Although the degree of mate competition, given extreme differences in sex ratio, explains much of the pattern of male-biased size dimorphism among diverse taxa, it fails for some species which have potential for inten...Although the degree of mate competition, given extreme differences in sex ratio, explains much of the pattern of male-biased size dimorphism among diverse taxa, it fails for some species which have potential for intense male competition for mates and yet exhibit little or no sexual size dimorphism （SSD）. This fact suggest that species with low SSD should be express the effect of evolutionary pressure in non-obvious geometrical shape promoted by sex ratio in an evolutionary time scale. To evaluate this hypothesis we used phylogenetic comparative method in a Bayesian framework to investigate the evolution of SSD and the role of sex ratio at inter-specific level in the species of Ceroglossus （Coleoptera： Carabidae）. In our results the proportion farthest from 1：1 is associated with more disparate body shape, even though the entire group has minimum variation in sex ratio, which is an intrinsic life history character of this group considering its phylogenetic conservatism or phylogenetic signal. We suggest that the sex ratio has determined the dimorphism degree during evolution of this group, since both traits have increased or decreased together during the species divergence （i.e. positive phylogenetic correlation： r2=0.85）. We suggest that morphological studies of SSD will benefit from using comparative method with Bayesian approaches to assess the effect of phylogenetic history and its uncertainty. Finally, this will be allow to researchers to quantify the uncertainty of specific evolutionary hypotheses accounting for observed sexual dimorphism patterns.展开更多
Dear Editors,Sexual dimorphism is the systematic difference in size,shape,color,physiology,and behavior,between male and female individuals of the same species（Mei and Gui,2015）.Some studies have indicated that the ...Dear Editors,Sexual dimorphism is the systematic difference in size,shape,color,physiology,and behavior,between male and female individuals of the same species（Mei and Gui,2015）.Some studies have indicated that the traits of sexual dimorphism in vertebrates are the consequences of sex-biased gene expression and are controlled by multiple critical genes during growth and development（Williams and Carroll,2009）.However,the exact molecular mechanism underlying sexual dimorphism remains unclear.展开更多
Why do two sexes of the same species differ in body size holds a long-standing question of evolutionary biology. While many across-species comparisons have focused on ultimate causes behind sexual size dimorphism （SS...Why do two sexes of the same species differ in body size holds a long-standing question of evolutionary biology. While many across-species comparisons have focused on ultimate causes behind sexual size dimorphism （SSD）, only have a few been directed toward elucidating its ontogenetic basis. Urodeles are an amphibian group in which the direction and degree of SSD vary greatly among species. Using demographic data yielded by skeletochronology for 33 urodele species, the current study re- veals a positive across-species correlation between SSD and the sex difference in mean age of adult animals, and the latter in- creases with the corresponding difference in age at maturity; annual growth rate does not differ between the sexes. We conclude that extended longevities in one sex, which is mediated by delayed maturation, would allow it to grow for longer and get larger, with growth rate making a weak contribution to body size. The sex-specific divergence in ontogenetic trajectory might be ex- plained by potentially high growth costs of reproduction to females in association with stronger fecundity selection, and to males that are expected to experience stronger sexual selection [Current Zoology 59 （1）： 142-150, 2013].展开更多
In polygynous mammals, mature males are usually much heavier than females. Competition for females is intense, and few males reproduce. Given the importance of the male＇s body size for the reproduction and social lif...In polygynous mammals, mature males are usually much heavier than females. Competition for females is intense, and few males reproduce. Given the importance of the male＇s body size for the reproduction and social life of these species, levels of sexual dimorphism were studied in 27 species of polygynous terrestrial cetartiodactyls at the 3 most significant stages of development： birth, 6 months of age, and adulthood. Overall, there were 3 different types of changes in male-to-female （M/F） mass ratios between birth and adulthood, corresponding to the 3 categories of adult dimorphism. The change in mass ratio between birth and 6 months of age was inversely correlated to the degree of dimorphism at birth. Most adult dimorphism was acquired after weaning. On the whole, postnatal maternal care seems to have no or even an inverse effect on the evolution of dimorphism, which is apparently not consistent with the assumption of greater maternal investment in male than in female offspring among polygynous mammals.展开更多
