Genetic analyses of resistance against Leptopilina victoriae in Drosophila bipectinata.

Drosophila bipectinata from Iriomote-jima (IR) is susceptible to the endoparasitoid Leptopilina victoriae from Kota Kinabalu (L. victoriae KK), but D. bipectinata from Kota Kinabalu (KK) and Bogor (BG) is resistant. The cross experiments between the resistant (KK) and susceptible (IR) populations of D. bipectinata suggested that the resistance to this parasitoid is a dominant trait and controlled by a single locus or few linked loci on an autosome. In the AFLP analysis using the IR, KK and BG populations of D. bipectinata and the resistant and susceptible populations derived from a mixed population of these three geographic populations, a DNA fragment almost specific to susceptible flies was detected. It also revealed that genes from the IR population were more frequently maintained in the mixed population compared with those from the KK and BG populations, suggesting that at least a number of genes from the IR population are more advantageous under the laboratory conditions. This explains our previous results that the resistance was lowered in the mixed population although the resistance itself is suggested to incur only low costs; i.e., the resistance gene(s) from the KK and BG populations would have been linked with some genes that are disadvantageous under the laboratory conditions.