AN EXPERIMENTAL EXPLORATION OF WADDINGTON EPIGENETIC LANDSCAPE

Variation in the branching morphologies of clonal plants, fungi, and sessile marine invertebrates is frequently correlated with a suite of life-history traits (e.g. 'phalanx' or 'guerilla'). These correlations have been interpreted to be the causal product of selection. A tacit assumption of selection on a trait is that development is canalized in the manner Waddington originally suggested for aclonal taxa, i.e. small perturbations in development result in a return to an equilibrial morphology. We tested this assumption by manipulating developing colonies of the hydroid Hydractinia echinata. The growth trajectory of these colonies follows a clone-specific schedule of production of three structures: feeding polyps, stolonal mat, and peripheral stolons. Isogeneic manipulations of the relative frequency of these structures show that developing colonies can regulate the rate of production of these three structures, but that regulation does not result in rapid convergence on a common growth trajectory.