Identification of complementary sex determination loci in a parasitoid wasp

The genetic or environmental signals that govern whether an organism develops into a male or female differ across species, and understanding their evolution is crucial to comprehend the biology of an organism. In this paper, we focus on complementary sex determination (CSD), a genetic sex determination system found in many species of bees, ants and wasps where heterozygosity at one or multiple genetic regions determines the sex of the individual. It is generally thought that CSD systems based on multiple regions would arise from duplications of an ancestral system with a single region. Here, we identify multiple genetic regions in the parasitoid wasp species Lysiphlebus fabarum that are likely underlying CSD. We show that these candidate CSD regions share no similarity with each other and that they differ from the CSD region known in the honey bee, the only species with a well-characterized CSD system. Our results suggest a novel molecular mechanism underlying CSD in the wasp and that multiple CSD regions do not necessarily arise from duplications.