Evolutionary stasis and lability in thermal physiology in a group of tropical lizards

TLDR

Understanding how rapidly physiological traits evolve is a key question, especially for how organisms adapt to climate warming, and adjustment to new thermal habitats can occur via behavioural changes, physiological adaptation, or both. The study tests whether evolutionary rates differ among physiological traits in cybotoid Anolis lizards across diverse thermal environments and discusses how selection on physiology shapes divergence and adaptive responses to climate warming. Because lizards behaviourally thermoregulate during the day to similar body temperatures, divergent selection on body temperature and heat tolerance is precluded, whereas night‑time temperatures can only be partially buffered, exposing organisms to selection on cold tolerance. Cold tolerance evolves considerably faster than heat tolerance, because behavioural thermoregulation more effectively shields organisms from selection on upper than lower temperature tolerances.

Abstract

Understanding how quickly physiological traits evolve is a topic of great interest, particularly in the context of how organisms can adapt in response to climate warming. Adjustment to novel thermal habitats may occur either through behavioural adjustments, physiological adaptation or both. Here, we test whether rates of evolution differ among physiological traits in the cybotoids, a clade of tropical Anolis lizards distributed in markedly different thermal environments on the Caribbean island of Hispaniola. We find that cold tolerance evolves considerably faster than heat tolerance, a difference that results because behavioural thermoregulation more effectively shields these organisms from selection on upper than lower temperature tolerances. Specifically, because lizards in very different environments behaviourally thermoregulate during the day to similar body temperatures, divergent selection on body temperature and heat tolerance is precluded, whereas night-time temperatures can only be partially buffered by behaviour, thereby exposing organisms to selection on cold tolerance. We discuss how exposure to selection on physiology influences divergence among tropical organisms and its implications for adaptive evolutionary response to climate warming.