Integrating the female masculinization and challenge hypotheses: Female dominance, male deference, and seasonal hormone fluctuations in adult blue-eyed black lemurs (Eulemur flavifrons)

• Published in: Hormones and behavior 2022-03, Vol.139, p.105108-105108, Article 105108
• Main Authors: Grebe, Nicholas M., Sheikh, Alizeh, Drea, Christine M.
• Format: Article
• Language: English
• Subjects: Aggression - physiology; Androgens - metabolism; Androstenedione - metabolism; Animals; Challenge hypothesis; Estrogens - metabolism; Female; Female dominance; Glucocorticoids - metabolism; Hypothalamo-Hypophyseal System - metabolism; Lemur - physiology; Male; Masculinization; Pituitary-Adrenal System - metabolism; Primates; Seasonal breeding; Seasons
• ISSN: 0018-506X; 1095-6867
• DOI: 10.1016/j.yhbeh.2022.105108

In the decades since female social dominance was first described in strepsirrhine primates, researchers have sought to uncover the proximate and ultimate explanations for its development. In the females of various female-dominant species, androgens have been implicated as regulators of behavior and/or predictors of seasonal fluctuations in aggression (the ‘Female Masculinization Hypothesis’). Males, more generally, respond to changing social demands via seasonal fluctuations in androgen-mediated behavior (the ‘Challenge Hypothesis’), that may also entail changes in activation of the hypothalamic-pituitary-adrenal axis. Here, we explore if androgens, glucocorticoids, and intersexual behavior fluctuate seasonally in the female-dominant, blue-eyed black lemur (Eulemur flavifrons), with potential consequences for understanding female aggression and male deference. Across two studies conducted during the breeding and nonbreeding seasons, we assessed rates of mixed-sex, dyadic social behavior (aggression and affiliation) and concentrations of fecal glucocorticoid metabolites (Study 1) and serum sex hormones (androstenedione, testosterone, and estradiol; Study 2). Our results align with several predictions inspired by the Female Masculinization and Challenge Hypotheses for intersexual relations: During the breeding season, specifically, both aggression and androstenedione peaked in females, while female-initiated affiliation decreased, potentially to facilitate female resource access and reproductive control. By comparison, all target hormones (androgens, estrogen, and glucocorticoids) peaked in males, with glucocorticoid concentrations potentially increasing in response to the surge in female aggression, and unusually high estrogen concentrations year-round potentially facilitating male deference via male-initiated affiliation. These results suggest complex, seasonally and hormonally mediated behavior in Eulemur flavifrons. •Understanding female-dominant species requires synthesizing frameworks in behavioral endocrinology.•Multiple steroids may seasonally influence female aggression and male deference.•We collected longitudinal behavioral and hormonal data on female-dominant E. flavifrons.•Results suggest complex, seasonal, hormonal modulation of intersexual interactions.