899A Poster - 14. Neural circuits and behavior
Thursday April 07, 2:00 PM - 4:00 PM

Authors:
Manali Dey ¹; Anupama Dahanukar ^1,2

Affiliations:
1) Interdepartmental Neuroscience Program, UCR, Riverside; 2) Department of Molecular, Cell and Systems Biology, UCR, Riverside

Keywords:
k. feeding behavior; q. adaptation

Comparative studies between generalist and specialist species enable us to learn how adaptations for a particular environment may lead to speciation. Drosophila sechellia, endemic to the Seychelles, is an obligate specialist that almost exclusively uses the fruit of Morinda citrifolia (noni) for feeding and oviposition. By contrast, its generalist relatives D. melanogaster and D. simulans take advantage of overripe fruits but avoid noni fruits, which are rich in short to medium chain fatty acids (FA) that are toxic for them. D. sechellia, however, are attracted to noni and are able to metabolize the fatty acids. To understand the contribution of the taste system in behavioral adaptation of D. sechellia, we undertook a comparative study of gustatory function in the three related species. In two independent behavior assays D. sechellia showed a feeding preference for noni acids, whereas the generalist species showed aversion. Genetic and surgical ablation experiments uncovered a contribution of olfaction in stimulating feeding preference for lower concentrations of noni acids, but largely olfaction-independent behavioral responses at the higher end of the concentration range. A systematic comparison of cellular responses with extracellular tip recordings identified two differences in D. sechellia that may facilitate their interaction with noni fruit – first, the responses of their deterrent (bitter-sensing) neurons to noni acids are weaker, and second, their appetitive (sugar-sensing) neurons are not strongly inhibited by noni acids. Further, D. simulans appears to exhibit phenotypic parameters that are like those of D. melanogaster in some cases, and those intermediate between D. melanogaster and D. sechellia in other cases, suggesting that multiple genetic changes may account for gustatory differences between D. melanogaster and D. sechellia. Ongoing studies are directed towards understanding the molecular basis of variation in Morinda acid taste between the three Drosophila species. Preliminary results suggest the involvement of at least three molecularly distinct pathways involving ionotropic receptors, gustatory receptors, and odorant-binding proteins. We are testing evolutionary roles of candidate genes by manipulating function in both D. melanogaster and D. sechellia.