Differential cold-shock resistance among acclimated European mussel populations

To study differential cold-shock resistance of marine mussel populations (Mytilus spp.) from different climatic regions in Europe, we sampled 12 populations, ranging from 43 to 58°N. Minimum critical temperatures for aerobic metabolism (CTmin) were determined before and after 3 months of common acclimatization in an outdoor mesocosm. Additionally, chill coma in response to cold shock was used to test for differences in physiological plasticity between the translocated populations. The CTmin followed a steep cline, being positively related to the ambient temperatures before translocation (p <0.0001), and became similar between populations after 3 months in the outdoor mesocosms (p > 0.05). Differential chill coma responses separated the populations into two groups that were also geographically separated by the English Channel. The southern populations showed a much stronger and faster sensitivity to chill than the northern populations, indicating differential physiological adaptation between the two groups. The results are discussed in relation to the genetic background and climatic isolation of the populations.