Low heritability and high phenotypic plasticity of salivary cortisol in response to environmental heterogeneity in a wild pinniped

Abstract

Individuals are unique in how they interact with and respond to their environment. Correspondingly, unpredictable challenges or environmental stressors often produce an individualized response of the hypothalamic‐pituitary‐adrenal (HPA) axis and its downstream effector cortisol. We used a fully crossed, repeated measures design to investigate the factors shaping individual variation in baseline cortisol in Antarctic fur seal pups and their mothers. Saliva samples were collected from focal individuals at two breeding colonies, one with low and the other with high density, during two consecutive years of contrasting food availability. Mothers and pups were sampled concurrently at birth and shortly before weaning, while pups were additionally sampled every 20 days. We found that heritability was low for baseline cortisol, while within‐individual repeatability and among‐individual variability were high. A substantial proportion of the variation in baseline cortisol could be explained in pups and mothers by a combination of intrinsic and extrinsic factors including sex, weight, day, season, and colony of birth. Our findings provide detailed insights into the individualization of endocrine phenotypes and their genetic and environmental drivers in a wild pinniped. Furthermore, the strong associations between cortisol and life history traits that we report in fur seals could have important implications for understanding the population dynamics of species impacted by environmental change.

Little evidence for inbreeding depression for birth mass, survival and growth in Antarctic fur seal pups

“…To provide more detailed insights into pup growth, we also collected serial weight measurements from a subset of pups as described by Nagel et al 75 . Briefly, during the breeding seasons of 2019 and 2020, a total of 100 unique mother–pup pairs ( n = 200 individuals) were captured, 50 from SSB and 50 from FWB.…”

“…Total genomic DNA was extracted using an adapted chloroform-isoamylalcohol protocol 75 and genotyped for 39 microsatellite loci as described by Paijmans et al 54 . Briefly, the microsatellite loci were PCR[amplified in five separate multiplexed reactions using a Type It Kit (Qiagen).…”

Little evidence of inbreeding depression for birth mass, survival and growth in Antarctic fur seal pups

“…To provide more detailed insights into pup growth, we also collected serial weight measurements from a subset of pups as described by Nagel et al 82 . Briefly, during the breeding seasons of 2019 and 2020, a total of 100 unique mother–pup pairs ( n = 200 individuals) were captured, 50 pairs from SSB and 50 pairs from FWB.…”

“…Total genomic DNA was extracted using an adapted chloroform-isoamylalcohol protocol 82 and genotyped for 39 microsatellite loci as described by Paijmans et al 42 . Briefly, the microsatellite loci were PCR‐amplified in five separate multiplexed reactions using a Type It Kit (Qiagen).…”

Life-history stage influences immune investment and oxidative stress in response to environmental heterogeneity in Antarctic fur seals

“…Saliva was also collected to assess baseline cortisol concentrations; for a more detailed description of our saliva sampling methods, cortisol concentration assessment, and analysis protocols, see ref. 49 .…”