Social support correlates with glucocorticoid concentrations in wild African elephant orphans

Abstract

Social relationships have physiological impacts. Here, we investigate whether loss of the mother/offspring relationship has lasting effects on fecal glucocorticoid metabolite (fGCM) concentrations in wild African elephant orphans several years following their mothers’ deaths. We find no difference in fGCM concentrations between orphans and nonorphans, but find lower fGCM concentrations in elephants with more age mates in their family. We also unexpectedly identify lower concentrations in orphans without their natal family versus nonorphans and natal orphans, which we speculate may be due to the development of hypocortisolism following a prolonged period without familial support. An index of plant productivity (i.e. food) shows the largest correlation with fGCM concentrations. Our findings indicate no lasting differences in glucocorticoid concentrations of surviving orphan elephants who are with their family, suggest the presence of age mates may reduce glucocorticoid concentrations in elephants, and emphasize that basic survival needs are the primary regulators of the stress response.

Orphaning stunts growth in wild African elephants

“…Our findings showed small but interesting correlations between height and the number of multiparous females and age mates within a core group. A previous study found similar relationships between faecal glucocorticoids (stress) and social conditions, notably that social buffering from age mates may reduce stress in wild African elephants ( Parker et al , 2022 ), which could foster growth ( Wu, 2021 ). However, the effect of adult females on the stress response was uncertain ( Parker et al , 2022 ), and our results here suggest the presence of more adult females marginally reduces growth.…”

“…A previous study found similar relationships between faecal glucocorticoids (stress) and social conditions, notably that social buffering from age mates may reduce stress in wild African elephants ( Parker et al , 2022 ), which could foster growth ( Wu, 2021 ). However, the effect of adult females on the stress response was uncertain ( Parker et al , 2022 ), and our results here suggest the presence of more adult females marginally reduces growth. Possibly adult females increase competition and limit access to resources for growth.…”

“…Reduced body mass and stress are known correlates ( Dickens and Romero, 2013 ; Wu, 2021 ); the release of glucocorticoids during stress diverts energy away from nonurgent uses like growth ( Sapolsky, 2004 ), and elevated glucocorticoid levels have been associated with lower levels of growth hormones and their binding proteins ( Gabbitas et al , 1996 ; Bernstein, 2010 ). Previous study suggests orphans do not sustain higher levels of stress hormones ≥2 years after their mother’s death ( Parker et al , 2022 ), but if there are short-term alterations that may affect growth. In chimpanzee orphans, short-term but not long-term alterations in glucocorticoid concentrations were observed ( Girard-Buttoz et al , 2021 ).…”

“…The next four covariates captured aspects of juvenile social status: (ii) orphan status (binary variable: 0 non-orphan, 1 orphan); (iii) years spent without mother, calculated by subtracting the mother’s estimated death date from date of measure and dividing by 365 such that partial years were represented by a decimal amount (non-orphans had a value of ‘0’ for this covariate); (iv) the number of adult multiparous females within an individual’s core group ( Wittemyer et al, 2005b ; Parker et al , 2022 ); and (v) the number of age mates within an individual’s core group ( Parker et al , 2022 ). To define associate adult females and age mates, we used long-term monitoring data for the 10 years between 2009 and 2019 to calculate association indices between each subject and each member of her extended family.…”

“…We incorporated rainfall in early life and estimated weaning age because available resources and early weaning affect nutrition and growth ( Altmann and Alberts, 2005 ; Dmitriew, 2011 ; Meale et al , 2015 ). We also assessed potential effects of an individual’s social environment, including the number of consistently available adult females and age mates, as these are important to juvenile elephant social interactions and physiology ( Goldenberg and Wittemyer, 2017 , 2018 ; Parker et al , 2022 ) and may influence degree of stunting for orphans. Our findings add to the literature on the effects of orphaning for weaned but immature individuals of social wildlife species.…”