth form (shape and size) using microCT images and quantitative 3D geometric morphometrics.

We characterize the ontogenetic and sexually dimorphic trajectories of tooth shapes and highlight the emergence of gynandric heterodonty with sexual maturation.

We also describe intra-individual tooth morphological variation and we discuss the developmental hypotheses that could be involved in the observed tooth diversity of S. stellaris. In total, 33 specimens of S. stellaris (16 females, 17 127 males; 2,467 teeth) were analyzed. Total length (TL, in 128 cm) was used to define the groups of same ontogenetic 129 stages. Female S. stellaris are considered sexually mature 130 at 79 cm TL and males at 77 cm TL (Fischer et al., 1987; 131 [START_REF] Musa | Oviparous elasmobranch development inside the egg case in 7 key stages[END_REF] but longer mature specimens were 132 chosen to avoid biases due to potential later maturation. 133

| MATERIALS AND METHODS

Juveniles were twice shorter than the mature specimens 134 and hatchling specimens were chosen as close as possi-135 ble from hatching [START_REF] Musa | Oviparous elasmobranch development inside the egg case in 7 key stages[END_REF] although umbilical 136 scars were never observed. We cannot evaluate how 137 these time points are distributed along the ontogeny of 138 the specimens because we have no information on the 139 age of each specimen, and no growth curve has been 140

published for this species beyond the hatchling stage 141 [START_REF] Musa | Oviparous elasmobranch development inside the egg case in 7 key stages[END_REF]. Growth rates may be sex-specific in 142 elasmobranchs (Hale and Lowe, 2008) so we may expect 143 age differences between males and females of similar to-144 tal length. Hatchling specimens were 17.7cm ± 3.3cm 145 TL (7 females, 5 males), juveniles were 57.7cm ± 3.2cm 146 TL (5 females, 5 males) and mature ones were 102.7cm 147 ± 7.2cm TL (4 females, 7 males) (Table 1 For each specimen, all 3D teeth were isolated from 158 the right palatoquadrate and Meckelian cartilages with 159 Amira software (v6.2.0) [START_REF] Stalling | Amira: 1229 A highly interactive system for visual data analysis[END_REF]. Each tooth 160 was identified within a file (or family) along the mesio-161 distal axis and by the generation within a tooth file (Fig.

| Geometric morphometrics

Seven 3D landmarks and 31 semilandmarks were placed on the cutting edge of each tooth (Fig. 1B) with the Landmark software (v3.0.0.6) (Wiley et al., 2005) and the data were preprocessed with Scyland3D (v1.1.0) (Berio and Bayle, 2020). The semilandmark density was made higher in the lateral sides of the teeth because gynandric heterodonty in scyliorhinids is known to involve the addition of lateral accessory cusps (Gosztonyi, 1973;[START_REF] Ellis | Ontogenic changes and sexual dimorphism in the head, mouth and teeth of the lesser spotted dogfish[END_REF][START_REF] Debiais-Thibaud | Tooth and scale morphogenesis in shark: an alternative process to the mammalian enamel knot system[END_REF][START_REF] Soares | The catshark genus Scyliorhinus (Chondrichthyes: Carcharhiniformes: Scyliorhinidae): taxonomy, morphology and distribution[END_REF]. Our form comparison analyses will be interpreted in light of this choice: the centroid size and shape parameters will be more affected by variations in the lateral zones (with higher density of semilandmarks) than in the main cusp and crown base zones. All analyses were performed separately for Meckelian and palatoquadrate teeth.

Crown base width was computed based on the distance between landmarks 1 and 33 (d1-33, Fig. 1B), while main cusp height was the mean of the distances between the main cusp and each side of the tooth (mean of d1-17 and d17-33, see Fig. 1B). We also used these measures to generate a ratio between main cusp height and crown base width, later referred to as the cuspcrown ratio. Tooth symmetry was measured by the ratio between d1-17 and d17-33 and a value of 1 implies a symmetric tooth.

A Generalized Procrustes Superimposition (GPA) was performed (Bookstein, 1991) during which the semilandmarks were slided based on minimizing bending energy (Bookstein, 1997). The tooth size patterns were investigated using centroid sizes computed based on the GPA and the tooth shape variation was displayed with principal component analyses (PCAs). In order to reduce the high dimensionality of the aligned coordinates, the data were reduced prior to multivariate analyses of variance (MANOVAs) to the axes containing 95% of the total variation (14 and 13 PCA axes for Meckelian and palatoquadrate teeth respectively, out of 114 available axes).

We defined the random variable as the tooth generation within a given tooth file, in a specimen. We used these generations as internal replicates from which we gen-erated an average tooth shape per tooth file, for each morphology 251 There were no symphyseal teeth on the palatoquadrate, isons). Palatoquadrate number of tooth files does not differ significantly between ontogenetic stages in males and in females (One-Way permutation ANOVAs, p-vals > 5.00e -2 ). Conversely, in both sexes, there are significantly more Meckelian tooth files in juvenile and mature specimens compared to hatchling ones (One-way permutation ANOVAs, p-vals < 5.00e -2 ), but no difference was detected between the juvenile and mature ontogenetic stages. Moreover, there is no significant difference in tooth file counts between males and females (Wilcoxon tests, p-val> 3.10e -1 for all tests).

A graded decrease of tooth size is observed along the mesio-distal axis of the jaw, except for the symphyseal teeth which are smaller than parasymphyseal ones (see Fig. 1, Fig. 2E, and Fig. 3E andI). In all sexes and stages, there is a graded increase of lateral bending of teeth from the symphysis to the commissure, producing asymmetric teeth (Fig. 2 and3). Teeth of male and female hatchlings are visually similar in shape with tricuspid teeth in both jaws (Fig. 2A to D and Fig. 3A to D).

Juvenile female and male teeth display little variability in cusp number along the jaw: mesial palatoquadrate teeth (Fig. 2E) often display one main cusp and four accessory cusps while the more distal ones have four to five cusps and often more accessory cusps in the mesial than in the distal part of the crown (Fig. 2E to H). A similar pattern is observed in Meckelian teeth (Fig. 3E to H), except for tricuspid symphyseal ones. Mature female teeth are similar in shape to those of juveniles except at the most distal positions where they exhibit up to six cusps (Fig. 2I to L and Fig. 3I to L). Mature male mesial teeth are always un-bent and unicuspidate while more distal teeth undergo an addition of one to two accessory cusps (Fig. 2M to P and Fig. 3M to P). Mature male teeth rarely display more than two accessory cusps (Fig. 2M to O and Fig. 3M to P), however a small third accessory cusp was detected on the distalmost teeth of some specimens (see arrow on Fig. 3P).

| Morphometric analyses

| Tooth size patterns

To support and quantify visual observations, morphometric measurements were performed and ratios of the main cusp height and the crown base width were computed. Ratio values are higher than 1, showing that the main cusp is higher than the crown base is wide (Fig. 4A andD).

In all groups, this ratio decreases along the mesiodistal axis of the jaw (Fig. 4A andD), with exceptions in the distalmost positions in Meckelian teeth of mature males and juvenile females (Fig. 4A andD). The variation of this ratio follows the gradual decrease of both measures, although stronger decrease is observed in the main cusp height (Additional figure). At each position, the measured cusp-crown ratio is very comparable between ontogenetic stages, but in the palato-F I G U R E 3 Meckelian tooth shape diversity in S. stellaris. A-D) Hatchling female teeth; E-H) Juvenile female teeth; I-L) Mature female teeth; M-P) Mature male teeth. Symphyseal (mesial) pole to the left. quadrate teeth of hatchling specimens we report higher 320 ratios (1.5-fold increase), with a minimum of 1.6 along 321 the mesio-distal axis (see position 19 in hatchling males 322 in Fig. 4D). The raw data on main cusp height and 323 crown base width show that hatchling palatoquadrate 324 teeth are different from Meckelian teeth because of 325 their smaller crown base (Additional figure, A and B). 326

Overall, these observations point to similar developmen-327 tal constraints on the overall geometry of teeth at all on-328 togenetic stages on Meckelian teeth and to a transition 329 of these developmental constraints between the hatch-330 ling and juvenile ontogenetic stages in palatoquadrate 331 teeth. though we also report a sudden fall of asymmetry values in the distalmost tooth files (Fig. 4B andE). In Meckelian teeth, the tooth asymmetry values of all groups (ontogenetic stages) are overlapping until the 15 th tooth file, but female teeth distal to this position tend to display higher asymmetries than teeth of other groups (Fig. 4B). A similar pattern is observed in the palatoquadrate: asymmetry values of all groups are very similar until the 14 th tooth file (Fig. 4E). However, contrary to Meckelian teeth, asymmetry patterns of hatchling teeth distal to the 14 th tooth file are distinct from those of juveniles with lower asymmetry values (Fig. 4E). Mature males display teeth whose symmetry values are in between those of hatchling and juvenile specimens (Fig. 4E). As for Meckelian teeth, mature female teeth are the most asymmetrical (Fig. 4E) with maximum values between the 19 th and 23 rd files (Fig. 4B). In the palatoquadrate, these maxima are reached between the 22 nd and 24 th tooth files in all groups (Fig. 4E). We also highlight that the anteriormost teeth (1 st file in the palatoquadrate and up to the 3 rd file in the Meckelian cartilage) are close to bilateral symmetry (Fig. 4B andE). These measurements highlight similar tooth mesio-distal asymmetry patterns within hatchling and juvenile specimens and higher asymmetry values in mature females compared to all other groups (Fig. 4B andE).

| Geometric morphometric analyses

In the previous two morphometric analyses, the mesiodistal variation of tooth shape could be discriminated in terms of relation of cusp height and crown width and in terms of asymmetry for juvenile and mature teeth. However, no strong difference of these parameters could be seen between sexes in either jaws of all three ontogenetic stages. In the following, we established the tooth centroid size patterns of variation along the mesio-distal jaw axis for each group.

