Sheridan, Letitia Anne Devoy; (1997) Sexual selection: Symmetry, inbreeding and mate choice in Trinidadian guppies. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis investigates whether asymmetry has a role in sexual selection in guppies. This is potentially interesting because it might illuminate whether the cues used in female mate choice correlate with male quality (the "good genes" hypothesis) or purely "aesthetic" choice. Guppies are well suited to investigations of mate choice as males have prominent sexual pigments which females use in mate choice decisions. Theory predicts that the symmetry of secondary sexual characters could indicate the quality of the male, as it is widely thought that fluctuating asymmetry (FA) is a sensitive indicator of developmental stress. Sexual coloration in guppies was found to be sensitive to genetic stress caused by-inbreeding. Several traits showed indications of inbreeding depression. Pigment areas and numbers of spots and colours all decreased with inbreeding. The response of different pigments was highly correlated with their importance to females in each population. Display rate and swimming performance also showed signs of inbreeding depression. The evidence on these traits is consistent with the "good genes" hypothesis. But there was no difference in pigment FA between inbred and control fish. This provides no evidence that genetic stress is reflected particularly well by FA. Females did not prefer outbred males, but preferred high display frequency above other cues. However, if display rate was controlled, females of both populations preferred males with symmetrical patterns when given choices between males differing in spot symmetry - but this is unusual FA as this concerned unpaired characters. Spot asymmetry showed no response to inbreeding and thus was a poor indicator of male condition. This cue appears to support the "aesthetic choice" hypothesis. Overall, this evidence suggests that most (but not all) traits preferred by females are good indicators of male quality. There was no evidence that any form of symmetry correlated with male condition.

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