title: Long-term dynamics of adaptive evolution in a globally important phytoplankton species to ocean acidification.
abstract: Marine phytoplankton may adapt to ocean change, such as acidification or warming, because of their large population sizes and short generation times. Long-term adaptation to novel environments is a dynamic process, and phenotypic change can take place thousands of generations after exposure to novel conditions. We conducted a long-term evolution experiment (4 years = 2100 generations), starting with a single clone of the abundant and widespread coccolithophore Emiliania huxleyi exposed to three different CO2 levels simulating ocean acidification (OA). Growth rates as a proxy for Darwinian fitness increased only moderately under both levels of OA [+3.4% and +4.8%, respectively, at 1100 and 2200 μatm partial pressure of CO2 (Pco2)] relative to control treatments (ambient CO2, 400 μatm). Long-term adaptation to OA was complex, and initial phenotypic responses of ecologically important traits were later reverted. The biogeochemically important trait of calcification, in particular, that had initially been restored within the first year of evolution was later reduced to levels lower than the performance of nonadapted populations under OA. Calcification was not constitutively lost but returned to control treatment levels when high CO2-adapted isolates were transferred back to present-day control CO2 conditions. Selection under elevated CO2 exacerbated a general decrease of cell sizes under long-term laboratory evolution. Our results show that phytoplankton may evolve complex phenotypic plasticity that can affect biogeochemically important traits, such as calcification. Adaptive evolution may play out over longer time scales (>1 year) in an unforeseen way under future ocean conditions that cannot be predicted from initial adaptation responses.
authors.affiliation: Evolutionary Ecology of Marine Fishes, GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany.
authors.forename: Lothar
authors.initials: L
authors.lastname: Schlüter
authors.affiliation: Evolutionary Ecology of Marine Fishes, GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany.
authors.forename: Kai T
authors.identifier: 0000-0003-3421-7112
authors.initials: KT
authors.lastname: Lohbeck
authors.affiliation: Living Marine Resources Research Unit, Thünen-Institute of Sea Fisheries, Palmaille 9, 22767 Hamburg, Germany.
authors.forename: Joachim P
authors.initials: JP
authors.lastname: Gröger
authors.affiliation: Biological Oceanography, GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany.
authors.forename: Ulf
authors.initials: U
authors.lastname: Riebesell
authors.affiliation: Evolutionary Ecology of Marine Fishes, GEOMAR Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany.
authors.forename: Thorsten B H
authors.initials: TB
authors.lastname: Reusch
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry / Q000633:toxicity; D058087:Haptophyta / Q000187:drug effects / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D010641:Phenotype; D012623:Seawater / Q000737:chemistry*
chemical_list: D002245:Carbon Dioxide
keywords: Calcification; ecology; environmental science; experimental evolution; phytoplankton