Assessment of fitness costs of resistance against the parasitoid Leptopilina victoriae in Drosophila bipectinata

Abstract

How insects evolve resistance or counter-resistance 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. After six generations of free mating, the 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 two replicated selected populations, while resistance of the control populations remained low at least for 20 generations. High resistance of the selected populations was maintained at least for 10 generations even if selection was stopped. Comparison of life history and stress tolerance revealed that both selected populations had lower female longevity than the two control populations, and at least one of the selected populations had shorter thorax length and lower female desiccation tolerance and adult heat tolerance than both or either of the control populations. On the other hand, selected populations had higher male starvation tolerance and longevity than 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. 3 Key wordsArtificial selection • coevolution • specificity • trade-offs 4 IntroductionAll insects have immune systems to defend themselves from infection of pathogens or parasites. However, their immune systems are not always effective, because some pathogens and parasites have means to avoid being detected by the host immune systems or suppress host immune responses (Edison et al. 1981;Shelby and Webb 1999; Eleftherianos et al. 2007). To cope with such enemy's adaptations, host insects often intensify their immune responses or modify their immune systems (Strand and Pech 1995; Carton et al. 2008). One of the important factors that affect such parasitoid-host coevolution is the costs of resistance and counter-resistance (Doebeli 1997;Sasaki and Godfray 1999). A powerful tool to examine these costs is the study of correlated responses to artificial selection. Kraaijeveld and Godfray (1997) tabida compared with the control populations (Fellowes et al. 1999). Thus, the resistance mechanism of D. melanogaster has parasitoid-species-or parasitoid-population-specific components.The above selection studies were based on within-population genetic variation.Resistance and counter-resistance aga...

Genetic analyses of resistance against Leptopilina victoriae in Drosophila bipectinata

“…Novković et al (2012) reported that a population of D. bipectinata from Iriomote-jima (IR: Japan) was susceptible to L. victoriae from Kota Kinabalu (L. victoriae KK), but those from Kota Kinabalu (KK: Malaysia) and Bogor (BG: Indonesia) were resistant to this parasitoid population. The number of genes causing this difference in resistance may be few, because an experimental population produced by mixing these IR, KK and BG populations rapidly responded artificial selection for increased resistance against L. victoriae KK in our previous study (Takigahira et al 2014). In this study, we verify this notion by cross experiments using the resistant KK and susceptible IR populations.…”

“…The selected and control populations were maintained under 15L: 9D at 23°C. At the 10th generation, the rate of successful parasitism by L. victoriae KK was less than 10 % in selected (resistant) populations and approximately 85 % in control (susceptible) populations (Takigahira et al 2014).…”

“…To test deviation from expectations by Menderian inheritance model, chi-square test and likelihood ratio test were performed using R version 2.10.1(R Development Core Team 2009). AFLP analysis AFLP analysis was conducted using the original IR, KK and BG populations and the resistant and susceptible populations produced by artificial selection from a base population that was established by mixing the three original populations (Takigahira et al 2014). The base population was established from 20 females and 20 males of each of the three original populations and maintained for six generations with free mating.…”

“…In our previous selection study (Takigahira et al 2014), a base population was established by mixing the IR, KK and BG populations of D. bipectinata and allowed to mate freely for six generations. At the sixth generation, the base population had low resistance against L. victoriae KK, although it was a mixture of one susceptible (IR) population and two resistant (KK and BG) populations with the same proportion (Takigahira et al 2014). Thereafter, however, the resistance changed little in the base (control) population at least for 10 generations (Takigahira et al 2014).…”

“…At the sixth generation, the base population had low resistance against L. victoriae KK, although it was a mixture of one susceptible (IR) population and two resistant (KK and BG) populations with the same proportion (Takigahira et al 2014). Thereafter, however, the resistance changed little in the base (control) population at least for 10 generations (Takigahira et al 2014). The resistance against L. victoriae KK may incur some costs and then may be selected against in the base population, or the resistance genes of the BG and KK populations may be linked with some deleterious genes.…”