Cryptic Kin Selection: Kin Structure in Vertebrate Populations and Opportunities for Kin‐Directed Cooperation

Abstract

Animal societies of varying complexity have been the favoured testing ground for inclusive fitness theory, and there is now abundant evidence that kin selection has played a critical role in the evolution of cooperative behaviour. One of the key theoretical and empirical findings underlying this conclusion is that cooperative systems have a degree of kin structure, often the product of delayed dispersal, that facilitates interactions with relatives. However, recent population genetic studies have revealed that many non‐cooperative animals also have kin‐structured populations, providing more cryptic opportunities for kin selection to operate. In this article, I first review the evidence that kin structure is widespread among non‐cooperative vertebrates, and then consider the various contexts in which kin selection may occur in such taxa, including: leks, brood parasitism, crèches, breeding associations, territoriality and population dynamics, foraging and predator deterrence. I describe the evidence that kin‐selected benefits arise from interacting with kin in each of these contexts, notwithstanding the potential costs of kin competition and inbreeding. I conclude that as the tools required to determine population genetic structure are readily available, measurement of kin structure and the potential for kin selection on a routine basis is likely to reveal that this process has been an important driver of evolutionary adaptation in many non‐cooperative as well as cooperative species.

Evolutionary routes to non-kin cooperative breeding in birds

“…Alternatively, offspring may disperse only a short distance to breed independently, then return to a relative's territory to help if their nesting attempt is not successful. This pattern of limited dispersal results in local concentrations of relatives known as 'kin neighbourhoods' that can also facilitate kin-based cooperation [12]. However, much less is known about the dispersal and recruitment patterns that lead to groups with low genetic relatedness, and data on group formation are available for only a small minority of species.…”

Groups of related belugas (Delphinapterus leucas) travel together during their seasonal migrations in and around Hudson Bay

“…Yet again, learning migration routes may not be the sole, and perhaps not the main, benefit associated with extended kin associations during migration. Indeed, cryptic kin selection has been associated with sharing of resources while foraging and anti-predator behaviour [66]. For example, while migrating in open waters, individuals, and in particular calves, may be better protected if they swim in groups [67].…”

Bell miner provisioning calls are more similar among relatives and are used by helpers at the nest to bias their effort towards kin

“…For example, spatial limits on cooperative interactions may be relevant, if environmental characteristics limit distances over which a kinship signal can be propagated. Conversely, if recognition mechanisms are relatively coarse or even absent, helpers may fail to provide differential aid that would have yielded greater indirect fitness benefits [10].…”

“…Despite this bias in research focus, kin selection is just as likely to be important in fostering cooperative behaviour among individuals in so-called 'complex societies', where both kin and non-kin frequently interact. Even if population viscosity creates large between-group differences in relatedness, favouring indirect fitness benefits via 'helping any group member', the potential benefits of recognizing and preferentially aiding kin within complex social groups may still foster strong kin-recognition mechanisms [4,9,10], independent of any additional direct fitness benefits from sources such as group augmentation [19].…”