No behavioural response to kin competition in a lekking species

Abstract

28The processes of kin selection and competition may occur simultaneously if limited individual 29 dispersal i.e. population viscosity, is the only cause of the interactions between kin. 30 Therefore, the net indirect benefits of a specific behaviour may largely depend on the 31 existence of mechanisms dampening the fitness costs of competing with kin. In lekking 32 species, males may increase the mating success of their close relatives (and hence gain 33 indirect fitness benefits) because female prefer large leks. At the same time, kin selection 34 may also lead to the evolution of mechanisms that dampen the costs of kin competition. As 35 this mechanism has largely been ignored to date, we used detailed behavioural and genetic 36 data collected in the black grouse Lyrurus tetrix to test whether males mitigate the costs of 37 kin competition through the modulation of their fighting behaviours according to kinship and 38 the avoidance of close relatives when establishing a lek territory. We found that neighbouring 39 males' fighting behaviour was unrelated to kinship and males did not avoid settling down with 40 close relatives on leks. As males' current and future mating success are strongly related to 41 their behaviour on the lek (including fighting behaviour and territory position), the costs of kin 42 competition may be negligible relative to the direct benefits of successful male-male 43 contests. As we previously showed that the indirect fitness benefits of group membership 44 were very limited in this black grouse population, these behavioural data support the idea 45 that direct fitness benefits gained by successful male-male encounters likely outbalance any 46 indirect fitness benefits. 47 49Keywords: dominance, indirect fitness benefits, kin selection, kin competition, territoriality, 50 sexual selection, sociality 51 52 3 Significance statement 53Kin selection might be involved in the formation of groups because the fitness benefits of 54 increasing group size can be accrued when groups hold close relatives. However, the fitness 55 costs of competing with kin could counter-balance these indirect fitness benefits unless 56 mechanisms enabling individuals to limit kin competition. Using data collected in the black 57 grouse (Lyrurus tetrix) we show that males do not modulate their fight frequency and 58 intensity according to their kinship and do not avoid establishing territories with closely 59 related neighbours. As we previously showed that the indirect fitness benefits of group 60 display were very small and as this study shows that males do not show any sign of kin 61 competition avoidance, the indirect effects associated with male group display are likely to be 62 very small in this system. 63 4 Introduction 64