Far from being choosy about potential suitors, green-veined white butterfly (Pieris napi) females exhibit a complete lack of selectivity, even when it comes to mating with their relatives. This failure to discern siblings from non-siblings prior to doing the deed means that incest is a regular occurrence.
Both males and females show the same lack of inbreeding avoidance, which could result in substantial reproductive costs.
Experimentally reared inbred larvae experience a 25 per cent lower hatching success and a 30 per cent lower survival rate to adulthood, which proves that mating with your siblings is a bad idea.
Interestingly, females significantly decrease their re-mating interval when they’ve “accidentally” copulated with their brothers, indicating that there are postcopulatory mechanisms in place to avoid the high costs of incest (although biologists have yet to determine the inticacies of what they are).
So in this instance polyandry serves as a safeguard against having mated with a biologically inappropriate partner.
This post is an adapted excerpt from my book “Wild Sex: The Science Behind Mating in the Animal Kingdom“