Heart and circulatory functions in a spider (Eurypelma californicum): the effects of hydraulic force generation

Summary

In the tarantulaEurypelma californicum, the relationships between heart activity, circulation and the generation of hydraulic pressure for locomotion were studied. Several new techniques were employed.

Mean resting heart rate was 21 beats min⁻¹ rising to 90 beats min⁻¹ after burst activity. Decay time to resting rates was related to the increase of heart rate. Post-recovery resting rates were usually elevated in comparison with rates after very long resting periods.

A relative measure of heart amplitude was obtained. Four distinct patterns could be distinguished: (i) regular beats; (ii) short-term fluctuations of amplitude within a few heart beats; (iii) a slow rhythmic change of heart/pericardium filling, and (iv) non-periodic, stronger amplitude changes during periods of activity.

During locomotion, heart rate rises with maximum rates often reached only minutes after the onset of activity. The rising phase is often characterized by irregularities and a reduction of heart amplitude.

Prosomal hemolymph pressure in resting, restrained animals was 41±19 Torr, rising to ca. 90, and 217±48 Torr during walking and fast sprints, respectively. Values in unrestrained spiders were similar. Opisthosomal hemolymph pressures were ca. 20 Torr in resting animals, rising to 40–60 Torr during locomotion.

Opisthosomal volume changes were measured. A small volume of hemolymph moved from the prosoma to the opisthosoma at the onset of locomotion, but following activity this volume quickly returned to the prosoma.

The simultaneous measurement of carapace depression, opisthosomal volume changes and hemolymph pressures, and heart activity revealed the relationship between circulation and hydraulic force generation. The direction of hemolymph flow was also studied. In non-active animals, the heart occasionally changes its main pumping direction. During locomotion, hemolymph flow from the heart to the prosoma is often reduced or stopped. With a slight delay, hemolymph flow to the opisthosoma is increased. The critical pressure at which prosomal perfusion from the heart is halted is 50–70 Torr.

It is concluded that anterior and posterior circulations are separate: hemolymph returning from the prosoma passes only through the anterior lungs, while hemolymph returning from the opisthosoma passes through the posterior lungs.