Meeting Abstract

115.3  Saturday, Jan. 7  Sex ratio adjustment in a solitary parasitoid wasp SOMJEE, Ummat*; ABLARD, Kelly; CRESPI, Bernard; SCHAEFER, Paul/W; GRIES, Gerhard; Simon Fraser University, Vancouver, Canada; Simon Fraser University, Vancouver, Canada; Simon Fraser University, Vancouver, Canada; US department of Agriculture, Newark, DE; Simon Fraser University, Vancouver, Canada

Sex ratio theory has yielded some of the clearest examples of adaptive evolution in animal behavior. A highly studied aspect of sex ratio theory is termed Local Mate Competition (LMC), which occurs when brothers compete with each other for mating opportunities, resulting in the selection for strongly female-biased sex ratios. LMC predicts that if two females oviposit in the same patch, their sons compete for mating opportunities also with non-brothers. Thus, females in the presence of other females should produce relatively more sons. The mating system of the parasitoid wasp Ooencyrtus kuvanae meets assumptions of LMC. Females insert a single egg into each accessible egg of gypsy moth, Lymantria dispar, host egg masses. Wasps complete development inside host eggs and emerge en masse as sexually mature adults, resulting in intense competition among (sibling) sons. We tested the hypothesis that O. kuvanae exhibits LMC by investigating the effect of number, size and relatedness of wasp foundresses on egg masses with identical number of eggs. As predicted by the LMC theory, with increasing numbers of wasp foundresses on an egg mass, the proportions of emerging sons increased. In contrast, the presence of a sibling or a non-sibling female during oviposition, or the size of a female, did not affect the number or sex ratio of offspring produced. With no Local Resource Competition (LRC) among O. kuvanae larvae, the sex ratio of emergent son and daughter wasps is due entirely to the sex allocation by ovipositing wasp foundresses on host egg masses. This is the first study to have experimentally decoupled the effect of LRC from that of LMC.