Phagotrophy by a flagellate selects for colonial prey: A possible origin of multicellularity
Authors: BORAAS M.E.1; SEALE D.B.1; BOXHORN J.E.1
Source: Evolutionary Ecology, Volume 12, Number 2, 1998 , pp. 153-164(12)
Publisher: Springer
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Abstract:
Predation was a powerful selective force promoting increased morphological complexity in a unicellular prey held in constant environmental conditions. The green alga, Chlorella vulgaris, is a well-studied eukaryote, which has retained its normal unicellular form in cultures in our laboratories for thousands of generations. For the experiments reported here, steady-state unicellular C. vulgaris continuous cultures were inoculated with the predator Ochromonas vallescia, a phagotrophic flagellated protist (`flagellate'). Within less than 100 generations of the prey, a multicellular Chlorella growth form became dominant in the culture (subsequently repeated in other cultures). The prey Chlorella first formed globose clusters of tens to hundreds of cells. After about 10–20 generations in the presence of the phagotroph, eight-celled colonies predominated. These colonies retained the eight-celled form indefinitely in continuous culture and when plated onto agar. These self-replicating, stable colonies were virtually immune to predation by the flagellate, but small enough that each Chlorella cell was exposed directly to the nutrient medium.
Keywords: algae; anti-predator adaptations; arms race; Chlorella vulgaris; chrysophytes; continuous culture; evolution; flagellates; multicellularity; Ochromonas vallescia; phagocyte; predator–prey interactions; selective pressure
Language: English
Document Type: Regular paper
Affiliations: 1: Department of Biological Sciences and Center for Great Lakes Studies, University of Wisconsin-Milwaukee, Box 413, Milwaukee, WI 53201, USA
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