ENDOGENOUS RHYTHMS OF HEMOLYMPH FLOW AND CARDIAC-PERFORMANCE IN THE CRAB CANCER-MAGISTER

Heart rate and arterial haemolymph flow rates were measured in freshly trapped Dungeness crabs, Cancer magister, using a pulsed-Doppler flow meter. Ln the laboratory, freshly collected subtidal crabs exhibited e ndogenous rhythms in both cardiac function and haemolymph flow through one or more arterial systems, of both tidal and diurnal periodicity. The strongest tidal rhythms were recorded in the sternal and paired an terolateral arteries. These endogenous rhythms of selective tissue per fusion are related to an underlying locomotor activity, but may also b e involved with hormonal transport or feeding. Changes in both heart r ate and stroke volume were responsible for the increases in haemolymph flow rates. These rhythms were not entrained by aerial exposure, sinc e confinement of arhythmic crabs in intertidal cages did not re-entrai n an endogenous tidal rhythm. Endogenous locomotory rhythms are known to be controlled by neurohormones released in cycles from the sinus gl and on the eyestalk. These hormones may also control the endogenous ca rdiovascular rhythms, since these were abolished after eyestalk ablati on in freshly collected Cancer magister. These results suggest that ho rmones synthesized and released by the X-organ/sinus gland complex may , together with pericardial hormones, play a role in modulation of cru stacean cardiovascular function. (C) 1998 Elsevier Science B.V.