Sexual Dimorphism In Body Shape Research Articles

Amphibian newts as experimental models for studying weight gain after castration.

Vertebrate animals often exhibit sexual dimorphism in body shape. In mammals, decreases in sex hormones caused by testicular castration can affect body shape and occasionally lead to pathologies such as obesity. Post-castration obesity can also be problematic for the health of companion animals, including non-mammals. In order to understand the mechanism of post-castration obesity in vertebrates other than mammals, experimental models are required. We examined whether the Iberian ribbed newt, which has recently become a popular experimental model for amphibian research, could serve as a model for analyzing changes in body shape after castration. In newts, new testes can be regenerated after removal of differentiated testes. We analyzed changes in body shape by removing the testes under conditions in which they could regenerate or conditions in which they could not regenerate. Removal of the testes reduced blood testosterone levels. The body weight and abdominal girth of the newts were increased compared with normal male newts. Transcriptome analysis of the liver showed that a set of genes related to lipid metabolism was continuously up-regulated in castrated newts. Our study suggests that changes in body shape after castration are common in vertebrates. Iberian ribbed newts are thus a suitable model for comparative studies of the long-term physiologic- and endocrine-level effects of castration.

New species and notes on Paravelia Breddin, 1898 (Heteroptera: Veliidae) from South America.

The new species Paravelia ameliae (Heteroptera: Veliidae) is described based on macropterous specimens from the Department of Putumayo, in the Amazonian region of Colombia. The new species can be distinguished from all congeners mainly by the bicolored pronotum (dark-brown on the anterior two-thirds and light-brown posteriorly); the absence of distinct pruinosity or silvery patches on the anterior lobe of the pronotum; the basal macula of the forewing small and roughly ovate; the grasping comb of the male fore tibia occupying more than half of its length; the male hind femur with a row of 15 spines on the basal two-thirds; and the male paramere notched basally on its dorsal surface. Furthermore, this species displays sexual dimorphism in body shape and in hind tibial length, with males having a slightly constricted mid-abdominal region and hind tibia distinctly longer than in females. Also, in order to describe external morphological characteristics not mentioned in previous studies, supplemental descriptions are provided for P. albotrimaculata (Kirkaldy, 1899), P. loutoni Polhemus, 2014, P. nieseri Moreira Barbosa, 2012, and P. rotundanotata (Hungerford, 1930). Illustrations and a distribution map of all species treated here are presented.

Multi-modal locomotor costs favor smaller males in a sexually dimorphic leaf-mimicking insect

BackgroundIn most arthropods, adult females are larger than males, and male competition is a race to quickly locate and mate with scattered females (scramble competition polygyny). Variation in body size among males may confer advantages that depend on context. Smaller males may be favored due to more efficient locomotion leading to higher mobility during mate searching. Alternatively, larger males may benefit from increased speed and higher survivorship. While the relationship between male body size and mobility has been investigated in several systems, how different aspects of male body morphology specifically affect their locomotor performance in different contexts is often unclear.ResultsUsing a combination of empirical measures of flight performance and modelling of body aerodynamics, we show that large body size impairs flight performance in male leaf insects (Phyllium philippinicum), a species where relatively small and skinny males fly through the canopy in search of large sedentary females. Smaller males were more agile in the air and ascended more rapidly during flight. Our models further predicted that variation in body shape would affect body lift and drag but suggested that flight costs may not explain the evolution of strong sexual dimorphism in body shape in this species. Finally, empirical measurements of substrate adhesion and subsequent modelling of landing impact forces suggested that smaller males had a lower risk of detaching from the substrates on which they walk and land.ConclusionsBy showing that male body size impairs their flight and substrate adhesion performance, we provide support to the hypothesis that smaller scrambling males benefit from an increased locomotor performance and shed light on the evolution of sexual dimorphism in scramble competition mating systems.

