27 Oral - Evolution I
Thursday April 07, 5:15 PM - 5:30 PM

Authors:
Alice Gadau ¹; Xin Yu Zhu Jiang ^1,2; Sylvia Durkin ¹; Nicolas Svetec ¹; Li Zhao ¹

Affiliations:
1) The Rockefeller University; 2) CUNY-Hunter College

Keywords:
d. evolution of gene expression; n. chemosensation

Adaptation is fundamental to the survival and reproduction of living organisms. However, the genetic and neural basis underlying adaptation to new environments remains largely unknown. Novel traits allow species to invade new ecological niches and habitats. Pest species therefore provide a unique opportunity to study adaptation as they exploit new environments. One pest species, Drosophila suzukii, has evolved a preference to oviposit in ripe fruits instead of rotten fruit, unlike most Drosophilids. The Drosophila sensory and central nervous system may contribute to adaptive behavioral shifts. To determine candidate genes that contribute to the adaptive shift in D. suzukii, we identified sensory genes under directional selection in D. suzukii and showed differential expression between D. suzukii and D. biarmipes, D. subpulchrella, and D. melanogaster using population genetic analysis and RNA-seq analysis. From this screen, 15 genes evolved under positive selection and were significantly differentially expressed between species. One candidate, the carbon dioxide receptor Gr63a, is of particular interest as its sequence has diverged in D. suzukii yet is expressed significantly more in D. subpulchrella. We hypothesize that CO₂ is playing a role in decision-making in the D.suzukii species complex. By conducting a two-choice preference trial for high and low CO₂ concentration, we found that D. suzukii and D. subpulchrella exhibited the same indifference to CO₂, which is significantly different from D. melanogaster’s aversion. In addition, we found that the CO₂ sensing neuron is more sensitive to CO₂ in D. suzukii and D. subpulchrella compared to D. melanogaster, using single sensillum electrophysiology. These data suggest that the behavior is conserved between the two species and that the evolution of Gr63a may have occurred at the regulatory region in D. subpulchrella yet the gene sequence in D. suzukii. To test this hypothesis, we use a GAL4-UAS system to dissect the role of regulatory and protein changes of D. subpulchrella and D.suzukii. Our results provide novel insight into the link between novel genotypes and phenotypes, and the complexity of the evolution of novel behavior.