Translator Disclaimer
1 February 2008 Evolution of Complexity in the Volvocine Algae: Transitions in Individuality Through Darwin's Eye
Author Affiliations +

The transition from unicellular to differentiated multicellular organisms constitutes an increase in the level complexity, because previously existing individuals are combined to form a new, higher-level individual. The volvocine algae represent a unique opportunity to study this transition because they diverged relatively recently from unicellular relatives and because extant species display a range of intermediate grades between unicellular and multicellular, with functional specialization of cells. Following the approach Darwin used to understand “organs of extreme perfection” such as the vertebrate eye, this jump in complexity can be reduced to a series of small steps that cumulatively describe a gradual transition between the two levels. We use phylogenetic reconstructions of ancestral character states to trace the evolution of steps involved in this transition in volvocine algae. The history of these characters includes several well-supported instances of multiple origins and reversals. The inferred changes can be understood as components of cooperation–conflict–conflict mediation cycles as predicted by multilevel selection theory. One such cycle may have taken place early in volvocine evolution, leading to the highly integrated colonies seen in extant volvocine algae. A second cycle, in which the defection of somatic cells must be prevented, may still be in progress.

Matthew D. Herron and Richard E. Michod "Evolution of Complexity in the Volvocine Algae: Transitions in Individuality Through Darwin's Eye," Evolution 62(2), 436-451, (1 February 2008).
Received: 14 September 2007; Accepted: 5 November 2007; Published: 1 February 2008

This article is only available to subscribers.
It is not available for individual sale.

Get copyright permission
Back to Top