Patterns Of Sexual Dimorphism Research Articles

Altitude and life-history shape the evolution of Heliconius wings.

Phenotypic divergence between closely related species has long interested biologists. Taxa that inhabit a range of environments and have diverse natural histories can help understand how selection drives phenotypic divergence. In butterflies, wing color patterns have been extensively studied but diversity in wing shape and size is less well understood. Here, we assess the relative importance of phylogenetic relatedness, natural history, and habitat on shaping wing morphology in a large dataset of over 3500 individuals, representing 13 Heliconius species from across the Neotropics. We find that both larval and adult behavioral ecology correlate with patterns of wing sexual dimorphism and adult size. Species with solitary larvae have larger adult males, in contrast to gregarious Heliconius species, and indeed most Lepidoptera, where females are larger. Species in the pupal‐mating clade are smaller than those in the adult‐mating clade. Interestingly, we find that high‐altitude species tend to have rounder wings and, in one of the two major Heliconius clades, are also bigger than their lowland relatives. Furthermore, within two widespread species, we find that high‐altitude populations also have rounder wings. Thus, we reveal novel adaptive wing morphological divergence among Heliconius species beyond that imposed by natural selection on aposematic wing coloration.

Three-Dimensional Morphological Variations of the Human Calcaneus Investigated Using Geometric Morphometrics.

The shape of the calcaneus determines the mechanical interaction of the foot with the ground during the heel-strike in human walking. Detailed knowledge of the pattern of sexual dimorphism of the human calcaneus could help to clarify the pathogenetic mechanism of foot and knee disorders, which are more prevalent in females. Therefore, the aim of this study was to characterize and visualize the three-dimensional shape variations of the calcaneus in relation to sex and age using geometric morphometrics. Computed tomography images of 56 feet without subtalar injuries or disorders were used in this study. Thirty-seven anatomical landmarks were identified on the bone model of the calcaneus to calculate principal components (PCs) of shape variations among specimens. The PC scores were compared between males and females, and their correlations with age were also analyzed. The female calcaneus was longer in length and shorter in height than that of males. The medial process of the calcaneal tuberosity in females was more inferiorly projected and the tuberosity was shifted more laterally. Also, the calcaneus was wider and the sustentaculum tali thickened with aging. Female structural features of the calcaneus alter the kinematics of the foot during walking and could be a structural factor in foot and knee disorders. This study contributes to a comprehensive understanding of shape variations in the human calcaneus. Clin. Anat., 33:751-758, 2020. © 2019 Wiley Periodicals, Inc.

Assessing Rensch’s rule in a newt: Roles of primary productivity and conspecific density in interpopulation variation of sexual size dimorphism

AbstractAimMajor efforts have been devoted to understanding the geographic pattern of sexual size dimorphism (SSD). Rensch's rule posits that SSD increases with body size in male‐biased SSD species and decreases with body size in female‐biased SSD species. This pattern, and its inverse, have been mainly explored at the interspecific level, whereas research at the intraspecific level has been largely neglected. Here, we test whether the allometric pattern of SSD in an urodele amphibian conforms to Rensch's rule and evaluate the relative role of four potential mechanisms: sexual selection, fecundity selection, density‐dependent resource availability and differential plasticity.LocationIberian Peninsula.TaxonLissotriton boscai (Amphibia: Caudata: Salamandridae).MethodsWe used original (field‐based) and published data on body size, courtship behaviour and fecundity parameters and a suite of climatic, ecological and genetic (mitochondrial and nuclear markers) predictors to assess these hypotheses.ResultsThe results showed that SSD increased with increasing female mean body size, supporting the inverse Rensch's rule pattern. Primary productivity‐related variables and female density were among the most relevant ecological predictors of SSD after accounting for genetic structure and capture date.Main conclusionsThis study reveals that the interplay between the density‐dependent resource availability hypothesis and the differential plasticity hypothesis explains the inverse Rensch's rule. We discuss how combining biogeographical and experimental approaches can provide alternative interpretations to the classical sexual and fecundity selection hypotheses on the interpopulation variation in SSD.

