Sexual Dimorphism In Body Size Research Articles

Male-inflicted wounds have opposite effects on hair cortisol for captive male and female rhesus macaques (Macaca mulatta) following new group formation.

Sexual dimorphism in body size, aggression, and dispersal patterns may affect the degree to which males and females perceive aggression from either sex as stressful. Whereas male macaques typically disperse to new groups at maturity, thus encountering many unfamiliar individuals of both sexes, females are philopatric, usually only encountering unfamiliar males who transfer into their natal groups. In rare circumstances, however, group fusions can expose both males and females to many novel individuals, which often increases aggression. Here, we use a captive new group formation of rhesus macaques (Macaca mulatta) as a model of social instability during fusions and examine differences in male and female chronic stress responses to male-pattern and female-pattern trauma (i.e., trauma inflicted by males or by females, respectively). We found that male- but not female-pattern traumas predicted hair cortisol concentrations during the first 9months after new group formation, but in opposite ways for males and females. A greater number of male-pattern traumas was linked to elevated hair cortisol concentrations in females but slightly lower hair cortisol concentrations in males. We suggest that the apparent importance of male-pattern trauma, but not female-pattern-trauma, in predicting higher hair cortisol concentrations in females can be attributed to the more acutely intense but less persistent nature of male aggression toward females.

Examining the relationship between sexual dimorphism in skin anatomy and body size in the white-lipped treefrog, Litoria infrafrenata (Anura: Hylidae).

Amphibians transport water, oxygen, carbon dioxide and various ions (e.g. sodium and potassium) across their skin. This cutaneous permeability is thought to affect their ability to respond to environmental change and to play a role in global population declines. Sexual dimorphism of skin anatomy has been accepted in some species, but rejected in others. The species in which such dimorphism has been detected have all been sexually dimorphic in body size, with males that are smaller and have thinner skin. It is unclear whether this difference in skin thickness manifests a functional difference or if it is related to body size alone. Skin thickness (epidermis, spongy dermis, compact dermis and total thickness) was examined in males and females of the white-lipped treefrog (Litoria infrafrenata). Although the skin of males is absolutely thinner than that of females, this difference is explained by body size differences between the sexes. Overall, we conclude that skin thickness in male and female L. infrafrenata correlates with body size dimorphism and suggest that future studies on amphibian skin anatomy include measures of body size, test the ecological significance of sexually dimorphic skin anatomy and better document the prevalence of sexually dimorphic amphibian skin anatomy.

Effects of the physical and social environment on flight response and habitat use in a solitary ungulate, the Japanese serow (Capricornis crispus)

Observations of the flight response of ungulates are commonly used to test behavioral responses to predation risk. In gregarious ungulates with sexual body-size dimorphism such responses are likely to be stronger in situations where individuals have perceptions of less security as well as among more-sensitive individuals, such as female groups or female groups with offspring which are understood to use safety habitats more often than males do. However, little is known about these behaviors in solitary ungulates with little sexual dimorphism. Therefore, we examined the flight response to human presence and the habitat use of Japanese serow (Capricornis crispus), a solitary ungulate with little sexual dimorphism, in relation to its physical and social environments, based on direct observations conducted over approximately four years. Based on a total of 335 sightings, serows took flight less often when in steep terrain, in closed habitat, or in low-visibility seasons, and they selectively used steep–closed habitat. These findings suggest that steep slopes and low-visibility conditions provide the species with greater security, and that serows select safer habitats to decrease predation risk. There were no significant differences in the flight responses and habitat use of solitary males and solitary females; the absence of differences is likely related to the serow’s habit of monogamy and its underdeveloped sexual dimorphism. Females with kids more frequently fled than other group types; this difference is thought to be linked to females’ priority to secure the survival of their offspring. This result shows the key role of offspring presence in affecting flight response in the serow. Conversely, there were no differences in habitat use between females with kids and other group types; here, the absence of such differences may be associated with intra-sexual territoriality of the serow, since all types of territory holders (including females with kids) need to continuously use the entire home range to maintain a territory.

Stat5b Regulates Sexually Dimorphic Gene Expression in Zebrafish Liver.

