Thermal specialization limits evolutionary responses to climate warming in lizards

Understanding how ectothermic animals perform under climate warming is key to predicting biodiversity responses to global change. We compiled empirical sprint speed data for 85 lizard species and fitted thermal performance curves (TPCs) using a mechanistic model capturing enzymatic and protein stability constraints. From the fitted TPC, we derived physiological traits related to the shape of the TPCs and tested whether body size, thermal environment and phylogeny predict performance. Species adapted to warmer habitats exhibited higher optimum temperatures and maximal performance values, supporting the hotter-is-better hypothesis. But warm-adapted specialists had a narrower thermal breadth and a steeper performance decrease under the highest thermal challenges than cold-adapted species. These results suggest an evolutionary trade-off between specialists and generalists, shaped by the evolutionary history. Our findings exhibit how evolutionary processes can tune performance to present climates but may limit adaptive potential to future warming.