Sexual Dimorphism and Size-Related Changes in Body Shape in Tule Perch (Family: Embiotocidae), a Native California Live-Bearing Fish

The Tule Perch, Hysterocarpus traskii, is a viviparous and externally monomorphic, internally fertilizing fish. Despite appearing monomorphic, males and females are expected to differ in body shape because the different reproductive roles occupied by the sexes should influence patterns of selection and, ultimately, lead to differences in morphology. The objectives of this study were to determine if the Sacramento–San Joaquin subspecies of Tule Perch (H. t. traskii) exhibit (1) sexual dimorphism in body shape, (2) size-related changes in body shape, and (3) sexual size dimorphism. Geometric morphometric analyses indicated that H. t. traskii exhibited significant sexual dimorphism of body shape and identified the mid-body and caudal peduncle regions as the most effective discriminators between the sexes. Females were narrower through the caudal peduncle and mid-body and had anal-fin origins that were more posteriorly located than males. Additionally, H. t. traskii exhibited significant size-related changes in body shape. Larger fish were deeper bodied with blunter snouts and wider caudal peduncles. The eyes of larger fish were relatively smaller and located higher on the body than those of smaller fish. Hysterocarpus t. traskii did not exhibit differences between the sexes in standard length, but males were significantly heavier than females.

Glucosylsphingosine concentration in the blood of Gaucher patients reflects the severity of GBA mutations - data from a large global cohort

The Oryzias woworae species group, composed of O. asinua, O. wolasi, and O. woworae, is widely distributed in southeastern Sulawesi, an island in the Indo-Australian Archipelago. Deep-elongated body shape divergence is evident among these three species to the extent that it is used as a species-diagnostic character. These fishes inhabit a variety of habitats, ranging from upper streams to ponds, suggesting that the body shape divergence among the three species may reflect adaptation to local environments. First, our geometric morphometrics among eight local populations of this species group revealed that the three species cannot be separated by body shape and that riverine populations had more elongated bodies and longer caudal parts than lacustrine populations. Second, their phylogenetic relationships did not support the presence of three species; phylogenies using mitochondrial DNA and genomic data obtained from RNA-Seq revealed that the eight populations could not be sorted into three different clades representing three described species. Third, phylogenetic corrections of body shape variations and ancestral state reconstruction of body shapes demonstrated that body shape divergence between riverine and lacustrine populations persisted even if the phylogenies were considered and that body shape evolved rapidly irrespective of phylogeny. Sexual dimorphism in body shape was also evident, but the degree of dimorphism did not significantly differ between riverine and lacustrine populations after phylogenetic corrections, suggesting that sexual selection may not substantially contribute to geographical variations in body shape. Overall, these results indicate that the deep-elongated body shape divergence of the O. woworae species group evolved locally in response to habitat environments, such as water currents, and that a thorough taxonomic reexamination of the O. woworae species group may be necessary.

Phylogenomics reveals habitat-associated body shape divergence in Oryzias woworae species group (Teleostei: Adrianichthyidae)

The Oryzias woworae species group, composed of O. asinua, O. wolasi, and O. woworae, is widely distributed in southeastern Sulawesi, an island in the Indo-Australian Archipelago. Deep-elongated body shape divergence is evident among these three species to the extent that it is used as a species-diagnostic character. These fishes inhabit a variety of habitats, ranging from upper streams to ponds, suggesting that the body shape divergence among the three species may reflect adaptation to local environments. First, our geometric morphometrics among eight local populations of this species group revealed that the three species cannot be separated by body shape and that riverine populations had more elongated bodies and longer caudal parts than lacustrine populations. Second, their phylogenetic relationships did not support the presence of three species; phylogenies using mitochondrial DNA and genomic data obtained from RNA-Seq revealed that the eight populations could not be sorted into three different clades representing three described species. Third, phylogenetic corrections of body shape variations and ancestral state reconstruction of body shapes demonstrated that body shape divergence between riverine and lacustrine populations persisted even if the phylogenies were considered and that body shape evolved rapidly irrespective of phylogeny. Sexual dimorphism in body shape was also evident, but the degree of dimorphism did not significantly differ between riverine and lacustrine populations after phylogenetic corrections, suggesting that sexual selection may not substantially contribute to geographical variations in body shape. Overall, these results indicate that the deep-elongated body shape divergence of the O. woworae species group evolved locally in response to habitat environments, such as water currents, and that a thorough taxonomic reexamination of the O. woworae species group may be necessary.

