Geographic variation in the effects of temperature on life-history traits in the large milkweed bug Oncopeltus fasciatus.

Complete sets of life-history data (sufficient to construct life-tables and calculate intrinsic rates of increase) were collected at each of three constant temperatures for descendants of two tropical populations of the Large Milkweed Bug, Oncopeltus fasciatus. Although the two populations occur only about 60 km apart, they experience quite different thermal regimes, with little variation in mean monthly temperature at either site. In addition to the pronounced effect of ambient temperature on life-history traits, significant population-by-temperature interactions were observed for six of the eight traits examined. The data and the recent history of the species' distribution are consistent with the hypothesis that natural selection in the cool habitat has favored improved survival and increased reproduction at cool temperatures, with some trade-offs with respect to performance at higher (but ecologically relevant) temperatures.