UC Santa Cruz

The complex dynamics of reproductive interactions drive organismal diversity. Thus, understanding these dynamics is an important goal for evolutionary biology. Reproductive interactions after mating can result in postmating sexual selection, selection on traits affecting fertilization success. My dissertation provides novel insights into how postmating sexual selection is influenced by (1) the social environment, (2) temperature, and (3) cryptic female choice, a process where females bias fertilization to specific males after mating. In Chapters 1 and 2, I used behavioral and experimental approaches on the ocellated wrasse, a fish with external fertilization. This species has three male morphs: a large nesting male, an intermediate-sized satellite male, and a small sneaker male. Females have a strong mating preference for nesting males. Sneakers override this preference by releasing more sperm than nesting males. Female reproductive fluid in this species decreases the importance of sperm number but increases the importance of sperm velocity in determining fertilization success, effectively favoring nesting males. I looked at how the social environment and male behaviors influence the timing of sneaking by conducting underwater behavioral observations. I found that sneaking time delays decreased (likely higher fertilization success) with increasing nest activity for sneakers. In Chapter 2, I tested how temperature influences the effect of female reproductive fluid on sperm performance. I found that cryptic female choice will be less effective at higher temperatures as female reproductive fluids no longer benefit nesting male sperm at high temperatures. For my final two chapters, I developed mathematical models to understand the evolutionary consequences of cryptic female choice. In Chapter 3, I found that incorporating cryptic female choice can drastically alter predictions of male reproductive investment compared to previous models that ignore cryptic female choice. I also found that male and female traits involved in cryptic female choice coevolve even with weak cryptic female choice. In Chapter 4, I found that this coevolution can help maintain reproductive isolation, helping the creation of new species. Overall, my dissertation demonstrates that postmating sexual selection can be influenced by both biotic and abiotic factors that are currently underappreciated.