Secular trends in cranial chord variables: a study of changes in sexual dimorphism of the North Indian population during 1954–2011

Background: Sex estimation of fragmentary remains is a critical problem which is further aggravated by the changing pattern of sexual dimorphism due to temporal/secular changes. Previously cranial chord variables were examined only to deduce cranial abnormalities and hominin evolution. In forensic anthropological literature to date, no studies have examined the importance of cranial chord variables in sex determination and neither have secular changes been reported in those measurements to date.Aim: The present study aims to examine the sexual dimorphism and temporal changes in chord measurements in the Indian population and to provide updated sex discriminant formulae.Subjects and methods: A total of 483 (contemporary: n = 158; sub-recent: n = 325) adult crania (18–70 years) from two temporally distinct North Indian populations were included in the study. Seven chord variables were measured and data were subjected to discriminant function analysis using SPSS 16.00.Results: Analysis of the data using the t-test demonstrated significant sexual and population variations over time. Univariate discriminant analysis revealed the glabella-bregma chord as the best variable in both populations (78.5 and 74.5% accuracy in the contemporary and sub-recent populations, respectively). Using multivariate analysis classification accuracy reached 86.1% in the contemporary sample.Conclusion: It is concluded that Indian crania are going through secular changes as the contemporary population has larger chord dimensions than their predecessors and chord variables can be applied for sex estimation in the Indian population.

Convergent evolution of sexual dimorphism in species of the family Dolichopodidae (Diptera)

Abstract. Chursina MA. 2019. Convergent evolution of sexual dimorphism in species of the family Dolichopodidae (Diptera). Biodiversitas 20: 2480-2485. In this study, we investigated patterns of sexual dimorphism in four dolichopodid species namely Dolichopus acuticornis Wiedemann, 1817, D. longicornis Stannius, 1831, Rhaphium appendiculatum Zetterstedt, 1849, and R. caliginosum Meigen, 1824 that are exhibiting similar patterns of sexual dimorphism. Although they are distantly related, males of all these species exhibit similar sexual dimorphic characters in term of elongation of postpedicel. A comparison of variation made it possible to assumed that although sexual selection acts differently, all four species exhibited similar patterns of sexual dimorphism in wings and legs; females possessed relatively widened wing and elongated fore and hind femora than males. Cluster analysis for the morphometry data demonstrated that the differences between sexes significantly exceeds the differences between species. These results may reflect the presence of some conservative genetic structure of covariation among characters.

Sexual Dimorphism in Titi Monkeys' Digit (2D:4D) Ratio is Associated with Maternal Urinary Sex Hormones During Pregnancy.

The second-to-fourth digit (2D:4D) ratio is a sexually-dimorphic biomarker for prenatal sex hormone exposure. We investigated whether titi monkeys (Plecturocebus cupreus) exhibit sexually-dimorphic 2D:4D ratio, and whether variation in 2D:4D ratio correlates with maternal testosterone and estrogen levels during early pregnancy. Subjects were 61 adult titi monkeys (32 males, 29 females). For 26 subjects, maternal urine samples were collected approximately 15-20weeks before birth and assayed for testosterone and estrone conjugate (E1 C). Titi monkeys exhibited a human-like pattern of sexual dimorphism in right-hand 2D:4D ratio, with females exhibiting higher 2D:4D ratio than males (β=-0.29, p=0.023). For left-hand 2D:4D ratio, high levels of maternal E1 C predicted low offspring 2D:4D ratio (β=-0.48, p=0.009). For right-hand 2D:4D ratio, high levels of testosterone (β=-0.53, p=0.005) and testosterone-to-E1 C ratio (β=-0.41, p=0.028) predicted low offspring 2D:4D ratio. For 2D:4D ratio asymmetry (right-hand - left-hand), high levels of testosterone (β=-0.43, p=0.03) and testosterone-to-E1 C ratio (β=-0.53, p=0.003) predicted low (right-biased) asymmetry. This is the first report of sexually-dimorphic 2D:4D ratio in New World monkeys, and the results support a growing literature suggesting prenatal sex hormones may modulate offspring 2D:4D ratio.

Voluntary Exercise-Induced Activation of Thyroid Axis and Reduction of White Fat Depots Is Attenuated by Chronic Stress in a Sex Dimorphic Pattern in Adult Rats.

