For my dissertation research, I am investigating the role of the hormone 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 gonadal steroids. Indeed, it is becoming increasingly clear that alternative neuroendocrine mechanisms, which are independent of circulating gonadal steroids, are critical in allowing animals to maintain high levels of aggression year-round. While we are starting to learn more about how these alternative neuroendocrine processes regulate aggressive behavior, it is unknown whether melatonin, a hormone that serves as the body’s biochemical cue 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, including increased aggression during the non-breeding season. 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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