Biophysical models unravel associations between glucocorticoids and thermoregulatory costs across avian species

Abstract

1. Glucocorticoids (GCs) are metabolic hormones that regulate physiological and behavioural responses to environmental change and mediate homeostasis maintenance in vertebrates. Despite the assumption that GCs covary with energy metabolism, we yet lack a mechanistic understanding of how environmental factors such as temperature modulate GC variation through their effect on organismal energy balance. In particular, the mechanisms linking temperature-dependent metabolic rate and GCs at broad spatial scales and across species remain poorly investigated.2. Here we used biophysical models to calculate thermoregulatory costs (i.e. the amount of heat required to keep body temperature in homeostasis) of freeliving birds as a function of environmental conditions, body size, shape and insulating layer of feathers. We then investigated the link between ambient temperature, cost of thermoregulation and baseline plasma GC concentrations in a comparative study including GC data from 94 bird species from HormoneBase.3. We found a significant, positive association between thermoregulatory costs and baseline GC concentrations. Interestingly, models including thermoregulatory costs better explained GC variation when compared to those including ambient temperature as a predictor variable. This result suggests that body size and shape fundamentally modulate energy requirements for thermoregulation and thereby GC concentrations in the wild. 4. By providing a mechanistic description of the link between ambient temperature and thermoregulatory costs, biophysical models provide a tool to predict the impact of environmental conditions on energy metabolism. Our work demonstrates that differences in thermoregulation modulate variation in GC concentrations across a broad climatic gradient.

Behavioral thermoregulation in primates: A review of literature and future avenues

“…Given that primates are expected to fare poorly under these scenarios (Graham et al, 2016) and possess few long‐term options to cope with climate change (Schloss et al, 2012), there is an urgency to move from correlative studies to quantification of a behavior's contribution to the overall health or energy balance. The use of biophysical models holds promise for providing predictive models that incorporate behaviors into the larger milieu of thermodynamics impacting animals (e.g., Mathewson et al, 2020; Moyer‐Horner et al, 2015; Rubalcaba & Jimeno, 2022). Monitoring physiological markers could also provide a potential route for assessing the impact of thermoregulatory behaviors.…”

Glucocorticoids and land cover: a largescale comparative approach to assess a physiological biomarker for avian conservation

“…We gathered GC data from HormoneBase, a comprehensive database containing records of GCs collected from adult, free-living vertebrates over the past six decades [54]. Since its publication, HormoneBase has facilitated the investigation of many similar comparative physiological questions at broad spatial and temporal scales, such as relating GCs to life-history traits [55], metabolic rate [56], energetic costs of thermoregulation [57] and conservation status [58], but no studies have assessed the utility of GCs in predicting organismal responses to available land cover types. We focused our study on birds due to their broad distributions, utilization of diverse habitats, extensively studied natural history and well-documented variation in GC (corticosterone in birds) concentrations across life-history stages.…”

Great tits differ in glucocorticoid plasticity in response to spring temperature

“…Population-level relationships with ambient temperature: baseline and stress-induced corticosterone concentrations are higher at lower ambient temperatures. This is a common pattern among endotherms (summaries: de Bruijn & Romero, 2018; Jessop et al, 2016; Ruuskanen et al, 2021; Wingfield & Ramenofsky, 2011), and likely results from more energy being expended on thermoregulation and increased foraging activity at lower temperatures (e.g., Rubalcaba & Jimeno, 2022). We also predicted that baseline and stress-induced corticosterone concentrations are more strongly associated with short-term (temperature at capture) than with longer-term temperature measurements (mean temperatures on capture day or on days preceding capture) because parental great tits should track short-term temperature changes as these affect their own energy requirements as well as their foraging effort.…”