Diploid male production correlates with genetic diversity in the parasitoid wasp Venturia canescens: a genetic approach with new microsatellite markers.

Marie Collet,Chloé Vayssade,Laurence Mouton,Xavier Fauvergue,Alexandra Auguste,Thibaut Malausa,Emmanuel Desouhant

doi:10.1002/ece3.2370

Abstract

Sex determination is ruled by haplodiploidy in Hymenoptera, with haploid males arising from unfertilized eggs and diploid females from fertilized eggs. However, diploid males with null fitness are produced under complementary sex determination (CSD), when individuals are homozygous for this locus. Diploid males are expected to be more frequent in genetically eroded populations (such as islands and captive populations), as genetic diversity at the csd locus should be low. However, only a few studies have focused on the relation between population size, genetic diversity, and the proportion of diploid males in the field. Here, we developed new microsatellite markers in order to assess and compare genetic diversity and diploid male proportion (DMP) in populations from three distinct habitat types – mainland, island, or captive –, in the parasitoid wasp Venturia canescens. Eroded genetic diversity and higher DMP were found in island and captive populations, and habitat type had large effect on genetic diversity. Therefore, DMP reflects the decreasing genetic diversity in small and isolated populations. Thus, Hymenopteran populations can be at high extinction risk due to habitat destruction or fragmentation.

Highlights

Sex determination takes on many different forms in animals (Beukeboom and Perrin 2014)
Under single-locus complementary sex determination, unfertilized eggs are hemizygous at the csd locus and develop normally into haploid males (Whiting 1943)
Only heterozygous individuals develop into females; homozygosity at the csd locus yields diploid males that are generally, but not always unviable or sterile (Cowan and Stahlhut 2004; Heimpel and de Boer 2008; Harpur et al 2013). sl-complementary sex determination (CSD) is the mechanism of sex determination for which empirical evidence prevails in Hymenoptera (Cook 1993; van Wilgenburg et al 2006; Heimpel and de Boer 2008), but other mechanisms such as multilocus CSD or genomic imprinting occur (Verhulst et al 2010)

Summary

Introduction

Sex determination takes on many different forms in animals (Beukeboom and Perrin 2014). In numerous species including sawflies, pollinating bees, social and solitary wasps, ants, and parasitoids, the underpinning genetic mechanism of sex determination relies on the complementarity of alleles at a single gene (Whiting 1943; van Wilgenburg et al 2006; Heimpel and de Boer 2008). This gene – csd, for complementary sex determiner – has been described in the honeybee and comes from the duplication of the transformer gene (Geuverink and Beukeboom 2014). Only heterozygous individuals develop into females; homozygosity at the csd locus yields diploid males that are generally, but not always unviable or sterile (Cowan and Stahlhut 2004; Heimpel and de Boer 2008; Harpur et al 2013). sl-CSD is the mechanism of sex determination for which empirical evidence prevails in Hymenoptera (Cook 1993; van Wilgenburg et al 2006; Heimpel and de Boer 2008), but other mechanisms such as multilocus CSD or genomic imprinting occur (Verhulst et al 2010)

Methods

Results

Conclusion