Meckelian teeth. Both sexes show similar tooth centroid size patterns along the mesio-distal axis of the jaw at hatchling and juvenile stages (Fig. 4C). Hatchling males and females display very little tooth centroid size variation along the jaw (Fig. 4C), as opposed to juvenile and mature specimens that share a maximum tooth cen-377 troid size in file 5 or 6 (Fig. 4C): values for juvenile teeth 378 are intermediate between the hatchling and mature val-379 ues. Overall, the mesio-distal tooth centroid size pat-380 tern is similar between juvenile and mature specimens 381 (Fig. 4C) but mature males display an exacerbated tooth 382 size pattern compared to mature females, except at the 383 symphyseal tooth positions (Fig. 4C).

384

Palatoquadrate teeth. Similar to the Meckelian teeth, 385 palatoquadrate tooth centroid sizes do not differ be-386 tween sexes at hatchling or juvenile stages, centroid 387 size increase with ontogenty, and mature males display 388 higher values compared to females (Fig. 4F). Juvenile 389 males and females have two local maximum tooth cen-390 troid sizes at the 3 rd and 12 th and 4 th and 10 th files 391 respectively, and a minimum centroid size at file 7 (Fig. 392 4F). Mature specimens display a clear bimodal tooth cen-393 troid size pattern from the symphysis to the commissure, 394 with local maximum values in the 3 rd and 10 th files and 395 a local minimum value in the 7 th file (Fig. 4F). Topologi-396 cally, the Meckelian file 5 (maximal value in adult males) 397 faces the palatoquadrate file 7 (local minimum in adult 398 males) which suggests functional constraints for these 399 variation of tooth size along the mesio-distal axis.

400

Our statistical tests corroborated the observation 401 that tooth centroid size varies according to the ontoge-402 netic stage in both cartilages (One-Way ANOVAs, p-vals 403 < 2.00e -16 , Table 2). Within all ontogenetic stages, the 404 Meckelian and palatoquadrate tooth mesio-distal posi-405 tion also significantly impacts the tooth centroid size 406 (One-Way ANOVAs, p-vals < 9.37e -4 , Table 2). The 407 Meckelian and palatoquadrate tooth centroid size of 408 mature specimens is also significantly impacted by sex 409 (One-Way ANOVAs, p-vals < 1.54e -2 , Table 2). We fi-410 nally report a significant interaction between sex and on-411 togenetic stage in the Meckelian and palatoquadrate full 412 datasets (Two-Way ANOVAs, p-vals < 3.24e -3 , Table 2), 413 as well as between ontogenetic stage and tooth mesio-414 distal position in Meckelian teeth (Two-Way ANOVA, p-415 val< 2.49e -3 , Table 2). 416

| Developmental trajectories

We performed independent PCAs in each jaw, and the extreme shapes on the PC1 and PC2 axes illustrate how similar shape parameters generate the main Meckelian and palatoquadrate variations of tooth shapes. This first observation highlights the fact that, although we treated them separately, teeth of the upper and lower jaw show similar shape variations along the first PCs. In both cases, the main axis of tooth shape variation relates to the main cusp proportions, and to the variation in the number of lateral accessory cusps (Fig. 5A and5B). The second axis of variation seems to relate to the size of lateral cusps relative to the main cusp size (Fig. 5A and5B).

The shape of Meckelian and palatoquadrate teeth of S. stellaris is mostly impacted by ontogenetic stage (One-Way MANOVAs, pvals< 2.20e -16 , 3.04e 1 <F approx< 4.58e 1 , Table 3) although the sex of the specimens and the tooth position along the mesio-distal axis of the jaw also significantly impact the tooth shape (One-Way MANOVAs, Sex: p-val< 6.13e -8 , 5.39<F approx<7.61; Tooth position: p-val< 3.12e -14 , 1.80<F approx<1.89, Table 3). Within ontogenetic stages, the mesio-distal position of a tooth significantly impacts the tooth shape of juveniles (One-Way MANOVAs, p-vals < 1.16e -4 for both jaws, Table 3) and palatoquadrate teeth of hatchling specimens (One-Way MANOVA, p-val< 2.28e -6 , Table 3). Conversely, for both jaws and within each ontogenetic stage, a sexual dimorphism of tooth shape was detected (One-Way MANOVAs, p-vals < 5.37e -3 , Table 3).

We finally report that the sexual dimorphism differs between stages and tooth mesio-distal positions for Meckelian and palatoquadrate teeth (Two-Way MANOVAs, pvals < 1.02e -2 , Table 3).

Comparison of developmental trajectories between

sexes. The full shape developmental trajectories (from hatchling to juvenile, and to mature stage) differ between sexes for most of the palatoquadrate tooth files that are distal to the 3 rd file and for all Meckelian tooth files distal to the 8 th file (p-vals < 1.60e -2 , Tables 4 and5). These differences arise from divergent juvenile-tomature developmental directions between males and fe-males (45/46 significant p-values, p-vals < 3.10e -2 , Ta-459 bles 4 and 5). Significant differences between males 460 and females for juvenile-to-mature trajectory lengths 461 are also reported for most tooth files and always in-462 volve longer trajectories in males than females (p-vals 463 < 3.40e -2 , Tables 4 and5). We report no such differ-464 ences between male and female hatchling-to-juvenile 465 trajectory lengths and angles (Tables 4 and5). This pat-466 tern highlights a shift between male and female tooth 467 shape developmental trajectories only after the juvenile 468 stage.

469

Comparison of developmental trajectories within sexes. 470 Significant differences were observed for all tooth files 471 of both jaws between the hatchling-to-juvenile and the 472 juvenile-to-mature trajectory angles within sexes (p-vals 473 < 1.20e -2 , Additional tables 1 and 2), showing that 474 whatever the mesio-distal position of a tooth, the shape 475 modifications between juvenile and mature stages can-476 not be considered a prolongation of the hatchling-to-477 juvenile modifications. Significant differences in tra-478 jectory lengths are reported for most female palato-479 quadrate files (19/25 significant p-values, Additional ta-480 ble 1) and for female Meckelian files distal to the 8 th 481 file (pvals< 4.40e -2 , Additional table 2). In all these 482 cases, the hatchling-to-juvenile trajectory is longer than 483 the juvenile-to-mature one (Additional tables 1 and 2), 484

showing that, in females, tooth shapes generated at sex-485 ual maturation are less dissimilar to juveniles than in 486 males. In contrast, male trajectory lengths significantly 487 differ only in a few tooth files (6/46 significant p-values, 488

Additional tables 1 and 2, p-vals < 4.60e -2 ). While the use of 2D data would have probably been less time-consuming, working on 3D data avoids biases due to parallax [START_REF] Mullin | The effects of parallax on geometric morphometric data[END_REF]Fruciano, 2016).

Moreover, 3D surfaces can provide insights into topological aspects such as ornamentations, which can be of interest for future studies.

From our analyses, we described the wide range of blade-shaped to crown-shaped teeth in S. stellaris, which we characterized through classical and geometric morphometric analyses. In S. stellaris, we quantified how classical tooth shape parameters (asymmetry and cusp-crown ratio) vary in a gradual and linear way along the mesio-distal axis of both jaws, with extreme variations at the mesial-most and distal-most tooth positions. Also, we captured a higher cusp-crown ratio for palatoquadrate hatchling teeth compared to other ontogenetic stages. Because the lack of asymmetry is a shared feature of hatchling teeth and symphyseal teeth of older specimens, we show that palatoquadrate and Meckelian teeth undergo similar transition in their development (asymmetry) once the hatching stage is passed, to the exception of the symphyseal teeth. According to visual observations, the palatoquadrate and Meckelian teeth of S. stellaris are very similar in shape (dignathic homodonty or weak dignathic heterodonty), which is consistent with previous works on scyliorhinids [START_REF] Herman | Contributions to the study of the comparative morphology of teeth and other relevant ichthyodorulites in living supraspecific taxa of Chondrichthyan fishes. Part A: Selachii. No. 2b: Order: Carcharhiniformes -Family: Scyliorhinidae[END_REF][START_REF] Ellis | Ontogenic changes and sexual dimorphism in the head, mouth and teeth of the lesser spotted dogfish[END_REF][START_REF] Soares | The catshark genus Scyliorhinus (Chondrichthyes: Carcharhiniformes: Scyliorhinidae): taxonomy, morphology and distribution[END_REF]. As opposed to Scyliorhinidae, dignathic heterodonty is very common in other shark groups, such as in Hexanchidae and most Squaliformes. The toothtype discrepancies between palatoquadrate and Meckelian teeth have been correlated with different functions in feeding: upper grasping teeth might help catching and holding a prey, whereas blade-shaped lower teeth might function in tearing a prey to pieces (Cappetta, 1986;Frazzetta, 1988;Cappetta, 2012). Beyond ecology, dignathic heterodonty might also convey a phylogenetic signal: sharks from distinct taxonomic groups might have overlapping trophic habits (especially in the case of opportunistic behavior) and, however, display different dignathic heterodonty patterns that diet alone cannot explain. Regarding whether the gynandric heterodonty follows similar patterns between both jaws, the data gathered hitherto on sharks are insufficient to 542 answer.

