Sociality may confer such benefits as reduced predation risk and/or increased acquisition of critical resources.  The evolution of sociality has been attributed to these potential benefits outweighing such costs as increased aggression, parasite/disease transmission, and intraspecific competition.  Ground-dwelling sciurids show a continuum of sociality ranging from solitary individuals (Franklin’s ground squirrels, Spermophilus franklinii) to integrated, cohesive family groups (Olympic marmot, Marmota olympus).  Several models attempt to describe and predict the levels of sociality in ground squirrels. These models suggest that social behaviors have evolved as a way to minimize aggressive and competitive interactions due to the timing of the annual activity cycle particularly for large bodied species (Armitage 1981, Michener 1984.)   Based on these sociality models, round-tailed ground squirrels, Spermophilus tereticaudus, are predicted to be a relatively asocial species.  Round-tailed ground squirrels are small bodied (~125g) and inhabit desert areas of the southwestern United States.  Little is known about round-tailed ground squirrels; however, early observational studies suggest that round-tailed ground squirrels form matriarchal colonies maintained by male-biased dispersal.  This higher level of social complexity has been used to explain various behaviors including increased rates of female vocalizations and incidences of burrow sharing.  In the current study we used a combination of field observation and microsatellite analyses to investigate the predictions of these earlier sociality models.  We used 7 pairs of microsatellite primers from other closely related species.

Results/Conclusions

Allelic richness ranged from 3-18 alleles per marker, with 4 highly polymorphic markers (>10 alleles.)  Five of 7 loci had a low frequency of null alleles and were not in Hardy-Weinberg equilibrium. Round-tailed ground squirrel population sub-structure suggests that subtle population structure occurs, however, matriarchal colonies are not formed.   Earlier studies may have overestimated the degree of social complexity in round-tailed ground squirrels, whereas the current study supports the predications of asociality for round-tailed ground squirrel made in earlier ground squirrel sociality models