DISSERTATION RESEARCH: Mechanisms of Female Mate Choice in a Coercive Mating System

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

Mechanisms of Post-Copulatory Choice in a Coercive Mating System Dr. Karen S. Oberhauser Michelle J. Solensy When sexual coercion, sometimes called forced copulation, is prevalent in a species, females have limited control over the outcome of individual mating attempts. However, they may evolve other means of determining the males with which they mate, or the males that actually fertilize their eggs. Mating attempts in monarch butterflies typically involve a lengthy ground struggle during which males sometimes force females to mate. Females may use this struggle to assess male quality and adjust their level of resistance accordingly (precopulatory choice), or they may bias sperm use in favor of high quality males (postcopulatory choice). Postcopulatory mate choice by females could be an important selective force driving the evolution of male reproductive strategies, and should be especially important in species in which coercion is a common mating strategy. In a preliminary study, there was little evidence to support the existence of precopulatory female choice in monarch butterflies. Studies addressing this topic will be continued in both laboratory and wild populations. Studies of postcopulatory choice will address the hypothesis that females use spermatophore size as an indicator of male mating history, and bias sperm use in favor of males that have mated previously. Spermatophore size is a reliable, honest, and detectable signal of male mating success, and previous work has demonstrated that male mating success is heritable. Thus, females may benefit by selecting sperm based on this cue since mating success should be transmitted to their sons. The proposed experimental design separates the effect of biased sperm use from the potentially confounding effect of sperm competitiveness.