Evolution of host specialization in the cactophilic fly, Drosophila mojavensis

• Main Author: Date, Priya
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2013
• Subjects: Biology; Ecology; Entomology; Evolution & development; Evolution and Development
• ISBN: 9781303516283; 1303516284

Adaptive divergence in traits associated with host plant specialization may cause reproductive isolation and promote speciation. Local adaptation is often a first step towards divergence and the proximate mechanisms underlying such divergence are less well understood. In this dissertation, I examine the evolution of host specialization in populations of Drosophila mojavensis on four different hosts across its range. The four host cacti differ in their headspace volatiles, as identified and quantified by GC-MS. These host specific olfactory cues are dynamic and complex with more than one odor important for host specific attraction. In response to these environmental changes the populations show alterations in their peripheral odor detection ability and olfactory behavior. Specifically, a Mojave Desert population that specializes on barrel cactus shows significant differences in electrophysiological responses to multiple odors in both olfactory organs and increased behavioral attraction to barrel cactus volatiles, its natural host. This divergence in olfactory related traits is supported by population specific gene expression differences in multiple chemosensory gene families. Additionally, when given a choice between different host cacti, the Mojave population shows a strong preference for its natural host whereas the other populations differ in their strength of behavioral preference. Preferences for alternative host plants are determined by similarity in host chemistry between cacti rather than phylogenetic relationships among cacti. Moreover, although the populations showing divergence in host preference behavior, their performance on their natural host is not necessarily linked to their preference. Populations do, however, vary in development time and body size depending on the cactus they are reared on. Together these results suggest that in D. mojavensis populations, differential host use has resulted in divergence in their physiology, behavior and life-history traits, and these factors contribute to reproductive isolation ultimately leading into ecological speciation in this species.