Sexual dimorphism

Reynolds, S. C. (2007a). Temporal variation in Plio-Pleistocene Antidorcas (Mammalia: Bovidae) horncores: the case from Bolt’s Farm and why size matters South African Journal of Science Volume 103:47-50.

by Sally Reynolds

Morphological differences in samples of fossil (Antidorcas recki)
and modern (A. marsupialis) springbok horncores... more Morphological differences in samples of fossil (Antidorcas recki)
and modern (A. marsupialis) springbok horncores suggest that the ancestral species shows less sexual dimorphism than is observed in the horn dimensions of modern springbok. This pattern may prove useful when evaluating lossil springbok specimens in South African Pfio-Pleistocene faunal assemblages. Undated Antidorcas craniodental specimens from Pit 3, Bolt's Farm (Cradle of Humankind, Gauteng, South Africa) have previously been referred to A. recki by Cooke. However, comparison with numerous other springbok samples suggests that these specimens are more likely to represent male and lemale fossils of the extant species, A. marsupialis. This re-evaluationa dds weight to the fossil evidence implying that the modern form of springbok is a southern Alrican endemic species which first appeared around 1.5-1.0 million years ago in Swartkrans Member 1. Bolt's Farm Pit 3 fossils are inferred
to be of a similar age.

A Reevaluation of Sexual Dimorphism in the Postcranium of the Chasmosaurine Ceratopsid Chasmosaurus belli (Dinosauria: Ornithischia)

by Jordan Mallon

Description of a complete and fully articulated chasmosaurine postcranium previously assigned to Anchiceratops (Dinosauria: Ceratopsia)

by Jordan Mallon

Matching dimorphic sexes and immature stages with adults: resolving the systematics of the Bekilya group of Malagasy assassin bugs (Hemiptera: Reduviidae: Peiratinae) [Systematic Entomology]

by Guanyang Zhang

Published in 'Systematic Entomology'

The Madagascar endemic assassin bugs Bekilya Villiers and Hovacoris Villiers were described from macropterous male... more The Madagascar endemic assassin bugs Bekilya Villiers and Hovacoris Villiers were described from macropterous male specimens with striking colour patterns, and are currently monotypic. Mutillocoris Villiers, with two species from Madagascar, was based on brachypterous female specimens that resemble female mutillid wasps. To investigate the validity of the three genera, recently collected specimens from Madagascar were studied with both morphological and molecular techniques. Morphology alone appeared to be of limited value for associating males with females, and immature stages with adults, because of drastic differences between the sexes and the life stages. However, the use of morphology in conjunction with molecular data resolved these associations and showed that species of Mutillocoris represent females of Bekilya and Hovacoris, which we transfer accordingly to these two genera and refer to them as the Bekilya group. The type species of Mutillocoris belongs in Bekilya, resulting in the synonymy of these two genera (Mutillocorissyn.n.). The Bekilya group is diagnosed and several new species are described: Bekilya mahafalyasp.n., Bekilya tenebrasp.n., Bekilya tulearasp.n., Hovacoris bicolornotumsp.n., Hovacoris melanocepssp.n. and Hovacoris rufiventrissp.n. A total of ten species are recognized within the Bekilya group. The monophyly of Bekilya, Hovacoris and the Bekilya group is confirmed by morphological and molecular phylogenetic analyses.

New hominid fossils from Member 1 of the Swartkrans formation, South Africa

by Jason Heaton

Co-Authored with Travis Pickering, Ron Clarke, Morris Sutton, Bob Brain and Kathy Kuman. From the "Journal of Human Evolution", May 2012.

Member 1 of the Swartkrans Formation is comprised of two sedimentary infills, the Lower Bank (LB) and the Hanging... more Member 1 of the Swartkrans Formation is comprised of two sedimentary infills, the Lower Bank (LB) and the Hanging Remnant (HR). Together, the LB and HR preserve fossils of early Homo and Paranthropus robustus, Earlier Stone Age lithic artifacts, purported bone digging tools and butchered animal bones. Collectively, this evidence was the first to establish the co-existence of two early Pleistocene hominid species and also led to inferences of plant root harvesting and meat-eating by one or both of those species. P. robustus is the more abundant of the two hominids at Swartrkrans, represented in Member 1 by hundreds of fossils that derive from at least 99 individuals. Thus, Swartkrans Member 1 stands as the world’s single largest repository of that extinct species. Here we add to the Member 1 sample of hominid fossils with descriptions of 14 newly discovered specimens.

Influence of female-biased sexual size dimorphism on dominance of female Townsend’s chipmunks

by Andrew Edelman

Edelman, A.J., and J.L. Koprowski. 2005. Influence of female-biased sexual size dimorphism on dominance of female Townsend’s chipmunks. Canadian Journal of Zoology 84:1859-1863.