文摘Although the degree of mate competition, given extreme differences in sex ratio, explains much of the pattern of male-biased size dimorphism among diverse taxa, it fails for some species which have potential for intense male competition for mates and yet exhibit little or no sexual size dimorphism （SSD）. This fact suggest that species with low SSD should be express the effect of evolutionary pressure in non-obvious geometrical shape promoted by sex ratio in an evolutionary time scale. To evaluate this hypothesis we used phylogenetic comparative method in a Bayesian framework to investigate the evolution of SSD and the role of sex ratio at inter-specific level in the species of Ceroglossus （Coleoptera： Carabidae）. In our results the proportion farthest from 1：1 is associated with more disparate body shape, even though the entire group has minimum variation in sex ratio, which is an intrinsic life history character of this group considering its phylogenetic conservatism or phylogenetic signal. We suggest that the sex ratio has determined the dimorphism degree during evolution of this group, since both traits have increased or decreased together during the species divergence （i.e. positive phylogenetic correlation： r2=0.85）. We suggest that morphological studies of SSD will benefit from using comparative method with Bayesian approaches to assess the effect of phylogenetic history and its uncertainty. Finally, this will be allow to researchers to quantify the uncertainty of specific evolutionary hypotheses accounting for observed sexual dimorphism patterns.
基金supported by the State Key Laboratory of Freshwater Ecology and Biotechnology (2015FB03)the Fundamental Research Funds for the Central Universities (52204-12018, 2013PY068)
文摘Dear Editors,Sexual dimorphism is the systematic difference in size,shape,color,physiology,and behavior,between male and female individuals of the same species（Mei and Gui,2015）.Some studies have indicated that the traits of sexual dimorphism in vertebrates are the consequences of sex-biased gene expression and are controlled by multiple critical genes during growth and development（Williams and Carroll,2009）.However,the exact molecular mechanism underlying sexual dimorphism remains unclear.
文摘Why do two sexes of the same species differ in body size holds a long-standing question of evolutionary biology. While many across-species comparisons have focused on ultimate causes behind sexual size dimorphism （SSD）, only have a few been directed toward elucidating its ontogenetic basis. Urodeles are an amphibian group in which the direction and degree of SSD vary greatly among species. Using demographic data yielded by skeletochronology for 33 urodele species, the current study re- veals a positive across-species correlation between SSD and the sex difference in mean age of adult animals, and the latter in- creases with the corresponding difference in age at maturity; annual growth rate does not differ between the sexes. We conclude that extended longevities in one sex, which is mediated by delayed maturation, would allow it to grow for longer and get larger, with growth rate making a weak contribution to body size. The sex-specific divergence in ontogenetic trajectory might be ex- plained by potentially high growth costs of reproduction to females in association with stronger fecundity selection, and to males that are expected to experience stronger sexual selection [Current Zoology 59 （1）： 142-150, 2013].
文摘In polygynous mammals, mature males are usually much heavier than females. Competition for females is intense, and few males reproduce. Given the importance of the male＇s body size for the reproduction and social life of these species, levels of sexual dimorphism were studied in 27 species of polygynous terrestrial cetartiodactyls at the 3 most significant stages of development： birth, 6 months of age, and adulthood. Overall, there were 3 different types of changes in male-to-female （M/F） mass ratios between birth and adulthood, corresponding to the 3 categories of adult dimorphism. The change in mass ratio between birth and 6 months of age was inversely correlated to the degree of dimorphism at birth. Most adult dimorphism was acquired after weaning. On the whole, postnatal maternal care seems to have no or even an inverse effect on the evolution of dimorphism, which is apparently not consistent with the assumption of greater maternal investment in male than in female offspring among polygynous mammals.
