Thesis (Ph. D.)--University of Oregon, 2006. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 96-103). Also available for download via the World Wide Web; free to University of Oregon users.

The legacy of historical biogeography impacts many organisms and results in a wide range of character variation over a latitudinal gradient. The pitcher-plant mosquito Wyeomyia smithii is one such organism that demonstrates a wide range of phenotypic and genotypic variation over the entirety of its range from the Gulf Coast to Canada. A geographic cline established by the presence and recession of the Laurentide Ice Sheet is manifest in the narrow range of thermal tolerance exhibited by different populations and also in the differing propensity of bloodfeeding by these mosquitoes. These contemporary clines were analyzed by a variety of experimental methods ranging from year-long fitness assays, scanning electron microscopy, and RNA-sequencing to determine the patterns underlying the resulting evolutionary differences among established populations. This dissertation includes both unpublished and co-authored material.

Photoperiodism is the ability of plants and animals to utilize day length or night length to mitigate seasonal exigencies. The circadian clock allows organisms to organize daily demands. Both process are set by light, and for more than 80 years a functional relationship has been pursued. Previous experiments have revealed, through phenotypic expression, that the daily circadian clock and seasonal photoperiodic timer have evolved independently, yet molecular evidence is lacking. Herein, we use the mosquito, Wyeomyia smithii, to understand the relationship between the photoperiodic response, diapause, and the daily circadian clock. We measured variation in the formal properties of the core circadian clock over a latitudinal and altitudinal gradient which we compare to the critical photoperiod, a measure of diapause, over the same geographic gradient. We found that there is no correlation with any of the formal properties of the core circadian clock and critical photoperiod, indicating independent evolution.

The pitcher plant mosquito Wyeomyia smithii maintains a broad geographic range from the Gulf of Mexico to central Canada, and throughout its range is genetically and phenotypically variable, though fully interfertile. Many of the traits that vary across the broad range of this mosquito owe their diversity to selection on populations, which maximize fitness in the unique environment in which each populations finds itself. While a diversity of traits vary by latitude and merit the interest of evolutionary biologists, including critical photoperiod, voltinism, and thermal tolerance, of interest in the following thesis is the variation in blood-feeding propensity within this single species of mosquito. In no other mosquito species are some populations obligate non-biters while in other populations willingly hematophagous. This thesis explores the evolutionary transition from biting to non-biting in the pitcher plant mosquito at multiple levels of biological integration, starting first by establishing a heritable basis for the transition, then moving to the fitness and life historical consequences of both the natural system and of a line artificially selected in the lab. The latter half of this thesis moves on to probe the genetic architecture underlying the shift in phenotype and ends after examining the transition to non-biting at the level of the gene using an RNA-sequencing experiment. The results stemming from this thesis are thoroughly discussed: in short, we find that fitness differs between biting and non-biting populations, that complex genetic architectures underlie the transition to non-biting in nature, but not under artificial selection, and finally, that many candidate loci are differentially regulated in biting populations relative to non-biting populations and that these loci most often cluster with metabolic biological pathways.