STUDIES ON THE PHYSIOLOGICAL VARIATION BETWEEN TROPICAL AND TEMPERATE ZONE FIDDLER CRABS OF THE GENUS UCA. III. THE INFLUENCE OF TEMPERATURE ACCLIMATION ON OXYGEN CONSUMPTION OF WHOLE ORGANISMS

¹ Duke University Marine Laboratory, Beaufort, North Carolina, and the Department of Zoology, Duke University, Durham, North Carolina

1. Studies on the metabolic response of tropical and temperate zone fiddler crabs (Genus Uca), after various periods of thermal acclimation, were done to assess the importance of this factor in the evolution and climatic adaptation of these forms.

2. U. pugnax, a temperate zone species, showed a significantly higher metabolic rate after acclimation to 15° than warm-acclimated forms when determined at 27°, 17° and 7°, but not at 33° and 39°. When animals were starved during the period of acclimation, the tendency to acclimate was apparent by days 6-8 and then was lost. Feeding maintained the pattern of acclimation for at least 21 days.

3. U. rapax from Jamaica, The West Indies, did not show any shift in metabolic response during acclimation to 15°, except when determined at 36°, where the rate of cold-acclimated forms was higher than warm-acclimated animals.

4. Population samples of U. rapax from Florida responded metabolically like temperate zone animals at low temperatures and the tropical animals at high temperatures.

5. Results of this study demonstrated that during the evolution and distribution of fiddler crabs different patterns of acclimation have resulted.