Does predation result in adult sex ratio skew in a sexually dimorphic insect genus?

by Priscilla (McAllum) Wehi

Theory proposes that sexually dimorphic, polygynous species are at particularly high risk of sex-biased predation,... more Theory proposes that sexually dimorphic, polygynous species are at particularly high risk of sex-biased predation, because conspicuous males are more often preyed upon compared to females. We tested the effects of predation on population sex ratio in a highly sexually dimorphic insect genus (Hemideina). In addition, introduction of a suite of novel mammalian predators to New Zealand during the last 800 years is likely to have modified selection pressures on native tree weta. We predicted that the balance between natural and sexual selection would be disrupted by the new predator species. We expected to see a sex ratio skew resulting from higher mortality in males with expensive secondary sexual weaponry; combat occurs outside refuge cavities between male tree weta. We took a meta-analytic approach using generalized linear mixed models to compare sex ratio variation in 58 populations for six of the seven species in Hemideina. We investigated adult sex ratio across these populations to determine how much variation in sex ratio can be attributed to sex-biased predation in populations with either low or high number of invasive mammalian predators. Surprisingly, we did not detect any significant deviation from 1 : 1 parity for adult sex ratio and found little difference between populations or species. We conclude that there is little evidence of sex-biased predation by either native or mammalian predators and observed sex ratio skew in individual populations of tree weta is probably an artefact of sampling error. We argue that sex-biased predation may be less prevalent in sexually dimorphic species than previously suspected and emphasize the usefulness of a meta-analytic approach to robustly analyse disparate and heterogeneous data.

Does predation result in adult sex ratio skew in a sexually dimorphic insect genus?

by Priscilla (McAllum) Wehi

Theory proposes that sexually dimorphic, polygynous species are at particularly high risk of sex-biased predation,... more Theory proposes that sexually dimorphic, polygynous species are at particularly high risk of sex-biased predation, because conspicuous males are more often preyed upon compared to females. We tested the effects of predation on population sex ratio in a highly sexually dimorphic insect genus (Hemideina). In addition, introduction of a suite of novel mammalian predators to New Zealand during the last 800 years is likely to have modified selection pressures on native tree weta. We predicted that the balance between natural and sexual selection would be disrupted by the new predator species. We expected to see a sex ratio skew resulting from higher mortality in males with expensive secondary sexual weaponry; combat occurs outside refuge cavities between male tree weta. We took a meta-analytic approach using generalized linear mixed models to compare sex ratio variation in 58 populations for six of the seven species in Hemideina. We investigated adult sex ratio across these populations to determine how much variation in sex ratio can be attributed to sex-biased predation in populations with either low or high number of invasive mammalian predators. Surprisingly, we did not detect any significant deviation from 1 : 1 parity for adult sex ratio and found little difference between populations or species. We conclude that there is little evidence of sex-biased predation by either native or mammalian predators and observed sex ratio skew in individual populations of tree weta is probably an artefact of sampling error. We argue that sex-biased predation may be less prevalent in sexually dimorphic species than previously suspected and emphasize the usefulness of a meta-analytic approach to robustly analyse disparate and heterogeneous data.

Facial Sexual Dimorphism and Judgments of Personality: A Literature Review

by John Shuler

Published in the Georgetown Undergraduate Journal of Health Sciences, 2012

Facial sexual dimorphism lends itself to myriad facial traits that result from an individual's unique exposure to the... more Facial sexual dimorphism lends itself to myriad facial traits that result from an individual's unique exposure to the sex hormones testosterone and estrogen. The following literature review will discuss psychological research from the late 20th century onwards pertaining to facial sexual dimorphism - facial masculinity and femininity - as it relates to the judgment of personality traits, specifically the Big Five personality traits proposed by Goldberg (1993): openness to experience, conscientiousness, extraversion, agreeableness and neuroticism. Research from the past three decades pertaining to facial judgments of personality has investigated correlations of specific personality traits with facial attractiveness as well as symmetry.

Gender‐based differences in the shape of the human corpus callosum are associated with allometric variations

by Jose Manuel de la Cuétara

Bruner E, de la Cuétara JM, Colom R, Martin-Loeches M. 2012. Gender-based differences in the shape of the human corpus callosum are associated with allometric variations. Journal of Anatomy, 220: 417–421.

