Year of Award

2008

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Organismal Biology and Ecology

Department or School/College

Division of Biological Sciences

Committee Chair

Douglas J. Emlen

Commitee Members

Mary Jane West-Eberhard, Erick P. Greene, Lila Fishman, Diana L. Six

Keywords

chrysomelid beetles, cryptic female choice, post-copulatory, Pre-copulatory, sexual selection, sperm compitition

Abstract

Females in nearly all sexually reproducing taxa mate with multiple males. In these species, male fitness is dependent on traits used during both the pre-copulatory processes influencing mate acquisition, as well as the post-copulatory processes influencing fertilization. However, few studies have simultaneously examined pre- and post-copulatory sexual selection within a particular species, and we therefore have little understanding of how these processes interact to determine male reproductive success.

The objective of my study was to gain a more comprehensive understanding of the evolution of sexually selected traits by examining the interactions between pre- and post-copulatory processes in the tortoise beetle Acromis sparsa.

I examined the relationship between traits involved in pre-copulatory strategies, such as secondary sexual characters, and traits involved in post-copulatory strategies, such as primary sexual characters and copulatory courtship. Primary and secondary sexual characters in A. sparsa were not correlated, indicating that males may be able to acquire and develop these traits independently of each other. On the other hand, copulatory courtship behaviors were negatively correlated with secondary sexual characters, suggesting that small males use courtship as a mechanism to compensate for decreased attractiveness to females, or to compensate for decreased access to females as a result of inferior fighting abilities. Thus, males may modulate the quality or intensity of their behaviors based on their pre-copulatory attributes.

I also examined the relative importance of primary and secondary sexual characters as well as copulatory courtship on the reproductive success of A. sparsa males using natural insectary experiments, double mating experiments, and paternity analyses. I found that, in natural settings, males with larger testes mated with and fertilized more and larger females, and sired more offspring overall. In double mating experiments, testes mass and copulatory courtship influenced male reproductive success. However, the effects of copulatory courtship were dependent on mating order. Thus, even in species with exaggerated secondary sexual traits, such as A. sparsa, under certain conditions, it is post-copulatory sexual traits that make the largest contributions to male fitness. Moreover, the degree to which these traits contribute to reproductive success can vary with mating context.

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© Copyright 2008 Paula Alejandra Trillo