Insects and incest: Sib‐mating tolerance in natural populations of a parasitoid wasp

Abstract

Sib‐mating avoidance is a pervasive behaviour that is expected to evolve in species subject to inbreeding depression. Although laboratory studies provide elegant demonstrations, small‐scaled bioassays minimize the costs of mate finding and choice, and thus may produce spurious findings. We therefore combined laboratory experiments with field observations to examine the existence of inbreeding avoidance using the parasitoid wasp Venturia canescens. In the laboratory, our approach consisted of mate‐choice experiments to assess kin discrimination in population cages with competitive interactions. A higher mating probability after sib rejections suggested that females could discriminate their sibs; however, in contrast to previous findings, sib‐mating avoidance was not observed. To compare our laboratory results to field data, we captured 241 individuals from two populations. Females laid eggs in the lab, and 226 daughters were obtained. All individuals were genotyped at 18 microsatellite loci, which allowed inference of the genotype of each female's mate and subsequently the relatedness within each mating pair. We found that the observed rate of sib‐mating did not differ from the probability that sibs encountered one another at random in the field, which is consistent with an absence of sib‐mating avoidance. In addition, we detected a weak but significant male‐biased dispersal, which could reduce encounters between sibs. We also found weak fitness costs associated with sib‐mating. As such, the sex‐biased dispersal that we found is probably sufficient to mitigate these costs. These results imply that kin discrimination has probably evolved for purposes other than mate choice, such as superparasitism avoidance.

The effects of functional response and host abundance fluctuations on genetic rescue in parasitoids with single‐locus sex determination

“…Our results agree with suggestions made by previous studies that being dispersive is a good strategy to maintain genetic diversity at the CSD locus and alleviate extinction risk (Antolin & Strand, 1992; Collet et al., 2020; Cook & Crozier, 1995; Faria et al., 2016; Ruf et al., 2011; van Wilgenburg et al., 2006). Solitary parasitoids are generally good fliers (Godfray, 1994; van Wilgenburg et al., 2006).…”

“…Moreover, Inbreeding avoidance is one of the factors that can promote the evolution of dispersal (Saastamoinen et al., 2018). Field studies have shown that parasitoids can disperse for 10s of meters up to 7.5 km (Collet et al., 2020; Couchoux et al., 2016; Nair et al., 2016; Roland et al., 2000) and can be wind‐borne over several kilometers (Kristensen, Schellhorn, Hulthen, Howie, & De Barro, 2013). Wing polymorphism and sex‐biased dispersal have been documented in multiple species of parasitoids (Asplen et al., 2009; Collet et al., 2020; Godfray, 1994; Ruf et al., 2011), suggesting that dispersal is adaptive.…”

“…Male and DMs can be chosen multiple times. No sib‐mating avoidance is assumed as evidence is scarce (Collet et al., 2020; van Wilgenburg et al., 2006). For each reproducing female, the number of daughters among her offspring is determined randomly with probability .…”

“…Field studies have shown that parasitoids can disperse for 10s of meters up to 7.5 km (Collet et al, 2020;Couchoux et al, 2016;Nair et al, 2016;Roland et al, 2000) and can be wind-borne over several kilometers (Kristensen, Schellhorn, Hulthen, Howie, & De Barro, 2013). Wing polymorphism and sex-biased dispersal have been documented in multiple species of parasitoids (Asplen et al, 2009;Collet et al, 2020;Godfray, 1994;Ruf et al, 2011), suggesting that dispersal is adaptive. Some species have a premating refractory period during which one or both sexes of newly emerged adults disperse before mating (Godfray, 1994;van Wilgenburg et al, 2006).…”

“…Some species have a premating refractory period during which one or both sexes of newly emerged adults disperse before mating (Godfray, 1994;van Wilgenburg et al, 2006). Collet et al (2020) observed sib-mating tolerance in natural populations of a parasitoid that possesses sl-CSD and produces sterile DMs and suggested that dispersal probably reduces production of DMs effectively enough for the parasitoid not to evolve other behavioral or genetic countermeasures.…”