Evidence for an one-step mechanism of endosymbiont-induced thelytoky in the parasitoid wasp,Muscidifurax uniraptor

Abstract

AbstractWolbachiamanipulates host reproduction in various haplodiploid insect species, in which fertilized eggs normally develop into diploid females while unfertilized eggs develop into haploid males. Females infected with a thelytoky-inducingWolbachiaproduce diploid daughters from unfertilized eggs (thelytoky), but in some infected species diploid males spontaneously occur in low numbers. This suggests that diploidization and feminization are induced separately. In theWolbachia-infected thelytokous parasitoid wasp,Muscidifurax uniraptor, occasional males have been found but with unknown ploidy. Therefore, we studied the mechanism ofWolbachia-induced thelytoky inM. uniraptorin the context of sex determination. We started by feeding different concentrations of tetracycline (antibiotic) toM. uniraptorfemales to gradually reduce theWolbachiatitre. We found that a decreasedWolbachiatitre leads to an increased proportion of haploid male offspring, but we found no diploid males. Next, we studied the effect ofWolbachiainfection on the expression and splicing of the sex determination genestransformer(Mutra) andtransformer-2(Mutra2) in female ovaries and conclude thatWolbachiadoes neither affect the expression nor the splicing ofMutraandMutra2. We then measuredMutraandMutra2expression levels in developing zygotes at different time points and found a two-foldMutraexpression increase inWol+ compared toWol-. Finally, we used the sexually reproducing sister species,Muscidifurax raptorellusand artificially created triploid females to determine whether diploidization is sufficient for feminization. These triploid females, when virgin, produced haploid sons and diploid daughters, showing that inMuscidifuraxfeminization solely depends on ploidy level. This strongly suggests thatWolbachiaonly needs to induce diploidization and that bi-allelicMutraexpression is sufficient for female development.