On the Evolutionary Constraint Surface of Hydra

Food consumption, body size, and budding rate were measured simultaneously in isolated individual hydra of six strains. For each individual hydra the three measurements define a point in the three dimensional space with axes: food consumption, budding rate, and body size. These points lie on a single surface, regardless of species. Floating rate and incidence of sexuality map onto this surface. We suggest that this surface is an example of a general class of evolutionary constraint surfaces derived from the conjunction of evolutionary theory and the theory of ecological resource budgets. These constraint surfaces correspond to microevolutionary domains.