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Journal ArticleDOI

Correlates of sexual dimorphism in primates: Ecological and size variables

TL;DR: It is suggested 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.
Abstract: 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.
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TL;DR: If ecological causation for dimorphism can be demonstrated in so many cases, despite the inadequacies of the available criteria, the degree of sexual sizeDimorphism in many other animal species may well also have been influenced by ecological factors, and it may be premature of dismiss this hypothesis.
Abstract: Can sexual dimorphism evolve because of ecological differences between the sexes? Although several examples of this phenomenon are well known from studies on birds, the idea has often been dismissed as lacking general applicability. This dismissal does not stem from contradictory data so much as from the difficulties inherent in testing the hypothesis, and its apparent lack of parsimony, in comparison to the alternative explanation of sexual selection. The only unequivocal evidence for the evolution of sexual dimorphism through intersexual niche partitioning would be disproportionate dimorphism in trophic structures (e.g., mouthparts). This criterion offers a minimum estimate of the importance of ecological causes for dimorphism, because it may fail to identify most cases. A review of published literature reveals examples of sexually dimorphic trophic structures in most animal phyla. Many of these examples seem to be attributable to sexual selection, but others reflect adaptations for niche divergence between the sexes. For example, dwarf non-feeding males without functional mouthparts have evolved independently in many taxa. In other cases, males and females differ in trophic structures apparently because of differences in diets. Such divergence may often reflect specific nutritional requirements for reproduction in females, or extreme (sexually selected?) differences between males and females in habitats or body sizes. Ecological competition between the sexes may be responsible for intersexual niche divergence in some cases, but the independent evolution of foraging specializations by each sex may be of more general importance. If ecological causation for dimorphism can be demonstrated in so many cases, despite the inadequacies of the available criteria, the degree of sexual size dimorphism in many other animal species may well also have been influenced by ecological factors. Hence, it may be premature to dismiss this hypothesis, despite the difficulty of testing it.

1,312 citations

Journal ArticleDOI
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

Journal ArticleDOI
TL;DR: These trends are derived from a sample of 40 independent clades of terrestrial animals, primarily vertebrates, and indicate that SSD increases with size where males are the larger sex, but decreases with sizeWhere females are larger, a trend formalized as “Rensch's rule.”
Abstract: Sexual size dimorphism (SSD) is common in both plants and animals, and current evidence suggests that it reflects the adaptation of males and females to their different reproductive roles. When species are compared within a clade, SSD is frequently found to vary with body size. This allometry is detected as β ≠ 1, where β is the slope of a model II regression of log(male size) on log(female size). Most frequently, β exceeds 1, indicating that SSD increases with size where males are the larger sex, but decreases with size where females are larger, a trend formalized as “Rensch's rule.” Exceptions are uncommon and associated with female-biased SSD. These trends are derived from a sample of 40 independent clades of terrestrial animals, primarily vertebrates. Their extension to plants and aquatic animals awaits quantitative assessments of allometry for SSD within these groups. Many functional hypotheses have been proposed to explain the evolution of allometry for SSD, most featuring sexual selection on males ...

898 citations

Journal ArticleDOI
TL;DR: The separation of phylogenetic from specific effects proposed here also allows phylogenetic factors to be explicitly included in cross‐species comparative analyses of adaptation, which solves a long‐standing problem in evolutionary comparative studies.
Abstract: We have presented a formal model for the quantitative analysis of phylogenetic and specific effects on the distribution of trait values among species. Total trait values are divided into phylogenetic values, inherited from an ancestral species, and specific values, the result of independent evolution. This allows a quantitative assessment of the strength of the phylogenetic inertia, or burden, displayed by a character in a lineage, so that questions concerning the relative importance of phylogenetic constraints in evolution can be answered. The separation of phylogenetic from specific effects proposed here also allows phylogenetic factors to be explicitly included in cross-species comparative analyses of adaptation. This solves a long-standing problem in evolutionary comparative studies. Only species' specific values can provide information concerning the independent evolution of characters in a set of related species. Therefore, only correlations among specific values for traits may be used as evidence for adaptation in cross-species comparative analyses. The phylogenetic autocorrelation model was applied to a comparative analysis of the determinants of sexual dimorphism in weight among 44 primate species. In addition to sexual dimorphism in weight, mating system, habitat, diet, and size (weight itself) were included in the analysis. All of the traits, except diet, were substantially influenced by phylogenetic inertia. The comparative analysis of the determinants of sexual dimorphism in weight indicates that 50% of the variation among primate species is due to phylogeny. Size, or scaling, could account for a total of 36% of the variance, making it almost as important as phylogeny in determining the level of dimorphism displayed by a species. Habitat, mating system, and diet follow, accounting for minor amounts of variation. Thus, in attempting to explain why a particular modern primate species is very dimorphic compared to other primates, we would say first because its ancestor was more dimorphic than average, second because it is a relatively large species, and third because it is terrestrial, polygynous, and folivorous.

