Pre- and post-spawning sexual selection in fishes: proximate and ultimate explanations of variation in reproductive fitness

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At the most fundamental level, evolution can be thought of in terms of allele frequency changes over generations. As such, one of the main goals of evolutionary biology is to explain why some individuals pass on more of their genes than others. My research program addresses this goal by elucidating factors that affect sexual selection, which alter reproductive skew and are thus responsible for changes in allele frequencies from one generation to the next. Until recently, sexual selection theory assumed most taxa were monogamous and selection was thought to operate mainly via processes prior to copulation, namely mate choice (typically females choosing amongst males) and competition for mates (typically among males). However, genetic and behavioural studies have recently shown that sexual promiscuity is common among most taxa. Multiple mating by females creates the potential for sexual selection to continue after copulation through sperm competition (the competition between sperm of different males for the fertilization of ova) and cryptic female choice (the differential use of sperm from one male over another, with a presumed genetic benefit to offspring fitness). As a result, reproductive fitness is now understood to be determined by the complex interactions of male and female traits during episodes of selection before and after copulation. Thus, a central question emerging in sexual selection theory is whether post-copulatory selection reinforces or counteracts pre-copulatory selection. Measurement of the relative importance of sexual selection during pre- and post-copulatory phases of paternity has rarely been examined, especially within a single mating system. My research program will use external fertilizing, non-resource based fish mating systems (Chinook salmon and redside dace) to examine pre- and post-spawning sexual selection (from both an ultimate and proximate manner) within mating systems, between populations and across species. Overall, this research program promises to produce high quality peer-reviewed publications, create innovative research tools for those who study sexual selection and train highly qualified personnel for academia, the private sector and government.