The Impacts of High Temperature and Precipitation on Genetic Retrogression South of the Hybrid Zone in Papilio Canadensis Butterflies
Nelson, Susan M.
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Swallowtail butterfly species closely related to P. canadensis have developed a hybrid zone in the United States. P. canadensis live in the North, P. glaucus and P. troilus live in the South and their hybrids inhabit the areas in between these two zones. Previous studies have explained the lack of northern introgression of P.glaucus. Currently, however, the reasons behind P. canadensis' restricted southward gravitation is unknown. This type of movement could maximize the number of generations they produce per year. The number of generations produced per year is dependent on the environmental conditions in the region where the adult lives and the resulting amount of time spent in each stage of metamorphosis. During diapause, the lowered metabolic state between pupae and adult metamorphosis, swallowtails are especially sensitive to their environment. It was predicted that high temperature and precipitation extremes would be remarkably influential climatic factors and therefore would play a substantial role in the limited southward movement of P. candensis. In order to study the impact of these climatic factors, an experiment was conducted on P. canadensis, P. troilus, and P.glaucus x P. canadensis hybrid pupae emerging from diapause. The two species and the hybrids were divided among four treatments: two different temperatures in dry or watered conditions. This was done in order to analyze variance in speed and success rate of eclosion. The two temperatures, 30°C and 36°C, proved to have very different impacts. The butterflies did not emerge more quickly at hotter temperatures as had been shown to occur in previous studies at lower temperatures. Very few eclosions proved 36°C to be essentially lethal, while 30°C was harmful to normal development and caused a high percentage of deformities. The impact of precipitation was minimal at both temperatures. At 36°C, the pupae could not survive regardless of the impact of precipitation and at 30°C the precipitation also played an inconsequential role.