Constraints on Modular Organisms: colony integration and the definition of modules.

Howard R. Lasker
Department of Biological Sciences
University at Buffalo
Buffalo, NY 14260

Zoologists interested in the growth and development of colonial forms generally characterize colony growth as the iterative replication of polyps and zooids. Although the growth trajectories of colonies can always be described interms of the numbers of "individuals," the processes that regulate growth may be based on properties of units that are larger than individual polyps and zooids.Thus models developed to describe the growth of sessile organisms often use as their basal unit modules that are much larger than single individuals. Thesemodules can range in size from a single polyp and attached stolon through to large branches each containing thousands of polyps.

The size and nature of interaction among modules will depend to a large extent on the integration within the colony. Many colonies may be composed i of modules that are functionally independent or only weakly interacting. Among colonies in which growth is controlled by source-sink resource gradients, the nature of those gradients will define the module, and the pattern of replication ofmodules. Those dynamics lead to a pattern of growth that is best modeled using modules such as branches, as illustrated by a stage-based model of colony growth of the gorgonian Pseudopterogorgia elisabethae.