Redox control and the evolution of multicellularity

Redox chemistry, involving the transfer of electrons and hydrogen atoms, is central to energy conversion in respiration; in addition, control of gene expression by redox state commonly occurs in bacteria, allowing a rapid res ponse to environmental changes, such as altered food supply. Colonial metaz oans often encrust surfaces over which the food supply varies in time or sp ace; hence, in these organisms redox control of the development of feeding structures and gastrovascular connections could be similarly adaptive, allo wing colonies to adjust the timing of development and spacing of structures in response to a variable food supply and other environmental factors. Exp erimental perturbations of redox state in colonial hydroids support this no tion of adaptive redox control, and redox signaling in metazoans may have e volved in this ecological context. At the same time, redox signaling has im portant consequences for the evolutionary transition from unicellular to mu lticellular organisms. Unlike protein or peptide signaling, redox signaling acting in concert with programmed cell death may automatically inflict a c ost on those cells that "defect," that is, selfishly favor their own replic ation rate over that of the multicellular group. In this way, redox signali ng may have allowed multicellular individuality to evolve and more easily b e maintained. (C) 2000 John Wiley & Sons, Inc.