Date

2019

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Integrative Biology

First Adviser

Itzkowitz, Murray

Abstract

Sexual selection is expected to favor females that allocate reproduction based on a male’s quality, but promiscuous females must be mating with males of varying quality. Because few studies have examined female choice as a series of mating decisions, this apparent conflict is not well understood. To better understand the processes by which females mate multiply this doctoral thesis used the sheepshead minnow (Cyprinodon variegatus), a species in which both sexes are highly promiscuous. In Chapter 1 of this dissertation, the consistency of both the promiscuous female C. variegatus mating strategy and the intensity that females allocated reproduction to their most-mated males were examined. Female C. variegatus adjusted their reproductive success and mating success after a recent encounter with the male population. Individual female C. variegatus similarly allocated reproduction to males and similarly ranked males in both presentations, suggesting that promiscuous female mate choices are consistent. Multiple female C. variegatus similarly allocated reproduction and hierarchically-rank males, suggesting that females use common preferences that are heritable within a population, and the promiscuous female mating strategy is less variable than previously thought. Since individuals are expected to adjust their mating strategy under various selection intensities, Chapter 2 of this doctoral thesis examined female mate choice and promiscuity in C. variegatus using three sex ratios: a female biased sex ratio (3 males: 6 females), an even sex ratio (6 males: 6 females) and a male biased sex ratio (12 males: 6 females). Female C. variegatus mating success, reproductive success and the proportion of reproduction allocated to female’s most-mated males were all unaffected by sex ratio biases. Unexpectedly, male and female selection intensities were unaffected by any of the sex ratios, and estimated sexual selection did not significantly differ in any examined sex ratio; but, male competition increased at higher male densities. These results suggest that the intensity of sexual selection acting on female C. variegatus is constant across the examined sex ratios, and therefore provides no incentive for females to adjust their mating strategy. Overall, the findings of this doctoral thesis expand our understanding of the processes used by promiscuous females to mate with multiple males, and ultimately provides a deeper understanding of how female promiscuity evolved.

Available for download on Monday, January 18, 2021

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