Rapid Adaptive Evolution of Photoperiodic Response during Invasion and Range Expansion across a Climatic Gradient

Understanding the mechanisms of adaptation to spatio-temporal environmental variation is a fundamental goal of evolutionary biology. This issue also has important implications for anticipating biological responses to contemporary climate warming and determining the processes by which invasive species are able to spread rapidly across broad geographic ranges. Here, we compare data from a historical study of latitudinal variation in photoperiodic response among Japanese and U. S. populations of the invasive Asian tiger mosquito Aedes albopictus with contemporary data obtained using comparable methods. Our results demonstrated rapid adaptive evolution of the photoperiodic response during invasion and range expansion across similar to 15 degrees of latitude in the United States. In contrast to the photoperiodic response, size-based morphological traits implicated in climatic adaptation in a wide range of other insects did not show evidence of adaptive variation in Ae. albopictus across either the U. S. (invasive) or Japanese (native) range. These results show that photoperiodism has been an important adaptation to climatic variation across the U. S. range of Ae. albopictus and, in conjunction with previous studies, strongly implicate the photoperiodic control of seasonal development as a critical evolutionary response to ongoing contemporary climate change. These results also emphasize that photoperiodism warrants increased attention in studies of the evolution of invasive species.