Climate change, heat stress, and animal evolution

Climate change has the potential to not only increase average temperatures around the world, but also to increase the likelihood and severity of now-rare temperature events, like heat waves.  The fate of many animal populations, therefore, can hinge on their ability to tolerate (relative) extreme heat.

In the April issue of Functional Ecology, scientists explore the possible responses of animal populations to a changing climate. Mike Angilletta of Indiana State contributes an editorial that poses two very relevant questions: Will physiological and evolutionary responses (i.e. acclimation and adaptation) allow animal populations to persist in the face of thermal stress?  And if so, will their compositions change radically?

The answers – of course – are not yet clear. Simon Bahrndorff of the University of Arhus in Denmark and his colleagues studied heat shock proteins, whose function is to keep other proteins from denaturing or folding improperly when temperatures get too hot or too cold. They found that in the wake of exposure to extreme heat, these proteins conferred greater thermotolerance on springtails, an insect-like arthropod. However, even though heat shock proteins were produced quickly, the springtails didn’t reach peak thermal tolerance for almost a day, suggesting that the response might not be quick enough to save the animals from a more extreme heat event.

Animals that don’t produce enough of these het-shock proteins are likely to be weeded out of populations; another paper by Jesper Sørensen, also of Aarhus, shows that fruit flies that can’t produce heat shock proteins could not find a food station on a hot day, whereas their normal conspecifics could.

What consequences will increased temperatures have for the overall demographics of animal populations? Lloyd Peck of the Natural Environment Research Council in the U.K. and his colleagues found that larger and more sedentary species are more susceptible to the negative consequences if increased temperatures, suggesting that natural selection might favor smaller, more active individuals under climate change scenarios.

A final paper headed by Anthony Dixon of the Institute of Systems Biology & Ecology in the Czech Republic suggests that in developing insects, tolerance to heat usually means lessened tolerance to cold. In these cases, the benefits of being a generalist with a large thermal tolerance must be weighed against the costs of achieving it.

Extreme heat events, the papers conclude, are just one more way that the climate change can shape the evolution of animal populations, and ecologists should keep a watchful eye on its progression.

Angilletta Jr., M. (2009). Looking for answers to questions about heat stress: researchers are getting warmer Functional Ecology, 23 (2), 231-232 DOI: 10.1111/j.1365-2435.2009.01548.x

Bahrndorff, S., Mariën, J., Loeschcke, V., & Ellers, J. (2009). Dynamics of heat-induced thermal stress resistance and hsp70 expression in the springtail, Orchesella cincta. Functional Ecology, 23 (2), 233-239 DOI: 10.1111/j.1365-2435.2009.01541.x

Sørensen, J., Loeschcke, V., & Kristensen, T. (2009). Lessons from the use of genetically modified Drosophila melanogaster in ecological studies: Hsf mutant lines show highly trait-specific performance in field and laboratory thermal assays. Functional Ecology, 23 (2), 240-247 DOI: 10.1111/j.1365-2435.2008.01491.x

Peck, L., Clark, M., Morley, S., Massey, A., & Rossetti, H. (2009). Animal temperature limits and ecological relevance: effects of size, activity and rates of change Functional Ecology, 23 (2), 248-256 DOI: 10.1111/j.1365-2435.2008.01537.x

Dixon, A., Honěk, A., Keil, P., Kotela, M., Šizling, A., & Jarošík, V. (2009). Relationship between the minimum and maximum temperature thresholds for development in insects Functional Ecology, 23 (2), 257-264 DOI: 10.1111/j.1365-2435.2008.01489.x