Postdispersal nepotism in male long‐tailed macaques (Macaca fascicularis)

Abstract

Cooperative behaviors are promoted by kin selection if the costs to the actor are smaller than the fitness benefits to the recipient, weighted by the coefficient of relatedness. In primates, cooperation occurs primarily among female dyads. Due to male dispersal before sexual maturity in many primate species, however, it is unknown whether there are sufficient opportunities for selective tolerance and occasional coalitionary support for kin selection to favor male nepotistic support. We studied the effect of the presence of male kin on correlates of male reproductive success (residence time, duration of high dominance rank) in non‐natal male long‐tailed macaques (Macaca fascicularis). We found that “related” (i.e., related at the half‐sibling level or higher) males in a group have a significantly higher probability to remain in the non‐natal group compared to males without relatives. Moreover, males stayed longer in a group when a relative was present at group entry or joined the same group within 3 months upon arrival. Males with co‐residing relatives also maintained a high rank for longer than those without. To our knowledge, this is the first demonstration of a potential nepotistic effect on residence and rank maintenance among non‐natal males in a social system without long‐term alliances.

Rank acquisition in rhesus macaque yearlings following permanent maternal separation: The importance of the social and physical environment

“…Coalitions were another mechanism yearlings used to maintain dominance rank, and we found evidence for nepotism, or kin bias, as coalitions were more frequent among peers that were reared together (and therefore either maternally or paternally related). Similarly, a recent study also found support for post-dispersal nepotism in male long-tailed macaques (Macaca fascicularis), as males that entered into a troop with relatives resided in that troop and maintained a higher rank for longer (Gerber, Krützen, de Ruiter, van Schaik, & van Noordwijk, 2016), suggesting that kin support continues in new social groups, similar to our results. Our results also suggest that coalitions were primarily a mechanism to reinforce, rather than challenge, the hierarchy (Smith et al, 2010).…”

Determinants of immigration strategies in male crested macaques (Macaca nigra)

“…Assuming the case where parallel immigrations occurred was not by chance, some advantages must be conferred for one or both males. Since in crested macaques, males of the same age are likely to be half-brothers due to the high reproductive skew in a group, post dispersal nepotism is likely to increase a male’s direct and indirect reproductive benefit as recently found in long tailed macaques 43 . However, since only a few males immigrated at the same day, and only one pair could be confirmed to show parallel dispersal (and therefore could be potential half-brothers), it is unlikely to be a strategy widely adopted by males.…”

Bonds of bros and brothers: Kinship and social bonding in postdispersal male macaques

“…Many of these studies have focused on species closely related to Assamese macaques, so it is plausible that the males in our study are capable of recognizing unfamiliar kin through similar mechanisms. Moreover, males can disperse from their natal group together with kin they grew up with and should be able to discriminate those joint dispersal partners as kin (Albers & Widdig, 2012; Gerber, Krützen, de Ruiter, van Schaik, & van Noordwijk, 2016; Perry, 2012; Schoof, Jack, & Isbell, 2009). Yet, based on a still limited sample size, even plausibly familiar kin do not seem to be preferred bonding partners in male Assamese macaques (average Elo‐rating over groups and years of related males known to have left the natal group together = 0.495, N = 11, based on five unique dyads).…”