Abstract
Species from colder climates tend to be more chill tolerant regardless of the chill tolerance trait measured, but for Drosophila melanogaster, population-level differences in chill tolerance among populations are not always found when a single trait is measured in the laboratory. We measured chill coma onset temperature, chill coma recovery time, and survival after chronic cold exposure in replicate lines derived from multiple paired African and European D. melanogaster populations. The populations in our study were previously found to differ in chronic cold survival ability, which is believed to have evolved independently in each population pair; however, they did not differ in chill coma onset temperature and chill coma recovery time in a manner that reflected their geographic origins, even though these traits are known to vary with origin latitude among Drosophila species and are among the most common metrics of thermal tolerance in insects. While it is common practice to measure only one chill tolerance trait when comparing chill tolerance among insect populations, our results emphasise the importance of measuring more than one thermal tolerance trait to minimize the risk of missing real adaptive variation in insect thermal tolerance.
Highlights
Species from colder climates tend to be more chill tolerant regardless of the chill tolerance trait measured, but for Drosophila melanogaster, population-level differences in chill tolerance among populations are not always found when a single trait is measured in the laboratory
Waves of spreading depolarisation first shut down the central nervous s ystem[7,8] at the critical thermal minimum (CTmin; the temperature at which movement becomes uncoordinated), and this is typically followed by muscle membrane depolarisation, and complete paralysis at the chill coma onset temperature (CCO)[9]
Ion and water homeostasis are typically maintained through active ion pumping in the renal organs—the Malpighian tubules and the rectum—but active transport slows in the c old[11]
Summary
Species from colder climates tend to be more chill tolerant regardless of the chill tolerance trait measured, but for Drosophila melanogaster, population-level differences in chill tolerance among populations are not always found when a single trait is measured in the laboratory. We measured chill coma onset temperature, chill coma recovery time, and survival after chronic cold exposure in replicate lines derived from multiple paired African and European D. melanogaster populations. The populations in our study were previously found to differ in chronic cold survival ability, which is believed to have evolved independently in each population pair; they did not differ in chill coma onset temperature and chill coma recovery time in a manner that reflected their geographic origins, even though these traits are known to vary with origin latitude among Drosophila species and are among the most common metrics of thermal tolerance in insects. High haemolymph [ K+] causes muscle cell depolarisation, so it is thought that ability to recover K+ homeostasis and the degree to which homeostasis is lost in the cold determine an insect’s chill coma recovery time[9,10,13,14]. Correlations among related traits are common in nature, and species and populations from colder regions tend to be Scientific Reports | (2021) 11:10876
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