Sexual Dimorphism In Primates Research Articles

Sexual dimorphism in postcranial skeletal shape suggests male-biased specialization for physical competition in anthropoid primates.

Sexual dimorphism often arises as a response to selection on traits that improve a male's ability to physically compete for access to mates. In primates, sexual dimorphism in body mass and canine size is more common in species with intense male-male competition. However, in addition to these traits, other musculoskeletal adaptations may improve male fighting performance. Postcranial traits that increase strength, agility, and maneuverability may also be under selection. To test the hypothesis that males, as compared to females, are more specialized for physical competition in their postcranial anatomy, we compared sex-specific skeletal shape using a set of functional indices predicted to improve fighting performance. Across species, we found significant sexual dimorphism in a subset of these indices, indicating the presence of skeletal shape sexual dimorphism in our sample of anthropoid primates. Mean skeletal shape sexual dimorphism was positively correlated with sexual dimorphism in body size, an indicator of the intensity of male-male competition, even when controlling for both body mass and phylogenetic relatedness. These results suggest that selection on male fighting ability has played a role in the evolution of postcranial sexual dimorphism in primates.

Development of Pelvic Sexual Dimorphism in Hylobatids: Testing the Obstetric Constraints Hypothesis.

Pelvic sexual dimorphism in primates is typically seen as the result of female-specific adaptations to obstetric constraints, which arise from the tight fit between the neonate head and the maternal pelvis. However, it remains debated to which extent pelvic dimorphism is a correlate of obstetric constraints, of body size dimorphism, and/or of other factors. Also, little is known on how pelvic dimorphism develops. Here we use methods of biomedical imaging and geometric morphometrics to address these questions in two hylobatid species, Hylobates lar and Symphalangus syndactylus. These species differ markedly in body size, but within each species, there is only little body size dimorphism. Results show that the neonates of H. lar are large compared to the maternal pelvis, resulting in high cephalopelvic proportions and substantial obstetric constraints. Pelvic sexual dimorphism is moderate but significant: During puberty, females develop a more capacious pelvic inlet than males, while overall pelvic size is similar in both sexes. S. syndactylus has substantially larger pelves than H. lar, but neonates are similar in size to those of H. lar. Cephalopelvic proportions are thus low, and there are no obstetric constraints. Pelvic sexual dimorphism is absent. Overall, these data indicate that pelvic sexual dimorphism in hylobatids reflects obstetric constraints. Anat Rec, 300:859-869, 2017. © 2017 Wiley Periodicals, Inc.

Estrogen regulation of microcephaly genes and evolution of brain sexual dimorphism in primates.

BackgroundSexual dimorphism in brain size is common among primates, including humans, apes and some Old World monkeys. In these species, the brain size of males is generally larger than that of females. Curiously, this dimorphism has persisted over the course of primate evolution and human origin, but there is no explanation for the underlying genetic controls that have maintained this disparity in brain size.ResultsIn the present study, we tested the effect of the female hormone (estradiol) on seven genes known to be related to brain size in both humans and nonhuman primates, and we identified half estrogen responsive elements (half EREs) in the promoter regions of four genes (MCPH1, ASPM, CDK5RAP2 and WDR62). Likewise, at sequence level, it appears that these half EREs are generally conserved across primates. Later testing via a reporter gene assay and cell-based endogenous expression measurement revealed that estradiol could significantly suppress the expression of the four affected genes involved in brain size. More intriguingly, when the half EREs were deleted from the promoters, the suppression effect disappeared, suggesting that the half EREs mediate the regulation of estradiol on the brain size genes. We next replicated these experiments using promoter sequences from chimpanzees and rhesus macaques, and observed a similar suppressive effect of estradiol on gene expression, suggesting that this mechanism is conserved among primate species that exhibit brain size dimorphism.ConclusionsBrain size dimorphism among certain primates, including humans, is likely regulated by estrogen through its sex-dependent suppression of brain size genes during development.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0398-x) contains supplementary material, which is available to authorized users.

