UCLA

In nature, species are constantly challenged by biotic and abiotic factors. In order to thrive, individuals need mechanisms that regulate their responses according to the experienced conditions. I have studied aspects of regulatory responses to gain insights into how individuals are affected by environmental challenges. All chapters capitalized on long-term data collected at individual level. Chapter 1 introduce and summarize all chapters. Chapter 2 explores how the social environment affects maternal stress levels (glucocorticoid hormones) in a flexibly social mammal. I found that agonistic behavior challenges mothers, while affiliative social bonds can lower stress levels in a context-specific manner. Pups from highly stressed mothers are less likely to survive unless they come from small litters. Chapter 3 uses the estimated biological age (or epigenetic age) to investigate how hibernation, an adaptation to survive highly challenging periods, may affect individual aging patterns. I observed a much slower biological aging during hibernation, which suggests that biological processes involved in hibernation suppress aging. While chapters 2 and 3 evaluate the influence of the surrounding environment on individual fitness, chapter 4 focus on how inbreeding, an intrinsic individual trait, is associated with a higher aging speed. Indeed, inbred individuals appear to exhibit a higher age acceleration, but only at older chronological ages, which may be explained by a higher vulnerability of inbred individuals to the cumulative effects of environmental and physiological stressors. Thus, individual traits influence the chances of successful responses to challenges. And, while it is generally assumed that challenges affect negatively individual fitness, chapter 2 and 3 uncover strategies that maximize individual fitness under duress, which highlights the role of selective pressure on plastic phenotypes. Another contribution from this dissertation is the use of physiological and molecular regulatory responses to estimate potential costs to individual fitness. Both glucocorticoid hormone levels and age acceleration are indirect measures of individual health and wellbeing that can be used to monitor wild populations. In particular, chapters 3 and 4 are among the first studies to use individual aging acceleration as a proxy of individual fitness in wildlife, a method that is becoming more accessible to wildlife managers.