SCOTTI, M.L.*; DEMAS, G.E.; Indiana University, Center for the Integrative Study of Animal Behavior; Indiana University, Center for the Integrative Study of Animal Behavior: Seasonal aggression in female Siberian hamsters (Phodopus sungorus)

Most seasonally breeding species demonstrate a suite of adaptations including reproductive regression and increased territorial aggression in short �winter-like� compared with long �summer-like� day lengths. For example, male Siberian hamsters (Phodopus sungorus) held in a short days (LD 8:16) express heightened levels of territorial aggression independent of gonadal steroid hormones. Similar findings have been reported for both male and female Syrian hamsters. Virtually nothing is known, however, regarding seasonal aggression in female Siberian hamsters. Thus, the present study was undertaken to determine if females, like males, express increased levels of aggression under short-day �winter-like� conditions. Specifically, females were individually housed in either short- (LD 8:16) or long-day (LD 16:8) photoperiods for 10 weeks. Assessment of aggression was accomplished by placing a long-day-housed female intruder in the home cage of a test animal and recording latency to attack as well and number of attacks. Prior to testing, estrous cycle stage was determined in long-day animals via vaginal cytology and females were tested during both the Diestrus I and Proestrus stages and matched with intruders in the same estrous stage. Short-day animals showed significantly higher levels of aggression than did long-day animals, and estrus stage did not affect aggression in long-day females. These results support previous findings of increased non-breeding aggression and suggest that gonadal steroids do not likely mediate short-day aggression. Collectively, these results suggest that endocrine regulation of seasonal aggression may be similar between the sexes.