Understanding the mechanisms of adaptation to spatiotemporal 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 ∼15° 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.

Aedes albopictus (Skuse) (Diptera: Culicidae) is an invasive, container-inhabiting mosquito that was introduced into North America from Japan in 1985. Although previous studies using neutral biochemical markers have found high levels of population differentiation across both the North American and global distribution of Ae. albopictus, relatively little is known regarding evolutionary differentiation of life history traits underpinning fitness. We performed common-garden and line-cross experiments to examine the genetic differentiation of fitness (r')and underlying performance traits at three spatial scales: 1) local (among populations within Florida), 2) regional (between populations from Florida and New Jersey), and 3) long distance (between populations from Florida and Hawaii, Malaysia, and Japan). We found that North American populations (Florida and New Jersey) had lower fitness (r') than populations from outside North America (Hawaii, Malaysia, and Japan). Bivariate means of female, but not male, pupal mass and developmental time differed among regions (Florida, New Jersey, outside North America). Larval survivorship did not differ among regions nor among populations within regions, whereas size-specific fecundity varied among populations within regions but not among regions. Population crosses resulted in significant heterosis and outbreeding depression Of F1 hybrids but the results of crossing did not depend on the geographic distance separating parental populations in a consistent manner. Together, our results imply a role for local genetic drift affecting the life-history differentiation of Ae. albopictus populations. These conclusions corroborate previous studies of population structure based on neutral biochemical markers.

Aedes albopictus (Skuse) (Diptera: Culicidae) invaded the United States in 1985 and spread rapidly across eastern North America, whereas Aedes japonicus (Theobald) invaded and became established in the United States more recently (1998). The two species may co-occur in container habitats, and they are of potential public health concern as arbovirus vectors. To evaluate ecological differences between Ae. albopictus and Ae.japonicus, we compared larval foraging behavior of these two species. Based on results from a previous competition experiment, we predicted that Ae. albopictus would be a more active forager than Ae. japonicus. However, Ae. japonicus exhibited greater foraging activity than Ae. albopictus in four of six food environments, including a "no food" control treatment. Our results, therefore, suggest that more active foraging does not connote superior competitive ability, and competitive interactions between these species may be mediated by factors other than feeding behavior.

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Aedes albopictus (Skuse) (Diptera: Culicidae) invaded the United States in 1985 and spread rapidly across eastern North America, whereas Aedes japonicus (Theobald) invaded and became established in the United States more recently (1998). The two species may co-occur in container habitats, and they are of potential public health concern as arbovirus vectors. To evaluate ecological differences between Ae. albopictus and Ae.japonicus, we compared larval foraging behavior of these two species. Based on results from a previous competition experiment, we predicted that Ae. albopictus would be a more active forager than Ae. japonicus. However, Ae. japonicus exhibited greater foraging activity than Ae. albopictus in four of six food environments, including a "no food" control treatment. Our results, therefore, suggest that more active foraging does not connote superior competitive ability, and competitive interactions between these species may be mediated by factors other than feeding behavior.

No abstract