Ground squirrel sociality and the quest for the "holy grail": Does kinship influence behavioral discrimination by juvenile Columbian ground squirrels?

Abstract

Research on social discrimination by ground-dwelling squirrels has focused on the ability of squirrels to discriminate kin from nonkin. The predominant mechanism underlying that abilily is social familiarization. Although familiarity-based mechanisms may result in kin discrimination where kin are associated reliably in space and time, past investigations have largely ignored additional levels of social discrimination that may result from ongoing familiarization in the natural context. Here we present data from a cross-fostering experiment that examines the relative contributions of rearing association and relatedness to sub-sequent behavioral discrimination among juvenile Columbian ground squirrels (Spermophilus columbianus). Rearing association significantly influenced recognitive and agonistic behavior among juveniles while relatedness proved insignificant in affecting behavioral interactions. Thus, direct familiarization in the natal burrow is both sufficient and necessary to account for the transitive appearance of kin-differential behavior among newly emerged juveniles documented in previous studies. Reanalyses of data from field experiments on S. columbianus social discrimination fail to detect any evidence of kin-biased behavior, and evidence from studies purporting to document kinship effects is equivocal at best. Taken together with more recent findings, the scant data suggestive of kin discrimination by Columbian ground squirrels are best viewed as an artifact of selection promoting the discrimination of familiar from unfamiliar individuals at the level of localized groups. Fitness payoffs of such discrimination may accrue via reciprocal altruism, or "dear-enemy" recognition, and would promote the evolution and maintenance of sociality without recourse to indirect components of inclusive fitness commonly invoked to explain ground squirrel sociality. Finally, our data call into doubt the notion that mechanisms allowing the direct assessment of kinship should be common among the more social sciurids.