No behavioural response to kin competition in a lekking species

Abstract

Abstract: The processes of kin selection and competition may occur simultaneously if limited individual dispersal, i.e. population viscosity, is the only cause of the interactions between kin. Therefore, the net indirect benefits of a specific behaviour may largely depend on the existence of mechanisms dampening the fitness costs of competing with kin. Because of female preference for large aggregations, males in lekking species may gain indirect fitness benefits by displaying with close relatives. At the same time, kin selection may also lead to the evolution of mechanisms that dampen the costs of kin competition. As this mechanism has largely been ignored to date, we used detailed behavioural and genetic data collected in the black grouse Lyrurus tetrix to test whether males mitigate the costs of kin competition through the modulation of their fighting behaviours according to kinship and the avoidance of close relatives when establishing a lek territory. We found that neighbouring males’ fighting behaviour was unrelated to kinship and males did not avoid settling with close relatives on leks. As males’ current and future mating success are strongly related to their behaviour on the lek (including fighting behaviour and territory position), the costs of kin competition may be negligible relative to the direct benefits of successful male-male contests. As we previously showed that the indirect fitness benefits of group membership were very limited in this black grouse population, these behavioural data support the idea that direct fitness benefits gained by successful male-male encounters likely outbalance any indirect fitness benefits. Significance statement: Kin selection might be involved in the formation of groups because the fitness benefits of increasing group size can be accrued when groups hold close relatives. However, the fitness costs of competing with kin could counter-balance these indirect fitness benefits unless mechanisms enabling individuals to limit kin competition. Here we show in a lekking species that males do not modulate their fight frequency and intensity according to their kinship and do not avoid establishing territories with closely related neighbours. As the indirect fitness benefits of group display were very small in this system and as this study shows that males do not show any sign of kin competition avoidance, the indirect effects associated with male group display are likely to be very small.