Best undergraduate poster award at the Society for Behavioral Neuroendocrinology conference, 2007It is broadly accepted that the environment influences the effects of genes on behavior, but the mechanisms mediating these environmental effects on phenotype are poorly defined. The present study examined whether photoperiod (day length) and reproductive experience, two important environmental variables, affect gene expression to influence aggressive behavior. Individuals respond to photoperiod because it predicts important variability in the environment; male rodents use photoperiod to time adaptive behaviors such as mating and aggression. For example, mating is more likely in rodents housed in long, summer-like days when testosterone concentrations are high, whereas aggression in some rodent species is paradoxically elevated when housed in short, winter-like days when testosterone concentrations are low. Previous work in Peromyscus polionotus indicated that brain estrogen receptor alpha expression is increased in short days (8L:16D), whereas brain estrogen receptor beta expression is increased in long days (16L:8D). Hormone manipulation studies suggested that the photoperiodic effect on aggression occurs independently of changes in estrogen receptor expression. This hypothesis was tested directly by examining the effects of photoperiod on aggression and estrogen receptor expression in monogamous P. californicus, which do not reduce testes size in short days. I also examined how aggression changes in relation to parental behavior. Nulliparous male P. californicus were significantly more aggressive when housed in short versus long days, and parental males were also significantly more aggressive than nulliparous mice kept in long days. Neither photoperiod nor reproductive experience affected the expression of either estrogen receptor subtype in brain nuclei that are components of the brain “social behavior network.” These results suggest that the effects of photoperiod and reproduction on aggression are independent of changes in estrogen receptor expression. Additionally, these data emphasize the importance of studying the biological mechanisms mediating aggression under different environmental conditions in order to better understand the neurobiological bases of this complex social behavior.
Advisor: Randy J. NelsonSBS Undergraduate Research Award to M.S.F.NIH MH57535 to R.J.N.NSF grant IOS-16897 to R.J.N.No embarg
