Abstract
ABSTRACT
Extreme climatic events (ECEs) could potentially induce episodes of rapid adaptive evolution, altering the evolutionary trajectories and viability of wild populations experiencing increasingly stochastic environments. Adaptive potential stems substantially from additive genetic variance (
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) in survival. However, the degree to which ECEs impact this variance, and the resulting evolutionary implications, have not been fully conceptualised or quantified in nature. These aims are highly challenging because underlying genetic and environmental variances have fundamentally non-linear effects on the dichotomous phenotypic outcome of survival versus death, while substantial data are required for estimation. We present a conceptual and analytical framework that formalises biological hypotheses for how
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depends on environmental severity, how such dependences are reshaped by non-linear genotype-environment-phenotype relationships and demographic structure, and the implications for evolutionary responses. We then use 25 years of survival and pedigree data from European shags (
Gulosus aristotelis
) to decompose variance in adult survival across diverse environmental conditions including ECEs. Using a capture-recapture animal model, we demonstrate non-negligible
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underlying adult survival across all years combined, implying notable adaptive potential. Yet, partitioning by environmental severity revealed substantial
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in good years with high survival but negligible
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in bad years with ECE-induced low survival, implying a genotype-by-environment interaction that constrains adaptive potential under severe conditions. However, scale transformations showed how the non-linear genotype-environment-phenotype relationship can distort or even reverse such patterns, by reducing the extent to which
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is phenotypically expressed in good conditions with high mean survival and amplifying it in more severe conditions with lower mean survival. Evolutionary responses to severe conditions could consequently be non-negligible even given small underlying
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. We thereby demonstrate how ECEs can reshape adaptive potential, highlighting the need to integrate impacts of environmental severity on genetic variation in fitness components into predictions of population resilience under climate change.
TEASER TEXT
Extreme climatic events (ECEs) could substantively reshape wild populations’ capacities for adaptive micro-evolution, but such effects have not yet been rigorously conceptualised or quantified in nature. We derive a general quantitative genetic framework that formalises how environmental severity could modulate adaptive potential by altering additive genetic variance in survival. We apply this framework to adult annual survival in a wild population of European shags, considering differing levels of environmental severity reflecting occurrences of ECEs. Notably, underlying additive genetic variance was substantial in good conditions, but clearly smaller in bad conditions. Yet, among-genotype variance manifested on the expressed phenotypic scale of survival versus death can be magnified by low survival in bad conditions, potentially enhancing the scope for evolutionary adaptation. We thereby show how ECEs can simultaneously constrain and restructure adaptive potential, implying that quantitative genetic impacts of environmental severity must be considered when predicting population resilience to climate change.