Glucocorticoids Across Life Stages in Northern Glassfrogs (Hyalinobatrachium fleischmanni)

Glucocorticoid steroid hormones (GCs) coordinate physiology and behavior across immediate, developmental, and evolutionary timescales. There are two main GCs produced by vertebrates, cortisol and corticosterone, and, based on taxonomic relationships, species are generally assumed to have one of the two as their primary GC. However, growing evidence demonstrates that GC abundance and regulation are more complex than previously thought, with the potential for variation across tissues, developmental time, and context. To understand GC patterns across the life cycle of Northern Glassfrogs (Hyalinobatrachium fleischmanni), we quantified both cortisol and corticosterone across seven life stages, from egg to adult, and two sampling methods, non-invasive waterborne sampling and invasive body sampling. As predicted for amphibians, we found that corticosterone was generally more abundant than cortisol. However, the magnitude of this difference varied across life stages and sampling method. Counter to expectations that water hormone levels consistently reflect those in the body, we found that this relationship differed across life stages. Our results emphasize the context-dependent nature of GCs, highlighting exciting avenues for future research and important considerations for researchers interested in non-invasive GC sampling.