Complementary sex determination in the parasitoid wasp Cotesia vestalis (C. plutellae)

Abstract

In the Hymenoptera, single locus complementary sex determination (sl‐CSD) describes a system where males develop either from unfertilized haploid eggs or from fertilized diploid eggs that are homozygous at a single polymorphic sex locus. Diploid males are often inviable or sterile, and are produced more frequently under inbreeding. Within families where sl‐CSD has been demonstrated, we predict that sl‐CSD should be more likely in species with solitary development than in species where siblings develop gregariously (and likely inbreed). We examine this prediction in the parasitoid wasp genus Cotesia, which contains both solitary and gregarious species. Previous studies have shown that sl‐CSD is absent in two gregarious species of Cotesia, but present in one gregarious species. Here, we demonstrate CSD in the solitary Cotesia vestalis, using microsatellite markers. Diploid sons are produced by inbred, but not outbred, females. However, frequencies of diploid males were lower than expected under sl‐CSD, suggesting that CSD in C. vestalis involves more than one locus.

Diploid males sire triploid daughters and sons in the parasitoid wasp Cotesia vestalis

“…However, CSD was recently demonstrated in C. glomerata (Gu and Dorn, 2003;Zhou et al, 2006), and it has been suggested to operate in C. rubecula (personal communication by Steiner in Stouthamer et al, 1992;de Boer unpublished). In addition, we have also demonstrated CSD in C. vestalis, a solitary endoparasitoid of diamond back moth larvae (de Boer et al, 2007). Diploid male survival in C. glomerata is estimated to be rather low (around 26%), whereas it appears to be relatively high in C. vestalis (approximately 70%).…”

“…There are several scenarios that may reduce the genetic load associated with CSD in C. vestalis. First, we suggest that CSD in C. vestalis is based on more than one locus (de Boer et al, 2007;de Boer et al, in preparation). Under multiple locus-CSD, diploid males only develop from fertilized eggs that are homozygous at each of two or more sex loci, and the frequency of diploid males is significantly lower than under sl-CSD (Crozier, 1971).…”

“…Under sl-CSD, triploid males are expected to occur as often as triploid females when parents share a sex allele. Although we believe that CSD in C. vestalis is based on more than one locus (de Boer et al, 2007), the wasps we used originated from lines that produced between 30 and 50% diploid males from fertilized eggs after inbreeding for 6-8 generations. We thus expected females mated to their diploid brothers to produce triploid sons and daughters in a 1:1 to 1:2.3 ratio.…”

“…These lines were set up to determine the number of loci on which CSD is based in C. vestalis. In short, iso-female lines were started with a mother-son cross (see de Boer et al, 2007), using female offspring of outcrosses between two unrelated colonies of C. vestalis: colony A was started with about 200 adult wasps obtained from Biofac Crop Care (Mathis, TX, USA) and colony B was started with about 90 adult wasps from Benin (supplied by Dr D Bordat, CIRAD, Montpellier-sur-Lez, France). Iso-female lines were maintained on diamond back moth larvae, Plutella xylostella L., for 6-8 generations of sibmating to ensure the production of diploid males before they were used in our experiment.…”

Bee genetics and conservation

“…Such adaptations include the evolution of more sex loci, restored fertility of diploid males, selective fertilization of non-matched sperm in polyandrous females, avoidance of matched matings through sex-allele signaling, and others (reviewed by Cook and Crozier, 1995;van Wilgenburg et al, 2006). Evidence for most of these hypotheses is either rare (Cowan and Stahlhut, 2004 report reproductive diploid males in an aculeate wasp; De Boer et al, 2007 report multiple locus CSD in a parasitoid wasp), or completely lacking (Cook and Crozier, 1995;van Wilgenburg et al, 2006). In the largely random-mating bees, it is unclear if 244 A. Zayed adaptations reducing the cost of diploid male production would arise in normally large populations where diploid males are rare and the costs of diploid male production are low.…”