Respiration in the tarantulaEurypelma californicum: evidence for diffusion lungs

Summary

• 1. Oxygen uptake and ventilatory volume changes were measured on individual book lungs of the tarantula,Eurypelma californicum, using micromanometers (Fig. 1). Heart activity was recorded by manometers mounted on the dorsal cuticle of the opisthosoma.

• 2. Three types of tidal volume changes were observed (Fig. 2): Type I, heart-synchronous oscillations with a peak-to-peak amplitude of usually 0.01–0.02 μl; Type II, less frequent changes with an amplitude of ca. 0.04–0.08 μl; and sometimes Type III, pulses with a maximum amplitude of ca. 0.7 μl. Type II and III ventilatory movements occur typically during recovery from activity. These tidal volumes represent only 0.2%, 0.8%, and 9% of the lung volume, respectively. The ventilatory volume changes appear to be caused by movements of the posterior wall of the lung atrium.

• 3. Simultaneous recording of O₂ uptake and tidal volume, appropriately filtered (Fig. 3) shows that oxygen uptake per ‘breath’ exceeds the tidal volume of ventilation Type I (Figs. 3, 4) by a factor of ca. 3.

• 4. After ‘burst activity’,$\dot V_{O_2 }$ may reach 8 times the resting value. This increase of oxygen consumption was seen even if Type II or Type III ventilation were virtually absent (Fig. 5).

• 5. During burst activity, oxygen uptake often decreases, or even ceases (Fig. 5). The spiracles were seen to close during intense activity.

• 6. Using$\dot V_{O_2 }$ values at rest and during recovery, anatomical data of the book lungs (Table 1) and Angersbach's (1978) data of hemolymph$P_{O_2 }$'s, the$P_{O_2 }$ gradients (1) from ambient air through the atrium to the openings of the lamellae (air sacs), (2) from there through the lamellae, and (3) across the lung wall were calculated (Table 2). These estimates indicate that diffusion alone can always account for the measured oxygen uptake. The atrial diffusion resistance, defined by the width of the spiracles and the geometry of the lung atrium, is a limiting factor for oxygen uptake at rest. After locomotory activity, the lung wall becomes the limiting diffusion barrier.

• 7. It is concluded that tarantula lungs are essentially diffusion lungs.