Neuroethology of Zooplankton

Abstract

Whereas the neural analysis of behavior of planktonic species and stages has been relatively neglected, we have many clues that it is going to be rich, diverse and interesting. The aims of this contribution are to defend that statement, with selected examples, and to suggest that neural analysis, particularly sensory physiology, has great explanatory power of ecologically significant behavior. I have to begin with a personal note about plankton, recalling the lasting impression made long ago by a film on invertebrates in the Arctic where scyphomedusan jellyfish were pulsing at a rate well within the range familiar in summer temperate waters, warmer by 20o C. I must have been influenced by this observation and my own experiences in a study of the neural basis of fluctuations in the rate of pulsation of medusae (Bullock 1943), some of which was made in December 1941 in Pensacola, where my wife and I collected Rhopilema cruising at random in the Sound, stopped now and then by Army bridge guards concerned about saboteurs in that first fortnight after Pearl Harbor. At any rate, by the early fifties about half of my laboratory group was devoted to the physiological ecology of temperature acclimation in marine invertebrates. That field, which I left in the early sixties, still offers a challenge in the ecologically fundamental question of why some species are able to acclimate much more than others. The proposal I made in 1955, that different rates in the same organism acclimate to different degrees, resulting in greater disharmony in some species than others, may still be viable and most likely applies to rate processes in sensory and central nervous functions, among others. Medusae are large animals, relatively, although generally treated as planktonic. The first reaction from most workers when neurophysiology of plankton is mentioned concerns their small size or gelatinous nature. The first message I bring is not new but also not widely appreciated.