The evolution of sexual size dimorphism in prosimian primates
TL;DR: In prosimians, inter‐specific differences in sexual dimorphism were not correlated with variance in male reproductive success, and it is suggested that speed and agility of males, rather than size and strength, might have been favored by intra‐sexual selection in most prosimian primates.
Abstract: The four major hypotheses advanced to explain the evolution of sexually dimorphic characters invoke sexual selection, natural selection, allometry, and phylogenetic inertia. In this paper, each of these hypotheses is examined for its usefulness in explaining the inter-specific variation in sexual size dimorphism among prosimian primates. Data on body weight and the degree of sexual dimorphism were obtained for 32 prosimian and 95 simian species. Although prosimians exhibited significantly less sexual dimorphism than simians, there was nevertheless significant variation in dimorphism among them. The degree of sexual dimorphism in prosimians did not show significant variance at any taxonomic level, but the majority of variance occurred within genera. Thus, sexual dimorphism in size among prosimians is probably not constrained by phylogeny at the generic level and above. There was no significant correlation between body size and the degree of sexual dimorphism in prosimians, suggesting the absence of an allometric effect. Similarly there was no relationship between body size and sexual dimorphism among simians in this size range. This result suggested that the expression of sexual dimorphism may nevertheless be influenced by absolute size. In prosimians, inter-specific differences in sexual dimorphism were not correlated with variance in male reproductive success. It is suggested that speed and agility of males, rather than size and strength, might have been favored by intra-sexual selection in most prosimians. It seems also plausible that the relative monomorphism of most prosimians, especially in the Lemuriformes, might be a result of increased female size favored by natural selection. Consideration of all natural and sexual selective pressures that affect size in both sexes separately is required to understand the adaptive function and evolution of primate size dimorphism.
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TL;DR: An analysis of variability in body mass indicates that the coefficient of variation for body mass increases with increasing species mean mass.
1,198 citations
TL;DR: Understanding of the behavioral/ecological correlates of growth and development, and of the expression of dimorphism as a function of separate changes in male and female traits, offers great potential for inferring evolutionary changes in behavior over time.
Abstract: Sexual dimorphism is a pervasive phenomenon among anthropoid primates. Comparative analyses over the past 30 years have greatly expanded our understanding of both variation in the expression of dimorphism among primates, and the underlying causes of sexual dimorphism. Dimorphism in body mass and canine tooth size is familiar, as is pelage and “sex skin” dimorphism. More recent analyses are documenting subtle differences in the pattern of skeletal dimorphism among primates. Comparative analyses have corroborated the sexual selection hypotheses, and have provided a more detailed understanding of the relationship between sexual selection, natural selection, and mating systems in primates. A clearer picture is emerging of the relative contribution of various selective and nonselective mechanisms in the evolution and expression of dimorphism. Most importantly, recent studies have shown that dimorphism is the product of changes in both male and female traits. Developmental studies demonstrate the variety of ontogenetic pathways that can lead to dimorphism, and provide additional insight into the selective mechanisms that influence dimorphism throughout the lifetime of an animal. Evidence from the fossil record suggests that dimorphism probably evolved in parallel twice, and the dimorphism in some extinct hominoids probably exceeded that of any living primate. Our advances in understanding the behavioral/ecological correlates of dimorphism in living primates have not improved our ability to reconstruct social systems in extinct species on the basis of dimorphism alone, beyond the inference of polygyny or intense male-male competition. However, our understanding of the behavioral/ecological correlates of growth and development, and of the expression of dimorphism as a function of separate changes in male and female traits, offers great potential for inferring evolutionary changes in behavior over time. Yrbk Phys Anthropol 44:25–53, 2001. © 2001 Wiley-Liss, Inc.
394 citations
TL;DR: Characteristics and testing for associations among the most dimorphic mammalian taxa—Macropodidae, Primates, Mustelidae, Pinnipedia, Elephantidae, Ruminantia, found that ruminants with tending and harem mating systems were moreDimorphic than those with territorial polygynous and monogamous mating systems.
