Abstract
Despite decades of studies on the differential distribution of polyploid
organisms, the causes of this pattern have yet to be elucidated. This
study aimed to explore some of the possible physiological mechanisms
explaining the differential northern distribution of polyploid clones of
Daphnia pulex compared to the one of the diploid parental species. The
critical thermal minimum (CTmin) was measured in 17 D. pulex clones of
contrasted ploidy (diploid and triploid) and geographic origins
(temperate and subarctic climates) reared under low and high
temperatures (16 and 24 °C). Triploid clones had better cold tolerance
(lower CTmin) than both sympatric and temperate diploid clones. No
significant association was found between CTmin and body size nor with
cell size. We suggest that triploids might express a cold shock
resistant phenotype related to higher gene expression and/or fatty acid
profiles. Cold tolerance can be viewed as one of the possible reasons
for polyploid preponderance in subarctic climates.