The activity of the hypothalamus-pituitary-thyroid (HPT) axis is inhibited by energy deficit, by acute or chronic stress, but activated by cold exposure or exercise. Because stress curtails acute cold induced activation of HPT, we evaluated the effect of chronic stress on HPT axis response to voluntary exercise, a persistent energy-demanding situation. Adult male and female Wistar rats were exposed to restraint stress, 30 min/day for 2 weeks, or to isolation (Iso) [post-natal day [PND] 30–63]. Exercise was performed (7 p.m.−7 a.m.) in a running wheel, sedentary controls stayed in individual cages (Sed); at 7 a.m. they were housed with their cage mate or individually (Iso); food intake by the exercised group was measured day and night to pair-fed Sed. At sacrifice, hormones, mRNA levels and tissue weights were quantified. Control or restrained adult rats had access to running wheel daily for 2 weeks. Compared to C, exercise decreased white adipose tissue (WAT) mass in females and males, increased hypothalamic paraventricular nucleus (PVN)-Trh expression in males proportionally to exercise performed, and increased TSH and T4 serum concentration in females. These changes were not detected in restrained groups. Starting at PND 63 control (2/cage) and isolated (1/cage) rats either exercised on 10 alternated nights or were sedentary. In control male animals, compared to Sed rats, exercise did not decrease WAT mass, nor changed HPT axis activity, but increased Pomc and deiodinase 2 (Dio2) expression in mediobasal hypothalamus (MBH), adrenergic receptor β3 and uncoupling protein-1 in brown adipose tissue. In control female animals, exercise decreased WAT mass, increased Pomc, Dio2, and Trhde expression in MBH, and TSH serum concentration. Iso females had lower TSH and T4 serum concentration, Dio2 and Trhde expression in MBH than controls. The stress response was higher in isolated males than females, but in males it did not alter the effects of exercise, in contrast to isolated females that had a blunted response to exercise compared to controls. In conclusion, chronic stress interferes with metabolic effects produced by exercise, such as loss of WAT mass, coincident with dampening of HPT activity.

Sexual dimorphism in the endemic Sardinian cave salamander (Atylodes genei)

Sexual dimorphism in the size and shape of the Sardinian cave salamander (Atylodes genei) was analysed using morphometric measurements. Males and females are roughly equal in body size (mean snout-vent length SVL: 53.8 and 53.4 mm, respectively) but differed in body shape. Relative to their SVL, males had comparatively larger heads, longer limbs and tails than females, which agrees with patterns of sexual dimorphism in other closely related species. This suggests the existence of phylogenetic conservatism in sexual differences in body shape. The lack of dimorphism in body size could be an ancestral trait in Atylodes genei.

Morphology and reproductive patterns of an assemblage of anurans from the Chihuahuan Desert Region, Mexico

Amphibian communities in arid and semi-arid environments are highly dependent on environmental factors for breeding activities. A large number of species can also show different reproductive patterns and variation between sexes. In this study, the morphology and reproductive patterns in an assemblage of seven anuran amphibians from the southeast region of the Chihuahuan Desert were evaluated. Data on snout–vent length, weight (body mass), and morphological structures (head width and head, femur and tibia length) were recorded. Three size classes (small, medium and large) were identified, as well as three patterns of sexual dimorphism: i) females larger than males, ii) females larger than males in some morphological variables, and iii) females similar to males in all measured variables. Variation in clutch size and laying mass (weight) among species was also described, as well as three reproductive patterns (short season, long season, and continuous reproduction). This study expands our knowledge about sexual dimorphism and reproductive patterns in anurans from arid environments. Further studies analyzing the animals’ use of resources are necessary to determine the arrangement and distribution of the resource space by amphibians in arid and semi-arid environments.