An ontogenetically stable sexual character in a montane agamid, Salea horsfieldii Gray, 1845 (Reptilia: Agamidae) from Nilgiris, India

ABSTRACTMany agamid lizards are known to show sexual dimorphism in body shape, colour and ornamentation or a combination of these traits. Adult males of Salea horsfieldii have a discontinuous dorsal crest at the nuchal region, which is a sexually dimorphic character. However, there is no information about the age or size at which this dimorphic ornamentation develops and if the species exhibits sexual shape dimorphism (SShD). The authors studied the morphology of S. horsfieldii and found that its ornamentation is an ontogenetically stable character present in all males, including juveniles. Seven morphological characters were measured to determine if they exhibited SShD at adult and juvenile stages. Analysis of covariance was used to identify differences in morphology between sexes. The results show that only adults exhibited SShD, but not juveniles. Adult males had larger head and foot lengths in comparison to females of the same size. Larger head length in adult males is a sexual fitness trait, which increases bite-force during intra-sexual combats. Although the presence of sexually dimorphic ornamentation right from the juvenile stage is rare in agamids, S. horsfieldii is an exception . The role of sexually dimorphic ornamentation at juvenile stages remains unknown and requires further investigation.

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.

Sex and sex steroids: impact on the kinetics of fatty acids underlying body shape.

Adult humans have a remarkable sexual dimorphism in body shape. Men tend to store relatively more fat in the upper body whereas women store more fat in the lower body. We do not have a complete understanding of the mechanisms underlying these differences, but we know that people who preferentially store abdominal fat are at greater risk of metabolic disease. It is also known that the changes in sex steroid concentrations during puberty and again with advancing age are accompanied by changes in body fat distribution. The objective of this review is to describe what has been learned regarding the mechanisms underlying changes in regional body fat distribution that occur as a result of changes in sex hormones and to delineate effects of sex steroids in modulating body composition.

Variation in sexual dimorphism and assortative mating do not predict genetic divergence in the sexually dimorphic Goodeid fish Girardinichthys multiradiatus

Abstract Sexual dimorphism is often used as a proxy for the intensity of sexual selection in comparative studies of sexual selection and diversification. The Mexican Goodeinae are a group of livebearing freshwater fishes with large variation between species in sexual dimorphism in body shape. Previously we found an association between variation in morphological sexual dimorphism between species and the amount of gene flow within populations in the Goodeinae. Here we have examined if morphological differentiation within a single dimorphic species is related to assortative mating or gene flow between populations. In the Amarillo fish Girardinichthys multiradiatus studies have shown that exaggerated male fins are targets of female preferences. We find that populations of the species differ in the level of sexual dimorphism displayed due to faster evolution of differences in male than female morphology. However, this does not predict variation in assortative mating tests in the laboratory; in fact differences in male morphology are negatively correlated with assortative mating. Microsatellite markers reveal significant genetic differences between populations. However, gene flow is not predicted by either morphological differences or assortative mating. Rather, it demonstrates a pattern of isolation by distance with greater differentiation between watersheds. We discuss the caveats of predicting behavioural and genetic divergence from so-called proxies of sexual selection.

