Postural Reflexes Coordinating Walking Legs in a Rock Lobster

It is well established that a proprioceptive organ in the walking legs of decapod Crustacea is able to influence not only the muscle of the joint where it is situated but also most of the other muscles of the same leg. Resistance reflexes elicited by several chordotonal organs have been described (Bush, 1962, 1965), and it has been demonstrated that one of them (the CB chordotonal organ) evokes a response in the main muscles of the same leg when it is passively stretched (or relaxed) (Clarac, Vedel & Bush, 1978). In addition to proximo-distal reflexes, such as CB proprioceptive action, disto-proximal controls also have been described. For example, an imposed merocarpus (M-C) movement influences the discharge of the motoneurones which command the muscles of the thoracico-coxal (T-C) or of the coxo-basal (C-B) joint (Ayers & Davis, 1977; Vedel & Clarac, 1979). When the reflexes are initiated by imposed joint movements, not only the chordotonal organs but also other kinds of receptors are stimulated. These include cuticular receptors such as the stress detector (c.s.D.), muscle receptor such as the thoracico-coxal muscle receptor (TCMRO), the myochordotonal organ (MCO) or the apodeme tension receptors (see Clarac, 1977). A very complex picture emerges from these proprioceptive interactions. Nevertheless most of the previous coupling described concern reflexes within a leg; very little information has been published on the coordination between legs. Only two short results have been presented; Evoy & Cohen (1969) demonstrated that a passive movement of the mero-carpus joint of leg 2 evokes a slight response in the leg 1 flexor muscle of the crab and Ayers & Davis (1977) found that in Homarus a passive movement of both T-C and C-B joints of leg 3 evokes a reflex response in the posterior levator of the homolateral leg 2. The present paper reports an experimental study of inter-leg reflexes in the walking legs of the rock lobster.