MORPHOLOGICAL COLOR CHANGE IN THE FIDDLER CRAB, UCA PUGNAX (S. I. SMITH)

¹ Marine Biological Laboratory, Woods Hole, Massachusetts 02543, and the Department of Zoology, University of Minnesota, Minneapolis, Minnesota 55455

1. The Uca black chromatophore pigment has been identified as a melanin on the basis of: (1) solubility and bleaching reactions; (2) incorporation of tyrosine and dihydroxyphenylalanine into the pigment; and (3) inhibition of tyrosine incorporation by phenylthiourea, a known inhibitor of melanin synthesis.

2. The incorporation of tyrosine-C¹⁴ into Uca melanin is linearly related to micrograms tyrosine injected in the range 0.88-208.00 µg. tyrosine per gram wet weight.

3. Melanin synthesis occurs rapidly under normal conditions and may be related to the influx of free tyrosine.

4. The incorporation of tyrosine-C¹⁴ into Uca melanin is temperature-dependent; the energy of activation, as calculated from the Arrhenius plot of the data, is 5757 calories.

5. Melanin, once labeled, retains the label for considerable periods of time, thereby indicating the stability of the pigment under these conditions.

6. Destalked crabs under similar conditions have a level of tyrosine incorporation approximately 70% higher than do normal animals. This may reflect the increased activity of the epidermis following eye-stalk ablation.

7. Melanin synthesis occurs independently of the state of pigment dispersion, whether naturally-occurring or artificially-induced.

8. Normal animals maintained on a white background under constant illumination show exponential destruction of melanin with a half-time of 48 hours.

9. The available evidence does not support a detailed correspondence between physiological and morphological color changes which would justify invoking the same control systems for both phenomena.