Dimorphism In Shape Research Articles

Shape Variation in the Dermatocranium of the Greater Short-Horned Lizard Phrynosoma hernandesi (Reptilia: Squamata: Phrynosomatidae)

Dermatocranial shape and horn morphology display great disparity among the species of Phrynosoma. Ontogenetic change in dermatocranial shape in a series of 79 specimens of the short-horned Phrynosoma hernandesi (54F: 25M) was examined using geometric morphometric techniques. A multivariate ANCOVA of Procrustes residuals with sex as a factor and ln(centroid size) as the covariate indicated sexual shape dimorphism. Separate multivariate regressions of Procrustes residuals on ln(centroid size) for each sex indicated that allometry accounts for ~52–54% of the total sample shape variance. Comparisons of ontogenetic shape change between sexes indicate that sexual shape dimorphism is minimal and of uncertain biological significance. Groupings of multivariate regression coefficients by magnitude and sign suggest that allometric integration of the dermatocranium is not uniform over the dermatocranium. Principal component analysis of the landmark configurations corrected for sex and allometry yields a first principal component which describes shape variance concentrated in the posterolateral and posterior regions of the dermatocranium, and again is indicative of non-uniform shape variation over the dermatocranium. Our findings for P. hernandesi indicate that the adult shape of the dermatocranium may contribute to a passive defence against predation. We hypothesize that the complexity in dermatocranial shape demonstrated here for P. hernandesi indicates parcellation of shape variance, which may contribute to explanations of the pronounced dermatocranial disparity exhibited by the species of Phrynosoma.

Common Noctule Bats Are Sexually Dimorphic in Migratory Behaviour and Body Size but Not Wing Shape.

Within the large order of bats, sexual size dimorphism measured by forearm length and body mass is often female-biased. Several studies have explained this through the effects on load carrying during pregnancy, intrasexual competition, as well as the fecundity and thermoregulation advantages of increased female body size. We hypothesized that wing shape should differ along with size and be under variable selection pressure in a species where there are large differences in flight behaviour. We tested whether load carrying, sex differential migration, or reproductive advantages of large females affect size and wing shape dimorphism in the common noctule (Nyctalus noctula), in which females are typically larger than males and only females migrate long distances each year. We tested for univariate and multivariate size and shape dimorphism using data sets derived from wing photos and biometric data collected during pre-migratory spring captures in Switzerland. Females had forearms that are on average 1% longer than males and are 1% heavier than males after emerging from hibernation, but we found no sex differences in other size, shape, or other functional characters in any wing parameters during this pre-migratory period. Female-biased size dimorphism without wing shape differences indicates that reproductive advantages of big mothers are most likely responsible for sexual dimorphism in this species, not load compensation or shape differences favouring aerodynamic efficiency during pregnancy or migration. Despite large behavioural and ecological sex differences, morphology associated with a specialized feeding niche may limit potential dimorphism in narrow-winged bats such as common noctules and the dramatic differences in migratory behaviour may then be accomplished through plasticity in wing kinematics.

Sexual dimorphism in a freshwater atyid shrimp (Decapoda: Caridea) with direct development: a geometric morphometrics approach.

Neocaridina davidi is a caridean shrimp that has gained popularity in recent years as an ornamental species. Using geometric morphometrics, we investigated sexual dimorphism in carapace and second abdominal segment shape of N. davidi. Adult females displayed a more elongated carapace and a longer rostrum than males. However, male carapace shape was similar to that of juvenile females. The second abdominal pleura was more elongated and wider in adult females than in males. Significant differences were found in centroid size for the carapace and the second abdominal segment between sexes, which is consistent with sexual size dimorphism. These results support the hypothesis of a "pure search" mating system in N. davidi, where small males search actively for receptive females, and after insemination they continue searching.

