ARE STAGED DYADIC ENCOUNTERS USEFUL FOR STUDYING AGGRESSIVE-BEHAVIOR OF ARVICOLINE RODENTS

We investigated the aggressiveness of adult prairie voles (Microtus oc hrogaster) in dyadic encounters staged in different types of arena tri als to determine if responses differed (i) between neutral arena trial s conducted in the laboratory and resident-intruder trials conducted i n the field, (ii) between trials staged before and after 3 months of i solation from social contact, (iii) between voles reared in the labora tory and voles reared in the field, and (iv) among trials staged with the same individual over time. Though rodents are usually expected to be more aggressive on their own home range, female prairie voles tende d to be more aggressive in neutral arenas. Males showed no difference in aggression between trials held in neutral arenas and trials held in arenas placed in their home ranges. Aggressiveness was not affected b y 3 months of isolation for either males or females, suggesting that r ecent social cues may not strongly influence aggressive behaviour in t his species. Voles reared in the laboratory were significantly more ag gressive than those reared in enclosed field populations, which sugges ts that direct comparisons of field and laboratory studies of aggressi ve behaviour may be suspect. Individuals showed little change in aggre ssiveness when tested over several weeks in three trials with differen t opponents. We conclude that encounters staged in arenas provide stan dardized estimates of aggressiveness that are robust to differences in testing procedures and are repeatable over time. Therefore, their con tinued use seems warranted for studying aggressive behaviour of voles and lemmings.