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Tuesday "Noon" Seminar : Oct. 24Luciano M. Matzkin on "The molecular basis of host adaptation in cactophilic Drosophila: Molecular evolution of Glutathione-s-transferase (Gst) genes in Drosophila mojavensis"
12:30-1:45 p.m. in Biosciences West (map of building location), Room 208 |
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Talk Abstract Patterns of transcriptional and sequence variation can be shaped in part by natural selection, especially during the process of adaptation to alternative natural environments. We have previously investigated the role of transcriptional variation in the adaptation of Drosophila mojavensis to its hosts and have produced a set of candidate loci that are differentially expressed in response to host shifts. Drosophila mojavensis is a cactophilic fly endemic to the north western deserts of North America. This species contains four genetically isolated cactus host races (Baja California, mainland Sonora, Mojave and Catalina Island) each individually specializing in the necrotic tissues of different cactus species (Stenocereus gummosus, S. thurberi, Ferocactus cylindraceus and Opuntia sp., respectively). The necrosis of each cactus species provides each of the resident D. mojavensis populations with a distinct chemical environment to which they must adapt. Members of the Glutathione-S-transferase gene family have been known to play a role in detoxification in many taxa, including insects. A gene with high homology to the D. melanogaster Glutathione-S-transferase-D1 (GstD1) locus was differentially expressed in a Baja California D. mojavensis isofemale line as a response to utilizing an alternative host (S. thurberi). In both D. melanogaster and in Anopheles gambiae, GstD1 has been implicated in the resistance of these species to the insecticide DDT. I have examined the pattern of sequence variation of the GstD1 locus from all four D. mojavensis populations, D. arizonae (its sister species) and D. navojoa (outgroup). The data suggest that in the Baja California and Sonora population of D. mojavensis GstD1 has gone through a period of adaptive amino acid evolution as reflected by the ratio of silent to replacement fixations and polymorphisms. Polarizing these data using D. navojoa indicates that the positive selection occurred in the lineage leading to these D. mojavensis populations. Further analyses indicate that of the seven amino acid fixations that occurred in the D. mojavensis lineage two of them occur in the active site pocket, potentially having a significant affect on substrate specificity and in the adaptation to alternative cactus hosts. |
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