543

Our results notably suggest a developmental transi-544 tion between hatchlings and juveniles, especially on the 545 palatoquadrate, that involves a global increase of the 546 crown size. Note that asymmetry and cusp-crown ra-547 tio poorly discriminate between the three ontogenetic 548 stages because they are corrected for size. As expected, 549 the variation of tooth centroid size strongly discrimi-550 nates between ontogenetic stages (Table 2) and shape 551 analyses also recover growth stage significant differ-552 ences (Table 3). In previous works, classical shape parameters did not 556 discriminate sex-dependent variation of tooth shape 557 in S. stellaris, although gynandric heterodonty is well-558 known in scyliorhinids (Gosztonyi, 1973;Ellis and Shack-559 ley, 1995;Cappetta, 2012;[START_REF] Debiais-Thibaud | Tooth and scale morphogenesis in shark: an alternative process to the mammalian enamel knot system[END_REF]; 560 [START_REF] Soares | The catshark genus Scyliorhinus (Chondrichthyes: Carcharhiniformes: Scyliorhinidae): taxonomy, morphology and distribution[END_REF]. In our geometric morpho-561 metric analyses of S. stellaris teeth, we detected no 562 significant centroid size differences between sexes at 563 hatching and juvenile ontogenetic stages, while we ob-564 served such difference at mature stages with male tooth 565 centroid sizes being larger than female ones. Centroid 566 size is, per construction, a feature with little sensitivity 567 to shape. However, because we weighted tooth zones 568 by positioning the majority of semilandmarks in the lat-569 eral sides and in the crown base of the teeth (see Mate-570 rial and Methods, and Fig. 1B), the abovementioned dif-571 ferences in centroid size might be marginally affected by 572 differences in tooth shape at these locations (Webster 573 and Sheets, 2010). For most specimens, these crown 574 sides and bases include lateral cusps (between land-575 marks 1-13 and 21-33, Fig. 1), but also other aspects of 576 tooth shape such as the labial notch where two succes-577 sive teeth can be in contact (between landmarks 33-1, 578 Fig. 1). Statistical analyses supported the observed sex-579 ual dimorphism of the centroid size and shape among 580 mature specimens, as well as a visually undetected sex-581 ual dimorphism in tooth shape at hatching and juvenile 582 stages (Table 2 andTable 3).

We generated developmental trajectories between the three ontogenetic stages at all tooth positions in order to compare the shape transitions along jaws and ontogeny. Our analyses were performed under the hypothesis of homology (equivalence between compared structures) between tooth files of different specimens, to allow the developmental comparisons of forms over the lifetime of specimens of a given sex. However, the biological support for this hypothesis is questionable as the number of tooth files is not a fixed parameter over time. In S. stellaris, we also observed variation in the number of tooth files between specimens of similar total length. We chose to accept this hypothesis of homology based on the fact that newly formed tooth files are generally considered to be added at the jaw distal extremity in elasmobranchs (see [START_REF] Smith | Vertebrate dentitions at the origin of jaws: when and how pattern evolved[END_REF]; [START_REF] Smith | Reiterative pattern of sonic hedgehog expression in the catshark dentition reveals a phylogenetic template for jawed vertebrates[END_REF]; [START_REF] Underwood | Cut-1242 ting blade dentitions in squaliform sharks form by mod-1243 ification of inherited alternate tooth ordering patterns[END_REF] for sharks and [START_REF] Underwood | De-1247 velopment and evolution of dentition pattern and tooth 1248 Order in the skates And rays (Batoidea; Chondrichthyes)[END_REF] for batoids). However, they also might be inserted between already existing tooth files [START_REF] Reif | Morphogenesis, pattern formation and 1154 function of the dentition of Heterodontus (Selachii)[END_REF](Reif, , 1980;;[START_REF] Smith | Pattern formation in development of chondrichthyan dentitions: a review of an evolutionary model[END_REF], which would skew the continuity of tooth file numbering over time (see [START_REF] Underwood | De-1247 velopment and evolution of dentition pattern and tooth 1248 Order in the skates And rays (Batoidea; Chondrichthyes)[END_REF]; [START_REF] Smith | Pattern formation in development of chondrichthyan dentitions: a review of an evolutionary model[END_REF] for similar remarks on batoids). Finally, we want to highlight that this homology (comparability) hypothesis is based under the assumption that the genesis of a tooth bud happens from a defined and continuous source, which is a strongly mammal-centered view of tooth morphogenesis. In contrast, tooth bud initiation in elasmobranchs is considered to happen through self-organisation of the dental lamina, the invaginated epithelial fold from which new teeth develop (Reif, 1982;[START_REF] Rasch | An ancient dental 1150 gene set governs development and continuous regen-1151 eration of teeth in sharks[END_REF]. For all these reasons, we interpreted our results as trends along the mesio-distal axis of a jaw but never under a strict homology hypothesis that would allow the comparison of a single given file between specimens, to the exception of the developmental trajectory analyses that necessitate a one-to-one comparison.

Over the time of sexual maturation, the juvenileto-mature tooth shape developmental trajectories diverged between males and females at all tooth positions.

In both sexes, these juvenile-to-mature developmental trajectories differed from the hatchling-to-juvenile ones (Tables 4 and5). However, this deviation is increased 626 in mature males ("angle cor" values are higher in males 627 than in females in Tables 4 and5). In males, mature 628 tooth morphogenesis is characterized by an elongation 629 of the main cusp and a reduction of the number of ac-630 cessory cusps, generating unicuspid to tricuspid teeth 631 similar to hatchling ones (Fig. 2 and3). In contrast, ma-632 ture female tooth shape patterns resemble those of ju-633 veniles although the most distal teeth of mature females 634 can reach a maximum of six accessory cusps (Fig. 2 and635 3). As a conclusion, during sexual maturation, all tooth 636 files in S. stellaris are affected by a slighter (females) or 637 stronger (males) modification of developmental trajec-638 tories, compared to their hatchling-to-juvenile trajecto-639 ries.

640

On the one hand, it is tempting to speculate on di-641 etary differences between sexes that would correlate 642 with morphological differences in teeth. It was reported 643 that S. stellaris juvenile and mature specimens mostly 644 feed on cephalopods and, to a lesser extent, on teleosts 645 and crustaceans (Capapé, 1975). Juvenile females were 646 reported to feed more on crustaceans than males and 647 mature females (Capapé, 1975). These observations do 648 not fit with any of the morphological shifts in tooth 649 shape described in this study, so we cannot discuss any 650 putative link between S. stellaris trophic ecology and 651 tooth shape variation. On the other hand, the gynan-652 dric heterodonty of mature S. stellaris is consistent with 653 reports on the role of teeth during copulation in elasmo-654 branchs (Springer, 1967;[START_REF] Mceachran | Reply to "Sexual dimorphism in skates (Rajidae)[END_REF]Kajiura and 655 Tricas, 1996;[START_REF] Pratt | A Review of Elas-1140 mobranch Reproductive Behavior with a Case Study on 1141 the Nurse Shark, Ginglymostoma cirratum[END_REF]; Gutteridge and 656 Bennett, 2014). The increased main cusp height of ma-657 ture male teeth might indeed enhance gripping, as com-658 pared to teeth with more accessory cusps and smaller 659 main cusp. However, this remains speculative as there 660 is no experimental data on comparative gripping effi-661 ciency for shark teeth, only a few studies that compared 662 flat versus cuspidate teeth in batoids (Kajiura and Tricas, 663 1996;Gutteridge and Bennett, 2014). tures that could constrain tooth bud growth within the 706 dental lamina are even scarcer although previous studies on mammals emphasized that a modification of the tooth bud physical environment can modify the final shape of a tooth [START_REF] Renvoisé | Mechanical constraint from growing jaw facili-1166 tates mammalian dental diversity[END_REF]. Several observations of the jaw morphology may still help discuss how these physical constraints can be linked to tooth development. Of course, these genetic and physical cues acting on tooth development should not be considered as acting independently of one another on tooth development: it is likely that developmental signaling pathways impact morphogenesis by modifying physical parameters at the cellular level, while geometrical and physical constraints at the jaw cartilage or dental lamina levels can induce differential diffusion of molecules [START_REF] Salazar-Ciudad | Tooth morphogenesis in vivo, in 1170 vitro, and in silico[END_REF][START_REF] Renvoisé | Mechanical constraint from growing jaw facili-1166 tates mammalian dental diversity[END_REF]Calamari et al., 2018). The parameters of this complex system that may be relevant for specific aspects of tooth morphology and its variational properties in time or space are essentially unknown. However, from our results in S. stellaris, we wish to draw three main discussion points on the putative sources of: (1) mesio-distal patterning,

(2) asymmetry, and (3) gynandric heterodonty.

