In many species, males compete aggressively for access to females and resources. Behavior patterns associated with aggression are regulated by both internal and external factors that the animal must integrate in order to make the appropriate behavioral response to a situation. Steroid hormones are excellent candidates for integrating external environmental cues and internal mechanisms such as brain gene expression. This research will use the African cichlid fish, Astatotilapia burtoni, to investigate the molecular processes by which the sex steroid hormone estrogen influences social behavior. Males of this species have two distinct social phenotypes that are reversible depending on social context. This plasticity will be utilized in order to gain insights into the biological mechanisms of male-male competition by investigating the neural, hormonal, and molecular underpinnings of aggression in dominant and subordinate males. Specifically, the brain gene expression changes in dominant and subordinate males will be measured after the estrogen pathway is pharmacologically disturbed, giving insight into which genes are under estrogenic influence. Ultimately, this research will provide insights into the molecular and hormonal processes that underlie male-male competition and its evolutionary consequences.
This project will provide excellent educational opportunities to high school students, undergraduates, and one graduate student. The PI is the organizer of a research internship program for student from an urban, largely minority high school in Austin. Both investigators frequently participate in science outreach programs both on the UT Austin campus and in the local community. Both investigators strive to enhance the infrastructure for research and education by establishing journal clubs and contributing to education panels for improvement of undergraduate science labs.
Understanding the physiological contributors to behavior within social communities is important, as the behavior of human and other animals is tightly embedded in social networks. We used the African cichlid, Astatotilapia burtoni, which form social hierarchies in community tanks to uncover the mechanisms by which sex steroid hormones (such as testosterone, estrogen, and progesterone) regulate social behavior within a community of individuals. In A. burtoni, dominant (DOM) males territorial, colorful, and aggressive while subordinate (SUB) males are reproductively suppressed, non-aggressive, and school with females. We examined how the sex steroid hormone estrogen regulates behavior, physiology, and the brain in DOM and SUB males. We discovered that the estrogen receptor (ER) regulates aggression in both DOMs and SUBs using agonists and antagonists. When we examined animals that received an ER antagonist, we observed that circulating estrogen levels and gonad size decreased in SUB males, but not DOM males. We then examined brain gene expression in the preoptic area of males that received either the ER antagonist or control. The preoptic area was chosen as this brain region is important in regulating male sexual behavior and aggression in both fish and mammals. We found that there were many gene expression changes in DOMs that had received the antagonist compared to controls and very little changes in gene expression in SUBs that had received the antagonist compared to controls. This allowed us to identify genes that are regulated by ER in two social phenotypes. More broadly, our results suggest that changes at one level of biological organization (behavior) are not always reflected in changes at other levels (hormones or brain gene expression). Our research provided training opportunities for graduate and undergraduate students as well as students from an urban high school in Austin, TX. In summary, these experiments have provided a greater understanding of how social environment and hormones affect the complex gene networks that regulate behavior, which is relevant to all vertebrate species.
