The Ontogeny of Kin Recognition in Two Species of Ground Squirrels1

Abstract

SYNOPSIS. We report results of a three year comparative laboratory study of kin recognition abilities in Arctic ground squirrels (Spermophilus parryii) and Belding's ground squirrels (S. beldingi), and a field investigation of kin recognition in S. beldingi. Our laboratory work shows that in both species, preweaned pups reared together, whether they are biological siblings or cross-fostered (unrelated) nestmates, are equally aggressive in subsequent paired arena tests. Thus, pups that share a natal nest are treated like siblings. Among pups reared apart, sister-sister pairs are less aggressive in arena tests than are pairs of nonkin females, whereas relatedness does not affect male-male or male-female aggression. Thus both relatedness and rearing environment mediate recognition among female S. parryii and S. beldingi. In free-living Belding's ground squirrels at Tioga Pass, California, dam-offspring and sister-sister recognition apparently first occur at weaning, coincident with aboveground emergence of juveniles. Most intriguing (electrophoretically identified) littermate full-sisters and maternal half-sisters, which result from multiple mating by females, seem to treat each other differently despite having shared a natal nest. The full-sisters are less agonistic and more cooperative than the half-sisters. In interpreting these laboratory and field results, we explore four proximal mechanisms by which kin might be identified, including one in which recognition is based on (learned) phenotypic similarity to an individual's nestmates or itself (phenotype matching). Our data and those of several recent investigators of recognition in other taxa implicate both association with relatives and phenotype matching in the ontogeny of kin recognition.