Squid as Elite Athletes: Locomotory, Respiratory, and Circulatory Integration

The giant axons of squid are among the best characterized animal cells, but we know much more about how they work in isolation than in the intact animal. This is largely because squid are high-strung and easier to work with dead than alive. Recent studies suggest that it is the inherent inefficiency of jet propulsion relative to undulatory propulsion in fish competitors that caused squid to become so evolutionarily strung-out (O’Dor and Webber, 1986). Even jet propelled flight of the large squid, Dosidicus gigas,in the open ocean has been filmed (Cole and Gilbert, 1970). Extrapolations from locomotor studies on smaller squid suggest if these squid would reach the size of the squid, Architeuthis ought to be able to swim around the world in 80 days (O’Dor, 1988c). The power output of a swimming squid approaches that of an air breather at similar size and temperature, and its oxygen consumption is higher than anything else in the sea. Since the jet automatically produces a large flow of water over the gills, squids are not limited by oxygen availability like other aquatic species (O’Dor, 1988a), but their basically molluscan circulatory systems seem to be prone to failure while operating near capacity (Wells, 1983). This chapter will outline what little we know about the integration of nerve, muscle, respiratory and circulatory systems in exercising squid, and will focus on new techniques which now make it possible to learn more.