Adjustment of sperm allocation under high risk of sperm competition across taxa: a meta-analysis

Authors


Javier delBarco-Trillo, Department of Evolutionary Anthropology, Duke University, 128 Biological Sciences Building, Box 90383, Durham, NC 27708, USA. Tel.: 919 660 7364; fax: 919 660 7348; e-mail: delbarcotrillo@gmail.com

Abstract

Sperm competition theory predicts that under high risk of sperm competition, males will increase the number of sperm that they allocate to a female. This prediction has been supported by some experimental studies but not by others. Here, I conducted a meta-analysis to determine whether the increase in sperm allocation under high risk of sperm competition is a generalized response across taxa. I collected data from 39 studies and 37 species. Across taxa, males under a high risk of sperm competition respond by increasing their sperm allocation (mean effect size = 0.32). Number of offspring did not explain a significant portion of the variation in effect sizes. A traditional meta-analysis (i.e. without phylogenetic information) described the variation among effect sizes better than a meta-analysis that incorporates the phylogenetic relationships among species, suggesting that the increase in sperm allocation under high risk of sperm competition is similarly prevalent across taxa.

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