Great tits differ in glucocorticoid plasticity in response to spring temperature

Abstract

Fluctuations in environmental temperature affect energy metabolism and stimulate the expression of reversible phenotypic plasticity in vertebrate behavioural and physiological traits. Changes in circulating concentrations of glucocorticoid hormones often underpin environmentally induced phenotypic plasticity. Ongoing climate change is predicted to increase fluctuations in environmental temperature globally, making it imperative to determine the standing phenotypic variation in glucocorticoid responses of free-living populations to evaluate their potential for coping via plastic or evolutionary changes. Using a reaction norm approach, we repeatedly sampled wild great tit ( Parus major ) individuals for circulating glucocorticoid concentrations during reproduction across five years to quantify individual variation in glucocorticoid plasticity along an environmental temperature gradient. As expected, baseline and stress-induced glucocorticoid concentrations increased with lower environmental temperatures at the population and within-individual level. Moreover, we provide unique evidence that individuals differ significantly in their plastic responses to the temperature gradient for both glucocorticoid traits, with some displaying greater plasticity than others. Average concentrations and degree of plasticity covaried for baseline glucocorticoids, indicating that these two reaction norm components are linked. Hence, individual variation in glucocorticoid plasticity in response to a key environmental factor exists in a wild vertebrate population, representing a crucial step to assess their potential to endure temperature fluctuations.

Breeding under pressure: Corticosterone is associated with reproductive investment under fluctuating predation risk in a long‐lived sea duck

“…Using long-term individual-based data, we showed that increas- Romero, 2018;Hau et al, 2022;Ruuskanen et al, 2021) or bottom-up effects linked to variation in food quality or availability (Kitaysky et al, 2010). In light of our results,…”

“…In the current context of climate change, other unmonitored environmental variables may have concomitantly fluctuated over the study period and affected baseline CORT levels. Such variables may for instance include changes in ambient temperature (De Bruijn & Romero, 2018; Hau et al, 2022; Mentesana & Hau, 2022; Ruuskanen et al, 2021) or bottom‐up effects linked to variation in food quality or availability (Kitaysky et al, 2010). In light of our results, we urge future studies to experimentally test for a causal relationship between predation pressure and baseline CORT levels, while controlling for other potential important environmental variables.…”

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

“…[53–55]). Recently, for the first time, individual differences in hormonal flexibility to temperature variation were demonstrated in free-living birds [26]; in this case, individuals differed in both average glucocorticoids (elevation) and flexibility (slope), but there was a negative covariation between the two traits for baseline corticosterone regulation [26]. Moving up to the species level, one recent paper also used a reaction norm approach to demonstrate that some components of glucocorticoid flexibility differ between species and are associated with the thermal environment in which species live [56].…”

“…However, there are research gaps that will necessitate novel datasets at different temporal and organizational scales to provide substantive answers. Currently, while we have a few examples of individual and species differences in endocrine reaction norms [26,56], we know very little about whether these differences can be attributed to flexibility or evolution, or about the degree to which the same selection pressures result in the evolution of similar patterns of endocrine flexibility (i.e. parallelism [112]).…”

Dietary nucleotides can prevent glucocorticoid‐induced telomere attrition in a fast‐growing wild vertebrate

“…Here we experimentally tested whether the catabolic actions of high glucocorticoid concentrations can be counteracted by the effects of high nucleotide availability on telomere dynamics during growth using a wild avian model ( Parus major , great tit) with known effects of glucocorticoids on telomere length during a phase of rapid growth (Casagrande et al, 2020). The great tit is a common passerine found throughout Europe and Asia that has become a popular model species for ecological studies in a variety of research areas (Hau et al, 2022; Laine et al, 2016; Ouyang et al, 2012; Regan & Sheldon, 2023; Verhagen et al, 2020), including telomere length (Atema et al, 2021; Casagrande et al, 2020; Stier et al, 2016, 2021), mitochondrial (Casagrande et al, 2020; Nord et al, 2021) and gene expression studies (Lindner et al, 2021). Great tits have been found to exhibit substantial variation in telomere length (Atema et al, 2019), which has been linked to various life history traits and environmental factors (Casagrande et al, 2020; Stier et al, 2016, 2021).…”