Abstract
Kin recognition is a key ability which facilitates the acquisition of inclusive fitness benefits and enables optimal outbreeding. In primates, phenotype matching is considered particularly important for the recognition of patrilineal relatives, as information on paternity is unlikely to be available via social familiarity. Phenotypic cues to both paternal and maternal relatedness exist in the facial features of humans and other primates. However, theoretical models suggest that in systems with uncertainty parentage it may be adaptive for offspring to conceal such cues when young, in order to avoid potential costs of being discriminated against by unrelated adults. Using experienced human raters, we demonstrate in a computer-based task that detection of parent-offspring resemblances in the faces of rhesus macaques (Macaca mulatta) increases significantly with offspring age. Moreover, this effect is specific to information about kinship, as raters were extremely successful at discriminating individuals even among the youngest animals. To our knowledge, this is the first evidence in non-humans for the age-dependent expression of visual cues used in kin recognition.
Highlights
Genetic relatedness is a fundamental variable that regulates a wide range of social behaviour [1]
Such kin recognition facilitates the acquisition of inclusive fitness benefits via nepotism, and allows individuals to optimize their mate choice decisions to avoid deleterious effects of inbreeding depression
The conclusions of theoretical models are mixed; while some predict that even very low levels of paternity uncertainty in a population will lead to individuals concealing their parentage [13,14], a model that simultaneously considered the evolutionary responses of both signallers and receivers instead suggested offspring should resemble their fathers, especially when paternity uncertainty is high [15]
Summary
Genetic relatedness is a fundamental variable that regulates a wide range of social behaviour [1]. In some cases social cues are unreliable for inferring genetic relatedness, for example where sibships involve mixed paternity due to polyandrous mating, or mixed maternity due to intraspecific brood parasitism or communal nursing of young Such species may use phenotype matching, whereby individuals are categorized as kin depending on how well their phenotypic traits match those of a learned or genetically determined template [4]. The conclusions of theoretical models are mixed; while some predict that even very low levels of paternity uncertainty in a population will lead to individuals concealing their parentage [13,14], a model that simultaneously considered the evolutionary responses of both signallers and receivers instead suggested offspring should resemble their fathers, especially when paternity uncertainty is high [15] This apparent contradiction can be resolved [14], as advertisement of identity may evolve or not, depending on the ratio between the costs of acceptance and rejection errors in specific evolutionary contexts. We use a computer-based task with human raters (a technique successfully used to detect kinship cues in macaque faces [20]), to test whether facial similarities between parents and offspring from a free-ranging population of rhesus macaques change with age
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