Present addresses: K. E. Levan, Division of Biological Sciences, University of California-San Diego, La Jolla, CA 92093, USA. T. Y. Fedina, Department of Ecology & Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA.
Testing multiple hypotheses for the maintenance of male homosexual copulatory behaviour in flour beetles
Article first published online: 13 OCT 2008
© 2008 The Authors. Journal Compilation © 2008 European Society For Evolutionary Biology
Journal of Evolutionary Biology
Volume 22, Issue 1, pages 60–70, January 2009
How to Cite
LEVAN, K. E., FEDINA, T. Y. and LEWIS, S. M. (2009), Testing multiple hypotheses for the maintenance of male homosexual copulatory behaviour in flour beetles. Journal of Evolutionary Biology, 22: 60–70. doi: 10.1111/j.1420-9101.2008.01616.x
- Issue published online: 18 DEC 2008
- Article first published online: 13 OCT 2008
- Received 29 May 2008; accepted 25 July 2008
- indirect sperm transfer;
- mating behaviour;
- sperm ageing;
- sperm dumping
Diverse animal groups exhibit homosexual interactions, yet the evolutionary maintenance of such behaviours remains enigmatic as they do not directly increase reproductive success by generating progeny. Here, we use Tribolium castaneum flour beetles, which exhibit frequent male homosexual copulations, to empirically test several hypotheses for the maintenance of such behaviours: (1) establishing social dominance; (2) practice for future heterosexual encounters; and (3) indirect sperm translocation. We found no evidence that Tribolium males use homosexual copulations either to establish dominance or to practice behaviours that increase their subsequent heterosexual reproductive performance. Our results provide limited support for the hypothesis of indirect sperm translocation: when males from two genetic strains mated with females immediately following a homosexual copulation, females produced progeny sired not only by the directly mating male, but also by that male’s homosexual partner. However, this phenomenon was detected in only 7% of homosexual pairs, and in each case such indirectly sired progeny accounted for < 0.5% of females’ total progeny. Direct observations indicated that mounting males often released spermatophores during homosexual copulations. These observations suggest that homosexual copulations may be a behavioural mechanism that allows males to expel older, potentially low-quality sperm. Additional work is needed to test this new hypothesis, and to determine whether sperm release during homosexual copulations occurs in other groups.