Socioendocrinology of a Coercive Primate: Correlates of Takeovers and Glucocorticoids in Wild Female and Male Hamadryas Baboons

Author

Alexis L. Amann-Lancer, The Graduate Center, City University of New YorkFollow

Date of Degree

6-2025

Document Type

Dissertation

Degree Name

Ph.D.

Program

Anthropology

Advisor

Larissa Swedell

Committee Members

Jacinta Beehner

Shahrina Chowdhury

Colleen McCann

Subject Categories

Animal Studies | Behavior and Ethology | Biological and Physical Anthropology | Evolution

Abstract

There is a dynamic interaction between the physiological underpinnings of reproduction, male behavioral strategies to increase fitness, and female counterstrategies to mitigate infant loss and maximize their own reproductive success. In my dissertation I explore these relationships in the hamadryas baboon (Papio hamadryas), a species characterized by strong sexual dimorphism, intense male-male competition, and female counterstrategies to infanticide. Hamadryas baboons have a unique multi-level social system with male philopatry in which multiple one-male units together form a clan, clans form a larger band, and bands come together at sleeping sites to form troops. Hamadryas males practice female defense polygyny within one-male units and coercively take over females individually, moving them between these units. Hamadryas also live in a more arid habitat than most other baboons, with high temperatures year round and larger home ranges than other baboons.

In my dissertation research, I investigated factors determining takeovers, how takeovers impact female reproduction, and how the hamadryas social system impacts both female and male physiology. To address these questions, I analyzed previously collected demographic from Filoha, Ethiopia, collected demographic data and fecal samples at Filoha, and conducted hormone analyses to investigate sources of variation in glucocorticoid hormone levels among females and males.

In Chapter 3, I report predictors and outcomes of male takeovers of females. I found that female reproductive state was not associated with likelihood of takeover, while parity was associated with takeovers, such that hamadryas males more frequently targeted nulliparous females compared to parous females for takeover. I also examined outcomes of pregnancy, infant fates, and birth rates post-takeover: I found that females were up to three times more likely to terminate pregnancy after takeovers than at other times, half the infants that were born prior to takeover died post-takeover, and females were over four times more likely to give birth during stable periods than during the six-month period immediately following a takeover.

In Chapter 4, I report correlates of variation in glucocorticoids among hamadryas baboon females. I found that pregnant females had higher glucocorticoids compared to lactating females, parous females had higher glucocorticoids than primiparous females, and multiparous females had higher glucocorticoids compared to both nulliparous females and primiparous females. While I did not find age to be a factor influencing glucocorticoid variation in females, I determined group size to have an effect, such that larger group sizes (OMUs of 6+ females) were associated with higher female glucocorticoid levels (with the caveat that hamadryas baboon one-male unit size is not conceptually equivalent to group size in other primate species).

In Chapter 5, I report correlates of variation in glucocorticoids among hamadryas baboon males. While age, social status, tenure length, group size, and rainfall did not appear to be associated with male glucocorticoid levels, temperature appeared to have an effect, such that all three types of males – leader males in particular – had higher glucocorticoid levels at higher temperatures. I also found that the presence of follower males was a significant predictor of glucocorticoid variation in leader males, such that leader males with followers had lower glucocorticoids than leader males without followers.

My dissertation is the first study to explore glucocorticoid variation in wild hamadryas baboon females and males. My research helps to advance our interpretation of stress physiology and sexual conflict in a polygynous, multi-level primate society.

Recommended Citation

Amann-Lancer, Alexis L., "Socioendocrinology of a Coercive Primate: Correlates of Takeovers and Glucocorticoids in Wild Female and Male Hamadryas Baboons" (2025). CUNY Academic Works.
https://academicworks.cuny.edu/gc_etds/6242