Abstract Zeh 9514245 Theoretical models generally portray sexual selection as a constant, undirectional force, driving a population towards a single, optimal male phenotype. Species are assumed to occupy homogeneous environments and to experience selection either through male competition or through mate choice by monogamous females. This view fails to explain why sexually-selected male characters are often precisely those which exhibit the greatest variability, perhaps because the models do not reflect the complexity of factors influencing trait evolution in nature. Many species, particularly those that exploit ephemeral resources, are subject to fluctuating environmental conditions. In addition, DNA fingerprinting has revealed that multiple paternity, and hence polyandry, is far more common than previously assumed. The research proposed here will test the hypothesis that sperm storage by polyandrous females, superimposed on male competition in a heterogeneous environment, can contribute to the maintenance of variability in male sexually-selected characters by carrying genotypes through episodes of unfavorable selection. The development of single-locus minisatellite DNA probes for a species whose natural history and reproductive biology are highly amenable to experimentation makes the neotropical pseudoscorpion, Cordylochernes scorpioides, a model system for testing this hypothesis. As an essential first step in carrying out a rigorous test of the sperm-storing females as carriers of male genetic variability hypothesis, the proposed research will determine whether all the elements of this model are present in the C. scorpioides system. First, to assess whether sexual selection favors a significantly smaller male phenotype within trees than on beetles, DNA fingerprinting will be used to quantify the relationship between male size and reproductive success in experimental tree populations. Second, to assess the ca pacity of females to act as carriers of male variability, DNA fingerprinting will be used to compare levels of multiple paternity in the broods of females captured in the act of boarding and of disembarking from beetles. In addition, sperm utilization patterns will be investigated in a semi-natural experimental simulation of a dispersal episode. Finally, to assess the potential for exaggerated male traits to respond to selection in the two environments, the design of the within-tree sexual selection experiment will provide field estimates of heritability based on paternity assignment and son/sire regression involving field-caught males (sires)and their male offspring recaptured after release and development to maturity in the field. Assuming that all the elements necessary for the model are found to exist in this pseudoscorpion system, the development of quantitative simulation models to investigate how selection in the two environments may be balanced will be the focus of future research.