Women have Relatively Larger Brains than Men: A Comment on the Misuse of General Linear Models in the Study of Sexual Dimorphism

General linear models (GLM) have become such universal tools of statistical inference, that their applicability to a particular data set is rarely questioned. These models are designed to minimize residuals along the y-axis, while assuming that the predictor (x-axis) is free of statistical noise (ordinary least square regression, OLS). However, in practice, this assumption is often violated, which can lead to erroneous conclusions, particularly when two predictors are correlated with each other. This is best illustrated by two examples from the study of allometry, which have received great interest: (1) the question of whether men or women have relatively larger brains after accounting for body size differences, and (2) whether men indeed have shorter index fingers relative to ring fingers (digit ratio) than women. In depth analysis of these examples clearly shows that GLMs produce spurious sexual dimorphism in body shape where there is none (e.g. relative brain size). Likewise, they may fail to detect existing sexual dimorphisms in which the larger sex has the lower trait values (e.g. digit ratio) and, conversely, tend to exaggerate sexual dimorphism in which the larger sex has the relatively larger trait value (e.g. most sexually selected traits). These artifacts can be avoided with reduced major axis regression (RMA), which simultaneously minimizes residuals along both the x and the y-axis. Alternatively, in cases where isometry can be established there are no objections against and good reasons for the continued use of ratios as a simple means of correcting for size differences.

Sexual dimorphism in body shape of Antarctic krill ( Euphausia superba) and its influence on target strength

Sexual dimorphism in the body shape of Antarctic krill ( Euphausia superba) was investigated and its influence on target strength (TS) was clarified using a theoretical scattering model. The TS which is used to convert acoustic backscatter to krill density was also presented. Body shape data were obtained from 456 specimens (54 juveniles, 200 males, and 202 females) collected off Adélie Land using a Rectangular Midwater Trawl. The sexual dimorphism manifested as a swollen cephalothorax in female krill with body lengths exceeding 40 mm. The TS of female krill was higher than those of male krill at low frequencies, even when body lengths were the same. This is because of the Rayleigh scattering region and the transition region to the geometric scattering region. The influence of the sexual dimorphism on the TS was small at frequencies exceeding 70 kHz, which are close to the geometric scattering region. The regression curve derived from the predicted TS of 456 specimens was in reasonable agreement with the measured TS in other previous studies, and the regression curve could be applied to the acoustic surveys of Antarctic krill.

Does sympatry predict life history and morphological diversification in the Mexican livebearing fish Poeciliopsis baenschi?

Understanding why some species coexist and others do not remains one of the fundamental challenges of ecology. Although there is evidence to suggest that closely-related species are unlikely to occupy the same habitat because of competitive exclusion, there are many cases where closely-related species do co-occur. Research comparing sympatric and allopatric populations of co-occurring species provides a framework for understanding the role of phenotypic diversification in species coexistence. In the present study, we compare phenotypic divergence between sympatric and allopatric populations of the livebearing fish, Poeciliopsis baenschi. We focus on life-history traits and body shape, comprising two sets of integrated traits likely to diverge in response to varying selective pressures. Given that males and females can express different phenotypic traits, we also test for patterns of divergence among sexes by comparing size at maturity and sexual dimorphism in body shape between males and females in each population type. We take advantage of a natural experiment in western Mexico where, in some locations, P. baenschi co-occur with a closely-related species, Poeciliopsis turneri (sympatric populations) and, in other locations, they occur in isolation (allopatric populations). The results obtained in the present study show that sympatric populations of P. baenschi differed significantly in life-history traits and in body shape compared to their allopatric counterparts. Additionally, males and females showed different responses for size at maturity in sympatric conditions versus allopatric conditions. However, the amount of sexual dimorphism did not differ between sympatric and allopatric populations of P. baenschi. Hence, we conclude that not all traits show similar levels of phenotypic divergence in response to sympatric conditions. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 608–618.

