9701108 Ryan Much of the variation among and within animal species arises as a result of differences in the strength of natural selection in different populations. This is particularly true for characteristics that are used in courtship and mate choice, and are therefore subject to sexual selection. Previous studies have concentrated on single traits; however, mate choice is usually based on suites of multiple traits. Natural selection can act in dramatically different ways on different traits. This study addresses the selection, and male conspicuousness in swordtail fish. Male swordtails vary greatly in body size, in the expression of a "sword" on the caudal fin of males, and in courtship in mate choice. This variation occurs at several levels of organization: among species, among populations of the same species, and within populations. Preliminary evidence suggests that sword length covaries with predation risk in three swordtail species. This research will (1) test for associations between male traits and predation risk in three populations each of the nine species in a group of closely related swordtails; (2) test for these associations in ten populations of one other swordtail species with a wide geographic distribution; (3) directly examine male predation in a subset of populations from both groups; and (4) test characters in swordtail populations with higher predation risks. This study should provide valuable insight into how forces of natural and sexual selection, such as predation and mate choice, interact to produce complex suites of conspicuous traits in animals.
