A mixed model of the evolution of polygyny and sexual size dimorphism in mammals

  title={A mixed model of the evolution of polygyny and sexual size dimorphism in mammals},
  author={Marcelo H. Cassini},
  journal={Mammal Review},
The theory of sexual selection is the most widely accepted theory explaining the evolution of mating systems and secondary sexual characters. Polygyny is the most common mating system in mammals, and there is a strong correlation between the degree of polygyny and the degree of sexual size dimorphism skewed towards males. Sexual selection theory posits that polygyny in mammals has evolved through direct, precopulatory, intrasexual selection in males, and that sexual size dimorphism is a result… 

Sexual size dimorphism and sexual selection in artiodactyls

An interspecific test using the variance in genetic paternity as a proxy for the Is suggests that sexual selection may have played a role in the evolution of sexual size dimorphism in Artiodactyla.

Sexual size dimorphism and sexual selection in primates

Results of this comparative analysis of sexual size dimorphism and sexual selection intensity in primates suggest that the use of intramale sexual selection theory to explain the evolution of polygyny and sexual Dimorphism in mammals should be reviewed, and that natural selection should be considered alongside sexual selection as an evolutionary driver.

Polygyny in the Era of Molecular Biology: Revisiting Bartholomew’s Model

  • M. Cassini
  • Biology
    Ethology and Behavioral Ecology of Otariids and the Odobenid
  • 2021
Testing the literature on paternity for otariids found that size of harem did correlate with paternity by territorial males but the slope was significantly lower than expected from behavioural estimations; differences in paternity between territorial and satellites males were not statistically significant in most studies.

Sexual aggression in mammals

In non‐human mammals, sexual conflict should be particularly intense because males rarely provide parental care. An expected consequence of sexual conflict is male aggression towards mates.

Sexual coercion in a natural mandrill population

The nature of male coercive strategies in wild mandrills (Mandrillus sphinx) is investigated, finding support for all three predictions of the sexual coercion hypothesis, namely that male aggression specifically targets sexually receptive females, inflicts costs to these females, and increases male mating success in the long-term.

Contrasting selection pressure on body and weapon size in a polygynous megaherbivore

Hippopotamus appear to be a rare example among ungulates whereby sexual selection favours increased weapon size over body mass, underlining the important role that species-specific ecology and physiology have in shaping SSD.

A new classification of mammalian uni-male multi-female groups based on the fundamental principles governing inter- and intrasexual relationships

This framework was able to successfully predict patterns of female-female cooperation and the presence of coercive male-female relationships, and provides a powerful lens for asking broad, comparative evolutionary questions about social evolution and socioecology.

Killing conspecific adults in mammals

The results indicate that the evolutionary pathways underlying the evolution of adulticide differ between sexes in mammals, and male and female adulticide mainly to defend offspring from infanticidal conspecifics.

Evaluating drivers of female dominance in the spotted hyena

Evidence is found for both mechanisms hypothesized to mediate female dominance in this species: male and female hyenas clearly differ in their aggressive and submissive tendencies, and realized social support plays an important role in shaping dominance relationships within a clan.



Sexual Dimorphism in Mammals: Avian Models and Unanswered Questions

  • K. Ralls
  • Biology
    The American Naturalist
  • 1977
An adequate mammalian model will have to include another set of factors which oppose the evolution of polygyny by increasing the spacing or mobility of females, and explain why sexual dimorphism has evolved more frequently in large mammals than in small ones.


This study provides novel insights into the role of sexual selection for the coevolutionary dynamics of SSD and mating system and calls for the inclusion of ecological variables when studying sexual selection and argues for caution when assuming causality between coevolving traits.

Do extra-group fertilizations increase the potential for sexual selection in male mammals?

It is found that EGP and social mating system can predict the potential for sexual selection in mammalian populations, but only when considered jointly and not individually.


A phylogeny of extant ungulate species, along with maximum-likelihood statistical techniques, are used to provide a test of Jarman's hypothesis, which states that sexual size dimorphism evolved in a three-step process.

On the Opportunity for Sexual Selection, the Bateman Gradient and the Maximum Intensity of Sexual Selection

  • A. Jones
  • Biology, Psychology
    Evolution; international journal of organic evolution
  • 2009
The meaning of Bateman's principles in the context of selection theory is considered, which provides a clearer focus on the important aspects of precopulatory sexual selection than other methods and therefore should be an important part of future studies of sexual selection.

Variance in male reproductive success and sexual size dimorphism in pinnipeds: testing an assumption of sexual selection theory

The theory of evolution by sexual selection for sexual size dimorphism postulates that SSD primarily reflects the adaptation of males and females to their different reproductive roles, and species with male-biased SSD are predicted to have greater variance in male reproductive success than those in which both sexes are similar in size.

Phylogenetic analyses of sexual selection and sexual size dimorphism in pinnipeds

The hypothesis that sexual size dimorphism in pinnipeds is the product of an exclusively male response to sexual selection is supported.

Sexual selection resulting from extrapair paternity in collared flycatchers

Estimates ofSexual selection gradients on male secondary sexual plumage characters resulting from extrapair paternity in the collared flycatcher Ficedula albicollis are reported, and the importance of this form of sexual selection with that resulting from variation in mate fecundity is compared.

Monogamy in Mammals

  • D. Kleiman
  • Biology
    The Quarterly Review of Biology
  • 1977
This review considers the behavioral, ecological, and reproductive characteristics of mammals exhibiting monogamy, i.e., mating exclusivity. From a discussion of the life histories of selected