Group member discrimination by Columbian ground squirrels via familiarity with substrate-borne chemical cues

Abstract

Abstract. Most studies of social discrimination by ground squirrels (Spermophilus) focus on the discrimination of conspecifics on the basis of kinship. However, juvenile Columbian ground squirrels, Spermophilus columbianus, discriminate members of their own local population (colony) from conspecifics inhabiting other colonies. In the present study, behavioural data were obtained from interactions of littermate pairs, non-neighbouring colony member (intra-site) pairs, and non-colony member (inter-site) pairs of juveniles. Colony member pairs were significantly more cohesive and less agonistic than were pairs of juveniles from separate colonies. To examine the role of indirect familiarization to colony member discrimination, live-traps were used as potential vectors for the transmission of chemical cues. Juveniles in each class (intra-site or inter-site) were either exposed to live-traps interchanged routinely between the interactant's natal areas, or to traps that were not interchanged. Juveniles exposed to interchanged traps were significantly more cohesive and tended to be less aggressive than juveniles reared without trap mixing. Littermates and colony members residing in areas where traps were interchanged were more cohesive and less aggressive than colony members that did not experience trap mixing (although these trends fell short of statistical significance). The results suggest that Columbian ground squirrels recognize local group members through a process of indirect familiarization that relies upon chemical discriminator substances. However, in the absence of trap-induced familiarity, the recognition of group members is apparently restricted to a more circumscribed area than was previously assumed. The discrimination of local group members promotes amicable interactions, reducing costs of aggression and could facilitate kin selection since residents of the same local area are likely to share genes through both maternal and paternal descent. The results also suggest that the amicable treatment of conspecifics can be artificially enhanced by trap-induced familiarity. That finding necessitates new caution in the execution and interpretation of experiments examining the behavioural ecology of ground squirrels where live-trapping is employed.