The proposed research examines the evolution of wing melanin pattern in two closely related lepidopteran species, Pieris occidentalis and P. protodice. Populations of P. occidentalis exhibit considerable latitudinal and elevational variation in melanin pattern, and both species exhibit seasonal variation. Melanin pattern functions in the regulation of body temperature and in courtship. Previous field experiments have demonstrated that P. occidentalis females prefer males with disproportionately large melanin characters in a specific region of the wing, and that they use the same characters to recognize and avoid males of P. protodice. Whether females benefit thereby is unknown. In P. occidentalis, the characters involved in mate choice are known to affect temperature regulation in other populations, but selection for thermoregulation favors reduced character size. In this research, field experiments will be used to measure female choice in P. occidentalis and P. protodice as a function of male melanin pattern variation, population density, and female reproductive status. The interaction between selection for temperature regulation and selected for reproductive success will be examined by measuring female choice in populations of P. occidentalis that differ in thermal environment. Whether females benefit from choosing highly melanized males will be measured in the laboratory by measuring several components of female reproductive success. Very little is known about how different kinds of selection interact to produce the observed variation in any character, because there are relatively few traits where all of the functions are well-understood. Studying how female choice for male melanin varies among populations with different thermal environments will provide such an opportunity. By quantifying the relationship between male wing color pattern and female mate choice, as well as the consequences for females of mate choice, the proposed research will address whether P. occidentalis females benefit from mate choice, and the extent to which female choice determines the evolution of male wing color pattern in this species. Comparisons of P. occidentalis with its close relative P. protodice will determine the importance of female mate choice for the differentiation of male color pattern between these two species.