653 citations

Journal ArticleDOI
TL;DR: The twodimensionality of the human mating environment, along with phylogeny, the spatial and temporal clustering of mates and competitors, and anatomical considerations, predict that contest competition should have been the primary mechanism of sexual selection in men and a functional analysis supports this prediction.

635 citations


Cites background from "Correlates of sexual dimorphism in ..."

  • ...Contests are also common among terrestrial primates, which exhibit greater body and canine size sexual dimorphism than arboreal and arboreal/terrestrial species (CluttonBrock et al., 1977; Leutenegger & Cheverud, 1982; Plavcan & van Schaik, 1997)....

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References
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5,406 citations


"Correlates of sexual dimorphism in ..." refers methods in this paper

  • ...Using principles of quantitative genetic theory ( Falconer, 1960; Lande, 1980), it can be shown that when selection is equally intense in both sexes, the change in sexual dimorphism per generation (Rso) wilI equal the difference between male and female responses to selection,...

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Book
01 Jan 1932
TL;DR: This detailed study of the different rates of growth of parts of the body relative to the body as a whole represents Sir Julian Huxley's great contribution to analytical morphology, and it is still a basis for modern investigations in morphometrics and evolutionary biology.
Abstract: This detailed study of the different rates of growth of parts of the body relative to the body as a whole represents Sir Julian Huxley's great contribution to analytical morphology, and it is still a basis for modern investigations in morphometrics and evolutionary biology. Huxley was the first to put the concept of relative growth - or allometry - upon a firm mathematical foundation, and since publication of this book in 1932, his work has been found to have greater implications than even he imagined. Problems of Relative Growth is at once a formulation of the basic principles of allometry and a survey of its many and various occurrences and applications. Examples are taken from such widely divergent areas as the development of the large claw in male fiddler-crabs, the size and number of points of deer antlers, heterogony in neuter social insects, the disproportionate growth of the human head from infancy to adulthood, and the formation of spiral shapes in certain mollusk shells and of the curved shape of the rhinoceros' horn. Starting from the fact of obvious disharmonic growth, Huxley formulates his first and fundamental law - that of the Constant Differential Growth Ratio. He then demonstrates that the distribution of growth potential occurs in an orderly and systematic way - that there are growth-gradients culminating in growth-centers. Other topics treated include multiplicative and accretionary kinds of growth, the role of hormones and mutations, and the relevance of the entire investigation to the problems of orthogenesis, recapitulation, vestigial organs, the existence of nonadaptive characters, physiological genetics, comparative physiology, and systematics. In theirintroduction to this unabridged facsimile republication of the original 1932 edition, Frederick B. Churchill and Richard E. Strauss place Huxley's work in the context of modern research in history and biology.

