Effects of early and adult environment conditions on the biology of long-lived species: testing the "predictive adaptive response" hypothesis

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Understanding what makes some individuals more susceptible or more resilient to harsh environmental conditions is of major interest in biology. There is growing appreciation that environmental conditions encountered early in life, including maternal effects, can have long-lasting effects on different traits in adulthood including morphology, reproduction, physiology and metabolism (Bateson et al 2014; Lemaitre et al 2015). However, different theories make contradicting predictions about the long-lasting effects. On one hand, life-history theory predicts a trade-off between early and late life (Lemaitre et al 2015). It thus predicts that, independently of the adult environment, an individual born in harsh environmental conditions will have lower reproduction and senesce faster than an individual born under prime conditions. On the other hand, the metabolic programming hypothesis considers that growing individuals adjust their physiology and metabolism to conditions they may become exposed to during adulthood (Bateson et al 2014). Thus, it predicts that individuals born under harsh conditions should be better adapted at adulthood to resist harsh conditions when compared to individuals born under prime conditions. Although both hypotheses received some support, they have not been addressed at the same time in an integrative framework. This PhD project will exploit a multi-generation dataset from a natural population of yellow-bellied marmots in Colorado, USA, to test how early and adult environmental conditions interact and influence reproduction, survival and physiology. New and archived samples collected on the same individuals during its life course will be used to test the contribution of candidate metabolic processes in shaping adaptation to the environment. Specifically, analyses will test for effects of early and adult conditions on changes in circulating levels of metabolic (leptin, T3, T4, insulin-like hormone) and stress (cortisol) hormones. Due to hibernation, the yellow-bellied marmot active season is reduced to five months in which individuals reproduce and accumulate fat reserves to survive the winter implying that spring and summer weather conditions have strong effect on all life stages including pups and yearling development, adult reproduction and survival (Martin et al 2014). Information on growth, survival and reproduction have been collected since 1965 and biological samples since 2002. The last two decades have been marked by much contrasted environmental conditions, and hence this system offers a unique opportunity to test for effects of early and adult environmental conditions on the biology of a long-lived organism.