(1) Sources of the mesio-distal patterning. The graded variation of cusp-crown ratio is a shared feature of all ontogenetic stages and both jaws: this observation suggests the occurrence of a graded signal along the mesiodistal axis of a jaw at all developmental stages. This signal may be of two non-mutually exclusive origins: a gradient of physical constraints, and a gradient of molecular signals along the jaw.

Very little is known on the potential variation of the shape, thickness, and curvature of the dental lamina at any developmental stage. However, previous observations of catshark jaws showed that hatchling tooth buds develop very close to the Meckel's cartilage surface (observations in S. canicula in Debiais-Thibaud et al. ( 2015)), suggesting the gradient of dental lamina invagination is weak or nonexistent at this stage, contrary to older specimens whose dental lamina is more deeply invaginated.

Therefore, the physical constraints on the dental lamina do not seem to explain the observed gradients of cuspcrown ratios. The overall jaw geometry may also be considered as another potential driver of the mesio-distal patterning. As for the dental lamina, its effects on the 750 mesio-distal patterning may however be non-linear: the 751 sexually dimorphic heads in mature scyliorhinids would 752 also affect the shape of jaw cartilages (Ellis and Shack-753 ley, 1995;[START_REF] Soares | Sexually dimorphic body proportions in the catshark genus Scyliorhinus (Chondrichthyes: Carcharhiniformes: Scyliorhinidae)[END_REF][START_REF] Soares | The catshark genus Scyliorhinus (Chondrichthyes: Carcharhiniformes: Scyliorhinidae): taxonomy, morphology and distribution[END_REF].

792

(3)Sources of gynandric heterodonty. Sex-related tooth shape dimorphism is visually detectable only in mature specimens. This dimorphism stands strongly in the relative size of the main cusp versus accessory cusps (higher in males), and in the number of accessory cusps (higher in females). Previous studies and modeling of mammalian tooth morphogenesis have recovered patterns of covariation between main cusp sharpness and the number and spacing of accessory cusps [START_REF] Jernvall | Linking development with generation of novelty in mammalian teeth[END_REF][START_REF] Salazar-Ciudad | A computational 1173 model of teeth and the developmental origins of mor-1174 phological variation[END_REF]. Although highly speculative to infer mammalian developmental patterns to sharks, the 2D-tooth shapes computed in this case study are very similar to the S. stellaris lateral teeth (especially those of the ringed seal Phoca hispida) [START_REF] Salazar-Ciudad | A computational 1173 model of teeth and the developmental origins of mor-1174 phological variation[END_REF]. In this case study, the authors have interpreted the observed relationship between the height of the main cusp and the height of accessory cusps as a product of the enamel knot signaling center spacing: the closer the secondary enamels knots as compared to the primary enamel knot, the higher and the more blunt the accessory cusps [START_REF] Jernvall | Linking development with generation of novelty in mammalian teeth[END_REF][START_REF] Salazar-Ciudad | A computational 1173 model of teeth and the developmental origins of mor-1174 phological variation[END_REF]. Conversely, when the distance between primary and secondary enamel knots is greater, sharper teeth with fewer and smaller accessory cusps develop [START_REF] Jernvall | Linking development with generation of novelty in mammalian teeth[END_REF][START_REF] Salazar-Ciudad | A computational 1173 model of teeth and the developmental origins of mor-1174 phological variation[END_REF]. The successive activation of enamel knots and their spacing is strongly regulated by the diffusion rate of signaling molecules such as Shh and Fgfs [START_REF] Thesleff | The role of growth fac-1239 tors in tooth development[END_REF][START_REF] Du | Lineage tracing of epithelial cells in developing teeth reveals two strategies for building signaling centers[END_REF]. Another developmental parameter in which variation was associated with this shape relationship is epithelial growth rate [START_REF] Salazar-Ciudad | A computational 1173 model of teeth and the developmental origins of mor-1174 phological variation[END_REF], e.g., the rate of cell division in the tooth bud that is growing from the dental lamina. Finally, the dental lamina characteristics (acting on diffusion rates and cell division rate) might exhibit sexual dimorphism, as a consequence of sexually dimorphic head dimensions in Scyliorhinidae [START_REF] Ellis | Ontogenic changes and sexual dimorphism in the head, mouth and teeth of the lesser spotted dogfish[END_REF][START_REF] Soares | Sexually dimorphic body proportions in the catshark genus Scyliorhinus (Chondrichthyes: Carcharhiniformes: Scyliorhinidae)[END_REF]. The longer and narrower jaw in males compared to females at mature stage is actually a recurrent feature in elasmobranchs and gives support to this hypothesis [START_REF] Ellis | Ontogenic changes and sexual dimorphism in the head, mouth and teeth of the lesser spotted dogfish[END_REF]Braccini and Chiaramonte, 2002;Erdogan et al., 2004;Geniz et al., 2007;[START_REF] Soares | Taxonomic review of catsharks of the Scyliorhinus haeckelii group, with the description of a new species (Chondrichthyes: Carcharhiniformes: Scyliorhinidae)[END_REF][START_REF] Soares | Sexually dimorphic body proportions in the catshark genus Scyliorhinus (Chondrichthyes: Carcharhiniformes: Scyliorhinidae)[END_REF]. Labial curva-ture of the jaw cartilages may then impact the physical constraints on dental lamina. A second hypothetical source, which might interact with the previous one, is based on the sex-hormone dependence of the molecular signalisation involved in tooth bud growth. This is supported by previous identification of a sex-hormone dependency for Shh expression in vertebrates, including elasmobranchs [START_REF] Ogino | Androgen dependent development of a modified anal fin, gonopodium, as a model to understand the mechanism of secondary sexual character expression in vertebrates[END_REF]Chew et al., 2014;[START_REF] O'shaughnessy | Molecular development of chondrichthyan claspers and the evolution of copulatory organs[END_REF]. Gene regulatory networks involved in elasmobranch tooth development have been most extensively investigated in S. canicula, where the expression of classical developmental genes was characterized [START_REF] Debiais-Thibaud | The homology of odontodes in gnathostomes: insights from Dlx gene expression in the dogfish, Scyliorhinus canicula[END_REF][START_REF] Moczek | Developmental plasticity and evolution-quo vadis?[END_REF][START_REF] Martin | Sox2+ progenitors in sharks link taste development with the evolution of regenerative teeth from denticles[END_REF][START_REF] Rasch | An ancient dental 1150 gene set governs development and continuous regen-1151 eration of teeth in sharks[END_REF]. If the situation in S. stellaris is comparable to what was observed in S. canicula, then a modification of balance between developmental genes (e.g., Shh) under the reception of sex-hormone signals in mature specimens could modify the balance between cell proliferation and differentiation that impacts the final shape of a tooth.

As discussed here, a variety of hypothetical physical and molecular factors might be involved in the generation of tooth shape plasticity in elasmobranchs.

To test these influences, morpho-anatomical and functional studies are still necessary although they are difficult to realize in non-model and threatened species such as most elasmobranchs. We expect that our extensive description of the actual tooth form diversity in S. stellaris will help to orientate the hypotheses to be further tested to identify the sources of heterodonty in elasmobranchs.

| Conclusion

Teeth are involved in two main functions in elasmobranchs: feeding and reproduction. Although ontogenetic shifts in tooth morphologies have been reported in different shark orders, very few studies focused on the changes from an embryonic to a mature dentition in males and females separately. Here we gave a description of the wide, natural, and intraspecific variation of tooth shapes in S. stellaris. We detailed the tooth form transitions between three ontogenetic stages and focused on: (i) graded variation of several morphomet-877 ric parameters along the mesio-distal axis of a jaw, only 878 starting during the juvenile stage and on (ii) gynandric 879 heterodonty at mature stage generated by a stronger 880 change in developmental trajectory for males (unicus-881 pid to tricuspid teeth) than for females (addition of lat-882 eral cusps). We hope that the detailed morphospaces 883 we provide here for S. stellaris teeth will be extended 884 in an interspecific framework to challenge hypotheses 885 on the developmental mechanisms that generate the 886 known elasmobranch tooth shape diversity.

