Chronological age, biological age, and individual variation in the stress response in the European starling: A follow-up study

Abstract

The responsiveness of the avian stress system declines with age. A recently published study of European starlings (Sturnus vulgaris) found that a marker of biological age predicted stress responsiveness even in individuals of the same chronological age.Specifically, birds that had experienced greater developmental telomere attrition showed a lower peak corticosterone response to an acute stressor, and more rapid recovery of corticosterone levels towards baseline. Here, we performed a follow-up study using the same capture-restraint-handling stressor in a separate cohort of 27 starlings. Unlike the original study, we measured the response at two different age points (4 and 18 months).We did not replicate the associations with developmental telomere attrition observed in the previous study at either age point. However, a meta-analysis of the present results combined with those of the earlier study still lent some support to the conclusions of the earlier paper. Estimates of familial influence on stress responsiveness differed across the two age points. We found little evidence of individual consistency in stress responsiveness between 4 and 18 months. Peak corticosterone was significantly lower at the second age point than the first, though interpretation of this as age-related decline is problematic due to the samples having been analysed at different times. found that a marker of biological age predicted stress responsiveness even in 21 individuals of the same chronological age. Specifically, birds that had experienced greater developmental 22 telomere attrition showed a lower peak corticosterone response to an acute stressor, and more rapid 23 recovery of corticosterone levels towards baseline. Here, we performed a follow-up study using the same 24 capture-restraint-handling stressor in a separate cohort of 27 starlings. Unlike the original study, we 25 measured the response at two different age points (4 and 18 months). We did not replicate the associations 26 with developmental telomere attrition observed in the previous study at either age point. However, a 27 meta-analysis of the present results combined with those of the earlier study still lent some support to the 28 conclusions of the earlier paper. Estimates of familial influence on stress responsiveness differed across 29 the two age points. We found little evidence of individual consistency in stress responsiveness between 4 30 and 18 months. Peak corticosterone was significantly lower at the second age point than the first, though 31 interpretation of this as age-related decline is problematic due to the samples having been analysed at 32 different times. , 2015). Biological age is by definition a better predictor of future lifespan than 45 chronological age is. Hence, we should expect markers of individual biological age to explain variation in 46 stress responsiveness that cannot be explained by chronological age alone. A possible reason that early-47 life conditions have often been observed to influence the functioning of the adult stress respon...

Developmental history, energetic state and choice impulsivity in European starlings, Sturnus vulgaris

“…Third, we investigated the direct effects of developmental treatments (the amount of food and the level of begging effort) on impulsivity in the current cohort of birds. Although the two previous starling studies (Bateson et al 2015 ; Nettle et al 2015a ), in line with evidence from other systems (Lovic et al 2011 ; Brydges et al 2015 ), found no direct effects of developmental treatments on impulsivity, in the present cohort of starlings, there is other evidence for direct treatment effects on adult behavioural phenotype (Neville et al 2017 ; Gott et al 2018 ). This may be because the developmental treatments in the current birds, who were hand-reared, were better controlled than earlier cross-fostering manipulations.…”

Accounting for demography in the assessment of wild animal welfare

“…The premise of this approach is that somatic damage and repair, which determine biological age, often result from physiological processes that are associated with affective states, such as stress or happiness. Indeed, adverse conditions such as sibling competition have been shown to lead to accelerated biological aging limited to the study period, especially when the individual is a weaker competitor (Gott et al, 2018). Surveying population-level variation or tracking individual longitudinal variation in the biological-to-chronological age ratio, through measurements such as telomere length, could be a cost-effective way to estimate relative age-specific welfare within wild populations.…”

Developmental history and stress responsiveness are related to response inhibition, but not judgement bias, in a cohort of European starlings (Sturnus vulgaris)

“…CORT profiles were measured from the same 31 birds when they were aged 127–134 days (methods described in Gott et al 2018 ; the data used here are ‘age point 1’ from that study as this is the closest in age to the judgement bias experiment). Briefly, we used a standardised capture-handling-restraint protocol employed previously in European starlings (Andrews et al 2017 ).…”

“…The three judgement bias variables were correlated with each of baseline CORT, peak CORT and ΔCORT. Correlations involving peak CORT were partial, controlling for baseline CORT, and correlations involving ΔCORT were partial, controlling for CORT at 15 min (see Gott et al 2018 ). An alpha level of significance of P < 0.05 was used throughout.…”

“…In the current cohort of birds, we did not manipulate CORT levels experimentally. However, we had measured individuals’ baseline CORT and CORT responses to an acute capture-handling-restraint stressor approximately 3 months prior to the present experiment (data previously published in Gott et al 2018 ). This allowed us to ask whether individual differences in judgement bias were related to individual differences in baseline CORT or the magnitude of the CORT response.…”