Abstract
Reproductive strategies often consist of two alternative tactics whereby males either compete for and guard females, or sneak copulations. By their nature, alternative tactics expose males to differing risks of sperm competition; sneaks will always be subject to sperm competition but guards will be subject to sperm competition with low probability, dependent on the number of sneaks. Recent game-theoretical models predict that males in the sneak role should have the greater gametic expenditure but that the disparity in expenditure should decrease with increasing numbers of sneaks. Male dung beetles in the genus Onthophagus can be separated into two morphs: major males have horns and guard females whereas minor males are hornless and sneak copulations. Here we compare testis size and ejaculate characteristics between these alternative morphs. We find that in O. binodis 30% of males are sneaks, and sneaks have larger testes, ejaculate volumes, and longer sperm than guards. In O. taurus 60% of males are sneaks and there are no differences in gametic traits. Our data thus provide empirical support for game-theoretical models of sperm competition.
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Selected References
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- doi: 10.1098/rspb.1997.0065. [DOI] [PMC free article] [Google Scholar]
- Parker G. A., Ball M. A., Stockley P., Gage M. J. Sperm competition games: a prospective analysis of risk assessment. Proc Biol Sci. 1997 Dec 22;264(1389):1793–1802. doi: 10.1098/rspb.1997.0249. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Parker G. A., Begon M. E. Sperm competition games: sperm size and number under gametic control. Proc Biol Sci. 1993 Sep 22;253(1338):255–262. doi: 10.1098/rspb.1993.0111. [DOI] [PubMed] [Google Scholar]
- Parker G. A. Sperm competition games: sperm size and sperm number under adult control. Proc Biol Sci. 1993 Sep 22;253(1338):245–254. doi: 10.1098/rspb.1993.0110. [DOI] [PubMed] [Google Scholar]
- Partridge L., Prowse N. The effects of reproduction on longevity and fertility in male Drosophila melanogaster. J Insect Physiol. 1997 Jun;43(6):501–512. doi: 10.1016/s0022-1910(97)00014-0. [DOI] [PubMed] [Google Scholar]