title: Evolutionary trade-off between defence against grazing and competitive ability in a simple unicellular alga, Chlorella vulgaris.
abstract: Trade-offs between defence and other fitness components are expected in principle, and can have major qualitative impacts on ecological dynamics. Here we show that such a trade-off exists even in the simple unicellular alga Chlorella vulgaris. We grew algal populations for multiple generations in either the presence ('grazed algae') or absence ('non-grazed algae') of the grazing rotifer Brachionus calyciflorus, and then evaluated their defence and competitive abilities. Grazed algae were better defended, yielding rotifer growth rate 32% below that of animals fed non-grazed algae, but they also had diminished competitive ability, with a growth rate under nutrient-limiting conditions 28% below that of non-grazed algae. Grazed algae also had a smaller cell size and were more concentrated in carbon and nitrogen. Thus, C. vulgaris genotypes vary phenotypically in their position along a trade-off curve between defence against grazing and competitive ability. This genetic variation underlies rapid algal evolution that significantly alters the ecological predator-prey cycles between rotifers and algae.
authors.affiliation: Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA. ty59@cornell.edu
authors.forename: Takehito
authors.initials: T
authors.lastname: Yoshida
authors.forename: Nelson G
authors.initials: NG
authors.lastname: Hairston
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Ellner
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002708:Chlorella / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D020387:Food Chain; D014644:Genetic Variation; D005838:Genotype; D008954:Models, Biological; D009566:Nitrates / Q000032:analysis; D011157:Population Dynamics; D012403:Rotifera / Q000502:physiology*; D012641:Selection, Genetic
chemical_list: D009566:Nitrates