Competition, Choice and Mating Success in the Darter Subgenus Catonotus

Mate choice and competition for mates can strongly influence fitness. Selection to compete within a sex varies with the operational sex ratio (OSR), the ratio of fertilizable females to males, with the more abundant sex being more competitive. In animals, males often appear to be the more competitive sex, as indicated by conspicuous male-male aggression, solicitation of females, and/or secondary sexual ornaments, such as the bright male nuptial coloration of most species of the darter genus Etheostoma. Species with paternal care, however, have male nuptial coloration that is less conspicuous to the human eye. In some fishes and birds with substantial paternal care, females are the more competitive sex, and males are choosier. In the first chapter, I investigate whether this pattern holds in the paternal care darter E. nigripinne by offering males and females a choice between either a conspecific or heterospecific mate. Females strongly preferred conspecific mates, while males showed no group-wide preference. In the second chapter, I examine life history characteristics in a local population of another paternal care darter, E. flabellare, to quantify the OSR experienced by reproductively active individuals. Results indicated that the OSR varies seasonally in this species, which may select for flexible levels of competitiveness and choosiness. To test whether such behavioral flexibility exists, in the third chapter I observed the competitive and solicitous behaviors of nine cohorts of males and females under manipulated OSRs over the course of two mating seasons. Male competitive behavior increased, and female competitiveness decreased, with the addition of more males. In the fourth chapter, I tested whether the observed changes in male behavior yielded increased reproductive success. Indeed, increased male-male aggression predicted increased male fitness. I conclude that male E. flabellare respond plastically and adaptively to OSR variance in a manner predicted by sexual selection theory