Finnegan, Sam Ronan; (2020) The effect of sex-ratio meiotic drive on sex, survival and size in the Malaysian stalk-eyed fly, 'Teleopsis dalmanni'. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Meiotic drive is a type of selfish genetic element that, in heterozygous males, disables or destroys non-carrier sperm in order to bias its own transmission. Meiotic drive genes are predicted to spread rapidly due to this transmission advantage and even, if sex-linked, cause population extinction due to the loss of one sex. Despite this, many meiotic drive genes are found at low/moderate, stable frequencies, which implies their carriers must bear unknown costs that balance this transmission advantage. Such costs may come about as direct or pleiotropic effects of the meiotic drive gene(s) themselves, or because drive is often associated with inversions that are expected to accumulate deleterious mutations. The theme of the thesis has been to search for costs of meiotic drive in the Malaysian stalk-eyed fly, Teleopsis dalmanni. First, I assess whether the expected low quality of meiotic drive males has impacted the strength of their mate preference for high quality females. I find that male mate preference does not depend on drive status but does depend on eyespan. Male eyespan is a sexually- selected ornamental trait and drive males typically have small eyespan. I also show that drive males are unable to mate as frequently as non-drive males. Second, I study the effect of meiotic drive on the egg-to-adult viability of stalk-eyed flies. I show that drive reduces the viability of both sexes, with drive males and homozygous drive females showing the greatest loss of 5 viability compared to their non-drive counterparts. Third, I study the effect of larval food stress on the drive-associated reduction in male eyespan. I find that drive males and females have reduced eyespan, but the magnitude of this reduction does not increase under high stress. This implies that the small eyespan of drive males is unlikely to be a condition-dependent effect of the expected increased mutation load. I discuss how small eyespan may instead be part of a suite of adaptations to maintain high fertility in the face of the destruction of half of all sperm. Finally, I use experimental evolution to track the frequency of meiotic drive in cage populations and find considerable heterogeneity. While one cage is driven extinct due to the loss of males, drive frequency generally declines in other populations, disappearing entirely from some after six generations.

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