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Climatic variability and the evolution of insect freeze tolerance
Brent J Sinclair1, A Addo-Bediako, Steven L Chown
1Spatial, Physiological and Conservation Ecology Research Group, Department of Zoology, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa. bjs@sun.ac.za
Summary
Insects survive cold using freeze tolerance or avoidance. Southern Hemisphere insects predominantly use freeze tolerance due to climate variability, unlike the Northern Hemisphere’s seasonal adaptation.
Area of Science:
- Insect physiology
- Evolutionary biology
- Ecology
Background:
- Insects employ freeze tolerance or avoidance to survive subzero temperatures.
- Freeze tolerance has evolved convergently multiple times in insects.
- The evolutionary drivers for adopting either strategy remain unclear.
Purpose of the Study:
- To investigate the reasons behind the differing prevalence of freeze tolerance in insects between the Northern and Southern Hemispheres.
- To explore the ecological and climatic factors influencing the evolution of insect cold-tolerance strategies.
Main Methods:
- Comparative analysis of insect cold-tolerance strategies reported in the literature.
- Statistical analysis (randomization test) to assess the significance of hemispheric differences.
- Review of climatic and habitat characteristics of the Northern and Southern Hemispheres.
Main Results:
- A significantly higher proportion of insect species exhibit freeze tolerance in the Southern Hemisphere (85%) compared to the Northern Hemisphere (29%).
- This hemispheric difference is statistically significant and not attributable to publication bias.
- Northern Hemisphere freeze tolerance is linked to surviving extreme cold seasonally, while Southern Hemisphere tolerance aids survival in unpredictable, milder climates.
Conclusions:
- Hemispheric climate differences, specifically oceanic influence and variability in the South, strongly select for freeze tolerance.
- Freeze tolerance has evolved convergently in insects for distinct adaptive reasons in different hemispheres.
- This highlights broad ecological disparities between Northern and Southern Hemisphere processes.