title: A twelve-step program for evolving multicellularity and a division of labor.
abstract: The volvocine algae provide an unrivalled opportunity to explore details of an evolutionary pathway leading from a unicellular ancestor to multicellular organisms with a division of labor between different cell types. Members of this monophyletic group of green flagellates range in complexity from unicellular Chlamydomonas through a series of extant organisms of intermediate size and complexity to Volvox, a genus of spherical organisms that have thousands of cells and a germ-soma division of labor. It is estimated that these organisms all shared a common ancestor about 50 +/- 20 MYA. Here we outline twelve important ways in which the developmental repertoire of an ancestral unicell similar to modern C. reinhardtii was modified to produce first a small colonial organism like Gonium that was capable of swimming directionally, then a sequence of larger organisms (such as Pandorina, Eudorina and Pleodorina) in which there was an increasing tendency to differentiate two cell types, and eventually Volvox carteri with its complete germ-soma division of labor.
authors.affiliation: Department of Biology, Washington University, Campus box 1229, St. Louis, MO 63130, USA. kirk@biology.wustl.edu
authors.forename: David L
authors.initials: DL
authors.lastname: Kirk
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002455:Cell Division / Q000502:physiology*; D016825:Chlamydomonas reinhardtii / Q000145:classification; D000460:Chlorophyta / Q000145:classification / Q000648:ultrastructure; D056890:Eukaryota / Q000145:classification; D010802:Phylogeny