Identity of “Apteronotus”bonapartii(Castelnau, 1855), a sexually dimorphic South American knifefish from the Amazon, with notes on its cranial osteology and on thetaxonomic status of “Apteronotus”apurensisFernández-Yépez, 1968 (Gymnotiformes, Apteronotidae)

“Apteronotus” bonapartii (Castelnau 1855) was described based on a single specimen caught in a lake draining into the Rio Ucayali, Peru, and is now reported from several rivers in South America. Because the generic placement of this species is currently uncertain, in this paper we use the genus name “Apteronotus” within quotes for reference to “Apteronotus” bonapartii (Castelnau, 1855) and “A.” apurensis Fernandez-Yepez, 1968; we use the genus name without quotes for the more precise usage referring to a putatively monophyletic group including the type species (A. albifrons). “Apteronotus” bonapartii has a laterally compressed body, subterminal mouth with the rictus passing the eyes and teeth present in both jaws. The species has been differentiated from others placed in the genus by the low number of scale rows (5–8) above the lateral line. There is substantial intraspecific variation among specimens, in part associated with pronounced sexual dimorphism in head shape. We describe aspects of the morphology and cranial osteology of 52 specimens of “A.” bonapartii from Central Amazon and 12 specimens from other localities in the Amazon and Orinoco basins including the holotype from Rio Ucayali. Males have slightly longer facial dimensions than females, and the holotype appears to fit on the male growth trajectory. Specimens from Napo, Metica, Orituco and Apure rivers are similar to specimens from the Central Amazon and the holotype. There is sexual dimorphism in the structure of the lower jaw, including its overall shape and profile (e.g., smooth curve of the dentary in males vs. a straight edge of the dentary in females), but no sexual dimorphism of teeth was noted. The postarticular portion of the lower jaw is formed equally by the anguloarticular and retroarticular. There is individual variation in the ossification of pharyngobranchial 4 and hypobranchial 4. We found no morphological differences between specimens of “A.” bonapartii from the Rio Apure and the species described as “A.” apurensis Fernandez-Yepez 1968.

Phylogeographic structure across one of the largest intact tropical savannahs: Molecular and morphological analysis of Australia’s iconic frilled lizard Chlamydosaurus kingii

The spectacular threat display of the savannah specialist Australo-Papuan frilled lizards has made them one of the world’s most iconic reptiles. They are increasingly used as a model system for research in evolutionary biology and ecology but little is known of their population structure. Their distribution across northern Australia and southern New Guinea also provides an opportunity to examine biogeographic patterns as they relate to the large-scale movement of savannah habitat during the Plio/Pleistocene and the associated increase in aridity. We generated sequence data for one mitochondrial and four nuclear DNA loci (5052 base pairs) for 83 frilled lizards sampled throughout their range. We also quantified body proportion variation for 279 individuals. Phylogenetic analyses based on maximum likelihood and Bayesian species-tree methods revealed three shallow clades that replace each other across the monsoon tropics. We found the expected pattern of male biased sexual size dimorphism in both maximum body size and head size but there was no sexual dimorphism in overall body shape or in frill size, relative to head size, supporting the hypothesis that the frill is used primarily as a threat display rather than a sexual display. The genetic clades are broadly consistent with known clinal variation in frill color that gradually shifts from west to east (red, orange, yellow/white) but otherwise show little morphological differentiation in body proportion measures. The biogeographic breaks between clades occur at the Carpentaria Gap and the lowlands surrounding the Ord River, and our ecological niche modeling predicts lower habitat suitability for C. kingii in these regions. While this biogeographic pattern is consistent with numerous other taxonomic groups in northern Australia, the overall low genetic diversity in frilled lizards across the entire monsoon tropics and southern New Guinea contrasts starkly to patterns seen in other terrestrial vertebrates. Extremely low intra-clade genetic diversity over vast geographic areas is indicative of recent gene flow that would likely have been facilitated by widespread savannah during interglacials, or alternatively may reflect population bottlenecks induced by extreme aridity during Pleistocene glacials. The shallow divergence between Australian and New Guinean samples is consistent with recent connectivity between Australia and New Guinea that would have been possible via a savannah corridor across the Torres Strait. Based on our molecular and morphological data, we do not support taxonomic recognition of any of the frilled lizard clades and instead consider C. kingii a single species with shallow phylogeographic structure and clinal variation in frill color.

Ontogenetic Scaling of Theoretical Bite Force in Southern Sea Otters (Enhydra lutris nereis).

