Predicting the impacts of environmental change on marine organisms, food webs and biogeochemical cycles presently relies almost exclusively on short-term physiological studies, while the possibility of adaptive evolution is often ignored. Here we assess adaptive evolution in the coccolithophore Emiliania huxleyi, a well-established model species in biological oceanography, in response to ocean acidification. We previously demonstrated that this globally important marine phytoplankton species adapts within 500 generations to elevated CO2. After 750 and 1000 generations no further fitness increase occurred, and we observed phenotypic convergence between replicate populations. In this study, we exposed adapted populations to two novel environments to investigate whether or not the underlying basis for high CO2-adaptation involves functional genetic divergence, where different novel mutations become apparent via divergent pleiotropic effects. The novel environment “high light” did not reveal such genetic divergence while growth in a low salinity environment revealed strong pleiotropic effects in high CO2 adapted populations, indicating divergent genetic bases for adaptation to high CO2. This suggests that pleiotropy plays an important role in adaptation of natural E. huxleyi populations to ocean acidification. Our study highlights the potential mutual benefits for oceanography and evolutionary biology of using ecologically important marine phytoplankton for microbial evolution experiments.
Lohbeck K. T., Riebesell U., Collins S. & Reusch T. B. H., in press. Functional genetic divergence in high CO2 adapted Emiliania huxleyi populations . Evolution. doi: 10.1111/j.1558-5646.2012.01812.x. Article (subscription required).
