Assessment of Fitness Costs of Resistance Against the Parasitoid Leptopilina victoriae in Drosophila bipectinata

How insects evolve resistance or counterresistance against antagonists is a basic issue in the study of host-parasitoid coevolution. One of the factors that affect their coevolution is fitness costs of resistance and counter-resistance. Here, we assess fitness costs of resistance against the parasitoid Leptopilina victoriae in Drosophila bipectinata on the basis of selection experiments. We made a base population by mixing three geographic fly populations that differed in resistance. The established base population was divided into four populations, two for selection of resistance against a L. victoriae population and two for control. Resistance increased rapidly in response to selection and reached a very high level within four generations in the selected populations, while resistance of the control populations remained low during 20 generations. High resistance of the selected populations was maintained at least for 10 generations after selection was stopped. Both selected populations had lower female longevity than the control populations, and at least one of the selected populations had shorter thorax length, lower female desiccation tolerance and adult heat tolerance than both or either of the control populations. On the other hand, the selected populations had higher male starvation tolerance and longevity than the control populations. There were no significant differences in resistance against another population of L. victoriae and two other parasitoid species between the selected and control populations. These results suggest that the resistance against the L. victoriae population in D. bipectinata may incur some but not so high costs and act parasitoid-species- and/or parasitoid-population-specifically. Ecol. Res., Vol. 29. Hal. 1033-1041