Sexual Dimorphism in Primates

Sexual Dimorphism in Primates

Craniofacial sexual dimorphism patterns and allometry among extant hominids

Craniofacial sexual dimorphism in primates varies in both magnitude and pattern among species. In the past two decades, there has been an increasing emphasis in exploring the correlations of these patterns with taxonomy and the variation in patterns within and among the craniofacial regions. Scrutinising these relationships for hominids, we decompose the craniofacial morphology in five taxa: Homo sapiens, Pan paniscus, Pan troglodytes, Gorilla gorilla and Pongo pygmaeus. 3D coordinates of 35 traditional landmarks and 61 semilandmarks, covering five ridge curves, are measured for each of 268 adult and sub-adult specimens and analysed using geometric morphometric methods. A multivariate analysis in size-shape space shows that ontogenetic scaling contributes to the development of sexual dimorphism in all five taxa, but to a varying extent. In absolute as well as in relative terms P. pygmaeus shows the greatest allometric component, followed by G. gorilla. Homo is intermediate, while in Pan the non-allometric constituent part contributes a large fraction to the actual sexual dimorphism, most markedly in the pygmy chimpanzee. An eigendecomposition of the five vectors of sexual dimorphism reveals two dimensions independent of allometry. One separates orang-utan sexual dimorphism from the African apes and Homo, and the other differentiates between the great apes and Homo with Pan mediating. We discuss these patterns and speculate on their use as characters for taxonomic analysis in the fossil record.

Sexual selection in primates: New and comparative perspectives

List of contributors Foreword Robert L. Trivers Preface Part I. Introduction: 1. Sexual selection in primates: review and selective preview Peter M. Kappeler and Carel P. van Schaik 2. What is sexual selection? Tim H. Clutton-Brock 3. Sex roles, contests for the control of reproduction and sexual selection Patricia Adair Gowaty Part II. Sexual Signals: Substrates and Function: 4. Sexual selection and communication Charles T. Snowdon 5. Sexual selection and exaggerated sexual swellings of female primates Dietmar P. Zinner, Charles L. Nunn, Carel P. van Schaik and Peter M. Kappeler 6. Female multiple mating and genetic benefits in humans: investigations of design Steven W. Gangestad and Randy Thornhill Part III. Sexual Selection in Action: 7. Sexual selection, behaviour and sexually transmitted diseases Charles L. Nunn and Sonia M. Altizer 8. Mating conflict in primates: infanticide, sexual harassment and female sexuality Carel P. van Schaik, Gauri R. Pradhan and Maria A. van Noordwijk 9. Post-copulatory sexual selection in birds and primates Tim R. Birkhead and Peter M. Kappeler Part IV. Development and Consequences: 10. Development and sexual selection in primates Joanna M. Setchell and Phyllis C. Lee 11. Alternative male reproductive strategies: male bimaturism in orangutans Suci Atmoko Utami and Jan A. R. A. M. van Hooff 12. Sexual selection and the careers of primate males: paternity concentration, dominance acquisition tactics and transfer decisions Maria A. van Noordwijk and Carel P. van Schaik 13. Sexual selection, measures of sexual selection and sexual dimorphism in primates J. Michael Plavcan 14. Sex ratios in primate groups Joan B. Silk and Gillian R. Brown 15. Natural and sexual selection and the evolution of multi-level societies: insights from zebras with comparisons to primates Daniel I. Rubenstein and Mace Hack Index.

What made us human? Reflections on sex and gender in human evolution

Stereotypical images of human prehistory projected by popular media, which frequently consign female hominids to a subordinate role in palaeolithic society, are reinforced by ideas of 'Man the Hunter' as a leading selection pressure in our evolution. Yet, an overwhelming consensus among scholars has long since rejected these deterministic notions as little more than cliches which serve to obscure the real significance of sexual differences during human evolution and the importance of gender relations in the rise of a hominid economy and society. This article presents the case that specific issues which relate directly to sex and gender were formative influences which directed human evolution. Accordingly, sexual dimorphism in primates is reviewed in relation to human evolution: the long-term reduction of major differences in the body weight and size of males and females is seen in terms of an emerging culturally directed foraging strategy 2 million years ago. The economic importance, and frequent superior...

Sexual dimorphism in primate neonatal body mass.

