Prey Evolution on the Time Scale of Predator-Prey Dynamics Revealed by Allele-Specific Quantitative PCR

• Published in: Proceedings of the National Academy of Sciences - PNAS 2006-07, Vol.103 (28), p.10690-10695
• Main Authors: Meyer, Justin R., Ellner, Stephen P., Hairston, Nelson G., Jones, Laura E., Yoshida, Takehito
• Format: Article
• Language: English
• Subjects: Alleles; Animals; Biological Evolution; Biological Sciences; Brachionus calyciflorus; Chlorella vulgaris; Chlorella vulgaris - genetics; Chlorella vulgaris - growth & development; Clone Cells; Ecological genetics; Ecology; Evolution; Evolutionary biology; Freshwater; Genetics, Population; Genotype & phenotype; Genotypes; Group dynamics; Nitrogen; Polymerase chain reaction; Polymerase Chain Reaction - methods; Population dynamics; Predation; Predatory Behavior; Rotifera; Species; Studies; Tradeoffs
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0600434103

Using rotifer-algal microcosms, we tracked rapid evolution resulting from temporally changing natural selection in ecological predator-prey dynamics. We previously demonstrated that predator-prey oscillations in rotifer-algal laboratory microcosms are qualitatively altered by the presence of genetic variation within the prey. In that study, changes in algal gene frequencies were inferred from their effects on population dynamics but not observed directly. Here, we document rapid prey evolution in this system by directly observing changes in Chlorella vulgaris genotype frequencies as the abundances of these algae and their consumer, Brachionus calyciflorus, change through time. We isolated a group of algal clones that we could distinguish by using microsatellite-DNA markers, and developed an allele-specific quantitative PCR technique (AsQ-PCR) to quantify the frequencies of pairs of clones in mixed culture. We showed that two of these genotypes exhibited a fitness tradeoff in which one was more resistant to predation (more digestion-resistant), and the other had faster population growth under limiting nitrogen concentrations. A fully specified mathematical model for the rotifer-algal population and evolutionary dynamics predicted that these two clones would undergo a single oscillation in clonal frequencies followed by asymptotic fixation of the more resistant clone, rather than the recurrent oscillations previously observed with other algal clones. We used AsQ-PCR to confirm this prediction: the superior competitor dominated initially, but as rotifer densities increased, the more predator-resistant clone predominated.