Plastic fantastic: phenotypic plasticity, evolution, and adaptation of marine picoplankton in response to elevated pCO2
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Date
27/11/2014Author
Schaum, Charlotte Elisa Luise
Metadata
Abstract
Small but mighty phytoplankton can be used as excellent model organisms to answer
questions that are of importance to marine biologists and researchers in experimental
evolution alike. For example, marine biologists are interested in finding out, how, in
a changing ocean, the phytoplankton foundation of the ocean ecosystem is going to
change - can we use short-term data to extrapolate to longer timescales? What are the
physiological consequences of selection in stable and fluctuating high-pCO2
environments? From a more evolutionary perspective, is elevated pCO2 alone
enough to drive evolution in marine algae? Can we select organisms to maintain
plasticity in fluctuating environments, and how does selection in a fluctuating
environment affect their ability to evolve? Can we detect a cost of plasticity? I have
used theoretical and practical approaches from both disciplines to answer these
questions, as they are ultimately similar questions that are important to address, and
the lack of communication between disciplines has lead to conflicting predictions on
the fate of populations in changing environments. Using evolutionary theory and
applying it to an organism with a known function in the marine environment allows
us to make ecologically relevant predictions while also enabling us to disentangle the
underlying evolutionary mechanisms. While there have been some studies focusing
on evolution of marine algae in climate change scenarios since I started my PhD, my
study is the first to test the link between phenotypic plasticity and adaptation
empirically, and it is also the first to use 16 rather than single or few genotypes of an
algae, thereby creating the statistical power necessary to make any predictions. In a
short-term CO2 enrichment study, and a selection experiment, those 16
physiologically and genetically distinct lineages of Ostreococcus, the smallest free
living eukaryote, were selected for 400 generations in fluctuating and stable high
pCO2 environments. I have shown that short-term plastic responses in phenotype can
predict the magnitude of long-term evolutionary ones. Ostreococcus lineages in
fluctuating environments evolve to be more plastic with no associated costs, and the
adaptive response to selection in a high pCO2 environment is to grow more slowly in
monoculture, but to be more successful competitors in mixed culture. High-pCO2
evolved lineages are genetically and physiologically different from their ancestors.
Importantly, their quality as a food source for zooplankton will change, with possible
repercussions for the ocean ecosystem at a whole. Furthermore, the lineages’ ability
to perceive pCO2 levels in the surrounding medium is altered after evolution in
fluctuating and high pCO2 environment, allowing them to broaden the window in
which they can respond to changes in their environment without suffering metabolic
stress.
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