Comparison of methods for determining dominance rank in male and female prairie voles (Microtus ochrogaster)

Dominance ranks in male and female prairie voles (Microtus ochrogaster) wer e determined from 6 measurements that mimicked environmental situations tha t might be encountered by prairie voles in communal groups, including agoni stic interactions resulting from competition for food and water and encount ers in bur-rows. Male and female groups of 6 individuals each were tested a gainst one another in pairwise encounters (i.e., dyads) for 5 of the measur ements and together as a group in a 6th measurement. Two types of response variables, aggressive behaviors and possession time of a limiting resource, were collected during trials, and those data were used to determine cardin al ranks and principal component ranks for all animals within each group. C ardinal ranks and principal component ranks seldom yielded similar rankings for each animal across measurements. However, dominance measurements that were conducted in similar environmental contexts, regardless of the respons e variable recorded, ranked animals similarly. Our results suggest that ind ividual dominance measurements assessed situation- or resource-specific res ponses. Our study demonstrates problems inherent in determining dominance r ankings of individuals within groups, including choosing measurements, resp onse variables, and statistical techniques. Researchers should avoid using a single measurement to represent social dominance until they have first de monstrated that a dominance relationship between 2 individuals has been lea rned (i.e., subsequent interactions show a reduced response rather than an escalation), that this relationship is relatively constant through time, an d that the relationship is not context dependent. Such assessments of domin ance status between all dyads then can be used to generate dominance rankin gs within social groups.