Condition dependence of developmental stability in the sexually dimorphic flyTelostylinus angusticollis(Diptera: Neriidae)

Developmental stability is widely regarded as a condition-dependent trait, but its relation to genotype and environment, and extent of developmental integration, remain contentious. In Telostylinus angusticollis, the dorsocentral bristles exhibit striking variation in developmental stability, manifested as fluctuating asymmetry (FA) in bristle position ('positional FA') and failure to develop some bristles ('bristle loss'), in natural and laboratory populations. To determine whether this variation reflects condition, I tested for effects of genotype and environment (larval diet quality), and examined covariation with condition-dependent traits. Positional FA was not affected by genotype or environment. However, positional FA covaried negatively with secondary sexual trait expression in males, and with sexual dimorphism in body shape, but covaried positively with body size in females. Bristle loss reflected both genotype and larval diet. Flies reared on poor-quality diet exhibited a similar rate of bristle loss as wild flies. Both positional FA and bristle loss were greater in males. These results suggest that the relation between developmental stability and condition is complex and sex dependent.

Habitat-dependent reduction of sexual dimorphism in geometric body shape of Haida Gwaii threespine stickleback

We investigated the extent of sexual dimorphism in body shape in adult threespine stickleback (Gasterosteus aculeatus) from 39 lakes, eight streams, and five marine (two brackish, three full marine) localities on the Haida Gwaii archipelago off the mid-coast of British Columbia, as well as three lakes from southern British Columbia with benthic–limnetic species pairs. Based on digital images of 709 males and 593 females, body shape was quantified using discriminant function analysis on partial warp scores generated from twelve homologous landmarks. All populations showed males with higher positive values for canonical vector 1, which are characterized by larger heads, larger gape, posteriad dorsal spines, posteriad pelvis, longer anal fin, and deep posterior caudal depth relative to those in females. Geographical variability was present, with the highest dimorphism occurring in two of the marine habitats in addition to large lakes, whereas reduced dimorphism occurs in small shallow dystrophic ponds. We suggest that this reduction is the derived condition and is primarily due to loss of niche breadth and convergence in body shape between the sexes in pond habitats. Analyses of two experimental pond populations indicate that up to 15% of the shape dimorphism can be attributed to habitat-induced phenotypic plasticity. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 505–516.

Sexual size and shape evolution in European newts (Amphibia: Caudata: Salamandridae) on the Balkan Peninsula

We used a phylogenetic perspective in an examination of the direction and extent of sexual dimorphism in body size and body shape in European newts from the Balkan Peninsula (alpine newts, Mesotriton alpestris; crested newts, Triturus cristatus superspecies; smooth newts, Lissotriton vulgaris). We found a strong, female-biased sexual size dimorphism (SSD) in the analysed clades of alpine newt, whereas within crested newts we found a less stringent female-biased SSD in Triturus carnifex, Triturus macedonicus and Triturus karelinii, and no significant SSD in T. cristatus or Triturus dobrogicus. Among the smooth newts, we found male-biased SSD in Lissotriton vulgaris vularis and Lissotriton vulgaris greacus and no SSD in Lissotriton vulgaris meridionalis. Most of these newts also exhibit a significant sexual dimorphism in body shape, which varied more randomly than body size, regardless of SSD level. Female and male body size as well as the degree of SSD displayed statistically significant phylogenetic signal, while sexual dimorphism in body shape was phylogenetically independent. The relationship between independent contrast data for female size and male size indicated that SSD in European newts could be driven by a disproportionate increase in female size as increase in female size was not accompanied by a proportional increase in male size.

Ontogeny of sexual dimorphism and phenotypic integration in heritable morphs

In this study we investigated the developmental basis of adult phenotypes in a non-model organism, a polymorphic damselfly (Ischnura elegans) with three female colour morphs. This polymorphic species presents an ideal opportunity to study intraspecific variation in growth trajectories, morphological variation in size and shape during the course of ontogeny, and to relate these juvenile differences to the phenotypic differences of the discrete adult phenotypes; the two sexes and the three female morphs. We raised larvae of different families in individual enclosures in the laboratory, and traced morphological changes during the course of ontogeny. We used principal components analysis to examine the effects of Sex, Maternal morph, and Own morph on body size and body shape. We also investigated the larval fitness consequences of variation in size and shape by relating these factors to emergence success. Females grew faster than males and were larger as adults, and there was sexual dimorphism in body shape in both larval and adult stages. There were also significant effects of both maternal morph and own morph on growth rate and body shape in the larval stage. There were significant differences in body shape, but not body size, between the adult female morphs, indicating phenotypic integration between colour, melanin patterning, and body shape. Individuals that emerged successfully grew faster and had different body shape in the larval stage, indicating internal (non-ecological) selection on larval morphology. Overall, morphological differences between individuals at the larval stage carried over to the adult stage. Thus, selection in the larval stage can potentially result in correlated responses in adult phenotypes and vice versa.

