Compensation of the effects of temperature on a motor system in the crab, Cancer borealis.

Rising ocean temperatures challenge ectothermic animals to maintain essential behaviors such as movement and feeding. We asked how a complete neuromuscular pathway preserves function when every component process responds differently to warming. In the pyloric system of the crab Cancer borealis, we simultaneously recorded motor nerve activity, muscle membrane potential, and contraction. Warming preserved rhythmic nerve activity and excitatory junctional potentials, but contraction declined and failed first. Fixed low-frequency stimulation, mimicking cold-temperature motor output, resulted in reduced contraction at warm temperatures, whereas higher-frequency stimulation, mimicking warm-temperature motor output, partially restored contraction. Warming hyperpolarized muscle fibers, moving them farther from contraction threshold, but also reduced input resistance, which together limited over-excitability. However, high-potassium stimulation revealed that the muscle contractile machinery remained functional. Thus, warming acts differently across levels, and overlapping compensatory mechanisms help preserve neuromuscular function across a wide range of temperatures.