Endocrine flexibility can facilitate or constrain the ability to cope with global change.

Abstract

Global climate change has increased average environmental temperatures world-wide, simultaneously intensifying temperature variability and extremes. Growing numbers of studies have documented phenological, behavioral, and morphological responses to climate change in wild populations. As systemic signals, hormones can contribute to orchestrating many of these phenotypic changes. Yet little is known about whether mechanisms like hormonal flexibility (reversible changes in hormone concentrations) facilitate or limit the ability of individuals, populations, and species to cope with a changing climate. In this perspective, we discuss different mechanisms by which hormonal flexibility, primarily in glucocorticoids, could promote versus hinder evolutionary adaptation to changing temperature regimes. We focus on temperature because it is a key gradient influenced by climate change, easy to quantify, and links to hormones are well established. We argue that reaction norm studies that connect individual responses to population-level and species-wide patterns will be critical for making progress in this field. We also develop a case study on urban heat islands, where several key questions regarding hormonal flexibility and adaptation to climate change can be addressed. Understanding the mechanisms that allow animals to cope when conditions become more challenging will help in predicting which populations are vulnerable to ongoing climate change.

Baseline glucocorticoids alone do not predict reproductive success across years, but in interaction with enzymatic antioxidants

“…Finally, our study sampled individuals only once, examining the relationship between glucocorticoids and fitness proxies at the population level. While this is a common methodology, it is essential to note that populations and individuals can differ in the correlation structures of traits (Malkoc et al., 2022; Niemelä & Dingemanse, 2018; Taff et al., 2024). Therefore, our study does not provide information on the relationship between individual glucocorticoid concentrations (where natural selection operates) and reproductive success.…”

Endocrine responses to environmental variation

“…Climate change and its associated increases in average temperatures and temperature fluctuations can impact animals directly by temperature-induced impairment of physiological rate functions, and of reproductive function and fitness [62]. Endocrine flexibility has the potential to alleviate the negative effects of warming and increased variability, in particular via glucocorticoid signalling [17]. However, there are likely to be taxonomic differences and limits in its efficacy to respond to extreme environments such as urban heat islands.…”

“…However, there are likely to be taxonomic differences and limits in its efficacy to respond to extreme environments such as urban heat islands. Future research should be directed to increase understanding of the endocrine mechanisms that allow animals to cope with variable conditions, which will help identify the populations that are most vulnerable to climate change [17]. Interestingly, an analysis of glucocorticoid concentrations in 51 species of birds in the USA showed a landscape-level association between stress-induced levels of glucocorticoids and usable land cover within and across species [63].…”

“…Anthropogenic endocrine disruption modifies endocrine-mediated responses to natural variation and links the fields of environmental science and toxicology to ecology and conservation biology [16,17]. Understanding of how anthropogenic impacts such as climate change, artificial light-at-night (ALAN) and endocrine disrupting chemicals (EDCs) alter evolved responses of animals is only now emerging [18].…”