Sexual size dimorphism is an interesting phenomenon occurred in many fish species. Wildtype zebrafish exhibits a significant sexual dimorphism in body size at the adult stage. Previous studies indicated that sexual size dimorphism was eliminated in stat5b-mutated zebrafish. Herein, the comparative transcriptome analysis was conducted to observe the genes and pathways involved in sexual size dimorphism. The number of male-biased and female-biased genes was much less in the liver of stat5b mutant zebrafish than in wildtype. Gene ontology (GO) enrichment and Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis indicated that multiple pathways related to metabolism were affected upon loss of stat5b function. qRT-PCR results also validated that sexually dimorphic expression of a set of genes was lost when stat5b was mutated. Furthermore, the weighted correlation network analysis (WGCNA) detected many candidate genes related to the growth traits and stat5b function, such as greb1, lepr, and igf2b. Our data suggest that stat5b should regulate the sexually dimorphic gene expression in zebrafish liver and add in understanding of the molecular mechanisms underlying sexual size dimorphism in fish species.

Reproductive strategies of a population of a freshwater amphipod (Crustacea, Amhipoda, Hyalellidae) from southern Brazil

Abstract: The aim of this study was to characterize the reproductive strategies of a population of Hyalella bonariensis from southern Brazil. Pairing success, reproductive period of males and females, fecundity, and body size at the onset of reproduction were evaluated. Animals were sampled four times (August 2012, October 2012, January 2013, and April 2013) with the 250 µm-mesh dip net during 20 minutes by only one person. In the field, precopulatory pairs and ovigerous females were individualized. In the laboratory, cephalothorax length (CL) were measured and eggs and juveniles were removed from the females' marsupium and counted. The mean CL of paired males and females was significantly higher than that of non-paired males and females. A sexual dimorphism in body size was observed in the population - both paired and non-paired males were larger than females. Probably larger males have a higher probability of losing females during precopulatory behavior. A significant correlation was observed between the size of paired males and females - larger males often paired with larger females and smaller males paired with smaller females (r = 0.81). The pairing success of males increased with body size and we can assume that males from all size classes are able to find mates. The pairing success of females was independent of body size - paired and non-paired females had similar mean CL. The reproductive success increased with body size in males and females, and was more evident in males. Females from the largest size classes had null reproductive success. The idea that larger females can produce more eggs but might have a lower probability of finding a mate than smaller females was corroborated by our results. Therefore, smaller females have higher pairing success because they are capable of mating with a higher percentage of males. The estimated mean fecundity of H. bonariensis was 17.4 (± 3.89) eggs/juveniles. Our results are similar to those of other species of Hyalella from Brazil.

Transcriptomics analysis revealing candidate networks and genes for the body size sexual dimorphism of Chinese tongue sole (Cynoglossus semilaevis).

The Chinese tongue sole (Cynoglossus semilaevis) is a typical female heterogamete species that exhibits female-biased sexual size dimorphism, which has severely hindered the sustainable development of the species in aquaculture. In the present study, four important somatotropic and reproductive tissues including brain, pituitary, liver, and gonad from 15 females and 15 males were used for transcriptome analysis via RNA-seq. A mean of 37,533,991 high-quality clean reads was obtained from each library and 806, 1482, 818, and 14,695 differentially expressed genes in female and male were identified from the brain, pituitary, liver, and gonad, respectively (fold change ≥ 2 and q < 0.05). Enrichment analyses of GO terms and KEGG pathways showed that nucleic acid-binding transcription factor activity, G-protein-coupled receptor activity, MAPK signaling pathway, steroid biosynthesis, and neuroactive ligand-receptor interaction may be involved in the sexual growth differences. Furthermore, via weighted gene co-expression network analyses, two modules (yellowgreen and salmon4) were identified to be significantly positive-correlated with female-biased sexual size dimorphism. An illustrated network map drawn by these two modules enabled the identification of a series of hub genes, including nipped-B-like protein A (nipbla), transcriptional activator protein Pur-beta-like (purb), and BDNF/NT-3 growth factors receptor (ntrk2). Detailed functional investigation of these networks and hub genes will further improve our understanding of the underlying molecular mechanism of sexual size dimorphism in fish.

