Although several biotic and abiotic factors change on a seasonal basis, photoperiod (i.e., day length) is the primary environmental cue that is used by most animals to shape seasonal shifts in reproductive physiology and its associated behaviors. These differences in physiology and behavior are produced via a complex neural circuit, which culminates in the secretion of melatonin, a hormone that plays a prominent role in establishing and maintaining biological rhythms, into circulation. Melatonin secretion tends to be highest during the nighttime hours; thus, seasonal changes in photoperiod cause associated changes in the pattern and duration of melatonin secretion, which convey information about day length to the central nervous system.
Previously, our lab has shown that administering timed melatonin injections to long day (LD, or breeding) male and female hamsters, which mimic short day (SD, or non-breeding)-like patterns of melatonin secretion, increases aggressive behavior. Furthermore, our data suggest that melatonin mediates peripheral steroidogenesis, specifically by altering DHEA output from the gonads and adrenal glands on a seasonal basis. While our findings thus far suggest that melatonin modulates seasonal aggression by altering steroid synthesis in the periphery, little is known about the mechanisms by which melatonin facilitates seasonal shifts in reproductive physiology and aggressive behavior. The goal of this project is to characterize the role of melatonin in mediating seasonal transitions in circulating androgen profiles and aggression in male hamsters, specifically by assessing how aggressive behavior and changes in circulating androgen levels following an aggressive encounter differ across seasonal phenotypes.