Coral polyp budding is probably promoted by a canalized ratio of two morphometric fields

Phenotypic plasticity is the ability of an organism to alter its developmental modes in response to changes in the environment. A major challenge, however, is to explore the existence of a stabilized "morphometric code", a morphological set of buffering rules used repeatedly by members of any species, regardless of environmental factors. Budding of polyps in reef-building corals, an accretive process of the asexual growth form, is thought to be a plastic developmental characteristic. However, we found that intra-tentacular polyp budding in the coral genus Favia from the Red Sea (6 colonies, 37 polyps during a period of 3 years) is not correlated with polyp size. It is initiated after reaching an allometric threshold ratio of two stereotypic, radially symmetrical morphometric landmarks, consisting of the surface area of the polyp and its perimeter.