Beyond sex allocation: the role of mating systems in sexual selection in parasitoid wasps

Abstract

Despite the diverse array of mating systems and life histories which characterise the parasitic Hymenoptera, sexual selection and sexual conflict in this taxon have been somewhat overlooked. For instance, parasitoid mating systems have typically been studied in terms of how mating structure affects sex allocation. In the past decade, however, some studies have sought to address sexual selection in the parasitoid wasps more explicitly and found that, despite the lack of obvious secondary sexual traits, sexual selection has the potential to shape a range of aspects of parasitoid reproductive behaviour and ecology. Moreover, various characteristics fundamental to the parasitoid way of life may provide innovative new ways to investigate different processes of sexual selection. The overall aim of this review therefore is to re-examine parasitoid biology with sexual selection in mind, for both parasitoid biologists and also researchers interested in sexual selection and the evolution of mating systems more generally. We will consider aspects of particular relevance that have already been well studied including local mating structure, sex allocation and sperm depletion. We go on to review what we already know about sexual selection in the parasitoid wasps and highlight areas which may prove fruitful for further investigation. In particular, sperm depletion and the costs of inbreeding under chromosomal sex determination provide novel opportunities for testing the role of direct and indirect benefits for the evolution of mate choice.

Determination of the optimal parasitoid‐to‐host ratio for efficient mass‐rearing of the parasitoid, Sclerodermus pupariae (Hymenoptera: Bethylidae)

“…In all our experiments, sex ratios of S. pupariae were always female-biased. In terms of biological pest control, a female-biased sex ratio is clearly highly desirable as it is females which are responsible for reducing the population size of pests (Boulton et al 2015). The numbers of males ranged from one to nine (mean = 3) when one maternal parasitoid was used.…”

Reproductive interference in insects

“…The parasitoid wasps Nasonia vitripennis Walker (Pteromalidae) and N. giraulti Darling (Pteromalidae) overlap in Eastern North America and have been found parasitising blow-fly pupae hosts in the same bird nests (Grillenberger et al, 2009). As with many parasitoids, the two species are mostly monandrous, with females typically mating once before dispersing to find new hosts (Boulton et al, 2015). The two species are reproductively isolated by endosymbiont-based incompatibilities, with the two species hosting different and bi-directionally incompatible strains of the bacteria Wolbachia (Breeuwer & Werren, 1990;Bordenstein & Werren, 1998).…”

Balancing selection maintains sex determining alleles in multiple‐locus complementary sex determination

“…At the start of a generation each female mates at random. Females mate once but males may mate with more than one female, which is common in solitary hymenopterans such as C. rubecula (Ridley 1993;Boulton et al 2014). The model allows for two commonly documented modes of diploid male participation in mating; (1) diploid males do not participate in mating, and (2) the diploid offspring of females mated with diploid males do not survive to adulthood (Stouthamer et al 1992;Heimpel and de Boer 2008).…”