Ectotherms, more sensitive to climate change due to temperature variation

Ectotherms are considered to be particularly vulnerable to climate warming. Ectotherms do not simply experience mean conditions, but are exposed to daily fluctuations in habitat temperatures. Using a mosquito as a model organism, a study published in Global Change Biology and led by Krijn Paaijmans, researcher at CRESIB, the research centre of ISGlobal, has found that temperature fluctuation reduces rate processes such as development under warm conditions, increases processes under cool conditions, and reduces both the optimum and the critical maximum temperature.

The temperature is highly dynamic and numerous studies provide evidence of insects and other ectotherms ‘integrating' the effects of temperature during the daily cycle. Climate change alters mean temperatures and daily temperature ranges. Understanding these effects is necessary to define the ‘realized' thermal reaction norms for different species and to quantify vulnerability to climate warming.

The study used the mosquito Anopheles stephensi as a model organism to ask whether the ‘fundamental' thermal reaction norms established under constant temperature conditions differ from those derived under more natural fluctuating temperatures. The researchers illustrate how daily temperature fluctuations can lower both the optimum and critical maximum temperatures of thermal reaction norms.

Ectotherms and daily temperature dynamics

It is known that smaller terrestrial ectotherms conform to ambient temperature, but certain ectotherms may limit temperature extremes via thermal behavior and hence, modulate the short-term influence of temperature variability. In the longer term, ectotherms can potentially modify responses through genotypic adaptation and/or phenotypic plasticity, further altering thermal reaction norms. "In our experiments, we focused on two immature life-history traits, development time and survival, to demonstrate the effects of fluctuation on thermal reaction norms, yet overall insect fitness is determined by a suite of traits, including adult longevity and life-time reproductive output, each with potentially different reaction norms", explained the study coordinator.

"The general lowering of thermal safety margin and maximum critical temperature, together with the potential for altered ecological interactions under fluctuating temperature conditions, might provide some explanation of the observation that terrestrial ectotherms are shifting much faster in response to climate change than previously predicted", concluded the researcher.

Reference: Paaijmans KP, Heinig RL, Seliga RA, Blanford JI, Blanford S, Murdock CC, Thomas MB. Temperature variation makes ectotherms more sensitive to climate change. Glob Chang Biol. 2013 Apr 30. doi: 10.1111/gcb.12240.