Harley, EM; (2013) Reproductive quality and mating strategies in stalk-eyed flies. Doctoral thesis (PhD), UCL (University College London).

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Abstract

Stalk-eyed flies are characterised by having eyes that project laterally from the head. Male eyespan is known to be subject to sexual selection via female mate preference for exaggerated ornaments. This thesis examines reproductive quality and mating strategy in both sexes, in laboratory and field populations, using two species that are sexually dimorphic for eyespan. Using the African stalk-eyed fly species Diasemopsis meigenii I examined male sperm allocation during single and multiple matings. I demonstrate that during single matings males allocate larger quantities of sperm to highly fecund females. However, large eyespan males do not transfer more sperm than small eyespan males, despite having larger reproductive organs. All males are subject to ejaculate depletion during multiple matings, but small eyespan, and thus unattractive, males suffer the greatest degree of depletion. I conducted novel field observations of the Malaysian stalk-eyed fly Teleopsis dalmanni to examine female sperm limitation and direct benefits of mating. Highly fertile females do not benefit from an additional mating, while less fertile females can dramatically increase their fertility with the sperm from a single mating. Sperm limited females show increased receptivity to additional matings by engaging in a first copulation sooner than recently mated females. Female fecundity was positively correlated with sperm storage, suggesting that the presence of sperm in the reproductive tract acts as a trigger for egg maturation. Finally, I asked whether male and female eyespan, and the different reproductive strategies believed to be associated with the eyespan trait, resulted in differences to the trade-off between reproduction and soma. Using dietary manipulation I show that both males and females incur a cost of reproduction, as reproductive traits show reduced size under harsh conditions. Using extractable lipid content as a measure of somatic investment, I show that both males and females retain fewer lipids in their soma under harsh dietary conditions. But I find very little evidence for varying reproductive and somatic investment with eyespan.

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