Phenotypic Plasticity Under Climate Extremes

Abstract

Phenotypic plasticity -- the capacity of a single genotype to produce multiple phenotypes in response to environmental variation -- represents a primary mechanism through which animal populations can buffer the immediate fitness consequences of climate extremes without requiring genetic change. As climate change intensifies the frequency, duration, and magnitude of heat waves, drought events, and extreme precipitation episodes, understanding the limits and costs of plastic responses has become a central question in evolutionary ecology and conservation biology. This study conducted a multi-generation experimental analysis of phenotypic plasticity in 24 ectotherm species spanning six orders -- Araneae, Coleoptera, Lepidoptera, Anura, Lacertilia, and Teleostei -- subjected to controlled climate extreme treatments mimicking projected IPCC RCP 8.5 conditions. Reaction norm breadth -- quantifying the range of environmental conditions over which fitness-relevant traits remained within 10% of the optimum -- averaged 8.4 +- 2.1 degrees C for thermal performance curves and 42.8 +- 12.4% for desiccation tolerance across species. Developmental plasticity in response to thermal extremes during embryogenesis produced heritable phenotypic modifications persisting for 2.4 +- 0.8 generations (transgenerational plasticity), significantly extending effective buffering capacity beyond that of within-generation acclimation alone. Plasticity costs -- quantified as fitness reduction under stable benign conditions in plastic relative to canalized genotypes -- averaged 7.4% +- 3.2% reduction in reproductive output, confirming theoretical predictions that plasticity is not cost-free. Species with the broadest reaction norms showed the lowest vulnerability indices under RCP 8.5 projections (r = -0.78, p < 0.001), providing a mechanistic basis for incorporating plasticity capacity into species climate vulnerability assessments.