Effects of inbreeding on fitness components of Cotesia glomerata, a parasitoid wasp with single-locus complementary sex determination (sl-CSD)

Abstract

Abstract In many hymenopteran species with single-locus complementary sex determination (sl-CSD) system, inbreeding will lead to an increase in the proportion of male offspring due to the production of diploid sons. Since diploid males are normally inviable or sterile, their production generates a genetic load to the population. Although it has been well documented that many sl-CSD species suffer sever inbreeding depression in sex ratio, the impact of inbreeding on other fitness components in such species is rarely known. In this study we pursue this issue in Cotesia glomerata, a gregarious parasitoid species with sl-CSD, by comparing three fitness traits (i.e., development time, brood size and body size), as well as sex ratio, between experimentally imposed inbred and outbred populations. Results of breeding experiments showed that one generation of full-sib mating in C. glomerata resulted in a significantly higher proportion of males (43%) compared with outbred control (29%), and the sex ratio shifts are largely in agreement with sl-CSD model. When the inbreeding level increased over four consecutive generations, brood sex ratios became more male-biased. However, no significant differences were found in the egg-to-adult development time and brood size between inbred and outbred groups. Inbreeding had no negative effect on the body size (measured as hind tibia length) of both female and male wasps. When the relationship of body size and brood size was analyzed with a general linear model, a significantly negative correlation was found for wasps of both sexes. These findings may have implications for the laboratory rearing of C. glomerata and the evolution of gregariousness and inbreeding in the parasitoids species with sl-CSD.