Differences in circulating corticosterone levels associated with elevation of breeding sites in Rufous-collared Sparrows Zonotrichia capensis

Yanina Poblete,Paulina L González-Gómez,Rodrigo A Vásquez,Victor Gutierrez,John C Wingfield

doi:10.1007/s10336-020-01846-w

Abstract

To facilitate breeding and any energetically costly activity, individuals of the same species can substantially vary their circulating corticosterone (CORT) levels to cope with local environmental conditions at different elevations. We compared baseline and the stress-induced plasma CORT levels during the parental care stage between free-living Rufous-collared Sparrows (Zonotrichia capensis) that breed at high (~ 2500 m) and low (~ 500 m) elevations in central Chile. We found that baseline CORT levels at different elevations were similar and that stress-induced levels were significantly lower in birds breeding at high elevation; however, we detected no sexual dimorphism in CORT levels related to elevation. We found that larger individuals had higher stress-induced CORT levels at low elevation regardless of sex. Our results show that environmental conditions at high elevation seem to be not severe enough to promote more elevated baseline CORT levels. However, breeding Rufous-collared Sparrow must still deal with both shorter breeding seasons and increased exposure to unpredictable events. Thus, a reduced stress response during the parental care stage would be more favorable for supporting breeding activities at high elevations. Future studies should focus on describing the life-history traits of these populations and the effects that other stressors, such as predation pressure and food availability, may have on the adrenocortical response in these environments to evaluate the consequences for survival and reproductive success. This information is important for enhancing our understanding of the ecological and evolutionary mechanisms that modulate variation in the adrenocortical response among populations of the same species.

Highlights

Corticosterone (CORT) is a steroidal hormone that plays a key role in responses to environmental variability, because it modulates the energy balance facilitating both physiological and behavioral changes needed for different life-history stages in the birds (Sapolsky et al 2000; McEwen and Wingfield 2003; Romero 2002; Landys et al 2006)
CORT levels induced by unpredictable events are driven by the adrenocortical stress response triggering a cascade effect: the hypothalamus secretes arginine vasotocin and corticotropin-releasing factor, which, in turn, activate the anterior pituitary release of adrenocorticotropin (ACTH), stimulating the synthesis and secretion of CORT by adrenal glands (Romero and Remage-Healey 2000; Romero and Wingfield 2016) resulting in plasma CORT levels significantly higher than those expressed during daily life predictable events (Romero, 2004; Landys et al 2006)
Tropical Rufous-collared Sparrows breeding at high elevation show higher sensitivity to stress during parental care compared to their northern congeners (Breuner and Hahn 2003), suggesting duration of the breeding season, temperature and life-history traits may play a role in the modulation of the adrenocortical stress response to cope effectively with local environmental conditions (Wada et al 2006)

Summary

Introduction

Corticosterone (CORT) is a steroidal hormone that plays a key role in responses to environmental variability, because it modulates the energy balance facilitating both physiological and behavioral changes needed for different life-history stages in the birds (Sapolsky et al 2000; McEwen and Wingfield 2003; Romero 2002; Landys et al 2006). Comparative studies have shown that at high elevations in temperate zones of the Northern Hemisphere, birds often down-regulate their adrenocortical stress response during parental care (Bears et al 2003; Breuner and Hahn 2003; Pereyra and Wingfield 2003), possibly to reduce negative effects of the stress response, such as nest abandonment (Romero et al 2000). Tropical Rufous-collared Sparrows breeding at high elevation show higher sensitivity to stress during parental care compared to their northern congeners (Breuner and Hahn 2003), suggesting duration of the breeding season, temperature and life-history traits may play a role in the modulation of the adrenocortical stress response to cope effectively with local environmental conditions (Wada et al 2006). Whether the adrenocortical stress response is down-regulated at high elevations in the temperate zones of the Southern Hemisphere during parental care is unclear because this issue has been comparatively understudied (but see Clark et al 2019)

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