For my dissertation research, I am investigating the role of melatonin in modulating the neuroendocrine mechanisms underlying non-breeding aggression in Siberian hamsters (Phodopus sungorus). Although most seasonally-breeding animals show high levels of aggression during the breeding season, some birds and rodents, such as Siberian hamsters, are more aggressive during the non-breeding season, despite gonadal regression and reduced levels of circulating androgens and estrogens. Indeed, numerous studies across animal taxa have provided evidence that aggression is not exclusively regulated by circulating gonadal steroids and that other alternative neuroendocrine mechanisms may allow these animals to maintain aggression year-round. While these alternative mechanisms have been examined across a suite of species over the past decade, it is unknown whether melatonin, a hormone that provides the physiological signal for photoperiod (i.e., day length), mediates seasonal changes in these hormonal processes.
Siberian hamsters (Phodopus sungorus) are an excellent model for examining how melatonin modulates the neuroendocrine mechanisms associated with aggressive behavior, since these animals exhibit robust shifts in morphology, physiology, and behavior on a seasonal basis. In addition, Siberian hamsters primarily use photoperiod as an environmental cue to coordinate reproduction and its associated behaviors with the breeding season. Thus, these natural seasonal adaptations can consistently be elicited in a laboratory setting by housing animals in light cycles that mimic the photoperiods of the breeding and non-breeding seasons.
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