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Journal of Experimental Biology 140,477-491 (1988)
Published by Company of Biologists 1988

Adaptations to a Terrestrial Existence by the Robber Crab Birgus Latro : I. An In Vitro Investigation of Blood Gas Transport

S. MORRIS ¹, P. GREENAWAY ², and B. R. McMAHON ²

¹ Department of Biological Sciences, University of Calgary, 2500 University Drive NW Calgary, Alberta T2N 1N4, Canada
² School of Biological Science, University of New South Wales PO Box 1, Kensington, NSW 2033, Australia

The gas-transporting properties of the haemolymph of Birgus latro L. were investigated in vitro. This terrestrial anomuran is restricted in distribution to the tropics, and on Christmas Island inhabits a highly stenothermal environment.

The effect of temperature on haemocyanin oxygen-affinity was pronounced (TH = -39 kJ mol^-1) and was considered to represent the absence of any specific adaptation to environmental temperature. The Bohr effect was large for a terrestrial decapod ( = -0.60), although reduced at low pH. Changes in [Ca] had a significant effect on oxygen affinity of dialysed haemolymph (TlogP₅₀/Tlog[Ca] = -0.39) whereas [Mg] had no effect. Increasing, [L-lactate] had a small effect on the oxygen affinity of dialysed haemolymph (TlogP₅₀/ Tlog[lactate] = -0.013) but not whole haemolymph. Dialysis increased oxygen affinity, suggesting the presence of a dialysable component that suppresses affinity. The effect of L-lactate was inhibited in whole haemolymph.

The oxygen affinity of Birgus haemolymph was largely insensitive to effector substances, with the possible exception of Ca. In the case of lactate, at least, this was not due to a reduced sensitivity of the haemocyanin, a situation different from that in closely related species.

Carbon dioxide transport was also affected by temperature. Birgus haemolymph showed a high nonbicarbonate buffer capacity (Tco₂/TpH = - 16mmol^-1 pH unit^-1) which could be correlated with a high haemocyanin concentration. It is concluded that terrestrial anomuran decapods depend on mechanical adjustments of ventilation and perfusion, rather than employing direct modulation of haemocyaninfunction, to optimize oxygen delivery.

Key words: Birgus, haemocyanin, landcrabs, oxygen, carbon dioxide

Accepted on June 9, 1988

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