Abstract
Divergence in host adaptive traits has been well studied from an ecological and evolutionary perspective, but identification of the proximate mechanisms underlying such divergence is less well understood. Behavioral preferences for host plants are often mediated by olfaction and shifts in preference may be accompanied by changes in the olfactory system. In this study, we examine the evolution of host plant preferences in cactophilic Drosophila mojavensis that feeds and breeds on different cacti throughout its range. We show divergence in electrophysiological responses and olfactory behavior among populations with host plant shifts. Specifically, significant divergence was observed in the Mojave Desert population that specializes on barrel cactus. Differences were observed in electrophysiological responses of the olfactory organs and in behavioral responses to barrel cactus volatiles. Together our results suggest that the peripheral nervous system has changed in response to different ecological environments and that these changes likely contribute to divergence among D. mojavensis populations.
Highlights
Divergence of morphological, physiological, and behavioral traits as a result of local adaptation to different ecological environments is well documented [1]
Behavioral Preferences for Cactus Fermentation Stage The four populations of D. mojavensis feed and breed on four different species of fermenting cacti, so we began our study of the role of olfaction in host plant shift by measuring the attraction of each population to their respective host plants across a range of fermentation stages
For the mainland Sonoran population, comparisons between uninoculated and five week fermented cacti are shown as no significant difference between uninoculated and one week fermented samples was found
Summary
Divergence of morphological, physiological, and behavioral traits as a result of local adaptation to different ecological environments is well documented [1]. Conspecific populations can shift to alternate host plants, often because of changes in host plant availability When such populations are geographically isolated, barriers to gene exchange can further contribute to divergence in host adaptive traits and may result in reproductive isolation among populations [4,5]. Promising are systems in which there is phenotypic divergence among populations of the same species from contrasting environments and for which extensive ecological data have been collected. Drosophila mojavensis represents such a system, and is a model of incipient speciation. D. arizonae, ranges from central Guatemala through mainland Mexico to Arizona, using columnar cacti and Opuntia hosts [8]
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