Cotton, AJ; (2016) What drives sexual selection? Meiotic drive, stress and mate choice in stalk-eyed flies. Doctoral thesis , UCL (University College London).

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Abstract

In many species females have been shown to preferentially mate with males that exhibit the most elaborate sexual ornaments. The handicap hypothesis is a major theory proposed to explain the evolution of such exaggerated traits. It postulates that the ornament is costly and handicaps the bearer such that only high quality males are able to produce the most exaggerated ornamentation. In this thesis I examined questions about male ornament evolution and the handicap hypothesis in the stalk-eyed fly, Teleopsis dalmanni. I examined how meiotic drive, a selfish genetic element that produces female-biased broods, associated with male eyespan (the sexually selected trait in T. dalmanni) in natural populations. I demonstrated a link between meiotic drive and ornament size, whereby small eyespan males were more likely to carry the meiotic drive X chromosome. I then examined how meiotic drive affected the condition-dependent expression of male eyespan. I found that although the mean eyespan of meiotic drive males was smaller, the overall degree of condition dependence was unaffected. Next, I explicitly tested whether there was empirical evidence for the handicap hypothesis in T. dalmanni. In wild populations, I found that under high experimental stress, survival was strongly correlated with male eyespan. In contrast, there was no relationship between eyespan and survival when flies were under low experimental stress. These results provide strong support for the handicap hypothesis. Laboratory experiments yielded similar results. I then explored how environmental quality influenced key components of sexual selection (lek structure and behaviour). I found that under low environmental quality, mean and variance in harem size and the strength of mate choice declined, suggesting reduced sexual selection in poor environments. Finally, I describe for the first time the existence of male mate choice in T. dalmanni, a species that had previously been invoked to exemplify a traditional model of female choice.

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