Sexual dimorphism attributed to niche divergence is often linked to differentiation between the sexes in both dietary resources and characters related to feeding and resource procurement. Although recent studies have indicated that southern sea otters (Enhydra lutris nereis) exhibit differences in dietary preferences as well as sexual dimorphism in skull size and shape, whether these intersexual differences translate to differentiation in feeding performances between the sexes remains to be investigated. To test the hypothesis that scaling patterns of bite force, a metric of feeding performance, differ between the sexes, we calculated theoretical bite forces for 55 naturally deceased male and female southern sea otters spanning the size ranges encountered over ontogeny. We then used standardized major axis regressions to simultaneously determine the scaling patterns of theoretical bite forces and skull components across ontogeny and assess whether these scaling patterns differed between the sexes. We found that positive allometric increases in theoretical bite force resulted from positive allometric increases in physiological cross-sectional area for the major jaw adductor muscle and mechanical advantage. Closer examination revealed that allometric increases in temporalis muscle mass and relative allometric decreases in out-lever lengths are driving these patterns. In our analysis of sexual dimorphism, we found that scaling patterns of theoretical bite force and morphological traits do not differ between the sexes. However, adult sea otters differed in their absolute bite forces, revealing that adult males exhibited greater bite forces as a result of their larger sizes. We found intersexual differences in biting ability that provide some support for the niche divergence hypothesis. Continued work in this field may link intersexual differences in feeding functional morphology with foraging ecology to show how niche divergence has the potential to reinforce sexual dimorphism in southern sea otters.

Shell shape variation of queen conch Strombus gigas (Mesograstropoda: Strombidae) from Southwest Caribbean

The endangered species Strombus gigas is a marine gastropod of significant economic importance through the Greater Caribbean region. In contrast to phenotypic plasticity, the role of genetics on shell variations in S. gigas has not been addressed so far, despite its importance in evolution, management and conservation of this species. This work used geometric morphometrics to investigate the phenotypic variation of 219 shells of S. gigas from eight sites of the Colombian Southwest Caribbean. Differences in mean size between sexes and among sites were contrasted by analysis of variance. Allometry was tested by multivariate regression and the hypothesis of common slope was contrasted by covariance multivariate analysis. Differences in the shell shape among sites were analyzed by principal component analysis. Sexual size dimorphism was not significant, whereas sexual shape dimorphism was significant and variable across sites. Differences in the shell shape among sites were concordant with genetic differences based on microsatellite data, supporting its genetic background. Besides, differences in the shell shape between populations genetically similar suggest a role of phenotypic plasticity in the morphometric variation of the shell shape. These outcomes evidence the role of genetic background and phenotypic plasticity in the shell shape of S. gigas. Thus, geometric morphometrics of shell shape may constitute a complementary tool to explore the genetic diversity of this species.

Ontogeny of sexual size dimorphism in the hornless rose chafer Pachnoda marginata (Coleoptera: Scarabaeidae: Cetoniinae)

Beetles of the subfamily Cetoniinae are distinct and well-known, yet their larval ontogeny, sexual size dimorphism and development remain unknown in most species. This group contains many species with large males with prominent secondary sexual structures, such as cephalic or pronotal horns and elongated forelimbs. The species studied here, Pachnoda marginata, belongs to those species without any obvious dimorphism, the males being almost indistinguishable from the females. In this paper we examine sexual dimorphism in body shape and size in this apparently ‘non-dimorphic’ species. We further investigate the larval development and proximate causes of sexual size dimorphism, in particular when and how the sexes diverge in their growth trajectories during ontogeny. We found that males are larger than females and that the sexes also differ in body shape – for example, males possess significantly longer forelimbs relative to body size than females. The male-biased sexual size dimorphism along with prolonged forelimbs suggests that sexual selection for larger males may not be limited merely to horned species of rose chafers. The dimorphism in size in P. marginata arises during the second larval instar and basically remains unchanged till maturity. In both sexes the maximum body mass as well as developmental time of particular larval instars were strongly correlated, but time spent in the pupal chamber was not related to previous growth and final body size. The correlation between developmental time and adult size was negative, which may be a reflection of differences in resource allocation or utilisation for growth and development among individuals.

