Reproduction and modulation of the stress response: an experimental test in the house sparrow

Abstract

The stress response is highly variable among individuals, but the causes of this variation remain largely unknown. In response to stressors, vertebrates secrete elevated levels of glucocorticoids which enhance survival, but concurrently interfere with reproduction. We tested the hypothesis that individuals flexibly modulate their stress response with respect to the reproductive value of their brood in free-living house sparrows (Passer domesticus). We experimentally increased or decreased clutch size during the nestling period and found that parents tending enlarged clutches responded less strongly to a stressor than those tending reduced clutches. In addition, we examined whether individuals responded less strongly to a stressor as the breeding season progressed and future reproductive opportunities declined. We found that the stress response decreased with breeding date during the birds' first breeding attempt, but it remained constant during their second breeding attempt. Within-individual variability in the stress response was related to the brood size manipulations the birds received in their two consecutive breeding attempts. These results provide the first experimental support for the hypothesis that individuals actively modulate their stress response with respect to the value of current reproduction.

Individual variation in baseline and stress-induced corticosterone and prolactin levels predicts parental effort by nesting mourning doves

“…In common murre (Uria aalge), SI CORT levels are best predicted by food availability the previous month, indicating that there may be a lag in the time between environmental stimuli that affect individuals and the upregulation of CORT production (Kitaysky et al, 2007). This stands in contrast to recent results for house sparrows (P. domesticus) where the SI CORT response was negatively related to reproductive value of offspring (Lendvai et al, 2007;Lendvai and Chastel, 2008) and to differences among species where birds with greater investment in young have smaller SI responses (Bókony et al, 2009). …”

“…An important component to improving our understanding of the role that hormonal control plays in reproductive plasticity in birds will be determining whether birds vary their hormonal responses in response to their environment rather than the variation being fixed among individuals. Given that endocrine systems have characteristics allowing organisms to respond to environmental influence (e.g., CORT and the HPA axis; Sapolsky et al, 2000) and have been shown to be responsive to environmental input (e.g., Romero, 2002;Lendvai et al, 2007;Bradshaw, 2007;Kempenaers et al, 2008;Lendvai and Chastel, 2008), we suspect that individual variation observed in this study includes both fixed and plastic components.…”

“…Differences among species in reproductive value of offspring predict differences in SI CORT responses (Bókony et al, 2009), indicating that life-history predictions may be important in driving variation in the response. An alternative approach to investigation is to examine individual variation in the stress response to determine if responses are modulated in response to life-history trade-offs (Lendvai et al, 2007;Williams, 2008).…”

The stress of being contaminated? Adrenocortical function and reproduction in relation to persistent organic pollutants in female black legged kittiwakes

“…To elucidate which aspects of the HPA axis are involved in mediating contaminant-related changes in the stress response, experimental ACTH injection would be useful to investigate if contaminant-related enhancement occurs at the level of the adrenal gland, or rather at the level of the pituitary, hypothalamus or perception of the stressor. An enhanced stress response is often the consequence of poor early-life experience across vertebrates as low body mass at birth, food restriction, maternal deprivation (Banerjee et al 2012;Heath and Dufty, 1998;Kitaysky et al 2001;Müllner et al 2004;Phillips and Jones 2006), while in adults it often mirrors poor fitness related traits as poor parental investment Bókony et al 2009;Goutte et al 2011a;Lendvai et al 2007) or an impacted survival (Blas et al 2007;Goutte et al 2010b;Romero 2012). Still, as mentioned previously, in our study we failed to relate POP levels to breeding success.…”

“…However, only a few studies have explored the impact of pollutants on both baseline and stress induced glucocorticoid levels, which depict different physiological functions: baseline corticosterone levels (CORT, the major glucocorticoid in birds) mirrors activity, metabolic rate and reflects the ratio between energy available and energy needed (Landys et al 2006), while stress-induced CORT can be used as an index of the sensitivity to stress of an individual, this value can be modulated in order to maximize either survival, either reproduction (Bókony et al 2009;Lendvai et al 2007). Regarding contaminant/HPA axis, the pattern seems clear in fish: i.e.…”