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The temperature-size rule in ectotherms: may a general explanation exist after all?
Richard John Walters1, Mark Hassall
1Center for Ecology, Evolution, and Conservation, School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom. richard.walters@zoologi.su.se
The American Naturalist
|May 4, 2006
Summary
Temperate grasshoppers are an exception to the temperature-size rule, maturing larger at higher temperatures. This occurs because their development rate has a lower temperature threshold than their growth rate.
Area of Science:
- Ecology
- Evolutionary Biology
- Physiology
Background:
- The temperature-size rule (TSR) states ectotherms mature at larger sizes when reared at lower temperatures.
- Explanations for the TSR remain elusive, with few species identified as exceptions.
Purpose of the Study:
- Investigate why the temperate grasshopper Chorthippus brunneus is an exception to the TSR.
- Explore proximate and ultimate causes for this deviation from the established rule.
Main Methods:
- Utilized complete life-history data to parameterize an established life-history model.
- Applied biophysical modeling principles, specifically the van der Have and de Jong model.
Main Results:
- C. brunneus optimally matures at a larger size at higher temperatures, contrary to the TSR.
- Adult size plasticity is dictated by the difference in temperature thresholds for growth and development.
- Exceptions to the TSR possess a lower temperature threshold for development rate than for growth rate.
Conclusions:
- The thermal biology of C. brunneus explains its exception to the TSR.
- The findings offer insights into the broader thermal biology of temperate grasshoppers and ectotherms.
- The relative temperature thresholds for growth and development are key to understanding TSR variations.
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