Unresponsive to change: Ectotherms fail to adjust physiology to daily temperature variation

Daily temperature fluctuations are a ubiquitous feature of natural environments, yet our understanding of how ectotherms respond to thermal variability remains incomplete. Previous frameworks have predicted that exposure to variable thermal conditions should reduce the temperature sensitivity of physiological rates, thereby enabling ectotherms to maintain stable functions in fluctuating environments. We conducted a comprehensive meta-analysis to test this hypothesis by synthesizing evidence from 26 studies examining the effects of daily temperature variation on ectotherm physiological rates. Our analysis included data on key physiological rates for broad groups of ectotherms. Contrary to expectations, our analysis reveals that daily temperature variability does not systematically reduce the thermal sensitivity of physiological rates in ectotherms. We found some taxonomic differences in thermal sensitivity, with reptiles and fish showing greater sensitivity to temperature variation, potentially exposing these groups to higher vulnerability under fluctuating temperatures. A lack of plasticity in thermal sensitivity suggests either limited capacity or limited need for plastic responses to predictable daily temperature variations. Ectotherms may rely on alternative mechanisms to cope with variable temperatures, including behavioural thermoregulation and acute physiological responses. Our findings challenge current paradigms in thermal biology and highlight potential vulnerabilities of ectotherms to increasing temperature fluctuations under climate change. This article is part of the theme issue 'Embracing variability in comparative physiology: why it matters and what to do with it'.