An allometric analysis of sexual dimorphism in Ctenomys australis: integrating classic morphometry and functional performance in vivo

The South American rodents of the genus Ctenomys (Rodentia, Hystricognathi), which use both forelimbs and incisors to dig, show strong, specialized morphological adaptations to living in the underground niche. In these rodents, the effectiveness of a bite − in this case the potential to inflict physical damage − mostly depends on the strength of the incisors (e.g. bending and torsion stresses) and the power of the masseteric muscle of the jaw. Ctenomys australis (the sand dune tuco-tuco) is a highly territorial subterranean rodent that builds large and exclusive burrow systems in coastal sand dunes found continuously along the Atlantic coast of the Buenos Aires province, Argentina. Incisors in this species are used both in agonistic encounters among congeners (i.e. reproductive or territorial intentions) as well as to dig and increase the size of their burrows daily (e.g. acquisition of plant material as food resources). We first characterized sexual dimorphism in cranial traits involved in aggressive interactions between males, analyzing ontogenetic trajectories of both sexes. We also analyzed some remarkable attributes of sexual dimorphism in subadult and adult individuals, the bending and torsion stresses and the bite performance in vivo, hypothesizing that males are able to apply comparatively stronger bite forces at their incisor tips than females, concordant with a broader mandible for the insertion of a powerful adductor musculature. Bite forces were measured in vivo in wild animals of both sexes using a strain gauge load cell force transducer. These individuals were also used to estimate the incisor area (CA), the 2nd moment of inertia of the incisors (I, or the bending strength to external forces), and the torsional strength of the incisor (J), all traits involved in the production of the force that can be withstood at the incisor tips. Ontogeny explained some sexual differences in the cranial traits of adults, expressed as (i) morphological changes related to body size variation, and (ii) morphological changes associated with differences in the slope of ontogenetic trajectories (regardless of body size variation). Recordings of in vivo bite forces were significantly higher in adult males than in females. These differences in bite forces were not associated with the sex itself, but the sexual dimorphism in body size. Although males did not show significantly higher allometric coefficients for I, J and CA than females, males still showed a strong sexual dimorphism in these traits due to body size variation. On the other hand, measurements of mandibular width – an estimator of the relative size of masseteric muscles – in vivo showed strong differences between sexes, suggesting higher force performance at the incisor tips for males. Overall, we observed that many attributes related to bite performance might have been molded by sexual selection, which implies differences in allometric coefficients from some morphological traits throughout ontogeny.

Sexual Dimorphism in Body Size and Shape of Beal's Eyed Turtle (Sacalia bealei)

Abstract We studied the sexual dimorphism in body size and shape of Beal's eyed turtle, Sacalia bealei, by measuring 15 morphological characteristics of 68 adult individuals (40 females, 28 males) collected from Fujian Province, China. Females were slightly larger than males in carapace length with a sexual dimorphism index of 0.09. This translated into greater absolute values of females for all the traits we measured except for tail length, preanal tail length, and analia to supracaudal junction length. Comparisons between the sexes of size-corrected morphological traits indicated that females exhibited a longer plastron and higher carapace relative to carapace length, thereby providing a larger internal volume. Females also exhibited relatively wider heads. In males, the plastron was smaller and more indented than in females and the openings between the plastron and the carapace were also more developed. Overall, females were larger in size and displayed a more voluminous shell than did males while male...

Features of the Biology of the False Zokor (Myospalax aspalax, Rodentia, Spalacidae) from Eastern Transbaikalia

The features, population characteristics of reproduction, nutrition, and lifestyle of an extremely poorly studied narrow-range species of underground rodents—the false zokor (Myospalax aspalax)—have been described on the basis of original field materials. The data were obtained within the Russian part of the species range in Zabaikal’skii krai. The false zokor is characterized by a pronounced sexual dimorphism in body size (males are larger) and a predominance of females in the population. Mating takes place in April; at other times of the year, zokors lead a solitary lifestyle. The size of the brood is small: 3.7 embryos per breeding female. Their preferred food is bulbs and rhizomes of Allium, Thermopsis, Phragmites, and Leymus. In Eastern Transbaikalia, they are active in winter.

