Hingle, Andrew Paul; (2001) Condition-dependent mate preference in the stalk-eyed fly Cyrtodiopsis dalmanni. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis investigates whether female mate preference is dependent upon female morphology or condition using the stalk-eyed fly, Cyrtodiopsis dalmanni, as a model. Workers in the field of sexual selection are interested in evidence for this type of variation in mate preference because it is believed it may affect the rate of evolution of male trait and female preference and increase our understanding of the mechanistic nature of mate choice. Little is known or understood about variation in female mating preferences despite the great attention paid to mating systems. There is some evidence for genetic variation in female preference. There is more evidence for environmental factors affecting preference, with sources as diverse as morphological phenotype, predation risk, parasitism, copying, age and experience having been identified. The phenotype of females was manipulated in two ways. First by varying larval food density to create females that varied in eyespan. Second, adult females were fed a sucrose diet to create a transient reduction in nutrition. Both manipulations are likely to have depressed female condition. Female eyespan correlates with body size and thus with fecundity. The sucrose diet also reduced female fecundity by causing a reduction of egg production. Under both manipulations, females in lower condition (small eyespan or sucrose diet) were less choosy. Female C. dalmanni normally prefer large eyespan males. Eyespan-dependent mate choice is probably due to large eyespan females having better vision and so being better able to distinguish between male phenotypes. Diet-dependent mate choice is caused by females with reduced egg production having weaker mate choice. Further investigation of eyespan-dependent mate preference was made by mixing large and small eyespan females in the same cage to see whether there was competition between the two female phenotypes for mates. The results did not provide evidence that females competed for mates. In addition, the use of fluctuating asymmetry (FA) as a tool for conservation biologists monitoring endangered populations was evaluated. Fluctuating asymmetry in exaggerated sexual ornaments has been proposed to show a strong positive relationship with environmental stress. No evidence was found to support this theory.

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