Molecular, physiological and life-history mechanisms of adaptation during range expansion of the mosquito Aedes albopictus

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Thesis (Ph.D.)--Georgetown University, 2011.; Includes bibliographical references.; Text (Electronic thesis) in PDF format. My thesis examines molecular, physiological and life-history mechanisms of adaptation during the invasion and range expansion of the mosquito Aedes albopictus. Photoperiodic diapause is a developmental arrest programmed during a photosensitive stage preceding the occurrence of unfavorable environmental conditions. Photoperiodic diapause is a critical adaptation to seasonal environmental variation in temperate habitats in a wide variety of arthropods. While the ecological significance of diapause is well-understood, the molecular basis remains largely unresolved. Therefore, I sought to identify transcriptional elements of diapause in Ae. albopictus. I identified two genes, fatty acyl coA elongase and epithelial membrane protein, upregulated in female follicles under diapausing-inducing short-day lengths in temperate populations but not in non-diapausing tropical populations. I further investigated potential physiological effects of the expression of fatty acyl coA elongase. As fatty acyl coA elongases are involved in the formation of long chain fatty acids, precursors to hydrocarbons, I hypothesized that an upregulation of the gene in adult females under diapausing conditions would result in increased production of egg surface hydrocarbons leading to increased desiccation resistance of diapause relative to non-diapause eggs. I determined that diapause eggs have one-third more surface hydrocarbons and one-half the water loss rate of non-diapause eggs; however, the hydrocarbon composition did not differ in diapause versus non-diapause eggs.; In another study, I utilized the invasion of Ae. albopictus into the US from Japan as a natural experiment to investigate the evolution of phenological (critical photoperiod) and morphological (pupal mass, winglength, egg volume) traits during range expansion across latitudinal gradients. For critical photoperiod, I compared data collected in 1988 on latitudinal variation in the US and Japan to contemporary data collected 20 years later. For morphological traits, I compared populations from a single contemporary collection from across the US and Japan. My results show rapid adaptive evolution of critical photoperiod during the invasion of Ae. albopictus into the US and a surprising lack of clinal variation for morphological traits in both countries. Overall, this research provides valuable insight into the molecular underpinnings of diapause and the evolutionary dynamics of phenological and morphological traits during range expansion in Ae. albopictus.
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