1 -5.11e -2 (5.40e -2 ) 1.70e -3 (9.54e -1 ) 1.21 (1.00e -3 1.00e -3 1.00e -3 ) 1.83 (1.00e -3 1.00e -3 1.00e -3 ) 2 -4.70e -2 (1.59e -1 ) -5.33e -2 (4.60e -2 4.60e -2 4.60e -2 ) 1.76 (1.00e -3 1.00e -3 1.00e -3 ) 1.99 (1.00e -3 1.00e -3 1.00e -3 ) 3 -8.42e -2 (3.20e -2 3.20e -2 3.20e -2 ) 2.08e -2 (5.40e -1 ) 1.62 (1.00e -3 1.00e -3 1.00e -3 ) 1.96 (1.00e -3 1.00e -3 1.00e -3 ) 4 -1.00e -1
(5.00e -3 5.00e -3 5.00e -3 ) -5.00e -4 (9.88e -1 ) 1.41 (1.00e -3 1.00e -3 1.00e -3 ) 2.00 (1.00e -3 1.00e -3 1.00e -3 ) 5 -3.93e -2 (1.77e -1 ) 3.60e -2 (2.40e -1 ) 1.29 (1.00e -3 1.00e -3 1.00e -3 ) 2.10 (1.00e -3 1.00e -3 1.00e -3 ) 6 -5.88e -2 (2.60e -2 2.60e -2 2.60e -2 ) 1.45e -2 (6.84e -1 ) 1.25 (1.00e -3 1.00e -3 1.00e -3 ) 2.20 (1.00e -3 1.00e -3 1.00e -3 ) 7 -4.40e -2 (7.10e -2 ) -2.18e -2 (4.56e -1 ) 1.08 (1.00e -3 1.00e -3 1.00e -3 ) 2.11 (1.00e -3 1.00e -3 1.00e -3 ) 8 -7.89e -2 (1.10e -2 1.10e -2 1.10e -2 ) -6.10e -3 (8.30e -1 ) 1.26 (1.00e -3 1.00e -3 1.00e -3 ) 2.13 (1.00e -3 1.00e -3 1.00e -3 ) 1.00e -3 1.00e -3 ) -1.42e -1 (9.00e -3 9.00e -3 9.00e -3 ) 1.54 (1.00e -3 1.00e -3 1.00e -3 ) 2.49 (1.00e -3 1.00e -3 1.00e -3 ) -1.13e -1 (4.00e -2 ) -9.82e -2 (1.11e -1 ) 1.43 (1.00e -3 1.00e -3 1.00e -3 ) 2.32 (7.00e -3 7.00e -3 7.00e -3 ) -1.14e -1 (2.50e -2 2.50e -2 2.50e -2 ) NA 1.45 (3.00e -3 3.00e -3 3.00e -3 ) NA -1.95e -1 (1.00e -2 1.00e 4.00e -3 ) 1.84 (1.00e -3 1.00e -3 1.00e -3 ) 2 1.23e -2 (6.64e -1 ) 1.25e -1 (1.00e -2 1.00e -2 1.00e -2 ) 2.17 (9.00e -3 9.00e -3 9.00e -3 ) 2.27 (1.00e -3 1.00e -3 1.00e -3 ) 3 -7.49e -4 (9.78e -1 ) 1.99e -2 (4.35e -1 ) 1.82 (1.00e -3 1.00e -3 1.00e -3 ) 1.99 (1.00e -3 1.00e -3 1.00e -3 ) 4 -7.83e -3 (6.50e -1 ) 8.41e -3 (7.00e -1 ) 1.74 (1.00e -3 1.00e -3 1.00e -3 ) 2.13 (1.00e -3 1.00e -3 1.00e -3 ) 5 -5.86e -3 (8.00e -1 ) 1.22e -2 (5.85e -1 ) 1.71 (1.00e -3 1.00e -3 1.00e -3 ) 2.07 (1.00e -3 1.00e -3 1.00e -3 ) 6 -3.00e -3 (9.12e -1 ) 4.08e -2 (1.17e -1 ) 1.85 (1.00e -3 1.00e -3 1.00e -3 ) 2.21 (1.00e -3 1.00e -3 1.00e -3 ) 7 3.85e -3 (8.60e -1 ) 1.55e -2 (5.85e -1 ) 1.55 (1.00e -3 1.00e -3 1.00e -3 ) 2.17 (1.00e -3 1.00e -3 1.00e -3 ) 1.53 (3.00e -3 3.00e -3 3.00e -3 ) 2.01 (1.00e -3 1.00e -3 1.00e -3 ) -1.27e -1 (1.00e -3 1.00e -3 1.00e -3 ) -2.11e -2 (4.39e -1 ) 1.41 (1.00e -3 1.00e -3 1.00e -3 ) 2.17 (1.00e -3 1.00e -3 1.00e -3 ) -1.51e -1 (1.00e -3 1.00e -3 1.00e -3 ) -4.49e -2 (1.90e -1 ) 1.20 (1.00e -3 1.00e -3 1.00e -3 ) 2.08 (1.00e -3 1.00e -3 1.00e -3 ) -1.49e -1 (6.00e -3 6.00e -3 6.00e -3 ) NA 2.39 (2.00e -3 2.00e -3 2.00e -3 ) NA -8.47e -2 (1.40e -2 1.40e -2 1.40e -2 ) NA 1.08 (1.00e -3 1.00e (5.04e Due to the difference in total tooth file number between stages, some comparisons could not be done (NAs). -, difference; dL, delta length; F, females; M, males. )

7.39e -2 (3.00e -3 3.00e -3 3.00e -3 ) 1.21 (1.00e -3 1.00e -3 1.00e -3 ) 2.12e -2 (4.89e -1 ) 6.57e -1 (1.20e -2 ) 2 1.13e -1 (5.90e -1 ) 4.14e -2 (9.60e -2 ) 1.04 (1.00e -3 1.00e -3 1.00e -3 ) 4.77e -2 (1.97e -1 ) 4.90e -1 (3.10e -2 ) 3 3.34e -1 (3.20e -2 ) 7.05e -2 (1.70e -2 1.70e -2 1.70e -2 ) 9.63e -1 (1.00e -3 1.00e -3 1.00e -3 ) -3.45e -2 (4.05e -1 ) 3.35e -1 (1.23e -1 ) 4 3.86e -1 (1.40e -2 1.40e -2 1.40e -2 ) 6.29e -2 (3.40e -2 3.40e -2 3.40e -2 ) 9.19e -1 (1.00e -3 1.00e -3 1.00e -3 ) -3.66e -2 (3.64e -1 ) 4.24e -1 (2.40e -2 ) 5 4.41e -1 (2.00e -3 2.00e -3 2.00e -3 ) 6.58e -2 (2.90e -2 2.90e -2 2.90e -2 ) 1.05 (1.00e -3 1.00e -3 1.00e -3 ) -9.50e -3 (7.45e -1 ) 6.44e -1 (2.30e -2 ) 6 4.95e -1 (1.00e -3 1.00e -3 1.00e -3 ) 7.13e -2 (1.10e -2 1.10e -2 1.10e -2 ) 1.03 (1.00e -3 1.00e -3 1.00e -3 ) -2.10e -3 (9.45e -1 ) 4.35e -1 (1.90e -2 ) 7 4.58e -1 (1.00e -3 1.00e -3 1.00e -3 ) 6.88e -2
(5.00e -3 5.00e -3 5.00e -3

)

1.22 (1.00e -3 1.00e -3 1.00e -3 ) 4.67e -2 (1.44e -1 ) 3.64e -1 (1.90e -2 ) 8 4.54e -1 (1.00e -3 1.00e -3 1.00e -3 ) 7.85e -2
(5.00e -3 5.00e -3 5.00e -3

) 9.69e -1

(1.00e -3 1.00e -3 1.00e -3

)

5.60e -3 (8.51e -1 ) 3.37e -1 (1.07e -1 ) 9 2.93e -1 (4.60e -2 ) 7.64e -2 (3.00e -3 3.00e -3 3.00e -3 ) 7.97e -1 (1.00e -3 1.00e -3 1.00e -3 ) 1.59e -2 (6.25e -1 ) 2.74e -1 (1.17e -1 ) 10 3.32e -1 (1.20e -2 1.20e -2 1.20e -2 ) 5.17e -2 (6.60e -2 ) 1.04 (1.00e -3 1.00e -3 1.00e -3 ) 2.76e -2 (3.66e -1 ) 3.47e -1 (8.30e -2 ) 11 3.14e -1 (3.50e -2 ) 9.38e -2 (3.00e -3 3.00e -3 3.00e -3 ) 6.26e -1 (4.00e -3 4.00e -3 4.00e -3 ) 1.30e -2 (7.25e -1 ) 3.07e -1 (2.20e -2 ) 12 4.11e -1 (3.00e -3 3.00e -3 3.00e -3 ) 1.02e -1 (1.00e -3 1.00e -3 1.00e -3 ) 8.58e -1 (2.00e -3 2.00e -3 2.00e -3 ) -5.80e -3 (8.75e -1 ) 3.47e -1 (1.00e -2 ) 13 2.55e -1 (1.82e -1 ) 8.29e -2 (1.20e -2 1.20e -2 1.20e -2 ) 6.53e -1 (2.60e -2 2.60e -2 2.60e -2 ) 3.48e -2 (4.18e -1 ) 3.68e -1 (1.80e -2 ) 14 4.76e -1
(5.00e -3 5.00e -3 5.00e -3