Sexual size dimorphism, allometry and fecundity in a lineage of South American viviparous lizards (Liolaemidae: Phymaturus)

In living organisms with sexual reproduction, the presence of sexual size dimorphism (SSD) is common. The main explanations for this phenomenon are based on sexual selection or the fecundity advantage hypothesis (natural selection). Here, we tested Rensch's rule in species of the viviparous lizard genus Phymaturus; additionally, we tested if there is a pattern of sexual size dimorphism or if it depends upon other morphological traits. We found no evidence for Rensch's rule in these lizards. After testing for multiple or single regime evolutionary models, we found that body size most likely evolved under multi-regime Ornstein-Uhlenbeck evolutionary model; the same was observed for abdomen width in females, a fecundity advantage hypothesis trait. For species with female biased SSD there is a positive relationship between snout-vent length and width of the belly, supporting the fecundity advantage hypothesis. Additionally, the relationship between brood size and brood mass with body size and body mass (respectively) were positive giving strength to the fecundity advantage hypothesis. Finally, our results show males did not show a clear pattern in relation to the sexual selection hypothesis, probably because sexual selection is a complex aspect that involves behavior and color. On the other hand, female body size and reproductive output are related to mean seasonal air temperature and its combination with mean annual air temperature in an evolutionary fashion framework, such as fecundity advantage hypothesis in these lizards.

Correction to: 'Sexual dimorphism in a top predator ( Notophthalmus viridescens) drives aquatic prey community assembly'.

You have accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Start D. and De Lisle S. 2019Correction to: ‘Sexual dimorphism in a top predator (Notophthalmus viridescens) drives aquatic prey community assembly’Proc. R. Soc. B.2862018289920182899http://doi.org/10.1098/rspb.2018.2899SectionYou have accessCorrectionsCorrection to: ‘Sexual dimorphism in a top predator (Notophthalmus viridescens) drives aquatic prey community assembly’ D. Start D. Start http://orcid.org/0000-0003-3036-9880 Google Scholar Find this author on PubMed Search for more papers by this author and S. De Lisle S. De Lisle http://orcid.org/0000-0001-9587-8665 Google Scholar Find this author on PubMed Search for more papers by this author D. Start D. Start http://orcid.org/0000-0003-3036-9880 Google Scholar Find this author on PubMed Search for more papers by this author and S. De Lisle S. De Lisle http://orcid.org/0000-0001-9587-8665 Google Scholar Find this author on PubMed Search for more papers by this author Published:06 February 2019https://doi.org/10.1098/rspb.2018.2899Proc. R. Soc. B285, 20181717. (Published 7 November 2018). (doi:10.1098/rspb.2018.1717)In our original article, we inadvertently overstated the novelty of our work. Specifically, we argued that our manuscript was the first to experimentally link patterns of sexual dimorphism to changes in prey community composition. In fact, Fryxell et al. [1] used a mesocosm approach similar to our own that linked sex-ratio manipulations of mosquito fish to trophic cascades in their aquatic communities. Fryxell et al. [1] was not, however, the first test of the idea that sexual dimorphism may influence the structure of ecological communities, as an old and rich body of correlative studies do so (e.g. [2–4]), a point we acknowledged in our original paper. Thus, our work adds to a growing number of recently published studies (including in plants; [5,6]) that together indicate that sex differences may have important consequences for ecological communities across a wide range of taxa and ecological settings.AcknowledgementsWe thank David Fryxell for making us aware of the interesting paper by Fryxell and colleagues.Footnotes© 2019 The Author(s)Published by the Royal Society. All rights reserved.

Patterns of sexual size dimorphism in stingless bees: Testing Rensch's rule and potential causes in highly eusocial bees (Hymenoptera: Apidae, Meliponini).

Eusocial insects offer a unique opportunity to analyze the evolution of body size differences between sexes in relation to social environment. The workers, being sterile females, are not subject to selection for reproductive function providing a natural control for parsing the effects of selection on reproductive function (i.e., sexual and fecundity selection) from other kinds of natural selection. Patterns of sexual size dimorphism (SSD) and testing of Rensch's rule controlling for phylogenetic effects were analyzed in the Meliponini or stingless bees. Theory predicts that queens may exhibit higher selection for fecundity in eusocial taxa, but contrary to this, we found mixed patterns of SSD in Meliponini. Non‐Melipona species generally have a female‐biased SSD, while all analyzed species of Melipona showed a male‐biased SSD, indicating that the direction and magnitude of the selective pressures do not operate in the same way for all members of this taxon. The phylogenetic regressions revealed that the rate of divergence has not differed between the two castes of females and the males, that is, stingless bees do not seem to follow Rensch's rule (a slope >1), adding this highly eusocial taxon to the various solitary insect taxa not conforming with it. Noteworthy, when Melipona was removed from the analysis, the phylogenetic regressions for the thorax width of males on queens had a slope significantly smaller than 1, suggesting that the evolutionary divergence has been larger in queens than males, and could be explained by stronger selection on female fecundity only in non‐Melipona species. Our results in the stingless bees question the classical explanation of female‐biased SSD via fecundity and provide a first evidence of a more complex determination of SSD in highly eusocial species. We suggest that in highly eusocial taxa, additional selection mechanisms, possibly related to individual and colonial interests, could influence the evolution of environmentally determined traits such as body size.

