High faecal glucocorticoid levels predict mortality in ring-tailed lemurs (Lemur catta)

Abstract

Glucocorticoid levels are commonly used as measures of stress in wild animal populations, but their relevance to individual fitness in a wild population has not been demonstrated. In this study I followed 93 ring-tailed lemurs (Lemur catta) at Berenty Reserve in Madagascar, collecting 1089 faecal samples from individually recognized animals, and recording their survival over a 2 year period. I evaluated faecal glucocorticoid levels as predictors of individual survival to the end of the study. Animals with high glucocorticoid levels had a significantly higher mortality rate. This result suggests that glucocorticoid measures can be useful predictors of individual survival probabilities in wild populations. The 'stress landscape' indicated by glucocorticoid patterns may approximate the fitness landscape to which animals adapt.

Figure 1

Survival probability decreased with higher cortisol. Vertical bars show median residual cortisol of animals that survived (−0.01 log ng g⁻¹ faeces; top row) and those that died (0.11 log ng g⁻¹ faeces; bottom row).

Figure 2

High-cortisol animals showed higher mortality than low-cortisol animals during the 2 year study.