The evolution of communication and social behaviour inDictyostelium discoideum
Exceptionally for a developing system, the pathways of intercellular communication are fairly well characterised in the cellular slime molds. This paper attempts to provide adaptive explanations for the origin of the following features and consequences of communication between cellular slime mold cells: the tendency to congregate, chemotaxis to a released signal, signal relay from cell to cell, oscillatory signal release and an invariant ratio of the terminally differentiated cell types. For the sake of specificity attention is directed at the speciesDictyostelium discoideum. Central to the entire analysis is the assumption that contiguous groups of feeding cells are, and in the past were, genetically identical. It is suggested that, in respect of most of the features listed above, the critical event which started things off must have been the acquisition by the cell membrane of permeability for a substance normally produced intracellularly as a response to the stress of starvation. An argument is presented for treating social behaviour in these organisms, and in particular the suicide by cells which differentiate into stalk, as an example of group selection.