Fertilization in The Sea: The Ecological and Evolutionary Consequences of Sperm Chemoattraction

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Disentangling the effects of female choice, contest competition and scramble competition for mates.M. Spritzer, D. Meikle, and N. Solomon lay abstractSexual selection is differential mating success caused by variation among members of one sex in a trait that influences acquisition of mates. Although sexual selection is one of the most intensively studied areas in the field of behavioral ecology, surprisingly little is known about the relative importance of the different mechanisms of sexual selection. The main goal of the proposed research is to determine the relative importance of female choice, contest competition, and scramble competition for mates in determining the mating success of males. Female choice involves females choosing to mate with a male based on conspicuous ornaments or behaviors. Contest competition involves direct aggressive interactions between males and scramble competition, in contrast, involves a male's ability to rapidly and accurately locate mates. Meadow voles were used as the study species because past studies suggest that all three of these mechanisms of sexual selection occur among these rodents. Male navigation ability was chosen as a trait believed to be favored by scramble competition, and male dominance rank was chosen as a trait believed to be favored by contest competition. In addition, the influence of female choice upon both of these traits will be tested. The specific objectives are to determine: (1) the relationship between male navigation ability and male mating success, (2) the relationship between dominance and navigation ability among male voles, (3) the relative influence of dominance and navigation ability upon male mating success, and (4) female mating preferences for males with varying levels of navigation ability and dominance. A series of lab and field experiments will be used to achieve these objectives. Navigation ability will be measured by scoring each male's ability to complete a maze test, and male dominance will be tested by scoring aggression between pairs of males in arena trials. Male reproductive success will be determined using genetic paternity analyses. The results of this project will be an important next step in understanding how sexual selection shapes the evolution of a species.