Complex variation of trabecular bone structure in the proximal humerus and femur of five modern human populations.

This project investigates trabecular bone structural variation in the proximal humerus and femur of hunter-gatherer, mixed-strategy agricultural, medieval, and human groups to address three questions: (a) What is the extent of trabecular bone structural variation in the humerus and femur between populations with different inferred activity levels? (b) How does variation in the proximal humerus relate to variation in the proximal femur? (c) Are trabecular bone microstructural variables sexually dimorphic? The proximal humerus and femur of 73 adults from five human groups with distinct subsistence strategies were scanned using a micro-computed tomography system. Centralized volumes of interest within the humeral and femoral heads were extracted and analyzed to quantify bone volume fraction, trabecular thickness, trabecular separation, connectivity density, degree of anisotropy, and bone surface density. In the humerus and femur, groups with the highest inferred activity levels have higher bone volume fraction and trabecular thickness, and lower bone surface density than those with lower inferred activity levels. However, the humeral pattern does not exactly mirror that of the femur, which demonstrates a steeper gradient of difference between subsistence groups. No significant differences were identified in trabecular separation. No consistent patterns of sexual dimorphism were present in the humerus or femur. Reduced skeletal robusticity of proximal humeral and femoral trabecular bone corresponds with reduced activity level inferred from subsistence strategy. However, human trabecular bone structural variation is complex and future work should explore how other factors (diet, climate, genetics, disease load, etc.), in addition to activity, influence bone structural variation.

Sexual dimorphism in a top predator (Notophthalmus viridescens) drives aquatic prey community assembly.

Intraspecific variation can have important consequences for the structure and function of ecological communities, and serves to link community ecology to evolutionary processes. Differences between the sexes are an overwhelmingly common form of intraspecific variation, but its community-level consequences have never been experimentally investigated. Here, we manipulate the sex ratio of a sexually dimorphic predacious newt in aquatic mesocosms, then track their impact on prey communities. Female and male newts preferentially forage in the benthic and pelagic zones, respectively, causing corresponding reductions in prey abundances in those habitats. Sex ratio differences also explained a large proportion (33%) of differences in the composition of entire pond communities. Ultimately, we demonstrate the impact of known patterns of sexual dimorphism in a predator on its prey, uncovering overlooked links between evolutionary adaptation and the structure of contemporary communities. Given the extreme prevalence of sexual dimorphism, we argue that the independent evolution of the sexes will often have important consequences for ecological communities.

Identification and dimorphic expression of sex-related genes during gonadal differentiation in sterlet Acipenser ruthenus, a primitive fish species