)

1.23e -1 (1.00e -3 1.00e -3 1.00e -3 ) 1.06 (1.00e -3 1.00e -3 1.00e -3 ) -3.50e -3 (9.46e -1 ) 3.59e -1 (4.00e -3 ) 15 4.85e -1 (1.00e -3 1.00e -3 1.00e -3 ) 1.25e -1 (2.00e -3 2.00e -3 2.00e -3 ) 1.22 (1.00e -3 1.00e -3 1.00e -3 ) 3.48e -2 (3.43e -1 ) 3.05e -1 (2.00e -2 ) 16 4.88e -1 (1.00e -3 1.00e -3 1.00e -3 ) 1.17e -1 (1.00e -3 1.00e -3 1.00e -3 ) 8.27e -1 (3.00e -3 3.00e -3 3.00e -3 ) -1.13e -2 (7.59e -1 ) 2.90e -1 (2.60e -2 ) 17 3.68e -1 (1.20e -2 1.20e -2 1.20e -2 ) 1.09e -1 (1.00e -3 1.00e -3 1.00e -3 ) 1.15 (1.00e -3 1.00e -3 1.00e -3 ) 2.40e -2 (5.14e -1 ) 3.63e -1 (1.20e -2 ) 18 4.63e -1 (2.00e -3 2.00e -3 2.00e -3 ) 6.49e -2 (3.30e -2 3.30e -2 3.30e -2 ) 1.38 (1.00e -3 1.00e -3 1.00e -3 ) 1.99e -2
(5.33e -1

)

3.45e -1 (6.90e -2 ) 19 4.41e -1 (2.00e -3 2.00e -3 2.00e -3 ) 9.03e -2 (4.00e -3 4.00e -3 4.00e -3 ) 1.58 (1.00e -3 1.00e -3 1.00e -3 ) 5.27e -2 (2.07e -1 ) 2.60e -1 (1.18e -1 ) 20 3.54e -1 (4.00e -3 4.00e -3 4.00e -3 ) 8.28e -2 (1.00e -3 1.00e -3 1.00e -3
) 1.17 (3.00e -3 3.00e -3 3.00e -3

) 2.24e -2

(5.34e -1

) )

3.25e -1 (3.40e -2 ) 21 3.36e -1 (9.00e -3 9.00e -3 9.00e -3 ) 8.08e -2 (1.00e -3 1.00e -3 1.00e -3 ) 1.08 (1.00e -3 1.00e -3 1.00e -3 ) 3.72e -2 (2.54e -1 ) 2.26e -1 (7.50e -2 ) 22 3.31e -1 (3.90e -2 ) 4.88e -2 (1.90e -2 1.90e -2 1.90e -2 ) 1.25 (9.00e -3 9.00e -3 9.00e -3 ) 4.20e -3 (9.16e -1 ) 2.95e -1 (2.50e -2 ) 23 3.77e -1 (1.14e -1 ) 3.16e -2 (2.44e -1 ) 1.37 (2.00e -3 2.00e -3 2.00e -3 ) 1.71e -2 (7.15e -1 ) 3.29e -1 (2.00e -
4.88e -2 (2.10e -2 2.10e -2 2.10e -2 ) 1.14 (1.00e -3 1.00e -3 1.00e -3 ) 2.14e -2 (3.11e -1 ) 9.65e -1 (1.10e -2 ) 2 3.11e -1
(2.56e -1

)

1.54e -1

(1.00e -3 1.00e -3 1.00e -3 (3.00e -3 3.00e -3 3.00e -3

) 3.88e -2

(1.86e -1

) 7.27e -1

(5.00e -3

) 4

2.07e -1

(1.19e (1.60e -2 1.60e -2 1.60e -2

)

1.01e -1

(1.00e -3 1.00e -3 1.00e -3

) 8.20e -1

(1.00e -2 1.00e -2 1.00e -2 ) 3.85e -2

(2.20e -1 ) 6.42e -1

(1.10e -2

) 10 4.82e -1 (6.00e -3 6.00e -3 6.00e -3

) 1.15e -1

(1.00e -3 1.00e -3 1.00e -3

) 9.85e -1

(3.00e -3 3.00e -3 3.00e -3

) 8.46e -3

(7.74e -1

) 5.45e -1

(5.70e -2

) 11 3.76e -1

(1.40e -2 1.40e -2 1.40e -2

)

1.03e -1

(1.00e -3 1.00e -3 1.00e -3

) 9.61e -1 (4.00e -3 4.00e -3 4.00e -3

) 3.86e -2

(1.84e -1

) 4.83e -1

(2.10e -2

) 12 3.88e -1

(1.60e -2 1.60e -2 1.60e -2

)

1.05e -1

(1.00e -3 1.00e -3 1.00e -3

) 8.80e -1

(2.00e -3 2.00e -3 2.00e -3

) 3.01e -2

(2.92e -1

) 4.74e -1

(5.10e -2

) 13 4.97e -1

(2.00e -3 2.00e -3 2.00e -3

) 1.23e -1

(1.00e -3 1.00e -3 1.00e -3

) 8.04e -1

(1.00e -3 1.00e -3 1.00e -3

) 3.61e -2

(2.20e -1 ) 3.94e -1

(1.00e -1 ) 14 4.72e -1 (4.00e -3 4.00e -3 4.00e -3

) 1.43e -1

(1.00e -3 1.00e -3 1.00e -3 (2.00e -3 2.00e -3 2.00e -3

) 1.33e -1

(1.00e -3 1.00e -3 1.00e -3

) 1.02 (1.00e -3 1.00e -3 1.00e -3

)

1.19e -2 (7.40e -1
) 2.78e -1

(2.43e -1

) 16 5.11e -1

(2.00e -3 2.00e -3 2.00e -3

) 1.07e -1

(1.00e -3 1.00e -3 1.00e -3

) 1.01 (1.00e -3 1.00e -3 1.00e -3

) -3.27e -3 (9.17e -1 ) 3.68e -1

(1.39e -1

) 17 5.99e -1

(2.00e -3 2.00e -3 2.00e -3

) 1.15e -1

(1.00e -3 1.00e -3 1.00e -3

) 1.17 (3.00e -3 3.00e -3 3.00e -3

) -4.49e -2

(2.42e -1

) 7.78e -1

(2.90e -2

) 18 5.02e -1

(1.00e -3 1.00e -3 1.00e -3

) 9.26e -2 (6.00e -3 6.00e -3 6.00e -3

) 1.23 (5.00e -3 5.00e -3 5.00e -3

) -1.33e -2 (7.28e -1 ) 3.75e -1

(1.42e -1

) 19 4.43e -1

(1.00e -3 1.00e -3 1.00e -3

) 5.94e -2

(1.50e -2 1.50e -2 1.50e -2

  1621A). Within each tooth file, we analyzed 1 to 4, func-163 tional but not worn, generations. F I G U R E 1 Tooth identification within a jaw and landmarking. A) microCT image of a right Meckel's cartilage of a juvenile female S. stellaris, dorsal view. f, file as defined from the symphysis (dotted line) to the commissure; g, generation. Scale bar represents 2.5mm for the jaw and 1mm for the zoomed teeth; B) Mesial (top) and distal (bottom) examples of landmark (purple) and semilandmark (empty dots) setting. The teeth were not clustered into classically used 165 tooth-type denominations (e.g., symphyseal, parasym-166 physeal, lateral, commissural) (Reif, 1976; Lucifora et al., 167 2001) on purpose since we did not visually identify 168 abrupt tooth shape or size change along the mesio-distal 169 axis, except for the symphyseal teeth on the lower jaw 170 (Fig. 1A). These symphyseal teeth are located between 171 the right and left Meckelian cartilages and are not lo-172 cated above jaw cartilages, contrary to all other teeth. 173 All subsequent analyses were performed under the hy-174 pothesis of homology between tooth files of different 175 specimens, which for example means that the most sym-176 physeal Meckelian tooth file of a given hatchling male is 177 considered equivalent to the most symphyseal Mecke-178 lian tooth file of a mature female.

  179

252

  but one symphyseal file on the Meckelian cartilage (for 253 41% of the specimens). Although the second Meck-254 elian tooth file is partially located above the Mecke-255 lian mesial edge, the teeth display size and morpho-256 logical similarities to the symphyseal ones (for 59% of 257 the specimens). We report no significant difference in 258 tooth file counts between right and left sides of the jaw 259 within each ontogenetic stage for each sex (Wilcoxon 260 matched-pairs signed rank tests, p-val> 4.60e -2 for all 261 tests; we observed a maximum difference of two tooth files between the right and left jaws, in 13/51 compar-

F

  I G U R E 2 Palatoquadrate tooth shape diversity in S. stellaris. A-D) Hatchling female teeth; E-H) Juvenile female teeth; I-L) Mature female teeth; M-P) Mature male teeth. Symphyseal (mesial) pole to the left.