Abstract: I examined influence of body size and mating systems on sexual-size dimorphism by summarizing characteristics and testing for associations among the most dimorphic mammalian taxa—Macropodidae, Primates, Mustelidae, Pinnipedia, Elephantidae, Ruminantia. The most dimorphic taxa were seals in Otariidae. On average, males were three times larger than females, and all otariids displayed extensive dimorphism. Except for the Strepsirhini, most taxa had dimorphism ratios (mass of males:mass of females) between 1.2–1.8. Extent of dimorphism increased with body size but the effect was slight (power function between masses of males and females, 1.04–1.05) for most taxa. Phocid seals and macropodid marsupials had power functions of ca. 1.2. Mating systems were associated with size dimorphism in simian primates and ruminants. Monogamous simian primates were less dimorphic than simians that had polygynous mating systems. Ruminants with tending and harem mating systems were more dimorphic than those with territorial polygynous and monogamous mating systems. Polygyny and how it was conducted were associated with the extent of sexual size dimorphism.
357 citations
TL;DR: Re-evaluate variation in adult body weight dimorphism in anthropoids, testing the sexual selection hypothesis using categorical estimates of the degree of male-male intrasexual competition ("competition levels"), and test the hypotheses that interspecific variation in body weightDimorphism is associated with female body weight and categorical Estimates of diet, substrate use, and phylogeny.
Abstract: Body weight dimorphism in anthropoid primates has been thought to be a consequence of sexual selection resulting from male-male competition for access to mates. However, while monogamous anthropoids show low degrees of weight dimorphism, as predicted by the sexual selection hypothesis, polygynous anthropoids show high variation in weight dimorphism that is not associated with measures of mating system or sex ratio. This observation has led many to debate the role of other factors such as dietary constraints, predation pressure, substrate constraints, allometric effects, and phylogeny in the evolution of anthropoid weight dimorphism. Here, we re-evaluate variation in adult body weight dimorphism in anthropoids, testing the sexual selection hypothesis using categorical estimates of the degree of male-male intrasexual competition (“competition levels”). We also test the hypotheses that interspecific variation in body weight dimorphism is associated with female body weight and categorical estimates of diet, substrate use, and phylogeny. Weight dimorphism is strongly associated with competition levels, corroborating the sexual selection hypothesis. Weight dimorphism is positively correlated with increasing female body weight, but evidence suggests that the correlation reflects an interaction between overall size and behavior. Arboreal species are, on average, less dimorphic than terrestrial species, while more frugivorous species tend to be more dimorphic than folivorous or insectivorous species. Several alternative hypotheses can explain these latter results. Weight dimorphism is correlated with taxonomy, but so too are competition levels. We suggest that most taxonomic correlations of weight dimorphism represent “phylogenetic niche conservatism”; however, colobines show consistently low degrees of weight dimorphism for reasons that are not clear. Am J Phys Anthropol 103:37–68, 1997. © 1997 Wiley-Liss, Inc.
305 citations
TL;DR: A weight-corrected measure of sexual dimorphism and a biologically realistic assay of mating competition, the operational sex ratio, are employed to reexamine the factors favoring the evolution of sexual sizeDimorphism in primates and produce results consistent with the sexual selection hypothesis.
Abstract: Male mating competition is generally regarded to account for sexual dimorphism in body size, but levels of sexual dimorphism do not appear to be associated with the intensity of intrasexual selection in polygynous mammals. In contrast, observations of accentuated dimorphism in certain taxa and in large species are consistent with nonadaptive explanations for the evolution of sexual size dimorphism based on phylogenetic inertia and allometry. Here we employ a weight-corrected measure of sexual dimorphism and a biologically realistic assay of mating competition, the operational sex ratio, to reexamine the factors favoring the evolution of sexual size dimorphism in primates. Independent contrasts that control for the effects of allometry and phylogeny produce results consistent with the sexual selection hypothesis; a strong relationship exists between sexual dimorphism in size and the intensity of male mating competition among polygynously mating primates. Increased sexual dimorphism in large primates may no...