Variación fenotípica de la langosta espinosa Panulirus argus (Decapoda: Paniluridae) en el Caribe Suroccidental

The spiny lobster Panulirus argus is an important fishery species in the Western Central Atlantic. Changes in the dispersion range through its life cycle and heterogeneous habitats, suggest that P. argus exhibit phenotypic plasticity. However, the morphometric variation of this species is unknown so far, although this information is relevant in evolutionary studies as well as to solve questions of fishery interest. Thus, the aim of this study was to determine whether P. argus exhibit phenotypic variation between sexes, among five geographic origins and three oceanographic conditions of Southwest Caribbean (Colombian archipelago San Andrés, Providencia y Santa Catalina). A total of 193 P. argus adults were submitted to geometric morphometrics using six landmarks that delimit one half of the sternal plate. The differences in sternal plate size were compared with Kruskal-Wallis and Mann-Whitney Tests. The allometric effect was estimated using Multivariate Regression Analysis, the model of allometric slopes was tested by Multivariate analysis of covariance and the sternal plate shape differences was explored using non-parametric comparisons of Euclidian distances and Neighbour Joinnig trees. The results showed that the morphometric variation of sternal plate of this spiny lobster varied according to the gender since the sexual size and shape dimorphisms were significant. In both sexes, the sternal plate shape differed among oceanographic scenarios as it was evidenced by significant differences among Euclidian distances, and the tendency to cluster by North, Centre and South sections of San Andrés archipelago. Additionally, the morphometric variation resulting from phenotypic plasticity to variable ecological contexts may explain the phenotypic differences among genetically similar populations. This information permits to define management units, support the selection of regulatory policies of this fishery and complement the genetic analysis of the species in this Caribbean region.

Evaluation of stock variation and sexual dimorphism of beak shape of neon flying squid, Ommastrephes bartramii, based on geometric morphometrics

Variability in the shape of hard structures such as mandibles (beaks) due to stock variation or sexual dimorphism is common in cephalopods, and could prove useful in the discrimination of stocks or sexes. In this study, geometric morphometrics of upper and lower beak’s shape are used to analyze the variation between sexes and stocks in Ommastrephes bartramii of the northwestern Pacific Ocean. This species is targeted by the Chinese jigging fleet during the fishing period May–October 2013. Variation in the beak’s pigmentation stage was also investigated. According to our analyses, upper and lower beak shapes of O. bartramii differed significantly between eastern and western stocks of O. bartramii (MANCOVA, P < 0.01), and different allometric growths were also detected. The degree of pigmentation by pigmentation stage, changed in upper beaks between the two stocks and in lower beaks with beak size. In the western stock, only lower beak shape and pigmentation stages of upper beak shape showed significant differences between sexes, while the degree of pigmentation stage changed with different beak sizes in the lower beak. Squid stocks could be effectively identified based on the results of a principal component analysis of beak shape, but sexes could not be identified with this technique. We hypothesize that reason for these differences may be caused by the variation of feeding habits between stocks but the sharing of a similar habitat by both sexes.

Spatially dense morphometrics of craniofacial sexual dimorphism in 1-year-olds.

Recent advances in the field of geometric morphometrics allow for powerful statistical hypothesis testing for effects of biological and environmental variables on anatomical shape. This study used partial least-squares regression (PLSR) and the recently developed bootstrapped response-based imputation modelling (BRIM) algorithm to test for sexual dimorphism in the craniofacial shape of 1-year-old humans. We observed a recession of the forehead in boys relative to girls, and differences in the nose, consistent with adult dimorphism. Results also suggest that the degree to which individuals express dimorphic traits is continuous throughout the population. This is also seen in adult dimorphism but in 1-year-olds the amount of overlap between groups is much higher, indicating the strength of dimorphism between sexes is lower. Our results demonstrate early sexual dimorphism that is not attributable to the influx of sex hormones at puberty. This highlights the need to look at very early ontogeny for the origins of sexual dimorphism. We suggest that future work look at potential mediating effects of this early dimorphism on the later impact of puberty. The subtle shape differences we have detected, may also be applied to sexing fossilised crania. A common artefact in 3D images of faces of young children is that they often have their mouths open to varying degrees, introducing variability in the data unrelated to anatomy. We describe two PLSR-based methods of correcting this. These methods may facilitate surgical planning and assessment of young children based on 3D images.

Horn length is not correlated with calling efforts in the horn-headed cricketLoxoblemmus doenitzi(Orthoptera: Gryllidae)

Field cricket species are ideal model organisms for the study of sexual selection because cricket calling songs, used to attract mating partners, are pronouncedly sexually dimorphic. However, few studies have focused on other sexually dimorphic traits of field crickets. The horn-headed cricket, Loxoblemmus doenitzi, exhibits exaggerated sexual dimorphism in head shape: males have flat heads with triangular horns, while females lack horns. This study examines the relationship between horn length, male calling efforts and diet quality. Horn length was not found to be significantly correlated with calling efforts. When diet was manipulated for late-stage nymphs, calling efforts in the group with poor-quality diet treatment was significantly lower than that of crickets in the group with high-quality diet treatment. However, horn length was not affected by diet quality. The implication of these results in the context of the evolution of multiple signals and sexual dimorphism is discussed.

