Evol Ecol Res 8: 345-356 (2006)     Full PDF if your library subscribes.

Ejaculate investment in a promiscuous rodent, Peromyscus maniculatus: effects of population density and social role

Tristan A.F. Long* and Robert Montgomerie

Department of Biology, Queen’s University, Kingston, Ontario K7L 3N6, Canada

Author to whom all correspondence should be addressed.
e-mail: longt@biology.queensu.ca


Questions: How does average male investment in ejaculates vary with changing population density (and thus with the risk of sperm competition) in a promiscuous species? Do individual male investment strategies vary with population density?

Data studied: Total testicular mass, somatic mass and annual population density for wild-caught male deer mice, Peromyscus maniculatus, collected by snap-trapping over a 23-year period in Algonquin Provincial Park, Ontario, Canada.

Search methods: We analysed the relation between mean testicular mass and mouse population densities across years. To investigate individual investment patterns, we compared the relation between total testicular mass and somatic mass among males for years differing in population density.

Conclusions: Average investment in the testes was positively correlated with annual population density. An individual’s investment in testes depended on both the abundance of rival males and on relative body size, a trait associated with social rank.

Keywords: ejaculate investment, mating system, Peromyscus maniculatus, population density, sexual selection, sperm competition, testicular mass.

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        © 2006 Tristan A.F. Long. All EER articles are copyrighted by their authors. All authors endorse, permit and license Evolutionary Ecology Ltd. to grant its subscribing institutions/libraries the copying privileges specified below without additional consideration or payment to them or to Evolutionary Ecology, Ltd. These endorsements, in writing, are on file in the office of Evolutionary Ecology, Ltd. Consult authors for permission to use any portion of their work in derivative works, compilations or to distribute their work in any commercial manner.

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