Abstract
Sperm competition is a widespread phenomenon influencing the evolution of male anatomy, physiology and behaviour. Bats are an ideal group for studying sperm competition. Females store fertile sperm for up to 200 days and the size of social groups varies from single animals to groups of hundreds of thousands. This study examines the relationship between social group size and investment in spermatogenesis across 31 species of microchiropteran bat using new and published data on testis mass and sperm length. In addition to male competition, I examined the effects of female reproductive biology on characteristics of spermatogenesis. Comparative studies indicate that relative testis mass is positively related to sperm competition risk in a wide range of taxa. Social group size may also influence the level of sperm competition, and one of the costs of living in groups may be decreased confidence of paternity. I used comparative analysis of independent contrast (CAIC) to control for phylogeny. Using two possible phylogenies and two measures of social group size, I found a significant positive relationship between social group size and testis mass. There was no relationship between testis mass and the dimension of the female reproductive tract or oestrus duration. Sperm length was not significantly related to body mass or group size, nor was it related to oestrus duration.
Full Text
The Full Text of this article is available as a PDF (275.1 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Cummins J. M., Woodall P. F. On mammalian sperm dimensions. J Reprod Fertil. 1985 Sep;75(1):153–175. doi: 10.1530/jrf.0.0750153. [DOI] [PubMed] [Google Scholar]
- Gomendio M., Roldan E. R. Sperm competition influences sperm size in mammals. Proc Biol Sci. 1991 Mar 22;243(1308):181–185. doi: 10.1098/rspb.1991.0029. [DOI] [PubMed] [Google Scholar]
- Grafen A. The phylogenetic regression. Philos Trans R Soc Lond B Biol Sci. 1989 Dec 21;326(1233):119–157. doi: 10.1098/rstb.1989.0106. [DOI] [PubMed] [Google Scholar]
- Gustafson A. W. Male reproductive patterns in hibernating bats. J Reprod Fertil. 1979 May;56(1):317–331. doi: 10.1530/jrf.0.0560317. [DOI] [PubMed] [Google Scholar]
- Harcourt A. H., Harvey P. H., Larson S. G., Short R. V. Testis weight, body weight and breeding system in primates. Nature. 1981 Sep 3;293(5827):55–57. doi: 10.1038/293055a0. [DOI] [PubMed] [Google Scholar]
- Nakatsuru K., Kramer D. L. Is sperm cheap? Limited male fertility and female choice in the lemon tetra (pisces, characidae). Science. 1982 May 14;216(4547):753–755. doi: 10.1126/science.216.4547.753. [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]
- Parker G. A. Why are there so many tiny sperm? Sperm competition and the maintenance of two sexes. J Theor Biol. 1982 May 21;96(2):281–294. doi: 10.1016/0022-5193(82)90225-9. [DOI] [PubMed] [Google Scholar]
- Racey P. A. The prolonged storage and survival of spermatozoa in Chiroptera. J Reprod Fertil. 1979 May;56(1):391–402. doi: 10.1530/jrf.0.0560391. [DOI] [PubMed] [Google Scholar]