Research Fellows Directory
Professor Nina Wedell
University of Exeter
It is unknown why females mate with multiple males when mating is costly and a single copulation provides enough sperm to fertilize the female’s eggs. Multiple mating may allow females to increase offspring fitness if fertilization is biased towards the sperm of high fitness males. Selfish genetic elements spread through populations by subverting normal patterns of inheritance to increase their representation in the next generation, often at a cost to the bearer. They are ubiquitous in living organisms and can make up a large part of the genome. Several selfish genetic elements, such as meiotic drivers, B chromosomes and endosymbionts, are associated with reduced male fertility, and female fitness is frequently reduced when mating to males that carry them. However, by mating with several males, females can reduce the risk of only mating with males carrying selfish genetic elements. Multiple mating also results in sperm competition, where sperm from several males compete for fertilization. By promoting sperm competition, females can swamp the sperm of males carrying selfish genetic elements with normal males sperm. This is likely to be the case as selfish genetic elements are often associated with reduced male fertility. I have examined the impact of female multiple mating when facing the risk of mating to males that carry selfish genes. Not only do multiply mating females have higher fitness than singly mated females in this situation, female can also rapidly evolve increased remating rates in populations harbouring males carrying selfish genes. A wide range of selfish genetic elements are associated with reduced male fertility and therefore potentially provides the critical combination of low sperm competitive ability and low fitness that could favour polyandry. Because such selfish elements are ubiquitous in living organisms and frequently compromise male fertility they may provide a generally overlooked explanation for why polyandry is remarkably widespread.
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