Insects and incest: field evidence for dangerous liaisons in a parasitoid wasp

1. Sib mating avoidance is a pervasive behaviour, which likely evolves in species that sare subject to inbreeding depression. Laboratory studies have provided elegant demonstrations, but small-scale bioassays often minimize the costs associated with mate finding and mate-choice and may for this reason produce spurious findings. 2. We inferred the mating behaviour of the parasitoid wasp Venturia canescens from the genetic analyses of natural populations. We used V. canescens as a model organism because in this species, laboratory experiments have shown that sib mating yields a 25% decrease in fertile offspring, and congruently, sib mating is partially avoided. 3. Our study consisted in genotyping 86 wild-caught males, 155 wild-caught-females and their 226 daughters at eighteen microsatellite loci. With these data, we were able to reconstruct the genotype of females’ mate and estimate the relatedness of each mating pairs. 4. We found that the effective rate of sib mating does not differ from the probability that sibs encounter one another at random, which suggest a sib mating tolerance in this species. However, complementary lab experiments confirmed that kin discrimination exist in this species, with related pairs having a lower mating latency. 5. These results suggest that V. canescens tolerate sib mating in the field despite kin discrimination, and therefore call into question the common beliefs on inbreeding depression in species with single-locus complementary sex determination. This inbreeding tolerance also opens up the question of the maintenance of the kin discrimination in this species. Key-words: Field assay, Inbreeding tolerance, Kin recognition, Parasitoid wasp, single-locus Complementary Sex Determination