Female social dominance (FSD) over males characterizes most Malagasy lemurs, which represent almost 30% of all primates; yet, little is known about the evolution or mechanism of this unusual phenomenon. Associated with FSD is a suite of behavioral, physiological, and morphological traits in females that implicates (as a possible mechanism) 'masculinization' via androgen exposure. In light of this association, this project by doctoral student Joseph Petty (Duke University), under the guidance of Dr. Christine Drea, takes a comparative and integrative approach to investigating the role of the neuroendocrine system, particularly androgens, in regulating FSD in lemurs. Studying mixed-sex pairs of six closely related Eulemur species that express a gradient of behavioral variation, from aggressive FSD to co-dominance between the sexes, this project will characterize the expression of intersexual dominance, affiliation, and aggression for each species. It will further provide novel information about the neuroendocrine correlates of behavior through the analysis of blood samples for the steroid hormones androstenedione (A4), testosterone (T), and estradiol (E2), as well as the neurotransmitter serotonin (5-HT). Lastly, to provide evidence of a direct causal linkage across species between behavior associated with FSD and neuroendocrine networks, the endocrine system will be experimentally manipulated, using a gonadotrophin-releasing hormone antagonist (antide), to assess the behavioral and social effects on masculinized behavior in female lemurs.
This project's unique comparative and experimental perspective will provide an increased understanding of the evolution of female dominance in primate social systems, as well as insight into the direct activational role of naturally circulating hormones in the regulation of female behavior. Its nontraditional focus has the potential to help update current definitions of sexual selection to better reflect the importance of intrasexual competition in females and to transform current understanding of the proximate mechanisms that underlie the physiology and expression of social dominance.
This project will be conducted at the Duke Lemur Center in Durham, NC, where it provides opportunities for collaborations with research, technical, and educational staff. Through these collaborations, this project facilitates mentorship of undergraduate researchers, dissemination of information relevant to lemur biology and conservation, public outreach, and hands-on science experience for children.
