The Evolution of Soma in the Volvocales

Publisher Website
Google Scholar
Abstract
The presence of soma and the manner in which it segregates from the germ line is a fundamental aspect of development. This article examines the origin and evolution of soma in the Volvocales, the flagellated forms of green algae by analyzing data on cell division and development of 370 species. Phylogenetic analysis suggests that the cell wall is a preadaptation for the evolution of large multicellular colonies with deterministic development. The allometry of soma and germ supports the idea that soma functions to provide functional flagella during the embryogenesis of large colonies (Volvocaceae). The need for soma arises from a constraint that prevents simultaneous flagellation and cell division of cells surrounded by rigid walls: basal bodies cannot remain attached to their flagella while migrating to the mitotic poles. The con-straint is different from those that may cause the separation of flagellation and cell division in metazoan cells. Apart from a few developmental variations, which may represent adaptations to larger size, the Volvocaceae can be obtained by heterochronic changes in the timing of cell division. Their small size compared to the size of nonflagellated relatives can be attributed to their locomotion by flagella, which limits the maximum amount of germ that can be carried by the soma. This limitation is manifested in a negative correlation between size and number of germ cells among the largest species of Volvocaceae (Volvox). the opposite of a positive one among the smaller species.

This publication has 0 references indexed in Scilit: