Context‐dependent stress responses and their connections to fitness in a landscape of fear

Abstract

The acute glucocorticoid stress response is presumed to facilitate escape from life‐threatening situations such as predation and thus it is assumed to be linked to fitness. However, the fitness effects of glucocorticoid reactivity remain controversial, as these effects may be context‐dependent. Individuals differing in their emphasis on current versus future reproduction may differ in their risk‐taking under threat of predation; this variation in risk‐taking may be mediated by variations in stress reactivity. We set out to test whether predation risk (island‐ and year‐specific proportion of depredated nests) modified the relationships between stress responsiveness and current reproductive investment (clutch weight) and between stress responsiveness and reproductive success (viable proportion of the clutch) in the long‐lived female eider Somateria mollissima. This study system shows large spatial and annual fluctuations in predation risk, indexed by the annual island‐specific proportion of depredated nests. The capture stress‐related corticosterone output was attenuated with increasing clutch weight under low predation pressure but elevated under severe predation pressure, and females in well‐concealed nests had lower stress responsiveness. The viable proportion of the clutch decreased with increasing corticosterone reactivity under low to moderate predation pressure, but slightly increased under severe predation pressure. The acute stress response may thus mediate adaptive plasticity; dampened stress reactivity may ensure successful reproduction under low predation threat or in nest sites reducing detection by visual predators, whereas preparing for potential attacks may be favoured under elevated predation risk.

Nest cover and faecal glucocorticoid metabolites are linked to hatching success and telomere length in breeding Common Eiders (Somateria mollissima)

“…Annually all study islands are searched through with equal thoroughness so that all nesting events are recorded. The number of nests on the islands ranged between 0-94 (mean ± SD = 15.7 ± 2.1) during the study period (Jaatinen et al 2014). Female eiders in the study population nest at low densities and previous evidence suggests that nest-site selection is not affected by female competition or nest-site limitation (Öst et al 2008;Öst and Steele 2010;Ekroos et al 2012;Seltmann et al 2014), which contrasts with the situation described for eiders in other populations that nest in dense colonies (e.g., D'Alba et al 2011).…”

“…Thus, GCs enhance vigilance behavior (e.g., Romero and Butler 2007) and causally affect flight initiation distance (Thaker et al 2010). In incubating female eiders, flight initiation distance increases with the magnitude of the acute handling-induced corticosterone (a major GC in birds) response (Seltmann et al 2012), while handling-induced corticosterone responsiveness decreases with increasing nest cover (Schmidt et al 2009;Jaatinen et al 2014). This earlier work also suggests a positive link between enhanced GC responsiveness and reproductive success under high risk of predation .…”

“…Further, incubating females encounter a spatially and temporally varying risk of attack by predators, posing a considerable threat for this ground-nesting bird (Ekroos et al 2012). The relationship between the acute (handling-induced) stress response and reproductive investment has previously been shown to be modulated by predation risk (Jaatinen et al 2014). Finally, the number of years of maternal experience, a proxy for age, does not explain the variability in telomere length observed among adult eider females (this study), and thus age is not likely to confound or mask the associations under focus here.…”

Faecal Glucocorticoid Metabolites and H/L Ratio Are Related Markers of Stress in Semi-Captive Asian Timber Elephants

“…Furthermore, stress can occur when suffering from a disease, when confronted with dominant conspecifics (social stress), or when experiencing extreme environmental situations that threaten homeostasis [11][12][13]. In addition, various internal and external factors can affect stress or stress responsiveness in animals, such as age [14,15], sex [16][17][18], and ecological conditions [19][20][21], or even positive challenges such as breeding interactions, and interpreting stress hormone concentrations is therefore not always straightforward [22,23] and can be context-dependent [24]. Nevertheless, how well an animal can cope with threatening situations is generally reflected by its stress response and therefore, measuring stress can be a useful biomarker to assess the health or well-being of animals.…”

Survival of adult barn owls is linked to corticosterone levels

“…As a mediator of the trade-off between self-maintenance and reproduction (see review Wingfield and Sapolsky, 2003), variation in corticosterone levels may also suggest differences in life-history strategies between individuals (Lancaster et al, 2008) or coping strategies . This may explain why "high" and "low" stress response phenotypes are maintained in our population, in particular, if variation in stress response is associated to fitness in a context-dependent manner (Jaatinen et al, 2014).…”