Department Aquatic Ecology

ChlamEE: Chlamydomonas reinhardtii experimental evolution

Darwin was the first to hypothesize that closely related species should be ecologically more similar than distantly related species. As a result, he predicted that closely related species should be more likely to compete strongly for limiting resources, and should be less likely to coexist than distantly related species. In a series of recent papers, my collaborators and I have repeatedly found that phylogenetic relationships among species of freshwater green algae, which represent the extent of their common ancestry on a molecular phylogeny, do not predict their ecology. In the first paper, we showed that neither the niche nor fitness differences among species - aspects of competitive coexistence - are predicted by phylogenetic relatedness. In the second paper, we demonstrated that species interaction strengths are not significantly related to phylogenetic distance. In the third paper, we show that algal species are randomly distributed with respect to their ancestry in 99% of the lakes sampled by the EPA (>1,000 lakes) as part of the 2007 National Lakes assessment survey. In the last paper, we show that 15 out of 17 ecological traits do not display a phylogenetic signal across the phylogeny, and common ancestry does not explain ecological trait variation in green algae. Together, these studies provide robust support for the conclusion that phylogeny does not predict the ecology in freshwater green algae. This leads to the exciting hypothesis that competitive traits in these algae are evolutionarily labile, and adapt rapidly.

We are currently following up on these results, using evolution experiments on the freshwater green alga, Chlamydomoas reinhardtii. Specifically, we are investigating the impact of evolution on the genetics, proteomics and phenotypic traits that control competitive species interactions and community assembly in freshwater algae. After ~300 generations of selection for improved competitive ability, we investigated how metabolic and population-level phenotypes have changed. In the first publication from this project, we characterized the protein expression of descendant lineages and found that numerous major responses to resource limitation are convergent across different types of limitation. These responses tend to be indicative of greater carbon metabolic efficiency (i.e. more carbon is fixed per unit of limiting resource). We found that C:N and C:P ratios also tend to increase. We also found that minimum resource requirements (R*) for some resources could respond to selection, and evolve to become lower over evolutionary time. Lastly, we are testing whether selection for improved competitive ability can alter the outcome of competition between Chlamydomonas and other freshwater algae.



Tamminen, M.; Betz, A.; Pereira, A. L.; Thali, M.; Matthews, B.; Suter, M. J. -F.; Narwani, A. (2018) Proteome evolution under non-substitutable resource limitation, Nature Communications, 9(1), 4650 (10 pp.), doi:10.1038/s41467-018-07106-z, Institutional Repository