Meade, Lara; (2018) Fitness consequences of sex-ratio meiotic drive and female multiple mating in a stalk-eyed fly, Teleopsis dalmanni. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Meiotic drive genes are a class of segregation distorter that gain a transmission advantage in heterozygous males by causing degeneration of non-carrier sperm. This advantage must be balanced by fertility or viability costs if drive is to remain at stable frequencies in a population. A reduction in male fertility due to sperm destruction reduces the fitness of the rest of the genome, accordingly mechanisms to circumvent the effects of drive may evolve. Such adaptations will have implications for how likely it is that drive will persist. The primary theme of this thesis has been examining fertility consequences of meiotic drive in a Malaysian stalk-eyed fly, Teleopsis dalmanni. I demonstrate that drive carrier males are not sperm limited, despite the destruction of half their sperm. They produce ejaculates with sperm numbers equivalent to wildtype male ejaculates. Furthermore, drive males achieve this with greatly enlarged testes. However, resources are not unlimited; drive males also have reduced body size, and reduced accessory glands and eyespan for their body size. Accessory gland size limits male mating frequency, and male eyespan is a sexually selected trait used in female choice and male-male competition. I discuss how these patters fit with theoretical models that predict males should invest in producing an optimal ejaculate according to levels of expected sperm competition, even if they are low-fertility males. A second interrelated theme of this thesis has been to examine the benefits of polyandry, female mating with multiple males, using wild-caught individuals. Polyandry is widespread across many taxa and almost ubiquitous in insects. However, there is much debate around its proximate and ultimate causes. There are many costs associated with mating and so polyandry requires an adaptive explanation. I utilise data on wild-caught T. dalmanni to explore how natural variation amongst females and males influences fertility gains for females.

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