SYNERGISM AND ANTAGONISM IN THE INDUCTION OF METAMORPHOSIS OF BUGULA LARVAE BY NEUTRAL RED DYE

¹ St. Ambrose College, Davenport, Iowa, and the Marine Biological Laboratory, Woods Hole, Mass.

1. Both absolute ethyl alcohol and 0.001 M KCN inhibit metamorphosis. A 3.3% solution of the former completely suppresses setting. But sea water containing 0.001 M KCN merely retards the onset of metamorphosis and reduces the number of attached forms in comparison to the controls. Inhibition by KCN persists for at least an hour after removal of the organisms to sea water. The induction of metamorphosis by neutral red is greatly inhibited by a 3% alcohol solution when the concentration of dye is low (1:300,000) but very little when the concentration of dye is high (1:100,000). Lowering the concentration of either factor while the other remains constant reduces the degree of antagonism.

2. Neutral red acts photodynamically in the induction of metamorphosis.

3. Mechanical agitation, for the duration of shaking used in these experiments, does not affect the rate of metamorphosis at the end of one hour or at the end of two hours after agitation ceases. But ten minutes after shaking the number of larvae metamorphosed in the control groups is almost significantly larger (P = .08) than that of the larvae exposed to agitation. This may indicate that shaking merely interferes with the mechanical process of setting, which requires quiescence on the part of the organisms, and does not affect the state of larval protoplasm.

4. When the pH of sea water is dropped to 5.5 the motility of the larvae decreases to nearly zero. Metamorphosis, also, is inhibited by a pH below 5.8 or 6.0. Acid inhibition of metamorphosis persists after the larvae are removed to their normal medium from sea water acidulated to the pH values used in these experiments (5.5 and 4.5). Below a pH of 5.5 the behavior of the larvae depends on the hydronium ion concentration alone, regardless of the agent used to drop the pH of sea water. Within a range of 6.0 to 7.0, however, both sodium and potassium Mcllvaine buffers interfere with setting and cause the larvae to lose adhesive fluid while swimming. At the concentrations employed in the experiments, no significant difference in the behavior of experimental and control larvae could be detected when glycine, borate or acetate buffers were added to sea water. The initiation of metamorphosis by neutral red is inhibited partially within a pH range of 6.5-7.0 and completely at a pH of 5.5.

5. The data support the hypothesis that inhibition of metamorphosis is actually a kind of anaesthesia brought about by a reduction in viscosity of the larvae or of some of their tissues such as muscles or nerves. These experiments and others can be interpreted best by assuming that the initiation of metamorphosis in bryozoans is a response to stimulation involving viscosity changes in the protoplasm opposite to those ensuing when inhibition occurs.