333

  Teeth of S. stellaris undergo a global increase of bilateral 334 asymmetry from the symphysis to the commissure al-335

  study, we generated 3D images and collected 3D 494 coordinates of landmarks and semilandmarks on the cut-495 ting edge of the tooth surface. Despite the 3D nature 496 of the surface data, the described tooth outline finally 497 includes very little information in the third dimension. 498

  features linked to tooth develop-667 mental plasticity in several ontogenetic dimensions. The 668 notion of developmental plasticity classically refers to 669 the building of distinct phenotypes from the expression 670 of a same genome in different environments (Moczek, 671 2015). Here, we want to use a modified version of this 672 concept and apply it to tooth shape variation: (i) of differ-673 ent teeth at the intra-individual level and (ii) of compara-674 ble teeth between successive ontogenetic stages. First, 675 the intra-individual variation points to developmental 676 plasticity which is here dependent on the mesio-distal 677 position of the tooth bud, and which we could name "po-678 sitional developmental plasticity". Second, the compar-679 ison between different ontogenetic stages -although 680 an extrapolation of a situation with constant genome-681 questions developmental plasticity in the temporal di-682 mension, assuming comparable tooth files between suc-683 cessive ontogenetic stages. We name this process "suc-684 cessive developmental plasticity", generated through 685 tooth successional replacement. Here we have quanti-686 fied a peculiarity of successive developmental plasticity: 687 the divergence of its developmental trajectory between 688 males and females during sexual maturation. 689 From these observations, we want to speculate on 690 the potential developmental mechanisms that might 691 generate these developmental plasticities, considering 692 the physical and molecular cues acting on tooth bud 693 growth within the dental lamina. To our knowledge, 694 there are very scarce genetic data available on tooth 695 morphogenesis in S. stellaris (Rasch et al., 2016) but gene 696 regulatory networks involved in elasmobranch tooth de-697 velopment have been investigated in S. canicula. The 698 expression of classical developmental genes was char-699 acterized in tooth buds (Debiais-Thibaud et al., 2011, 700 2015; Martin et al., 2016; Rasch et al., 2016), including 701 the well-known signaling factor Shh that acts as both a 702 tooth bud initiation signal and a proliferation signal dur-703 ing tooth morphogenesis (Berio and Debiais-Thibaud, 704 2019; Hosoya et al., 2020). Data on the physical fea-705

754

  This would suggest a sexual dimorphism in the gradient 755 of cusp-crown ratio by affecting differently the labial-756 lingual local curvature of the dental lamina where the 757 tooth buds develop. However, this is not obvious from 758 our observations, although mature males tend to have a 759 higher cusp-crown ratio in Meckelian teeth than females 760 do, and compare best to juveniles in that respect. 761 On the other hand, the mesio-distal patterning of 762 jaws by developmental genes was demonstrated in 763 model organisms (Van Otterloo et al., 2018) and molec-764 ular signaling is known to generate the mesio-distal 765 gradient in tooth morphology in mouse (reviewed in 766 Cobourne and Sharpe (2003)). The genes involved in 767 jaw patterning and tooth morphogenesis of mammals 768 are also expressed in S. canicula (Debiais-Thibaud et al., 769 2013, 2015; Rasch et al., 2016). Yet, there is no avail-770 able empirical evidence about how this signaling gra-771 dient may change during the ontogeny of scyliorhinids 772 and whether it does correlate with the cusp-crown ratio 773 gradient. 774 (2) Sources of asymmetry. The first generation of tooth 775 buds in embryos or just hatched specimens of S. canic-776 ula develops very close to the surface of the jaw epithe-777 lium, within a superficial dental lamina (Debiais-Thibaud 778 et al., 2011, 2015; Rasch et al., 2016). In addition, given 779 the topology of the jaw symphysis (without underlying 780 cartilage), we speculate that the situation is similar for 781 symphyseal teeth. We therefore consider the possibility 782 of tooth asymmetry as being correlated with the depth 783 and topology of the dental lamina invagination. Some of 784 our preliminary tests on modeling tooth development in 785 sharks suggest that the mechanical stresses exerted on 786 a tooth bud by the surrounding tissues (the dental lam-787 ina and the underlying cartilage) may be key to breaking 788 the symmetry of the tooth morphology. We speculate 789 that the deeper the dental lamina, the higher the likeli-790 hood of an asymmetry in the boundary conditions of the 791 growing tooth bud reflecting into its final shape.

  to Sylvain Adnet, Henri Cappetta, Guil-889 laume Guinot, and Suzanne Jiquel for giving access to 890 the collections (University of Montpellier). We also 891 thank Sophie Germain-Pigno from the Aquarium du 892 Cap d'Agde for providing fresh specimens, Sabrina Re-893 naud for her advices on geometric morphometrics, and 894 Yann Bayle, Julien Claude, Guillaume Guinot, and Roland 895 Zimm for insightful proofreading. We acknowledge 896 the contribution of SFR Biosciences (UMS3444/CNRS, 897 US8/Inserm, ENS de Lyon, UCBL) facilities: AniRA-898 ImmOs (Mathilde Bouchet-Combe) and the contribution 899 of MRI platform, member of the national infrastructure 900 France-BioImaging supported by the French National 901 Research Agency (ANR-10-INBS-04, "Investments for 902 the future"), the labex CEMEB (ANR-10-LABX-0004) 903 and NUMEV (ANR-10-LABX-0020) (Renaud Lebrun). 904 The authors declare no conflict of interest. The datasets 905 generated and analyzed in the current study are not pub-906 licly available due to ongoing other project but are avail-907 able from the corresponding author on reasonable reanalyzed the data; FB and AE de-911 signed the statistical analyses; FB, NG and MDT de-912 signed the experimental setup; FB and MDT drafted the 913 manuscript. 914 Wiley, D., Amenta, N., Alcantara, D., Ghosh, D., Kil, Y., Delson, E., Harcourt-Smith, W., Rohlf, F., St. John, K. and Hamann, B. (2005) Evolutionary Morphing. In Proceedings of the IEEE International Conference on Visualization, 431-438. Minneapolis: Institute of Electrical and Electronics Engineers (IEEE). Wilga, C. D. and Motta, P. J. (2000) Durophagy in sharks: feeding mechanics of the hammerhead Sphyrna tiburo. The Journal of Experimental Biology, 203, 2781-2796. F I G U R E 4 Tooth dimensions of S. stellaris right Meckelian and palatoquadrate teeth. A and D) Morphometric measure of the ratio between main cusp height and crown base width; B and E) Deviation to tooth bilateral symmetry: difference between the tooth tip and each crown base extremity distances. C and F) Tooth centroid sizes. At each tooth position, mean values are computed among all tooth generations (internal replicates), before being computed among all specimens. Error bars are standard deviations among replicates and specimens. F I G U R E 5 2D representation (PC1xPC2) of tooth developmental trajectories in S. stellaris. A) 2D trajectories for palatoquadrate tooth files 3, 10, 15 and 20; B) 2D trajectories for Meckel's tooth files 1, 5, 15, and 20. The trajectory representations are drawn between the mean shape of hatchling (starting point), juvenile, and mature (arrow tip) specimen teeth. Purple and green shades are for females and males trajectories respectively. Mesial to distal files appear in light to deep shades. 7 | SUPPLEMENTARY MATERIAL 1275 A D D I T I O N A L F I G U R E Tooth main cusp height and crown base width in S. stellaris. A) Meckelian teeth of hatchlings; B) Palatoquadrate teeth of hatchlings; C) Meckelian teeth of juveniles; D) Palatoquadrate teeth of juveniles; E) Meckelian teeth of matures; F) Palatoquadrate teeth of matures. The main cusp values are the mean lengths between the mesial-most landmark of the tooth and the main cusp tip, and the distal-most landmark of the tooth and the main cusp tip (d1-17 and d17-33). The crown base values are the lengths between the mesial-most and the distal-most landmarks on the tooth (d1-38). A D D I T I O N A L TA B L E 1 Developmental trajectory values within sexes for palatoquadrate teeth.Significant p-values after Benjamini & Hochberg correction are in bold. Due to the difference in total tooth file number between stages, some comparisons could not be done (NAs). -, difference; dL, delta length; HJ, hatchling-to-juvenile; JM, juvenile-to-mature.

  Developmental trajectory values between sexes for Meckelian teeth. Significant p-values after Benjamini & Hochberg correction are in bold. Due to the difference in total tooth file number between stages, some comparisons could not be done (NAs). -, difference; dL, delta length; F, females; M, males.