Sturgeons (Acipenseriformes) are ancient and endangered but valuable commercial aquaculture species. Due to an increasing interest in sturgeon aquaculture and breeding, especially for the production of caviar, a precise sex molecular marker is desired for the early sex identification of sturgeon. Because of the smallest size as well as the shortest sexual maturation period, the sterlet (Acipenser ruthenus) is considered to be an excellent model for studying of gonad differentiation in sturgeons. The present work investigated temporal expression of 13 genes, encoding regulatory factors, steroid receptors and transcription factors, during sex differentiation in sterlet from 6 months post-fertilization (mpf) to 15 mpf. Meanwhile, histological observation and determination of steroids levels of 11-ketotestosterone (11-KT) and 17β-estradiol (E2) in serum were performed to aid in sex identification. The gonad development of sterlet showed obvious asynchrony. Sex differentiation was first observed at 6 mpf, while some fish even retained undifferentiated gonads at 15 mpf. Expression of 13 genes revealed that only foxl2 and cyp19a1 maintained significant sexual dimorphic expression and had higher expression in female from the sex differentiation stage of 6 mpf. The male related genes amh and dmrt1 showed sexual dimorphic expression since spermatogonial proliferation stage, while hsd11b2 and gsdf had significantly higher expression in mid-spermatogenesis stage. The expression of dax1 and dkk1 showed a different pattern in sterlets in comparison to different mammals and other teleost: they increased with ovarian development and showed significantly difference since ovary perinucleolus stage, but maintained low expression at all stages of testes. The other five genes (sf-1, rspo, ar, era and erb) showed no sexual dimorphic expression pattern during sex differentiation. Serum 11-KT and E2 levels remained were low in all individuals with no sexual dimorphic expression pattern during sex differentiation. Taken together, our results suggest that mRNA levels of foxl2 and cyp19a1 could be used as molecular markers for sterlet sexing as early as the beginning of sex differentiation.

Sex estimation from cranial morphological traits: Use of the methods across American Indians, modern North Americans, and ancient Egyptians

This paper focuses on estimating sex by visual assessment of human cranial morphology. Practitioners in the field report variation in sexual dimorphism across populations. This study evaluates again the general hypothesis that populations vary in their pattern of sexual dimorphism. Specifically, the study tests the degree of expression of four cranial morphological traits (glabella, supraorbital margins, nuchal crest, and mastoid process) across three samples from different time periods and which vary in sociocultural transitions: 1) modern Americans of rural and urban areas spanning the last 186 years; 2) Dynastic Egyptians; and 3) Averbuch American Indians, spanning approximately 1255 CE to 1425 CE, from the southeastern United States. These three populations were specifically chosen for sampling as they represent distinct temporal and groups of varied ancestral composition. Crania from these samples were scored 1–5, with 1 being consistent with expected female morphology. The estimated sex was compared to either documented sex (when available) or discriminant functions derived from craniometrics. Freeman-Fisher-Halton tests examined sample differences, within sexes, affecting the visual assessment method. Post hoc tests were applied to pinpoint where the differences lie between the samples. The findings of this study support the hypothesis that the method does not estimate the sex of crania from all populations in the same manner, indicating that populations display differing patterns of sexual dimorphism. However, understanding these patterns and adjusting for how the method is applied will lead to reliable assessments. A relative frequency table and graphs of distributions are provided for practitioners who can use the information to make successful assessments of sex.

Sexual Size and Shape Dimorphism in Three Species of Parasitoid Wasps with Burrowing Females: Spalangia endius, Spalangia nigroaenea, and Spalangia nigra (Hymenoptera: Pteromalidae).

The parasitoid wasps Spalangia endius Walker, Spalangia nigroaenea Curtis, and Spalangia nigra Latrielle (Hymenoptera: Pteromalidae) develop on filth fly pupae. Females burrow through decaying organic matter and parasitize hosts; whereas, at least in S. endius, males tend to stay above ground searching for mates. Both sexes lack obvious digging morphology such as enlarged forelegs and are not known to exhibit physical aggression. Size data were obtained from specimens from Illinois field-collected hosts for all three species and from a Florida laboratory colony for S. endius. The degree of sexual size dimorphism varied with body part and species, but the direction of bias was consistent between the field and laboratory specimens of S. endius. Females had wider abdomens in S. nigroaenea and S. nigra (not measured in S. endius). In all three species, females had longer heads than males, both in absolute size and relative to width. The latter is referred to as narrowness. Forewings were significantly narrower in females compared with in males for both S. endius and S. nigroaenea. Thorax narrowness was either greater in males (S. endius) or was not significantly different between the sexes (S. nigroaenea and S. nigra). Patterns of sexual size dimorphism seem consistent with females’ need to store eggs and burrow. For all three species, there was overlap between males and females in all body parts measured. Thus, these size measurements will be unreliable to differentiate the sexes. Size ratios also overlapped.

The influences of genes, the environment, and social factors on the evolution of skin color diversity in India.

