Glucocorticoids, state-dependent reproductive investment and success in the face of danger in a long-lived bird

Abstract

Glucocorticoid hormones may mediate trade-offs between current and future reproduction. However, understanding their role is complicated by predation risk, which simultaneously affects the value of the current reproductive investment and elevates glucocorticoid levels. Here, we shed light on these issues in long-lived female Eiders (Somateria mollissima) by investigating how current reproductive investment (clutch size) and hatching success relate to faecal glucocorticoid metabolite [fGCM] level and residual reproductive value (minimum years of breeding experience, body condition, relative telomere length) under spatially variable predation risk. Our results showed a positive relationship between colony-specific predation risk and mean colony-specific fGCM levels. Clutch size and female fGCM were negatively correlated only under high nest predation and in females in good body condition, previously shown to have a longer life expectancy. We also found that younger females with longer telomeres had smaller clutches. The drop in hatching success with increasing fGCM levels was least pronounced under high nest predation risk, suggesting that elevated fGCM levels may allow females to ensure some reproductive success under such conditions. Hatching success was positively associated with female body condition, with relative telomere length, particularly in younger females, and with female minimum age, particularly under low predation risk, showing the utility of these metrics as indicators of individual quality. In line with a trade-off between current and future reproduction, our results show that high potential for future breeding prospects and increased predation risk shift the balance toward investment in future reproduction, with glucocorticoids playing a role in the resolution of this trade-off.

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

“…Accordingly, there is ample experimental and theoretical evidence that reproductive performance increases with age and experience before declining at very old ages (e.g. in eiders; Mohring et al, 2022; Noreikienė et al, 2021). To our knowledge, our study provides the first evidence of a within‐individual decrease in baseline CORT levels at old age (but see Lendvai et al (2015) for an individual‐specific decrease in the CORT stress response with age), supporting the idea that CORT can mirror reproductive senescence in wild animals.…”

“…Accordingly, there is ample experimental and theoretical evidence that reproductive performance increases with age and experience before declining at very old ages (e.g. in eiders; Mohring et al, 2022;Noreikienė et al, 2021).…”

“…Circulating glucocorticoid levels can thus fluctuate in response to challenging extrinsic or intrinsic conditions, and are thought to mirror higher energetic demands under harsh conditions (Harris, 2020; Landys et al, 2006; Wingfield, 2013). Several studies have demonstrated elevated baseline glucocorticoid levels under high predation pressure (Clinchy et al, 2004; Hik et al, 2001; Middlemis Maher et al, 2013; Noreikienė et al, 2021; Scheuerlein et al, 2001; Spong et al, 2020), or under nutritional stress, notably during years of poor or unpredictable food availability (Angelier et al, 2015; Kitaysky et al, 1999; Pravosudov et al, 2001).…”