Faecal glucocorticoid metabolite profiles in diademed sifakas increase during seasonal fruit scarcity with interactive effects of age/sex class and habitat degradation.

Stacey R Tecot,Jean-Luc Raharison,Mitchell T Irwin,Steven Cooke

doi:10.1093/conphys/coz001

Stacey R Tecot, Jean-Luc Raharison + Show 2 more

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https://doi.org/10.1093/conphys/coz001

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Abstract

Glucocorticoids are metabolic byproducts of animals' physiological responses to ecological or social challenges and are thought to represent an adaptive response allowing beneficial responses to short-term challenges. Glucocorticoid metabolites (GCs) can be assayed non-invasively through faeces and therefore can be a useful tool to gauge the health of populations experiencing natural and/or anthropogenic stressors. However, the response of GCs to anthropogenic stressors varies, with both higher and lower GC levels reported. Here, we describe variation in GC secretion within eight diademed sifaka (Propithecus diadema) groups across 1 year. These groups span a gradient of anthropogenic habitat disturbance, including groups in continuous forest ('CONT') and disturbed fragments ('FRAG'), and indicators of health suggest that FRAG groups are negatively impacted by habitat disturbance. We monitored phenology, used focal animal follows to quantify diet and collected faeces (n = 547) from which we quantified GC content using enzyme immunoassay. All groups showed elevated lean-season GCs, but with a single, brief peak. GCs were inversely correlated with feeding time. No overall effect of habitat (CONT vs. FRAG) was found, but the lean-season peak was significantly higher in CONT groups. There was a significant season*age-sex interaction; adult females had an attenuated lean-season response compared with groupmates. The observed lean-season 'challenge' is consistent with previous lemur studies, as well as mammals in general. Low and largely invariable GC levels in FRAG, within the context of observed health and nutritional declines, suggest that FRAG groups employ a strategy whereby the adrenal response to stressors is downregulated. More research is needed to contextualize our observations of GC variation and health on an individual level, both in terms of corroborating evidence for ecological and social stressors, and longer-term quantification of reproductive success and fitness.

Highlights

As habitat alteration progresses and few environments remain untouched by humans, determining the effects of anthropogenic change on populations and ecosystems is increasingly important for conservation, and to understand processes of selection (Madliger and Love, 2014; Wingfield, 2008)
For the first model we examined the effects of site (CONT/FRAG), season, age/sex class and all interactions
Faecal Glucocorticoid metabolites (GCs) are a useful proxy for HPA axis activation in many wild vertebrates, but one difficulty has been that both healthy and distressed individuals can have low GC levels

Summary

Introduction

As habitat alteration progresses and few environments remain untouched by humans, determining the effects of anthropogenic change on populations and ecosystems is increasingly important for conservation, and to understand processes of selection (Madliger and Love, 2014; Wingfield, 2008). Glucocorticoids are expected to reflect the intensity of a response to a stressor (Hennessy et al, 1979), and have been termed ‘anti-stress hormones’ (Wingfield and Kitaysky, 2002). If this response is prolonged, long-term functions may become chronically inhibited (e.g. anovulation, increased susceptibility to disease); the stress response becomes maladaptive insofar as long-term glucocorticoid elevations impact health and fitness (Sapolsky, 1998; Sapolsky et al, 2000; Selye, 1978)

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