Skin color is a highly visible and variable trait across human populations. It is not yet clear how evolutionary forces interact to generate phenotypic diversity. Here, we sought to unravel through an integrative framework the role played by three factors-demography and migration, sexual selection, and natural selection-in driving skin color diversity in India. Skin reflectance data were collected from 10 diverse socio-cultural populations along the latitudinal expanse of India, including both sexes. We first looked at how skin color varies within and between these populations. Second, we compared patterns of sexual dimorphism in skin color. Third, we studied the influence of ultraviolet radiation on skin color throughout India. Finally, we attempted to disentangle the interactions between these factors in the context of available genetic data. We found that the relative importance of these forces varied between populations. Social factors and population structure have played a stronger role than natural selection in shaping skin color diversity across India. Phenotypic overprinting resulted from additional genetic mutations overriding the skin lightening effect of variants such as the SLC24A5 rs1426654-A allele in some populations, in the context of the variable influence of sexual selection. Furthermore, specific genotypes are not associated reliably with specific skin color phenotypes. This result has relevance for DNA forensics and ancient DNA research. India is a crucible of macro- and micro-evolutionary forces, and the complex interactions of physical and social forces are visible in the patterns of skin color seen today in the country.

Cortical bone adaptation and mineral mobilization in the subterranean mammal Bathyergus suillus (Rodentia: Bathyergidae): effects of age and sex.

The patterns of bone modeling and mineral mobilization (skeletal homeostasis) among mammals other than humans and laboratory rodents are still poorly known. In this study we assessed the pattern of bone formation and bone resorption in the femur of a wild population of Cape dune molerats, Bathyergus suillus (n = 41) (Bathyergidae), a solitary subterranean mammal with a marked extended longevity among rodents, and which also lives in a naturally deficient state of vitamin D. In order to determine ontogenetic and sex effects on histomorphometric parameters of transversal undecalcified bone sections, two-way ANOVA, linear mixed-effects model and regression statistical analyses were performed. During ontogeny, B. suillus increased their cross sectional area, cortical area and cortical thickness, and most importantly, they showed scarce endosteal bone resorption which resulted in a retained medullary cavity size during ontogeny. This resulted in a positively imbalanced bone modeling, where bone formation considerably surpasses bone loss by almost 100-fold in adulthood. This differs markedly from other terrestrial mammals with relatively thin cortical walls. Regarding bone loss and remodeling, three main processes involving intracortical resorption were observed: modeling-related bone loss in early postnatal growth; secondary osteon formation occurring in both sexes; and subendosteal secondary reconstruction observed only in females. The latter is accompanied by females having six-fold more relative bone loss than males, which is evidenced by the development of enlarged resorption cavities (RCs) distributed circumferentially around the medullary cavity. Males have smaller, more circular and randomly distributed RCs. In general, our data indicate no age-related decline in mineral content in B. suillus, and provides strong support for a pattern of sexual dimorphism in skeletal homeostasis, similar to that occurring in humans and other mammals, with females losing more bone throughout aging as compared to males due to reproductive factors. Interestingly as well, despite the high mechanical loads experienced during burrow construction, bone remodeling in B. suillus is kept at very low levels throughout their lifespan, and dense Haversian tissue never forms. This study represents the first comprehensive assessment of skeletal homeostasis in a subterranean mammal, and it enables a better understanding of the complex processes governing the acquisition and maintenance of bone properties in this species with extraordinary fossorial adaptations.

Sexual size dimorphism and assortative mating in the Plain Laughingthrush (Garrulax davidi concolor)

ABSTRACT In the breeding seasons of 2014 and 2015, we determined sexual size dimorphism and mating pattern in a breeding population of the Plain Laughingthrush (Garrulax davidi concolor) at Lianhuashan Nature Reserve in Gansu, China. We found that males were significantly larger and heavier than females, with a 104.8 body mass dimorphism index. Positive assortative mating based on culmen length was found across breeding pairs. Male-biased territory defense and mate-guarding suggest that sexual selection may be responsible for sexual size dimorphism in this bird. We also found significant positive correlations of body mass and body temperature between breeding pairs. We propose that this type of positive assortative mating could be a consequence of synchronous breeding by pairs in a similar physiological state.