Adaptation to Low Temperature Exposure Increases Metabolic Rates Independently of Growth Rates.
Metabolic cold adaptation is a pattern where ectotherms from cold, high-latitude, or -altitude habitats have higher metabolic rates than ectotherms from warmer habitats. When found, metabolic cold adaptation is often attributed to countergradient selection, wherein short, cool growing seasons select for a compensatory increase in growth rates and development times of ectotherms. Yet, ectotherms in high-latitude and -altitude environments face many challenges in addition to thermal and time constraints on lifecycles. In addition to short, cool growing seasons, high-latitude and - altitude environments are characterized by regular exposure to extreme low temperatures, which cause ectotherms to enter a transient state of immobility termed chill coma. The ability to resume activity quickly after chill coma increases with latitude and altitude in patterns consistent with local adaptation to cold conditions. We show that artificial selection for fast and slow chill coma recovery among lines of the fly Drosophila melanogaster also affects rates of respiratory metabolism. Cold-hardy fly lines, with fast recovery from chill coma, had higher respiratory metabolic rates than control lines, with cold-susceptible slow-recovering lines having the lowest metabolic rates. Fast chill coma recovery was also associated with higher respiratory metabolism in a set of lines derived from a natural population. Although their metabolic rates were higher than control lines, fast-recovering cold-hardy lines did not have faster growth rates or development times than control lines. This suggests that raised metabolic rates in high-latitude and -altitude species may be driven by adaptation to extreme low temperatures, illustrating the importance of moving "Beyond the Mean".
*Department of Integrative Biology, University of California, 3040 Valley Life Sciences Building No. 3140, Berkeley, CA 94720-3140, USA cmw@berkeley.edu.
Caroline M
CM
Williams
Department of Entomology and Nematology, University of Florida, Gainesville, FL 32601, USA.
Andre
A
Szejner-Sigal
Division of Biology, Kansas State University, Manhattan, KS 66506, USA.
Theodore J
TJ
Morgan
Departments of Genetics and Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602, USA.
Arthur S
AS
Edison
School of Public Health, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
David B
DB
Allison
Department of Entomology and Nematology, University of Florida, Gainesville, FL 32601, USA.
Daniel A
DA
Hahn
D000064:Acclimatization; D000818:Animals; D003080:Cold Temperature; D004331:Drosophila melanogaster / Q000502:physiology*; D005260:Female