The development of a hydroid colony

Abstract

The development of pattern has been analyzed in asexual Cordylophora colonies growing under a single set of standard conditions. For the analysis, a colony is considered to be composed of a series of tubes of uniform diameter. On the basis of positional and developmental criteria, these tubes are of three types: stolon tubes, upright tubes, and branch tubes. All types of tubes grow at constant rates once they reach a certain length. However the relative rates for the three types of tubes are different; stolons grow at about twice the rate of uprights, and uprights grow more rapidly than branches. A model was developed integrating the relative growth rates and patterning of the tubes to describe the development of a single stolon (Fig. 10); by following the development of individual young colonies this model was shown to be correct. The linear growth of tubes posed a paradox, since the number of hydranths in an entire colony, as well as the mass and total tube length, had been found to increase exponentially. The model of colony development does not predict exponential growth. Colonies were shown to achieve exponential growth by the addition of secondary stolons at appropriate time intervals. The analysis of colony development poses specific questions for the study of pattern formation.