Absence of single-locus complementary sex determination in the braconid wasps Asobara tabida and Alysia manducator

In species with single-locus complementary sex determination (sl-CSD), sex is determined by multiple alleles at a single locus. In the haplodiploid Hy menoptera, sl-CSD results in females, if individuals are heterozygous at th e sex locus, and in males, if individuals are hemizygous (haploid males) or homozygous (diploid males). Several hymenopteran species have been shown t o have sl-CSD, but in several others sl-CSD is absent and the phylogenetic distribution remains unclear. In the family Braconidae, all four species te sted so far were shown to possess sl-CSD. In this study, inbreeding experim ents were used to test for the presence of sl-CSD in two species belonging to a subfamily of the Braconidae, Asobara tabida and Alysia manducator (Aly siinae). In both species inbreeding experiments showed no difference in bro od size or sex ratio compared to the (outbred) control group. Furthermore, the sex ratios found in the inbreeding treatment differed significantly fro m the sex ratios expected under sl-CSD. Therefore, we conclude that sl-CSD is absent in these species. This study is the first to show the lack of sl- CSD in species of the Braconidae family and that hymenopteran sex-determini ng mechanisms can vary, even within a family.