Data were collected on neonatal body mass for 109 primate species. For 23 species with sample sizes of nine or more for each sex, dimorphism (male/female ratio) in neonatal body mass ranged from 0.94 in Galago senegalensis and Aotus trivirgatus to 1.19 in Pongo pygmaeus. Dimorphism in neonatal body mass was positively correlated both with adult body mass and with dimorphism in adult body mass, but the apparent relationship with adult mass was eliminated after controlling for the relationship with adult dimorphism. Comparative studies concerned with neonatal body mass in primates have almost always ignored sexual dimorphism. However, neonatal sexual dimorphism in primates does exist and appears to be of sufficient magnitude to be biologically significant in some species. It may be important to consider the consequences of neonatal dimorphism for a variety of research questions related to maternal investment, life history, postnatal growth, and the relationship between neonatal size and adult female pelvic dimensions, both in extant and in extinct primates.

Competition, coalitions and canine size in primates

Explanations of the evolution of canine tooth size sexual dimorphism in primates implicitly assume that male canine size is the primary target of natural or sexual selection, even though there is substantial unexplained variation in female canine size. Here we demonstrate that the canines of both males and females are relatively larger in species where agonistic interactions are more likely to escalate. Hence, the canine teeth of both sexes are influenced by selection for the development of weaponry, though the nature of the selection (natural or sexual) favoring development of the canines as weapons depends on the objects of competition (mates vs. food, for example). However, we also suggest that where the outcome of fights is typically determined between coalitions of individuals, selection for weaponry is reduced, even though agonistic competition can be very intense. Coalitionary aggression between males occurs in only a handful of anthropoid primates, but it is common among female anthropoids, and helps explain, in part, the extreme sexual dimorphism in the canine teeth of a number of catarrhine species. This is the first demonstration that cooperation among animals may affect their morphology. The lack of sexual dimorphism in canine size among prosimian primates is also consistent with the model. This analysis demonstrates that a better understanding of the interspecific variation in sexual dimorphism among primates is gained by considering behavioral variation in both sexes.

A statistical analysis of the literature on sexual dimorphism in primates

The annotated bibliography on sexual dimorphism in primates compiled by the authors was analysed considering the distribution of entries by keytitles, keywords, kind of periodicals and years of publication. A growing interest in this field was observed especially since the 1970s, but a relative scarcity of basic methodological papers was found. Articles on extant human populations and on living nonhuman primates are much more frequent than works on fossil primates and ancient humans.

Annotated bibliography on sexual dimorphism in primates. By S.M. Borgognini Tarli and E. Marini. v + 250 pp. Pisa: ETS Editrice. 1990

American Journal of Human BiologyVolume 4, Issue 2 p. 278-279 Book Review Annotated bibliography on sexual dimorphism in primates. By S.M. Borgognini Tarli and E. Marini. v + 250 pp. Pisa: ETS Editrice. 1990 Roberta L. Hall, Roberta L. Hall Oregon State University, Corvallis, OregonSearch for more papers by this author Roberta L. Hall, Roberta L. Hall Oregon State University, Corvallis, OregonSearch for more papers by this author First published: 1992 https://doi.org/10.1002/ajhb.1310040218AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume4, Issue21992Pages 278-279 RelatedInformation

The earliest fossil evidence for sexual dimorphism in primates.

Recently obtained material of the early Eocene primate Notharctus venticolus, including two partial skulls from a single stratigraphic horizon, provides the geologically earliest evidence of sexual dimorphism in canine size and shape in primates and the only unequivocal evidence for such dimorphism in strepsirhines. By analogy with living platyrrhines, these data suggest that Notharctus venticolus may have lived in polygynous social groups characterized by a relatively high level of intermale competition for mates and other limited resources. The anatomy of the upper incisors and related evidence imply that Notharctus is not as closely related to extant lemuriform primates as has been recently proposed. The early Eocene evidence for canine sexual dimorphism reported here, and its occurrence in a nonanthropoid, indicates that in the order Primates such a condition is either primitive or evolved independently more than once.

Spatial autocorrelation, phylogenetic constraints, and the causes of sexual dimorphism in primates

Cheverud et al. (1985) apply the important and relatively new methodology of spatial autocorrelation to the quantification of phylogenetic constraints on adaptation and illustrate the use of these methods in an allometric study of sexual dimorphism in body size among extant nonhuman primates. Though of potentially broad applicability, the technique was completely overlooked in a recent review of methods to control for the effects of common descent in comparative studies (Bell, 1989). Their approach therefore deserves a wider recognition. However, their specific conclusion, that phytogeny is the primary determinant of patterns of sexual dimorphism among primates, has been uncritically accepted. We present four main methodological problems with their approach that should temper the interpretation of their analysis: biased phylogenetic relatedness scores, biased sample selection, size dependence in sex dimorphism measurement, and deficiencies in selection of a structural path model. We conclude that, even in terms of the analysis by Cheverud and co-workers (1985), phylogenetic inertia is not the primary reason for body size dimorphism.

