Grant, Claire Anne; (2003) The evolution of multiple mating in the stalk-eyed fly, Cyrtodiopsis dalmanni. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In the stalk-eyed fly, Cyrtodiopsis dalmanni, male eyespan is under sexual selection. This species has an extremely high mating frequency, however, the reasons for multiple mating by females are unclear. There are a number of adaptive hypotheses proposing either direct or indirect (genetic) benefits. I investigated three hypotheses that propose direct benefits for female multiple mating. (1) Sperm replenishment. Large females were found to have a higher number of eggs than small females and thus may require more sperm. Large females did not receive more ejaculate per mating but did mate at a higher frequency than small eyespan females. I concluded that females mate multiply to gain fertility benefits. (2) Ejaculate-derived fecundity enhancement. Mating increases female fecundity, representing a potential direct benefit of multiple mating. I established that male accessory gland proteins (components of the ejaculate) are partly or wholly responsible for the elevated fecundity caused by mating. (3) Reduction in female receptivity in response to mating. If mating is costly, then a reduction in receptivity to mating would constitute a direct benefit to females. I found no evidence that receptivity is reduced following mating. Two non-adaptive hypotheses for multiple mating by females were also evaluated. (1) Genetic correlation in male and female mating frequency. Female mating frequency may have evolved as a correlated response to selection on male mating frequency. I found no difference in the mating frequency of females from lines of flies that had been artificially selected for increased and decreased male mating frequency. There was therefore no evidence for a genetic correlation in mating frequency between the sexes. (2) Male control of mating frequency. I made phenotypic manipulations of male eyespan (and therefore attractiveness to females) in lines artificially selected for increased and decreased male mating frequency. I found that both female preference, and male mating propensity were important determinants of mating frequency suggesting that predominant male control of mating cannot explain female multiple mating.

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