Character displacement under influence of Bergmann's rule in Cerdocyon thous (Mammalia: Canidae)

In South America, the crab-eating fox Cerdocyon thous occurs in sympatry to the ecologically similar, and phylogenetically close Lycalopex vetulus to the North, and Lycalopex gymnocercus to the South of its range. We studied character displacement in Cerdocyon under the effect of Bergmann's rule and the presence (or absence either) of Lycalopex within the crab-eating fox range. We performed skull shape analysis on 191 C. thous specimens and divided them in three distinct groups, depending on whether Cerdocyon occurs in sympatry or in allopatry to Lycalopex species. We tested for differences in size and shape between Cerdocyon groups and regressed both skull size and sexual size dimorphism against latitude and temperature, while controlling for spatial autocorrelation in the phenotypes. Southern Cerdocyon specimens present enlarged temporalis muscle and slender carnassial, both suggestive of a shift towards increased carnivory. Such a niche shift is interpreted as a mean to reduce competition to the larger Lycalopex species, which is still smaller than Cerdocyon . Consistently with the above, the degree of sexual shape and size dimorphism in Cerdocyon increases southward. We found a complex but coherent pattern of size and shape differentiation in Cerdocyon groups, which is consistent with the effects of both competition and Bergmann's rule. Cerdocyon reduces competition to Lycalopex by growing larger in the North. To the South, Cerdocyon is still larger, in keeping with Bergmann's rule, but strongly differs in skull shape from both its Lycalopex competitor and from any other Cerdocyon . Since the Southern Lycalopex species is much more similar in size to Cerdocyon than its Northern congeneric, this suggests that shape differences serve the goal of reducing competition between Cerdocyon and Lycalopex to the South, as size differences do to the North. The absence of the hypercarnivorous canid Speothos venaticus from the southern range of Cerdocyon may have allowed such a pattern to take place.

Facial Masculinity and Beardedness Determine Men’s Explicit, but Not Their Implicit, Responses to Male Dominance

Sexual dimorphism in facial shape and beardedness are salient human secondary sexual traits that enhance perceptions of men’s social dominance. The majority of this evidence, however, comes from studies measuring explicit ratings. To our knowledge, few studies have tested whether facial masculinity and beardedness are implicitly associated with dominance. In the current study, we use a within-subjects design to test whether facial masculinity and beardedness drive implicit reactions and overt ratings of male dominance. Participants viewed stimuli depicting the same men when clean-shaven, with heavy stubble, and fully bearded that were morphed to be either more masculine or less masculine using computer graphic software. Participants completed an affective priming word categorisation task as well as explicit ratings of social dominance. No facilitation effects were observed for masculinised or bearded faces on implicit judgements relating to dominance. In contrast, results revealed that masculinized versions of clean-shaven, stubbled and fully bearded faces received higher explicit dominance ratings than feminized versions. However, the effects of facial masculinity were largest within clean-shaven stimuli and decreased as faces became more hirsute, suggesting that facial masculinity had diminishing returns on dominance ratings. Our results support a role for masculine facial shape and beardedness in explicit, but not implicit, judgments of dominance among men.

Ecological and evolutionary influences on body size and shape in the Galápagos marine iguana (Amblyrhynchus cristatus).

Oceanic islands are often inhabited by endemic species that have undergone substantial morphological evolutionary change due to processes of multiple colonizations from various source populations, dispersal, and local adaptation. Galápagos marine iguanas are an example of an island endemic exhibiting high morphological diversity, including substantial body size variation among populations and sexes, but the causes and magnitude of this variation are not well understood. We obtained morphological measurements from marine iguanas throughout their distribution range. These data were combined with genetic and local environmental data from each population to investigate the effects of evolutionary history and environmental conditions on body size and shape variation and sexual dimorphism. Our results indicate that body size and shape are highly variable among populations. Sea surface temperature and island perimeter, but not evolutionary history as depicted by phylogeographic patterns in this species, explain variation in body size among populations. Conversely, evolutionary history, but not environmental parameters or island size, was found to influence variation in body shape among populations. Finally, in all populations except one, we found strong sexual dimorphism in body size and shape in which males are larger, with higher heads than females, while females have longer heads than males. Differences among populations suggest that plasticity and/or genetic adaptation may shape body size and shape variation in marine iguanas. This study will help target future investigations to address the contribution of plasticity versus genetic adaptation on size and shape variation in marine iguanas.

