Date of Award
Doctor of Philosophy (PhD)
Simple invertebrate metazoa offer many potentialities for study of growth and differentiation - potentialities which have not been realized because the organisms usually have been difficult to handle in the laboratory. A simple coelenterate, the brackish-water colonial hydroid Cordylophora lacustris, was selected for the present work, and was domesticated so that ii: it could be grown and manipulated under controlled laboratory conditions. Methods have been developed permitting exponential increase in hydranth number with a doubling time of about three days. Five ions - Na.+, K+, ca++, Mg++, c1- - have been found to be required for growth in the defined aqueous environment, and other variables influencing growth rate have been systematically studied . The colonies are fed daily with living larvae of the brine shrimp, Artemia . The control of the feeding reaction has .been studied. It has been found that, as in Hydra (Loomis, 1955) , a single molecular species released from captured prey induces the feeding reaction. The active compound has been isolated from Artemia extract and identified as the imino acid proline, and reagent proline has been found to induce the feeding reaction at lo-5 molar . Magnesium, and possibly phosphate ions, have be.en shown to influence the response to proline. Perhaps the most interesting aspect of this discover ~ is from the point of view of comparative biochemistry and evolution, for previous workers have found that the feeding reactions of three other Hydrozoa are controlled by reduced glutathione. Time-lapse cinematography of the colonies has revealed proximallyoriented peristaltic waves which apparently act to circulate nutrients through the colonies . These waves are rhythmic, and occur about once every twentyfive minutes in resting colonies. After feeding, the frequency of the waves ;increases to one every eight minutes, and falls back to the resting rate over the course of several hours. The most striking feature of the peristalsis is that it is synchronized throughout a colony, in that the waves begin at the tip of each hydranth simultaneously. The time-lapse movies have also elucidated a series of rhythmic movements which occur during the reconstitution of hydranths from tissue fragments . The major emphasis of the .study has been an attempt to gain an understanding of the asexual development of a Cordylophora colony. While at first glance a colony appears to be a fore.st of little trees, on closer examination one finds that a colony may be considered a series of tubes of uniform diameter. The shape of a colony may be considered to result from the (1) relative rates of growth, (2) spacing, and (3) angles of these tubes . A descriptive study of the development of shape under one set of culture conditions has been made. On the basis of the three parameters, thre~ types of tubes may be distinguished: stolon tubes, upright tubes, and branch tubes. These tubes were all found to grow at constant, but different rates. This linear growth of tubes posed a paradox, since the number of hydranths in a colony had been found to increase exponentially. It was shown that the dry weight of a colony also increases exponentially, and a model was developed permitting the resolution of linear growth of parts iv into exponential growth of the whole. Study of the development of individual colonies using .a marking technique showed that the development of shape in these colonies proceeded essentially as predicted by the model.
Fulton, Chandler Montgomery, "The Biology of a Colonial Hydroid" (1960). Student Theses and Dissertations. 209.