The Evolution of Condition‐Dependent Sexual Dimorphism

Theory suggests that the net benefit of allocating resources to a sexual trait depends both on the strength of sexual selection on that trait and on individual condition. This predicts a tight coevolution between sexual dimorphism and condition dependence and suggests that these patterns of within-sex and between-sex variation may share a common genetic and developmental basis. Although condition-dependent expression of sexual traits is widely documented, the extent of covariation between condition dependence and sexual dimorphism remains poorly known. I investigated the effects of condition (larval diet quality) on multivariate sexual dimorphism in the fly Telostylinus angusticollis (Neriidae). Condition determined the direction of sexual size dimorphism and modulated sexual shape dimorphism by affecting allometric slopes and/or intercepts of sexually homologous traits in both sexes. Although the greatest responses to condition manipulation were observed in male sexual traits, both sexual and nonsexual traits exhibited substantial variation in the nature and magnitude of condition effects. Nonetheless, condition dependence and sexual dimorphism were remarkably congruent: variation in the strength of condition effects on male traits explained more than 90% of the variation in the magnitude of sexual dimorphism, whether quantified in terms of trait size or allometric slope. The genetic mechanisms that give rise to multivariate sexual dimorphism in body shape thus function in a strongly condition-dependent manner in this species, suggesting a common genetic basis for body shape variation within and between sexes.

Misinterpretation of character scaling: a tale of sexual dimorphism in body shape of common lizards

Male-biased sexual dimorphism in head, limbs, and tail scaled to snout–vent length has been reported in many lizard species. Consequently, various hypotheses have been proposed to explain observed body-shape dimorphism. According to the majority of them, the proportions of body components are adaptively related to sexual differences in ecology as well as in reproductive behaviour. Our study shows an alternative, much more parsimonious explanation in the common lizard (Lacerta vivipara). According to our analyses, the exaggeration of a single trait, specifically trunk length in females, may explain the whole pattern of sexual differences in body shape. The only consistent adaptive hypothesis, then, is that females with a larger abdominal cavity, and consequently a longer trunk, have a reproductive advantage. Size-adjusted heads, limbs, and tails traditionally reported to be larger in males than in females, features ascribed to numerous evolutionary mechanisms, thus appear to be just an artifact of inappropriate scaling to a sexually dimorphic trait (snout–vent length). As scaling to a single trait has been routinely used in many studies carried out in animals, we warn against quick interpretations based on such analyses and recommend more cautious inspection of allometries.

Sexual Dimorphism in Plains Minnow,Hybognathus placitus

Abstract Hybognathus placitus collected from several west Texas streams exhibit sexual dimorphism in body form, which is unusual in cyprinids. Seventeen morphological measurements, including standard length, were made on 62 specimens and analyzed for sexual dimorphism. Partial warp scores were used to describe sexual dimorphism in body shape. There was no difference in standard length between males and females (ANOVA, P = 0.9038, F1,60 = 0.0147), but there was a highly significant (MANOVA, F1,60 = 4.78, P < 0.001) sexual dimorphism in body shape. Overall, males have relatively longer first dorsal fin rays, larger heads, and caudal peduncles, whereas females are deeper bodied and have relatively longer trunks, from the pelvic fin insertion to the anal vent. Differences between male and female H. placitus in length of the first dorsal fin ray are readily apparent and can potentially be used for field identification.