The sex-limited effects of mutations in the EGFR and TGF-β signaling pathways on shape and size sexual dimorphism and allometry in the Drosophila wing.

Much of the morphological diversity in nature-including among sexes within a species-is a direct consequence of variation in size and shape. However, disentangling variation in sexual dimorphism for both shape (SShD), size (SSD), and their relationship with one another remains complex. Understanding how genetic variation influences both size and shape together, and how this in turn influences SSD and SShD, is challenging. In this study, we utilize Drosophila wing size and shape as a model system to investigate how mutations influence size and shape as modulated by sex. Previous work has demonstrated that mutations in epidermal growth factor receptor (EGFR) and transforming growth factor-β (TGF-β) signaling components can influence both wing size and shape. In this study, we re-analyze this data to specifically address how they impact the relationship between size and shape in a sex-specific manner, in turn altering the pattern of sexual dimorphism. While most mutations influence shape overall, only a subset have a genotypic specific effect that influences SShD. Furthermore, while we observe sex-specific patterns of allometric shape variation, the effects of most mutations on allometry tend to be small. We discuss this within the context of using mutational analysis to understand sexual size and shape dimorphism.

Effects of selection for high voluntary wheel running on sexual dimorphism in the sacrum of Mus musculus

Comparative studies have shown that pelvic girdle (os coxae and sacrum) morphology may be influenced by sex and/or locomotion and that a possible evolutionary trade‐off exists between reproductive constraints and locomotor activity. Previous unpublished work explored how sexual dimorphism in the os coxae responds to locomotor activity in Mus musculus through analyses of mice from an artificial selection experiment that bred mice for high voluntary wheel running. Three of the eight lines from this experiment were sampled, representing control (C), selected (HRNORMAL), and selected mini‐muscle (HRMINI) groups, with the mini‐muscle individuals possessing a Mendelian recessive mutation that causes a 50% decrease in skeletal muscle mass. Based on prior comparative work on the pelvis and the specific results from the os coxae of these mice showing differing patterns of dimorphism in shape, density and bone volume, we hypothesized that a similar pattern would be present in the sacrum. Using 122 specimens from the aforementioned experiment, we obtained shape and size (mass and centroid size) metrics of the sacra and compiled these with previously recorded body masses and lengths. ANOVAs of size metrics showed significant differences in body length, mass and sacral centroid size between the lines and sexes. On all metrics, both HR lines were smaller than the C line and the HRMINI line was smaller than the HRNORMAL line. In addition, females were smaller than males in all metrics. Finally, there was no significant sex‐by‐line interaction for either body size metrics or centroid size, indicating no differential sexual dimorphism patterns in these variables between lines.Results of MANOVAs showed that sex and line, but not body mass, had a significant effect on sacral shape, and there was no significant sex‐by‐line interaction. Further, we calculated a proxy measurement of sacral density using a ratio of sacral mass to sacral centroid size. ANOVAs showed a significant effect of sex, line, and the sex‐by‐line interaction, with females showing a greater mean bone density than males (a result opposite that found in a similar proxy metric in the os coxae). Overall, these results support the hypothesis that sacral morphology is influenced by sex, selection for high locomotor activity, and the presence of the mini‐muscle mutation in a complex manner, which affects specific skeletal elements in different ways.Support or Funding InformationMurdock Charitable Trust

Variation in sexual dimorphism of mouse os coxae shape, volume, and bone mineral density in response to selection for high voluntary wheel running

