Acid‐base balance following temperature acclimation in land crabs

Abstract

AbstractAcid‐base responses to change in body temperature have been described for terrestrial ectothermic vertebrates, but not for terrestrial invertebrates. The present study described changes in pH, carbon dioxide contents (C), and partial pressures (P) in prebranchial hemolymph of three supralittoral crustaceans acclimated 5 days to three temperatures.The anomuran Coenobita brevimanus, a land hermit crab, and the brachyuran Cardiosoma carnifex, were acclimated to 25°, 15°, 25°, 35°, 25° in that order. Exposure to 15° caused extreme torpidy in these species, and thus Birgus latro were exposed to 25–35–25–20° temperature steps.All animals tested showed ΔpH/Δt relationships similar to those of other ectotherms (Birgus 0.023, Coenobita 0.017, Cardisoma 0.017 pH units, °C). The manner of acid‐base status regulation, however, varied between species. Birgus allowed P levels to rise and maintained a constant C level as temperature rose, as do many terrestrial ectothermic vertebrates. Cardisoma showed a rise in P without significant change in C only between 25°C and 35°C. At 15°C no significant fall in P occurred, whereas C increased significantly, a situation similar to that seen in many aquatic ectotherms. Coenobita also showed responses intermediate between those typical of air‐breathing and water‐breathing ectotherms. These data suggest that while Birgus, reputedly the most “terrestrial” of the three species studied, apparently controls acid‐base status in a manner similar to that of most terrestrial ectothermic vertebrates, both Coenobita, which has water available in the shell, and Cardisoma, which has water available in the burrow, can also utilize mechanisms typical of aquatic ectotherms. Possibly these latter animals are bimodal breathers and can switch from one mechanism of acid‐base regulation to the other depending on the availability of water and other physiological needs.