2,198 citations

Journal ArticleDOI
TL;DR: Sexual dimorphism may result from natural and/or sexual selection, and systems of mating are often thought to evolve in response to ecological pressures, although mating preferences may be self-reinforcing.
Abstract: Conspicuous sexual dimorphism is a feature of many species of higher animals. The genetic basis of variation in metrical characters, including that in sexual dimorphism between families or lines, is usually polygenic (Falconer, 1960; Frankham, 1968b; Wright, 1968, 1977; Bird and Schaffer, 1972; Ehrman and Parsons, 1976). Genetic experiments on mice, birds and Drosophila flies indicate that artificial selection practiced on a character of one sex causes not only a direct response of the character in the selected sex, but also a correlated response of the homologous character, if any, in the opposite sex (Shaklee et al., 1952; Harrison, 1953; Korkman, 1957; Becker et al., 1964; Eisen and Legates, 1966; Frankham, 1968a, 1968b; Eisen and Hanrahan, 1972). Such correlated selective responses are attributable to pleiotropy (and linkage) of genes affecting the characters of both sexes, that is, correlations between the additive effects of genes as expressed in males and females. The genetic correlation between homologous characters of the sexes is often quite high (op. cit.). As will be shown, this greatly restricts the rate of evolution of sexual dimorphism relative to that for the average phenotype of the two sexes. Sexual dimorphism may result from natural and/or sexual selection. Darwin (1874, Part 2) elucidated how natural selection operating differently on males and females arises from their distinctive roles in reproduction, or from competition between the sexes for resources such as food, leading to adaptive sexual dimorphism. He also reasoned that intrasexual contests for mates and intersexual mating preferences exert sexual selection, usually on the males, producing sexual dimorphism which is maladaptive with respect to natural selection. Comparisons within and between closely related species led Darwin to conclude that adult males typically are more modified than adult females or juveniles of either sex, but that females have often acquired male characters by "transference." It was difficult for Darwin to believe that sex-limitation of characters could evolve by selection, but Fisher (1958, Ch. 6) outlined how divergent selection on the two sexes could accumulate genes with different effects in males and females, causing a character at first expressed equally in both sexes to become sexually dimorphic and finally sex-limited. The strength of sexual selection is enhanced by a polygamous mating system, but the possibility of sexual selection in monogamous systems of mating exists due to male competition for early-breeding females, and mate choice exercised by these females (Darwin, 1874; Fisher, 1958; O'Donald, 1977). Systems of mating are often thought to evolve in response to ecological pressures (reviewed by Selander, 1972; Brown, 1975; Emlen and Oring, 1977), although mating preferences may be self-reinforcing (Fisher, 1958; O'Donald, 1967, 1977; Lande, unpubl.). Darwin and Fisher described qualitative methods by which an observed sexual dimorphism could be attributed mainly to either natural or sexual selection. To assign natural selection as the primary cause requires ecological observations that males and females follow different ways of life and employ the dimorphic character(s) adaptively in their distinct modes of survival or reproduction. Darwin presented several such examples, mostly among the lower classes of animals. Selander (1972) 292

1,692 citations

Journal ArticleDOI
TL;DR: The adaptive significance of Variation in body size, sexual dimorphism and socionomic sex ratio is discussed and as would be predicted on energetic grounds, home range size and day range length are positively related to group weight and are greater in frugivores than in folivores.
Abstract: Estimates of body weight, group size, home range size, day range length, socionomic sex ratio and sexual dimorphism are compared between 100 primate species, allocated to seven ecological categories. As would be predicted on energetic grounds, home range size and day range length are positively related to group weight and are greater in frugivores than in folivores; population density is negatively related to body weight; and group size is positively related to body weight. The adaptive significance of Variation in body size, sexual dimorphism and socionomic sex ratio is also discussed.

1,020 citations


"Correlates of sexual dimorphism in ..." refers background or result in this paper

  • ...This is in accordance with the hypothesis that energetic constraints-which presumably limit the increase in male size (Clutton-Brock and Harvey, 1977)-may be more restricting in some dietary groups than in others (Leutenegger and Kelly, 1977)....

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  • ...In order to account more fully for the variance, additional variables, primarily ecological factors, such as habitat, diet, distribution and abundance of food resources, predator defense or avoidance, and positional behavior, have been invoked (Crook and Gartlan, 1966; Crook, 1972; Eisenberg et al., 1972; Clutton-Brock and Harvey, 1977; 1978; Clutton-Brock et al., 1977; Leutenegger and Kelly, 1977; Rails, 1977; Leutenegger, 1978, 1982; Alexander et al., 1979)....

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  • ...This dichotomous classification of mating system is used instead of an interval-scale measure, such as socionomic sex ratio (Clutton-Brock and Harvey, 1977), because intervallevel measures are often difficult to measure accurately due to their wide variability within species and because of their often uncertain relationship to the intensity of intermale competition....

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  • ...Factors of evolutionary heritage, in the sense of "phylogenetic legacy" (Raup, 1972) or "phylogenetic inertia" (Wilson, 1975), may also affect sexual dimorphism (Clutton-Brock and Harvey, 1977; HarveY et al., 1978a)....

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  • ...Among primates, for example, although dimorphism has been shown to be positively related to breeding sex ratio, a major portion of the variance remains unexplained (Clutton-Brock and Harvey, 1977)....

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Journal ArticleDOI
18 Jun 1966-Nature
TL;DR: Find loads of the the evolution of primate societies book catalogues in this site as the choice of you visiting this page.
Abstract: Find loads of the the evolution of primate societies book catalogues in this site as the choice of you visiting this page. You can also join to the website book library that will show you numerous books from any types. Literature, science, politics, and many more catalogues are presented to offer you the best book to find. The book that really makes you feels satisfied. Or that's the book that will save you from your job deadline.

601 citations