Sex ratios under asymmetrical local mate competition in the parasitoid wasp Nasonia vitripennis

Abstract

Sex ratio theory has proved remarkably useful in testing the adaptive nature of animal behavior. A particularly productive area in this respect is Hamilton's theory of local mate competition (LMC), which has been extended in numerous directions to include greater biological realism, allowing more detailed tests in specific organisms. We have presented one such extension, termed asymmetrical LMC, which occurs when egg laying by females on a patch is asynchronous, and emerging males do not disperse, resulting in the extent of LMC on a patch varying over time. Our aim here is to test whether the parasitoid wasp Nasonia vitripennis responds to variation in the degree of asymmetrical LMC. Specifically, we show that females adjust their offspring sex ratios in response to (1) variation in the amount of asynchrony in emergence between broods on a patch and (2) the number and proportion of previously parasitized hosts on the patch. Our results provide qualitative support for the predictions of theory, suggesting new levels of complexity in the sex ratio behavior of this much-studied organism. However, our results do not always provide quantitative support for theory, suggesting further complexities that must be clarified.