The physiological ecology of haemocyanin in some selected crabs. II. The characteristics of haemocyanin in relation to terrestrialness

Abstract

The haemocyanins of five crabs ranging in habit from aquatic to terrestrial have been investigated. The mean P 50 values of the respiratory pigments were determined at 0 mm Hg CO 2 and 28 °C (the average environmental temperature of all the species). Comparison of these data adjusted to the individual mean physiological pH indicate an increase in P 50 with terrestrialization, perhaps related to the greater abundance of oxygen in the aerial than in some the aquatic habits, and the progressive elaboration of lung breathing with terrestrialization. The Bohr shifts ( Δ log P 50 ΔpH ) were determined (using different P CO 2 values to vary pH) and were found to decrease with terrestrialization, perhaps in adaptation to an associated rise in internal P CO 2 (6–8-fold between the aquatic Callinectes sapidus Rathbun and the terrestrial Cardisoma guanhumi Latreille and probably resulting from progressive gill reduction. The temperature shifts (ΔH cal/mol) of the haemoeyanins were found and it is suggested that they diminish with increasing evironmental temperature and temperature fluctuation accompanying terrestrialization.