277 citations
References
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Book•
01 Jan 1956
TL;DR: This is the revision of the classic text in the field, adding two new chapters and thoroughly updating all others as discussed by the authors, and the original structure is retained, and the book continues to serve as a combined text/reference.
Abstract: This is the revision of the classic text in the field, adding two new chapters and thoroughly updating all others. The original structure is retained, and the book continues to serve as a combined text/reference.
35,552 citations
Book•
24 Feb 1871
TL;DR: In this paper, secondary sexual characters of fishes, amphibians and reptiles are presented. But the authors focus on the secondary sexual characteristics of fishes and amphibians rather than the primary sexual characters.
Abstract: Part II. Sexual Selection (continued): 12. Secondary sexual characters of fishes, amphibians and reptiles 13. Secondary sexual characters of birds 14. Birds (continued) 15. Birds (continued) 16. Birds (concluded) 17. Secondary sexual characters of mammals 18. Secondary sexual characters of mammals (continued) 19. Secondary sexual characters of man 20. Secondary sexual characters of man (continued) 21. General summary and conclusion Index.
11,302 citations
12 Jul 2017
TL;DR: The p,cnetics of sex nas now becn clarif ied, and Fishcr ( 1958 ) hrs produccd , n,od"l to cxplarn sex ratios at coDception, a nrodel recently extendcd to include special mccha_ nisms that operate under inbreeding (Hunrilron I96?).
Abstract: There is a tendency among biologists studying social behavior to regard the adult sex ratio as an independent variable to which the species reacts with appropriate adaptations D Lack often interprets social behavior as an adaptation in part to an unbalanced (or balanced) sex ratio, and J Verner has summarized other instances of this tendency The only mechanism that will generate differential mortality independent of sexual differences clearly related to parental investment and sexual selection is the chromosomal mechanism, applied especially to humans and other mammals: the unguarded X chromosome of the male is presumed to predispose him to higher mortality Each offspring can be viewed as an investment independent of other offspring, increasing investment in one offspring tending to decrease investment in others Species can be classified according to the relative parental investment of the sexes in their young In the vast majority of species, the male's only contribution to the survival of his offspring is his sex cells
10,571 citations
TL;DR: A method of correcting for the phylogeny has been proposed, which specifies a set of contrasts among species, contrasts that are statistically independent and can be used in regression or correlation studies.
Abstract: Recent years have seen a growth in numerical studies using the comparative method. The method usually involves a comparison of two phenotypes across a range of species or higher taxa, or a comparison of one phenotype with an environmental variable. Objectives of such studies vary, and include assessing whether one variable is correlated with another and assessing whether the regression of one variable on another differs significantly from some expected value. Notable recent studies using statistical methods of this type include Pilbeam and Gould's (1974) regressions of tooth area on several size measurements in mammals; Sherman's (1979) test of the relation between insect chromosome numbers and social behavior; Damuth's (1981) investigation of population density and body size in mammals; Martin's (1981) regression of brain weight in mammals on body weight; Givnish's (1982) examination of traits associated with dioecy across the families of angiosperms; and Armstrong's (1983) regressions of brain weight on body weight and basal metabolism rate in mammals. My intention is to point out a serious statistical problem with this approach, a problem that affects all of these studies. It arises from the fact that species are part of a hierarchically structured phylogeny, and thus cannot be regarded for statistical purposes as if drawn independently from the same distribution. This problem has been noticed before, and previous suggestions of ways of coping with it are briefly discussed. The nonindependence can be circumvented in principle if adequate information on the phylogeny is available. The information needed to do so and the limitations on its use will be discussed. The problem will be discussed and illustrated with reference to continuous variables, but the same statistical issues arise when one or both of the variables are discrete, in which case the statistical methods involve contingency tables rather than regressions and correlations.
8,833 citations
Journal Article•
TL;DR: Part I. Sexual Selection (continued): Secondary sexual characters of fishes, amphibians and reptiles, and secondarySexual characters of birds.
6,894 citations