Pelvic (os coxae and sacrum) dimorphism is common in mammals. Studies (primarily on human and non‐human primates) of pelvic dimorphism suggest that dimorphism results from an evolutionary trade‐off between reproduction and locomotion. Previous work has shown that pelvic morphology varies in relation to locomotor modes among species and that, along with other girdle elements such as the scapula, high levels of voluntary activity cause training responses in mice. We analyzed three lines of laboratory mice, from an ongoing selection experiment, two of which have been bred for 59 generations for high levels of voluntary wheel running (HR) and one that is a non‐selected control (C) line. One selected line (HRMINI) is fixed for a “mighty mini‐muscle” mutation that reduces skeletal muscle mass by up to 50%. The other selected line (HRNORMAL) does not possess this mutation.We used two dimensional geometric morphometric techniques to produce quantitative descriptors of os coxae shape (Relative Warp scores) and geometric (centroid) size. In addition, we used X‐ray micro computed tomography (μCT) to measure elements of bone microstructure (bone mineral density (BMD) and bone volume (BV)).ANOVAs showed significant differences in body size (length and mass) among the lines and between the sexes. Both HR lines were smaller than the C line, and the HRMINI line was smaller than the HRNORMAL line. However, although females were smaller than males in all three lines, os coxae centroid size was greater in females. Finally, for all size metrics, no significant sex‐by‐line interaction was present, indicating no differential sexual dimorphism among lines.Analyses of μCT data, with body size as a covariate, showed significant differences in BMD and BV of the os coxae among lines and between sexes. Females had higher BMD and BV than males, and HR lines had lower values than the C line (the HRMINI line showed the largest decrease). Additionally, a significant sex‐by‐line interaction in the analysis of BMD suggests a stronger effect of selection on males than on females.Finally, MANCOVAs, with body size as a covariate, revealed significant shape differences among lines and between sexes. A significant sex‐by‐line interaction was also found, indicating different patterns of shape difference between males and females, depending on line.These results indicate that although there is no effect of selective breeding or the mini‐muscle mutation on patterns of sexual dimorphism in body and os coxae size, this is not the case for patterns of sexual dimorphism in other components of coxal morphology. Male and female differences in os coxae shape and bone microstructure have different trajectories and magnitudes depending on line, suggesting that in some cases, males and females respond to selection and the mini‐muscle mutation in different ways.Support or Funding InformationMJ Murdock Charitable Trust to HS, KB &amp; CHU.C. Riverside Chancellor's Postdoctoral Fellowship to HSNSF IOS‐1121273 to TG

Sexual selection on skeletal shape in Carnivora.

Lifetime reproductive success of males is often dependent upon the ability to physically compete for mates. However, species variation in social structure leads to differences in the relative importance of intraspecific aggression. Here, we present a large comparative dataset on sexual dimorphism in skeletal shape in Carnivora to test the hypotheses that carnivorans exhibit sexual dimorphism in skeletal anatomy that is reflective of greater specialization for physical aggression in males relative to females and that this dimorphism is associated with the intensity of sexual selection. We tested these hypotheses using a set of functional indices predicted to improve aggressive performance. Our results indicate that skeletal shape dimorphism is widespread within our sample. Functional traits thought to enhance aggressive performance are more pronounced in males. Phylogenetic model selection suggests that the evolution of this dimorphism is driven by sexual selection, with the best-fitting model indicating greater dimorphism in polygynous versus nonpolygynous species. Skeletal shape dimorphism is correlated with body size dimorphism, a common indicator of the intensity of male-male competition, but not with mean body size. These results represent the first evidence of sexual dimorphism in the primary locomotor system of a large sample of mammals.

Sexual dimorphism in the shell of a nassariid gastropod. A 3D geometric morphometrics approach

Among gastropods, dimorphism is reported in shell size, radular characteristic, and to a lesser extent in shell shape. The relationship of dimorphic characters of the shell with spawning is scarcely studied in literature. Buccinanops globulosus is an interesting model to study sexual dimorphism in shell shape, because the adults attach their egg capsules to the females’ own shells (callus zone). Our hypothesis is that the shell dimorphism is evidenced in the form (size and shape) of callus zones of the females' shells, compared with the males'. In order to test this hypothesis we use a 3D geometric morphometrics (GM) method with several advantages over 2D GM. The relationship between callus shape and size was allometric. During growth, the main callus shape changes are related to the mean size increment, which is more evident in larger females. These callus zones are characteristically slender in males and small females, and more inflated in large females. Our analyses revealed that female shells are different from male ones and those differences are significant on the callus zone where the egg capsules are attached by the female. This finding suggests a relationship of the shell form with spawning. Our findings are not only relevant in terms of the shell dimorphism of the particular spawning substrate area (callus zones) and its reproductive implications, but also provide insights into the evaluation of shell shape variation on areas without type I or II anatomical landmarks in 3D GM.