Paternal kin discrimination: the evidence and likely mechanisms

Abstract

One of the most important assumptions of kin selection theory is that individuals behave differently towards kin than non-kin. In mammals, there is strong evidence that maternal kin are distinguished from non-kin via familiarity. However, little is known about whether or not mammals can also recognize paternal kin as many female mammals, including primates, mate with multiple males near the time of conception, potentially concealing paternal kinship. Genetic data in several mammalian species with a promiscuous mating system and male-biased dispersal reveal a high skew in male reproduction which leads to co-residing paternal half-siblings. In most primates, individuals also form stable bisexual groups creating opportunities for males to interact with their offspring. Here I consider close paternal kin co-resident in the same social group, such as father-offspring and paternal half-siblings (i.e. animals sharing the same father but who were born to different mothers) and review mammalian studies of paternal kin discrimination. Furthermore, I summarize the most likely mechanisms of paternal kin discrimination (familiarity and phenotype matching). When familiarity is the underlying mechanism, mothers and/or the sire could mediate familiarity among paternal half-siblings as well as between fathers and offspring assuming mothers and/or fathers can assess paternity. When animals use phenotype matching, they might use their fathers' template (when the father is present) or self (when the father is absent) to assess paternal kinship in others. Available evidence suggests that familiarity and phenotype matching might be used for paternal kin discrimination and that both mechanisms might apply to a wide range of social mammals characterized by a high skew in male reproduction and co-residence of paternal kin. Among primates, suggested evidence for phenotype matching can often have an alternative explanation, which emphasizes the crucial importance of controlling for familiarity as a potential confounding variable. However, the mechanism/s used to identify paternal kin might differ within a species (as a function of each individual's specific circumstances) as well as among species (depending upon the key sensory modalities of the species considered). Finally, I discuss the possible cues used in paternal kin discrimination and offer suggestions for future studies.

Cues to kinship and close relatedness during infancy in white-faced capuchin monkeys, Cebus capucinus

“…father) can theoretically increase familiarity between paternal siblings (Widdig, 2007), though we have yet to find evidence that paternal siblings discriminate each other from more distantly related kin.…”

“…Age proximity, and particularly peer group membership, is an important regulator of social interactions in capuchins (Schoof & Jack, 2014) and various other animals: gazelles (Walther, 1972), impalas (Murray, 1981), savannah baboons (Pereira, 1988;Alberts, 1999;Silk et al, 2006Silk et al, , 2010, rhesus macaques (Janus, 1992;Widdig et al, 2001Widdig et al, , 2002, chimpanzees (Mitani, 2009), humpback whales (Ramp et al, 2010), and giraffes: (Bercovitch & Berry, 2013). In species featuring high male reproductive skew during brief tenures, such as rhesus macaques, strong associations with peers can allow for different treatment of paternal half siblings as compared to more distant kin (Altmann, 1979;Widdig, 2007Widdig, , 2013.…”

“…Generally, cohort membership in primates is a good indicator of paternal sibship when high reproductive monopolization occurs during short alpha male tenures (Altmann 1979;Widdig 2007Widdig , 2013.…”

“…Peer group membership can serve as a cue to paternal sibship in species in which one or a few males monopolize reproduction during short breeding tenures, since this concentrates paternal siblings into similarly aged cohorts (Altman, 1979;Widdig, 2007Widdig, , 2013. Studies on baboons (Alberts, 1999;Silk et al, 2006;Smith et al, 2003), rhesus macaques (Widdig et al, 2001(Widdig et al, , 2002 Schülke et al, 2013), and mandrills (Charpentier et al, 2007) suggest that some primates recognize paternal siblings.…”

Social shaping of voices does not impair phenotype matching of kinship in mandrills

“…While these paternal kin are less familiar with each other than maternal relatives, they are somehow able to recognize each other as kin because they form stronger social bonds with paternal kin than non-kin [11][12][13] . Nevertheless, the proximate mechanisms underlying paternal kin discrimination remain poorly known 14 . The phenotype-matching hypothesis explains kin discrimination by holding that an individual matches its own phenotypic traits, or those of known kin, with those of unknown individuals to assess kinship 5,15 .…”