Natural selection and glucocorticoid physiology

Abstract

Glucocorticoid hormones are considered potent modulators of trade-offs between reproduction and survival. As such, selection should affect glucocorticoid physiology, although relatively little is known about how selection may act on glucocorticoid profiles. In general, the evolution of physiology is less studied and less well understood than morphological or life history traits. Here, we used a long-term data set from a population of mountain whitecrowned sparrows to estimate natural selection on glucocorticoid profiles. Our study suggests that survival selection favours higher hormone concentrations for multiple components of glucocorticoid physiology (both baseline and stressinduced glucocorticoid levels). Fecundity selection varies depending on the component of hypothalamic-pituitary-adrenal physiology; greater reproductive output was associated with higher baseline glucocorticoid levels, but lower stress-induced glucocorticoid levels. Additionally, the selection gradient was greater for glucocorticoids than for a morphological trait (wing length). These results support the hypothesis that stress-induced glucocorticoids increase survival over reproduction within a wild population (the CORT-trade-off hypothesis). Taken together, these results add to our knowledge of how selection operates on physiological traits and also provide an evolutionary and ecological perspective on several key open issues in the field of glucocorticoid physiology.

Testing hypotheses about individual variation in plasma corticosterone in free-living salamanders

“…In white-crowned sparrows, a species where females do the majority of nest building, incubating and feeding of offspring, reproductive success was positively associated with baseline CORT and was negatively associated with stressinduced CORT (Patterson et al, 2014). Amphibians actively engaged in reproductive behavior often have elevated plasma CORT (Harvey et al, 1997;Leary et al, 2004;Mendonça et al, 1985;Orchinik et al, 1988;Reedy et al, 2014).…”

“…Thus, the facilitation hypothesis predicts that plasma CORT would be positively correlated with energetically costly functions during non-challenging (baseline) times. Conversely, the relationship between CORT and energetically costly functions that are not imperative to survival may shift to negative during times of stress, which is the basis for the trade-off hypothesis, also sometimes called the re-allocation hypothesis (Almasi et al, 2013;Martin et al, 2012;McEwen and Wingfield, 2003;Patterson et al, 2014;Wingfield and Sapolsky, 2003). The trade-off hypothesis predicts that, during times of stress, plasma CORT levels are negatively correlated with functions like reproduction or immune processes that are both energetically costly and not necessary for survival of the threat.…”

“…The hypotheses can be categorized as follows: the current-condition hypothesis (closely related to the fitness hypothesis), the facilitation hypothesis (also called the adaptation hypothesis) and the trade-off hypothesis (also called the energy re-allocation hypothesis) (reviewed in Patterson et al, 2014). Broadly, the current-condition hypothesis proposes that elevated baseline CORT levels are indicative of poor condition that may translate into reduced performance or reduced fitness of either an individual or a population (Bonier et al, 2009a;Husak and Moore, 2008).…”

Ozone Exposure Increases Circulating Stress Hormones and Lipid Metabolites in Humans

“…Acute ozone exposure has been shown to activate central stress responsive regions and the nucleus tractus solitarius where pulmonary vagal nerves terminate in the brain (18,32). Thus, pulmonary vagal C fibers, likely through neurotransmission in the brain, can stimulate sympathetic and/or the HPA axis, leading to the release of stress hormones from sympathetic nerve endings and also from the adrenal gland (33,34). As a result, these stress hormones can target metabolic organs in a tissue-specific manner and alter glucose and lipid metabolism through activation of cellular glucocorticoids and adrenergic receptors.…”

How can we estimate natural selection on endocrine traits? Lessons from evolutionary biology

“…When considering among-individual variation-the variation upon which natural selection acts-evolutionary endocrinologists have drawn on classic approaches from evolutionary biology, particularly correlations between trait values (phenotypes) and fitness, to estimate selection (e.g. [3,4]). This approach, however, is likely to generate misleading and inaccurate estimates of both natural selection and the predicted responses to selection for traits that exhibit adaptive plasticity [5][6][7][8][9][10][11].…”