The corpus callosum displays considerable morphological variability between individuals. Although some characteristics... more The corpus callosum displays considerable morphological variability between individuals. Although some characteristics are thought to differ between male and female brains, there is no agreement regarding the source of this variation. Biomedical imaging and geometric morphometrics have provided tools to investigate shape and size variation in terms of integration and correlation. Here we analyze variations at the midsagittal outline of the corpus callosum in a sample of 102 young adults in order to describe and quantify the pattern of covariation associated with its morphology. Our results suggest that the shape of the corpus callosum is characterized by low levels of morphological integration, which explains the large variability. In larger brains, a minor allometric component involves a relative reduction of the splenium. Small differences between males and?females are associated with this allometric pattern, induced primarily by size variation rather than gender-specific characteristics.

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

by ivanovic ana

Sexual dimorphism in chin shape: Implications for adaptive hypotheses

by Zaneta Thayer

EFECTOS DE LA DEFORMACIÓN CRANEANA INTENCIONAL SOBRE LA EXPRESIÓN DEL DIMORFISMO SEXUAL EN CRÁNEOS ADULTOS: UN ANÁLISIS MORFOMÉTRICO GEOMÉTRICO

by Rodrigo Retamal

Rodrigo Retamal Yermani and German Manriquez Soto

Efectos de la deformación craneana intencional sobre la expresión del dimorfismo sexual en cráneos adultos

by Rodrigo Retamal

Adaptive speciation and sexual dimorphism contribute to diversity in form and function in the adaptive radiation of Lake Matano's sympatric roundfin sailfin silversides

by Jobst Pfaender

Pelvic dimorphism in relation to body size and body size dimorphism in humans

by Helen Kurki

Many mammalian species display sexual dimorphism in the pelvis, where females possess larger dimensions of the... more Many mammalian species display sexual dimorphism in the pelvis, where females possess larger dimensions of the obstetric (pelvic) canal than males. This is contrary to the general pattern of body size dimorphism, where males are larger than females. Pelvic dimorphism is often attributed to selection relating to parturition, or as a developmental consequence of secondary sexual differentiation (different allometric growth trajectories of each sex). Among anthropoid primates, species with higher body size dimorphism have higher pelvic dimorphism (in converse directions), which is consistent with an explanation of differential growth trajectories for pelvic dimorphism. This study investigates whether the pattern holds intraspecifically in humans by asking: Do human populations with high body size dimorphism also display high pelvic dimorphism? Previous research demonstrated that in some small-bodied populations, relative pelvic canal size can be larger than in large-bodied populations, while others have suggested that larger-bodied human populations display greater body size dimorphism. Eleven human skeletal samples (total N: male = 229, female = 208) were utilized, representing a range of body sizes and geographical regions. Skeletal measurements of the pelvis and femur were collected and indices of sexual dimorphism for the pelvis and femur were calculated for each sample [ln(M/F)]. Linear regression was used to examine the relationships between indices of pelvic and femoral size dimorphism, and between pelvic dimorphism and female femoral size. Contrary to expectations, the results suggest that pelvic dimorphism in humans is generally not correlated with body size dimorphism or female body size. These results indicate that divergent patterns of dimorphism exist for the pelvis and body size in humans. Implications for the evaluation of the evolution of pelvic dimorphism and rotational childbirth in Homo are considered.

Long‐term paternity skew and the opportunity for selection in a mammal with reversed sexual size dimorphism

by Stephen Rossiter

Very Small Ammonites (Micromorphs) from Lower Oxfordian Marls (Mariae Zone)

by Quentin Scouflaire

Application of wavelets in the analysis of sexual dimorphism in the skull of South American canids (Mammalia, Canidae)

by Erika Hingst-Zaher

Takemura, C. M., Cesar, R. M., Jr, Arantes, R. A. T., Costa, L. D. F., Hingst-Zaher, E., Reis, dos, S. F., & Bonato, V. (2004). Morphometrical data analysis using wavelets. Real-Time Imaging, 10(4), 239–250.

Sexual dimorphism is an important source of intraspecific variability in biological species, and so virtually all... more Sexual dimorphism is an important source of intraspecific variability in biological species, and so virtually all studies in populational or interspecific levels need to take differences among males and females into consideration. Here we examine patterns of sexual dimorphism among the sexes in a monophyletic clade formed by the south-american canids. In this family, broadly distributed throughout the world, differences in size and shape between sexes are usually related to mating systems and social organization. The south american members are among the less studied of the dogs, and little is known about possible differences among individuals of the same species. As in all groups that share a common ancestry, evolution of adaptive characters must be studied in an historical context.

Dimorfismo sexual y variación morfométrica geográfica en Hybreoleptops aureosignatus (Insecta: Coleoptera: Curculionidae)

by Edgardo Ortiz-Jaureguizar

Posadas, P.; Ortiz-Jaureguizar, E. & Pérez, M.E., 2009. Anales de la Academia Nacional de Ciencias Exactas, Físicas y Naturales, 59: 141-150.