If you need an accessible version of this item please contact JSTOR User Support

The Architecture of the Life Cycle in Small Organisms

Graham Bell and Vassiliki Koufopanou
Philosophical Transactions: Biological Sciences
Vol. 332, No. 1262, The Evolution of Reproductive Strategies (Apr. 29, 1991), pp. 81-89
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/55494
Page Count: 9
  • Download PDF
  • Cite this Item

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If you need an accessible version of this item please contact JSTOR User Support
The Architecture of the Life Cycle in Small Organisms
Preview not available

Abstract

The life cycle of eukaryotes has a dual nature, composed of a vegetative cycle of growth and reproduction, and a sexual cycle of fusion and reduction, linked by the spore. Large size is often favoured through interactions with other organisms, or as a means of exploiting locally or temporarily abundant resources, despite the metabolic penalty of size increase. Beyond a certain point, large organisms must be multicellular (or multinucleate) because of the requirement for more deoxyribonucleic acid (DNA) to service larger quantities of cytoplasm. Multicellularity evolves in some lineages but not in others because its evolution is constrained by the pattern of spore development, being favoured, for example, by the occurrence of multiple fission as the consequence of possessing a rigid cell wall. The separation of soma from germ is also the outcome of a developmental constraint, in this case the inability of cells to divide while flagellated, and also the necessity of remaining in motion. Once achieved, a general physiological advantage is realized through the specialization of soma as source and germ as sink. Large, complex multicellular organisms are fragile constructs that can only persist through deploying sophisticated devices for maintenance. Thus two crucial, and related, properties of life cycles are repair and repeatability. The dual life cycle achieves exogenous repair through spore production in the vegetative cycle and through outcrossing and recombination in the sexual cycle. Repeatability is enhanced by developmental mechanisms such as maternal control and germ-line sequestration, which by restricting the occurrence or the heritability of somatic mutations promote their own replication.

Page Thumbnails

  • Thumbnail: Page 
81
    81
  • Thumbnail: Page 
82
    82
  • Thumbnail: Page 
83
    83
  • Thumbnail: Page 
84
    84
  • Thumbnail: Page 
85
    85
  • Thumbnail: Page 
86
    86
  • Thumbnail: Page 
87
    87
  • Thumbnail: Page 
88
    88
  • Thumbnail: Page 
89
    89