Humans as a model species for sexual selection research.

Ever since Darwin, questions about humans have driven sexual selection research. While studies of other organisms are often justified as useful for improving understanding of humans, humans themselves can be useful models. Although humans present some drawbacks as model organisms (complicated societies, slow reproduction and strong ethical constraints on experimental options), humans nonetheless offer many advantages (being abundant, accessible and having detailed historical records for some populations). As an additional challenge, humans exhibit a rather puzzling combination of traits. Some traits (pair-bonding, biparental care and modest sexual dimorphism in body size) suggest selection for monogamous mating, while other traits (including sexual dimorphism in body composition and appearance) suggest selection for polygyny. Such puzzles have motivated research on other species, resulting in a rich set of comparative data that provides insights into humans and other species. Recent studies of visual trait dimorphism suggest that human appearance reflects adaptation for multi-level societies, rather than high levels of polygyny. In addition to biological traits, human cultural traits have undergone rapid evolution. Changes in subsistence strategies profoundly affect opportunities for sexual selection. The enormous variability of human behaviour and ecology provides abundant opportunities to test key hypotheses, and poses challenging puzzles for future research.

Sexual dimorphism and ontogenetic changes of Amazonian pit vipers (Bothrops atrox)

Sexual dimorphism of body size (SSD) is widespread in snakes and has been the subject of numerous studies, but few have examined sexual shape dimorphism (SShD). The present study explores sexual size and shape dimorphism in the Amazonian pit viper Bothrops atrox. We combine linear and geometric morphometrics to describe differences in body size and head shape between the sexes and how these differences are generated throughout ontogeny. Our study shows that B. atrox is sexually dimorphic, with females being larger than males, except for tail length. Females also have relatively larger heads, differing not only in size but also in shape. Our results reveal that both size and shape of the head vary significantly from neonates to adults. Head shape changes in B. atrox are associated with allometry and follow similar trends in both sexes: neonates have a relatively shorter and more robust head and shorter snout, while adults show a wider and flattened head. Although our results indicate that allometry is an important factor in determining sexual shape dimorphism, additional studies on diet and performance may be necessary to understand the ecological implications of such differences.

Explaining sex differences in lifespan in terms of optimal energy allocation in the baboon.

We provide a quantitative test of the hypothesis that sex role specialization may account for sex differences in lifespan in baboons if such specialization causes the dependency of fitness upon longevity, and consequently the optimal resolution to an energetic trade-off between somatic maintenance and other physiological functions, to differ between males and females. We present a model in which females provide all offspring care and males compete for access to reproductive females and in which the partitioning of available energy between the competing fitness-enhancing functions of growth, maintenance, and reproduction is modeled as a dynamic behavioral game, with the optimal decision for each individual depending upon his/her state and the behavior of other members of the population. Our model replicates the sexual dimorphism in body size and sex differences in longevity and reproductive scheduling seen in natural populations of baboons. We show that this outcome is generally robust to perturbations in model parameters, an important finding given that the same behavior is seen across multiple populations and species in the wild. This supports the idea that sex differences in longevity result from differences in the value of somatic maintenance relative to other fitness-enhancing functions in keeping with the disposable soma theory.

Comments on the current taxonomy of Brachycephalus (Anura: Brachycephalidae)

Since the first, and simplest, description of a species of the genus Brachycephalus Fitzinger 1826, by Spix (1824), an increasing number of informative traits has been investigated to facilitate species diagnoses, including those dealing with osteology (Izecksohn 1971), sexual dimorphism in body size (Alves et al. 2006), hyperossification of the skull and skeleton (Haddad et al. 2010) and advertisement call (Garey et al. 2012), plus traits from molecular data (Condez et al. 2016). However, the recent descriptions of nine species of Brachycephalus (see Pie &amp; Ribeiro 2015; Ribeiro et al. 2015; Bornschein et al. 2016) included inadequate diagnoses, which lacked indispensable information for any further comparisons among species. Herein, we intend to address the main flaws of these species descriptions and highlight the urgent need for a rigorous review of the genus Brachycephalus in order to assess the validity of these taxonomic proposals.

Reproductive biology of Philodryas patagoniensis (Snakes: Dipsadidae) in south Brazil: Female reproductive cycle

AbstractIn this study, we describe the female reproductive cycle of Philodryas patagoniensis in south Brazil, which was described through morpho‐anatomical and histological analyses. The peak of secondary vitellogenesis occurred during winter–spring (July–December), ovulation in spring (October–December), mating and fertilization in spring–summer (October–February), oviposition in spring–autumn (October–May) and births from late spring to autumn (December–July). The diameter of vitellogenic follicles/eggs was larger in winter–spring than in other seasons. The diameter of the shell glands was also larger in winter–spring. In spite of the clear reproductive peak, gonads only showed reduced activity in the autumn. Therefore, at the individual level, females have a discontinuous cyclical reproduction; in the populational level, the reproductive cycle is seasonal semisynchronous. We support the hypothesis that P. patagoniensis have the ability to produce multiple clutches with long‐term stored sperm. Sexual dimorphism in body size was evident, and females are significantly larger and heavier than males. Larger females were able to produce follicles and eggs in larger amount and size. The maternal body size was positively related to the reproductive effort and fecundity. To conclude, we deliberated about the proximal and distal causes that influence the reproductive traits and patterns of P. patagoniensis.

Morphological signatures of high-altitude adaptations in the Andean archaeological record: Distinguishing developmental plasticity and natural selection

High-altitude hypoxia is one of many environmental stressors affecting human populations in the highland Andes. Living highland Andeans show adaptive physiological responses to these conditions through both developmental plasticity and natural selection. Given the longevity of human settlement in this region, these same responses ought to have affected ancient Andeans. This paper tests whether developmental plasticity or natural selection best explains the morphological signatures of adaptations to high-altitude hypoxia in ancient highland Andeans. I compare four groups of skeletons: two groups from lowland regions and two groups from high elevations. Previous work shows that the two highland groups have small bodies and voluminous ribs compared with the lowland groups indicating morphological adaptations to high-altitude environments. This paper compares patterns of intrinsic variation and sexual dimorphism in body size, limb lengths, and rib morphology in highland and lowland groups to test if developmental plasticity or natural selection underlies these morphological differences. The four groups share similar patterns of sexual dimorphism and intrinsic variation in body size and limb lengths. The two highland samples show greater degrees of sexual dimorphism in rib morphology than the lowlanders. Patterns of intrinsic variation in rib morphology do not sort by altitude. Both natural selection and developmental plasticity in response to high-altitude hypoxia likely shaped skeletal morphology in ancient highland Andeans.

Sexual Dimorphism of Body Size Is Controlled by Dosage of the X-Chromosomal Gene Myc and by the Sex-Determining Gene tra in Drosophila.

Drosophila females are larger than males. In this article, we describe how X-chromosome dosage drives sexual dimorphism of body size through two means: first, through unbalanced expression of a key X-linked growth-regulating gene, and second, through female-specific activation of the sex-determination pathway. X-chromosome dosage determines phenotypic sex by regulating the genes of the sex-determining pathway. In the presence of two sets of X-chromosome signal elements (XSEs), Sex-lethal (Sxl) is activated in female (XX) but not male (XY) animals. Sxl activates transformer (tra), a gene that encodes a splicing factor essential for female-specific development. It has previously been shown that null mutations in the tra gene result in only a partial reduction of body size of XX animals, which shows that other factors must contribute to size determination. We tested whether X dosage directly affects animal size by analyzing males with duplications of X-chromosomal segments. Upon tiling across the X chromosome, we found four duplications that increase male size by >9%. Within these, we identified several genes that promote growth as a result of duplication. Only one of these, Myc, was found not to be dosage compensated. Together, our results indicate that both Myc dosage and tra expression play crucial roles in determining sex-specific size in Drosophila larvae and adult tissue. Since Myc also acts as an XSE that contributes to tra activation in early development, a double dose of Myc in females serves at least twice in development to promote sexual size dimorphism.

Comparative morphology and genetics of two populations of spiny lizards (genus Sceloporus) from Central Mexico

The spiny lizard Sceloporus minor exhibits substantial variation in a variety of life history traits, but the factors promoting this variation remain unclear. We analyzed within- and between-population variation in morphological traits in two populations (El Enzuelado and La Manzana, Hidalgo, Central Mexico), and estimated the genetic distance between populations on the basis of sequence variation of the mitochondrial genes encoding a fragment of the ND4 gene, all of tRNA-His and tRNA-Ser, and a fragment of tRNA-Leu. Consistent with earlier reports, males and females exhibited marked sexual dimorphism in body size and coloration. The genetic distance between the two populations was 0.024, slightly greater than the distance measured within each population (0.015 for La Manzana and 0.003 for El Enzuelado). Maximum likelihood analysis indicated that these populations were indeed conspecific, along with other studied populations of S. minor. The morphological differences and the previously described variation in reproductive traits contrast with the limited genetic variation between populations reported herein. This suggests that a combination of both phenotypic plasticity and genes of large effect may be contributing to variation in anatomical and physiological traits in Sceloporus minor.

Morphological variation among populations of Hemigrammus coeruleus (Characiformes: Characidae) in a Negro River tributary, Brazilian Amazon

ABSTRACT We explored patterns of phenotypic variation in Hemigrammus coeruleus from the Unini River basin, a blackwater river in the Brazilian Amazon. Geometric morphometrics was used to evaluate variation in body shape among populations from four tributaries (UN2-UN5). We found no evidence for sexual dimorphism in body size and shape. However, morphological differences among populations were detected as the analyses recovered significant groups corresponding to each sub-basin, with some overlap among them. The populations from UN2, UN3 and UN5 had more elongate bodies than fish from UN4. The most morphologically divergent population belonged to UN4, the tributary with the most divergent environmental conditions and the only one with seasonally-muddy waters. The morphological variation found among these populations is likely due to phenotypic plasticity or local adaptation, arising as a product of divergent ecological selection pressures among sub-basins. This work constitutes one of the first to employ a population-level geometric morphometric approach to assess phenotypic variation in Amazonian fishes. This method was able to distinguish subtle differences in body morphology, and its use with additional species can bring novel perspectives on the evaluation of general patterns of phenotypic differentiation in the Amazon.

New early Pleistocene hominin teeth from the Swartkrans Formation, South Africa

We describe 14 hominin teeth and tooth fragments excavated recently from Swartkrans Cave (South Africa). The fossils derive from Members 1 (Lower Bank) and 3, from the Member 2/3 interface and from two deposits not yet assigned to member (the “Talus Cone Deposit” and the “Underground North Excavation” [UNE]) of the Swartkrans Formation, and include the first hominin fossil from the UNE, the two smallest Paranthropus robustus deciduous maxillary second molars in the entire hominin fossil record, and one of the smallest P. robustus permanent maxillary second molars from Swartkrans. The small permanent molar is accompanied by another tooth from a different individual but from the same stratigraphic level of the Swartkrans Formation; this second tooth is among, if not, the largest P. robustus permanent maxillary first molars known from anywhere—lending credence to assertions that degrees of body size sexual dimorphism previously ascribed to this species may be underestimated. It is more equivocal whether this evidence also supports hypotheses proposing that P. robustus assemblages from Swartkrans (as well as those from other South African cave sites) formed through the taphonomically biasing actions of large carnivores.

Sexual Size Dimorphism and Assortative Mating in Elliot's LaughingthrushTrochalopteron elliotii

Many bird species express sexual dimorphism in body size, which is one of the most significant targets of natural and sexual selection, for it is tightly linked with fitness. During field studies in the breeding season of 2013 and 2014, we found significant differences in body morphometrics between sexes in a breeding population of Elliot's Laughingthrush Trochalopteron elliotii: males are larger than females in all body measurements. Positive assortative mating, based on culmen length, tarsus length and body mass, was found across breeding pairs. Male territory defence behaviour and assortative mating based on body size provide evidence that sexual selection may be responsible for sexual size dimorphism in this species.