The effect of body size dimorphism was examined using multiple regression with brain and testis size as the dependent variables and male body size and mass dimorphism as independent covariables. Bootstrapping was used to generate bias-free estimates of regression and correlation coefficients. Before employing a phylogenetically based comparative method, phylogenetic autocorrelation in relative brain size, body mass, and relative testicular size was tested using Phylogenetic Independence version 2.
The results of these tests not shown indicated these variables were significantly correlated with evolutionary history. The effects of shared evolutionary history on the relationships among measures of relative brain size, relative testes size, and dimorphism were therefore assessed using phylogenetically independent contrasts . Independent contrasts were estimated using the primate phylogeny presented in Purvis  with all branch lengths set to 1 Text S1.
The evolutionary relationship among variables was assessed using Pearson correlation coefficients and least-squares regression through the origin. I am grateful to M. Nargolwalla, N. Taylor, and S. Lehman for their technical assistance during portions of my analysis. Naturally, responsibility for any interpretations, errors, or omissions lies solely with the author.
Conceived and designed the experiments: MS. Performed the experiments: MS.
Analyzed the data: MS. Wrote the paper: MS. Browse Subject Areas? Click through the PLOS taxonomy to find articles in your field. Abstract Reproductive competition among males has long been considered a powerful force in the evolution of primates.
Sperm Competition and the Evolution of Animal Mating Systems describes the role of sperm competition in selection on a range of attributes from gamete. Sperm Competition and the Evolution of Animal Mating Systems. Book • Edited by: ROBERT L. SMITH. Browse book content. About the book. Search in.
Introduction Since Darwin's publication  on the evolution of humans and sexual selection, reproductive competition among males has been considered a powerful force in the evolution of primates and other mammals. Results Results from the analyses of covariance ANCOVA estimating the relationships of female promiscuity and mating system with brain size and testes size indicated mating system was associated significantly with brain size in primates after accounting for body mass, while female promiscuity was not Table 1. Download: PPT. Table 1. Results of analyses of covariance ANCOVA and variance ANOVA for the dependent log e -transformed variables: brain mass, testis mass, and mass dimorphism on measures of mating system and female promiscuity with body mass treated as a covariate.
Table 2. Results of the analysis of variance ANOVA comparing relative brain size, relative testis size, and sexual dimorphism across mating systems, and Mann-Whitney comparisons between promiscuity levels. Table 3.
Pearson correlation coefficients among variables listed above the diagonal and independent contrasts listed below the diagonal. Discussion The results of the study indicate that unlike bats, sperm competition did not significantly influence the evolution of brain size in primates.
Methods For the present study, relative testes size, or the gonadosomatic index, was used as a measure of the level of sperm competition  —  , and sexual mass dimorphism was used as a measure of the level of male competition for mates . Statistical analysis Like all mammals, brain size and testes size scale allometrically with body size in primates . Supporting Information.
Table S1. Table S2. Text S1. Acknowledgments I am grateful to M. Author Contributions Conceived and designed the experiments: MS. References 1. Darwin C The descent of man, and selection in relation to sex. London, UK: Murray. Dunbar RIM Neocortex size and group size in primates: a test of the hypothesis.
J Hum Evol — View Article Google Scholar 3. Dunbar RIM The social brain hypothesis. Evol Anthropol 6: — View Article Google Scholar 4.
Dunbar RIM The social brain: mind, language, and society in evolutionary perspective. Ann Rev Anthropol — View Article Google Scholar 5. Machiavellian intelligence II. In these analyses we controlled for phylogeny and a variety of ecological and life-history variables. We used testis size corrected for total body mass as an index of sperm competition in each species, because testis size is correlated with levels of extrapair paternity and is available for a large number of species. In contrast to recent studies, we found strong and consistent effects of social mating system on most forms of dimorphism.
Social mating system strongly influenced dimorphism in plumage, body mass, and wing length and had some effect on dimorphism in tail length. When it comes to reproduction, it seems, that anything goes. Individuals account for very little as everything is a mediocre "play by numbers". Fairly goo Fairly dry text, what you'd expect. Fairly good text though, in terms of research. The authors sure took their time to study.
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