Invertebrate muscle performance at high latitude: swimming activity in the Antarctic scallop, Adamussium colbecki

The escape swimming performance of the Antarctic scallop, Adamussium colbecki, was measured in animals acclimated for 6 weeks to -1, 0 or 2° C and tested at -1.5 to +1.5° C. Clap duration and swimming velocity were significantly related to temperature, but were not affected by acclimation, demonstrating no phenotypic plasticity. Comparisons of the mean swimming velocity of A. colbecki with the published data for temperate and tropical species showed little evidence for evolutionary compensation for temperature, with all data fitting to a single exponential relationship with a Q(10) of 2.08 (0-20° C). The contraction kinetics of the isolated fast adductor muscle of A. colbecki were determined and the times to 50% peak tension and 50% relaxation had Q(10)s (0-4° C) of 3.6 and 4.7, respectively. The Q(10) of the overall relationship for pooled time to peak twitch data for four scallop species was 2.05 (0-20° C). Field studies revealed low mobility and poor escape performance in wild A. colbecki. A combination of thermodynamic constraints, reduced food supply, and lower selective pressure probably explains the low levels of swimming performance seen in A. colbecki.