  Tooth identification within a jaw and landmarking. A) microCT image of a right lower jaw of a juvenile female S. stellaris, dorsal view. f, file as defined from the symphysis (dotted line) to the commissure; g, generation. Scale bar represents 5mm for the jaw and 3mm for the zoomed teeth; B) Examples of landmark (purple) and semilandmark (empty dots) setting on mesial (top) and distal (bottom) teeth of a juvenile female. F I G U R E 2 Palatoquadrate tooth shape diversity in S. stellaris. A-D) Hatchling female teeth; E-H) Juvenile female teeth; I-L) Mature female teeth; M-P) Mature male teeth. Symphyseal (mesial) pole to the left. F I G U R E 3 Meckelian tooth shape diversity in S. stellaris. A-D) Hatchling female teeth; E-H) Juvenile female teeth; I-L) Mature female teeth; M-P) Mature male teeth. Symphyseal (mesial) pole to the left. F I G U R E 4 Tooth dimensions of S. stellaris right Meckelian and palatoquadrate teeth. A and D) Morphometric measure of the ratio between main cusp height and crown base width; B and E) Deviation to tooth bilateral symmetry: difference between the tooth tip and each crown base extremity distances. C and F) Tooth centroid sizes. At each tooth position, mean values are computed among all tooth generations (internal replicates), before being computed among all specimens. Error bars are standard deviations among replicates and specimens.F I G U R E 5 2D representation (PC1xPC2) of tooth developmental trajectories in S. stellaris. A) 2D trajectories for palatoquadrate tooth files 3, 10, 15 and 20; B) 2D trajectories for Meckel's tooth files 1, 5, 15, and 20. The trajectory representations are drawn between the mean shape of hatchling (starting point), juvenile, and mature (arrow tip) specimen teeth. Purple and green shades are for females and males trajectories respectively. Mesial to distal files appear in light to deep shades. Wireframes depict extreme deformations of the mean shape at the positive and negative extremities of the PC1 and PC2 axes.

  ). Dried jaws 148 were provided by the Institute of Evolution Sciences of 149 Montpellier (France) and jaws preserved in ethanol were 150 provided by the Aquarium du Cap d'Agde (France).

		151
	2.2 | MicroCT scans	152
	Jaws were microCT scanned using a Phoenix Nanotom S 153
	with voxel sizes ranging from (10.7µm) to (30.0µm) and 154
	3D volumes were reconstructed using the correspond-155
	ing phoenix datos x2 reconstruction software (v2.3.0).	156
	2.3 | Tooth selection	157

  Developmental trajectory values between sexes for palatoquadrate teeth. Significant p-values after Benjamini & Hochberg correction are in bold.

	TA B L E 4	TA B L E 3 MANOVA results on shape data. Significant p-values after Benjamini & Hochberg correction are in bold. MD, mesio-distal.	Meckelian teeth	All Hatchling Juvenile Mature	F approx (p-val) F approx (p-val) F approx (p-val) F approx (p-val)	5.39 (6.13e -8 6.13e -8 6.13e -8 ) 4.02 (9.54e -4 9.54e -4 9.54e -4 ) 1.86e 1 (5.72e -12 5.72e -12 5.72e -12 ) 2.67e 1 (5.39e -14 5.39e -14 5.39e -14 ) Sex	3.04e 1 (< 2.20e -16 < 2.20e -16 < 2.20e -16 ) ---Stage	1.80 (3.12e -14 3.12e -14 3.12e -14 ) 1.09 (2.36e -1 ) 1.50 (1.16e -4 1.16e -4 1.16e -4 ) 1.03 (4.12e -1 ) ToothMD	1.05e 1 (< 2.20e -16 < 2.20e -16 < 2.20e -16 ) ---Sex:Stage	8.73e -1 (9.33e -1 ) ---Sex:ToothMD	1.18 (1.02e -2 1.02e -2 1.02e -2 ) ---Stage:ToothMD	Palatoquadrate teeth	All Hatchling Juvenile Mature	F approx (p-val) F approx (p-val) F approx (p-val) F approx (p-val)	-1 ) 1.00e -3 (9.70e -1 ) 1.48e 1 (3.32e -4 3.32e -4 3.32e -4 ) 7.61 (2.67e -11 2.67e -11 2.67e -11 ) 2.88 (5.37e -3 5.37e -3 5.37e -3 ) 4.84 (7.58e -5 7.58e -5 7.58e -5 ) 5.99e 1 (< 2.20e -16 < 2.20e -16 < 2.20e -16 ) Sex	Stage 2.24e 2 (2.00e -16 2.00e -16 2.00e -16 ) ---4.58e 1 (< 2.20e -16 < 2.20e -16 < 2.20e -16 ) ---Stage	ToothMD 8.29e -1 (7.03e -1 ) 1.91e 1 (3.44e -11 3.44e -11 3.44e -11 ) 2.72e 1 (1.33e -12 1.33e -12 1.33e -12 ) 3.56 (9.37e -4 9.37e -4 9.37e -4 ) 1.89 (3.36e -16 3.36e -16 3.36e -16 ) 1.65 (2.28e -6 2.28e -6 2.28e -6 ) 1.52 (9.56e -5 9.56e -5 9.56e -5 ) 1.17 (7.37e -2 ) ToothMD	Sex:Stage 1.59e 1 (5.48e -7 5.48e -7 5.48e -7 ) ---7.32 (< 2.20e -16 < 2.20e -16 < 2.20e -16 ) ---Sex:Stage	Sex:ToothMD 1.50e -2 (1.00) ---8.63e -1 (9.53e -1 ) ---Sex:ToothMD	Stage:ToothMD 1.33 (1.28e -1 ) ---1.50 (4.16e -9 4.16e -9 4.16e -9 ) ---Stage:ToothMD

-8.76e -2 (2.00e -3 2.00e -3 2.00e -3 ) -2.71e -2 (9.70e -1 ) 1.56 (1.00e -3 1.00e -3 1.00e -3 ) 2.01 (1.00e -3 1.00e -3 1.00e -3 ) -5.10e -2 (6.10e -2 ) -2.69e -2 (4.59e -1 ) 1.36 (1.00e -3 1.00e -3 1.00e -3 ) 2.06 (1.00e -3 1.00e

3.00e -3 3.00e -3 ) -1.86e -2 (5.70e -1 ) 1.56 (2.00e -3 2.00e -3 2.00e -3 ) 2.00 (1.00e -3 1.00e -3 1.00e -3 ) -9.78e -2 (1.10e -2 1.10e -2 1.10e -2 ) -4.97e -2 (2.08e -1 ) 1.74 (3.00e -3 3.00e -3 3.00e -3 ) 2.03 (1.00e -3 1.00e -3 1.00e -3 ) -1.45e -1 (3.00e -3

3.00e -3 3.00e -3 ) -1.83e -2 (6.13e -1 ) 1.56 (1.00e -3 1.00e -3 1.00e -3 ) 2.15 (1.00e

4.40e -2 4.40e -2 ) 5.72e -2 (5.40e -1 ) 1.56 (2.00e -3 2.00e -3 2.00e -3 ) 2.04 (1.00e -3 1.00e -3 1.00e -3 ) -5.60e -2 (1.40e -2 1.40e -2 1.40e -2 ) 8.30e -3 (7.63e -1 ) 1.73 (1.00e -3 1.00e -3 1.00e -3 ) 2.12 (1.00e -3 1.00e -3 1.00e -3 ) -5.02e -2 (3.80e -2 3.80e -2 3.80e -2 ) 2.43e -2 (3.11e -1 ) 1.57 (1.00e -3 1.00e -3 1.00e -3 ) 2.03 (1.00e -3 1.00e -3 1.00e -3 ) -6.95e -2 (4.00e -3 4.00e -3 4.00e -3 ) 1.73e -2 (6.30e -1 ) 1.61 (1.00e -3 1.00e -3 1.00e -3 ) 2.22 (2.00e -3 2.00e -3 2.00e -3 ) -8.06e -2 (1.00e -3 1.00e -3 1.00e -3 ) 1.12e -3 (9.77e -1 ) 1.59 (1.00e -3 1.00e -3 1.00e -3 ) 2.19 (1.00e -3 1.00e -3 1.00e -3 ) -8.27e -2 (8.00e -3 8.00e -3 8.00e -3 ) 3.86e -2 (3.04e -1 ) 1.51 (1.00e -3 1.00e -3 1.00e -3 ) 2.25 (2.00e -3 2.00e -3 2.00e -3 ) -9.22e -2 (1.00e -3 1.00e -3 1.00e -3 ) 1.86e -2 (5.42e -1 ) 1.66 (1.00e -3 1.00e -3 1.00e -3 ) 2.17 (1.00e -3 1.00e -3 1.00e -3 ) -1.11e -1 (1.00e -3 1.00e -3 1.00e -3 ) 4.87e -2 (1.91e -1 )

This study uncovers the wide intraspecific diversity of tooth form in the large-spotted catshark Scyliorhinus stellaris using micro-computed tomography and 3D geometric morphometrics. We characterize the emergence of sexual dimorphism along ontogenetic stages using sex-specific ontogenetic trajectories. We discuss the physical and chemical parameters acting on tooth morphogenesis that may generate the described developmental plasticity in elasmobranchs.