In primate reproductive ecology, the role of energy as a constraint on reproduction has often focused on females. Yet across mammals, including humans, male reproductive effort can often entail substantial metabolic costs. This doctoral dissertation project will examine how energy constrains male behavior and reproduction in a wild primate, the gelada monkey. The project will provide insight into how animal physiology and reproductive efforts adjust to natural ecological change, and examine how testosterone, a regulatory mechanism for male reproductive behavior, may be directly limited by energy. By examining the effects of energetics on the allocation of testosterone-mediated reproductive effort in a nonhuman primate, this project will shed light on the selective pressures and potential influence of energetics in shaping non-human primate and hominin species. Through the course of this research, the Co-PI will provide training in lab-based behavioral endocrinology techniques for undergraduate students from groups underrepresented in STEM fields. In addition, the Co-PI will conduct science education and conservation outreach at various domestic and international venues.
This project will study wild gelada monkeys as a model to examine the relationship between male energetic condition, physiology, and male quality as assessed from vocal and visual signals used in male-male competition. Towards this end, this project will combine classic behavioral observations with innovative methods in (1) digital photogrammetry to assess male chest patch coloration, and (2) endocrinology to determine energetic condition from non-invasively collected urine and fecal samples. The polygynous mating system of gelada monkeys provides an ideal model to investigate contrasts in male reproductive energetics: harem-holding gelada leader males sire the vast majority of offspring while bachelor males in all-male groups lack reproductive opportunities. Reproductive success is therefore heavily skewed towards gelada leader males, and bachelors must overthrow a leader during energetically challenging "takeover" events to gain reproductive access to females. This research will evaluate the underlying seasonal variation in male energetic condition, how this variation relates to male social status, and whether energetic condition ultimately constrains testosterone-dependent signaling and male reproductive strategies. Although ample evidence suggests that lower food availability and energy may constrain male reproductive physiology, a comprehensive picture of the interrelationship between testosterone, energy, and reproduction in male primates is needed. This research will be one of the first to assess how energy may be a limiting factor for male reproductive success in wild primates.
