Influence of walking on swimmeret beating in the lobster Homarus gammarus

Influence of walking on swimmeret beating in intact lobsters, Homarus gammarus, has been analyzed using a treadmill experimental device. Belt movement activates both leg stepping and swimmeret beating. The simultaneity of the onset of the two motor systems in this situation is demonstrated to be the result of a startle response initiated when the belt begins to move. This reaction consists of a non-specific motor activity involving several antagonist postural and dynamic muscles. Abdominal extension and vigorous swimmeret beating are the main features of this reaction. The main characteristics of the swimmeret beating as defined by Davis (1969) has been observed here in sequences without walking. However during long walking sequences a very different swimmeret beating pattern occurs. It is suggested that this slow swimmeret beating is completely subordinate to the walking rhythm during sequences of absolute coordination. In more rapid swimmeret beating a relative coordination with leg stepping is very common. The functional meaning of this linkage between legs and swimmerets is discussed.