Impacts of reproductive state and social environment on glucocorticoid concentrations in female Rwenzori Angolan colobus monkeys (Colobus angolensis ruwenzorii).

Glucocorticoids (GCs) are hormones that are secreted in response to energetic demands, allowing animals to cope with internal and external challenges. We investigated the factors impacting fecal GC metabolite (FGM) concentrations (a proxy of blood GC concentrations) in a population of Rwenzori Angolan colobus monkeys (Colobus angolensis ruwenzorii) in Uganda. These monkeys live in a multi-level society with three tiers of non-random association: the core unit (individuals that feed, rest, and travel together), the clan (core units that associate preferentially), and the band (core units that share a home range). We used linear mixed-effect models to assess the impact of reproductive state, fruit availability, and core unit composition on FGM concentrations of reproductive females. We found that FGM concentrations increased over the course of pregnancy and decreased over the course of lactation. There was a quadratic relationship between FGM concentrations and core unit size, with FGM concentrations being lower for mothers living in intermediate-sized core units compared to those living in smaller and larger core units. This aligns with previous work on this population showing that individuals living in intermediate-sized core units expend the least energy travelling. Future work should investigate the impact of FGM concentrations on infant growth and development in this subspecies.

Iowa State University
University of Toronto