Effect of male–female relatedness on aggression and inbreeding in an egg parasitoid wasp

Aggressive behavior is important for acquiring crucial resources in many animals. As such behavior is costly, selection favors contestants that can accurately gather information regarding the likely costs and benefits of conflict to enable appropriate tactical decisions. Mate choice based on relatedness is widespread among animals and has severe consequences. Theoretically, due to the potential costs of inbreeding, contestants may benefit from discriminating between relative and nonrelative mates and adjusting their behavior accordingly. If inbreeding results in fitness costs, related mates might be perceived as less valuable and individuals might be expected to invest less in costly aggression, and vice versa. However, the role of male–female relatedness in aggression has been less addressed. The egg parasitoid wasp Anastatus disparis, which exhibits extreme male–male aggressive behavior for mating opportunities, was used as an experimental model to explore the role of male–female relatedness in aggression. Inconsistent with our prediction, male–female relatedness had no significant effect on male–male fighting frequency or intensity in A. disparis. The ability of males to discriminate relative from nonrelative females is a prerequisite for male–female relatedness to affect males’ aggression. However, A. disparis males did not exhibit any mating preferences for relative or nonrelative females. Besides, inbreeding did not result in depression in terms of longevity, fecundity or sex ratio in A. disparis. Our finding of no effect of male–female relatedness on male–male fights in A. disparis may be caused by a lack of kin discrimination ability or/and a lack of benefits from discriminating relatives from nonrelatives.