THE RELATION OF SOROCARP SIZE TO PHOTOTAXIS IN THE CELLULAR SLIME MOLD, DICTYOSTELIUM PURPUREUM

Large fruiting bodies of the cellular slime mold, Dictyostelium purpureum, orient more effectively towards a source of light of low intensity than do small ones. The threshold of sensitivity can be changed either by changes in size of the sorocarp or by changes in the light intensity. However, in chemical gradients small cell masses are as sensitive as large ones. Therefore, if orientation to light is of adaptive value, selection pressure for size increase would be expected.