Evolution of behavioral defenses against parasitoid wasps in the melanogaster subgroup. Zachary Lynch, Balint Kacsoh, Todd Schlenke. Biology Department, Emory University, 1510 Clifton Rd, Atlanta, GA 30322.
Parasites reduce the fitness of their hosts and thus impose strong selective pressures on hosts for the evolution of defense mechanisms. However, molecular, cellular, and behavioral defense mechanisms can be costly to employ. Therefore, if multiple possible defenses against a particular parasite exist, we might expect hosts to specialize in one form of defense. Preliminary evidence for this type of tradeoff was found in the sister species Drosophila melanogaster and D. simulans, both of which are attacked by the parasitoid wasp Leptopilina boulardi in nature. D. simulans melanotically encapsulates and kills L. boulardi eggs, whereas D. melanogaster does not show this ability. However, D. melanogaster reduces its oviposition rate in the presence of wasps to limit the overall likelihood of offspring infection. Thus, D. melanogaster appears to rely on behavioral defense to compensate for its poor cellular defense. I am assaying behavioral and cellular defense abilities of the nine species in the melanogaster subgroup to look for repeated patterns of tradeoffs among immune mechanisms. In particular I will assay three behavioral immune mechanisms: (i) reduced oviposition rate in the presence of wasps, (ii) oviposition in food sources that are more toxic to wasps than flies, such as ethanol for D. melanogaster and octanoic acid for D. sechellia, in the presence of wasps, and (iii) increased consumption of toxins by infected larvae. I expect that species with strong cellular immune defenses such as D. simulans and D. yakuba will rely less on behavioral immune defenses.