Ontogenetic approaches to sexual dimorphism in anthropoids

Studies of sexual dimorphism have traditionally focused on the static differences in size and shape between adult males and females. In this paper, I suggest that an investigation of the ontogenetic bases of sexual dimorphism can provide new insights and information unobtainable from studies concerned only with adult endpoints. While growth is often viewed as simply the developmental pathway utilized to attain final adult size and shape, we must recognize that it is the entire pattern of sex-differentiated growth, and not merely the adult endpoints, which is adaptive and the target of natural selection. The importance of an ontogenetic approach to the analysis of sexual dimorphism is also demonstrated by the fact that a given morphologicalresult (e.g., a certain degree of adult weight dimorphism) may be attained by very different developmentalprocesses, signalling selection for quite different factors. The need to analyze the ontogenetic bases of sexual dimorphism in size and shape has recently been recognized by Jarman, in his study of dimorphism in large terrestrial herbivores. Here I combine aspects of Jarman’s approach with those of allometry and heterochrony in an analysis of sexual dimorphism in selected anthropoid primates. It is demonstrated that although all dimorphic anthropoids appear to be characterized by somebimaturism, the degree varies significantly. Marked weight dimorphism in certain species is primarily produced by an increased differentiation of female and male growthrates, while in other species the primary change involves differences in thetime or duration of growth between the sexes. These variations are illustrated with anthropoid genera such asMiopithecus, Cercopithecus, Erythrocebus, Macaca, Papio, Pan, andGorilla. It is suggested that additional ontogenetic investigations of other anthropoids will help clarify some of the socioecological bases of this variation in the ways of attaining an adult dimorphic state. This will contribute to our understanding of the complex factors underlying and producing sexual dimorphism in primates and other mammals.

Sexual dimorphism in primates: Where are we and where do we go from here?

There are currently several debates taking place in palaeoanthropological circles in which the issue of sexual dimorphism is crucial. During the 60th Jubilee of the discovery of the TaungAustralopithecus skull, the authors concurred that much of the debate was due to differences in perception concerning dimorphism, and it was suggested that a study session dealing principally with sexual dimorphism in Primates should be organised with a view to determining what, if anything, could be observed in extant primates that might be utilised for determining the existence of dimorphism in fossil species. An advertisement was placed in the Journal of Human Evolution, calling for papers. Response was encouraging, suggesting that there was indeed a need for such a meeting, which was organised to take place late in November in Italy. Seventeen scientists sent abstracts, but due to the rather short notice, several were unable to attend the meeting. Nevertheless, papers were received and read at the meeting which form the basis for this issue of the Journal of Human Evolution. What remains to be done now, is for a second meeting to be organised at which the findings of the first meeting can be extended backwards in time into the fossil record.

Correlates of sexual dimorphism in primates: Ecological and size variables

The effects of a series of ecological and size factors on the degree of sexual dimorphism in body weight and canine size were studied among subsets of 70 primate species. Variation in body-weight dimorphism can be almost entirely attributed to body weight (83% of variance R2 of weight dimorphism). Much smaller amounts of the variation can be attributed to mating system (R2 =6.8%,polygynous species being more dimorphic than monogamous ones) and diet (R2 = 2.5%,frugivorous species being more dimorphic than folivorous ones). Habitat (arboreal vs. terrestrial) and activity rhythm (nocturnal vs. diurnal) have only an indirect effect on weight dimorphism. Variation in canine-size dimorphism can be explained in terms of canine size (R2 =49%),activity rhythm (R2 = 20%,diurnal species being more dimorphic than nocturnal ones), and mating system (R2 = 10%).Habitat and diet do not play a significant role in canine-size dimorphism. The unexpectedly high contribution of size to sexual dimorphism coupled with the observation of increased sexual dimorphism with increased size leads us to formulate a new selection model for the evolution of sexual dimorphism. We suggest that if there is selection for size increase, whatever its cause, directional selection in both males and females will lead to an increase in sexual dimorphism based on differences in genetic variance between the sexes. Sexual selection, resource division between the sexes, or lopsided reproductive selection need not play a role in such a model.