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In a world first, a recent study at The University of Western Australia has explored the evolutionary effects of female mate-choice and male/male competition in one environment.

In order to understand why multiple mating evolved and remains a breeding strategy across the animal kingdom, 24 male and 24 female house mice from 16 generations of both polygamous and monogamous selection lines were placed in free-range enclosures for 11 weeks where they had to compete for resources and mates.

Dr Renee Firman, a researcher from UWA's School of Evolutionary Biology, found that the female mice benefitted from multiple mating (polyandry) by producing sons with increased reproductive success in a competitive environment.

"I removed animals from laboratory-reared monogamous and polygamous selection lines and placed them in large enclosures, allowing them to roam and interact freely," Dr Firman said.  "In providing a semi-natural environment, I ensured that male mice had to defend nest boxes and compete for territories and all individuals competed for mates.

"I found that males from the polygamous lines sired more offspring.  The increased fitness of males from lineages evolving with sperm competition may be explained by a genetic benefit associated with polyandry.  An evolutionary history of multiple mating in the polygamous lines may have allowed for the selection of good genes, such that those males that were successful in sperm competition had an intrinsic quality that resulted in offspring of greater fitness.

"Females may have preferentially mated with the polygamous line males to obtain genetic benefits for their offspring.  In a singe oestrous period, female house mice will copulate with both dominant and subordinate males, but more frequently with dominant males that may be deemed of higher genetic quality.

"This experiment provided support for the ‘good sperm' hypothesis, one of the explanations for the existence of polyandry, and showed that males that were successful in sperm competition sired more viable offspring," Dr Firman said.

Dr Firman's study is published this month in Proceedings of the Royal Society B .

Media references

Dr Renee Firman (UWA Centre for Evolutionary  (+61 8)  6488 2699  /  (+61 4) 39 099 587
Biology)
Janine MacDonald (UWA Public Affairs)  (+61 8)  6488 5563  /  (+61 4) 32 637 716