Marine Ökologie

Ocean acidification

 

Rapid evolution of a key phytoplankton species to ocean acidification

BMBF project BIOACID

Kai T. Lohbeck, Ulf Riebesell and Thorsten B. H. Reusch

  

  • E.Hux
  • Labor
  • Proben

The uptake of anthropogenic derived CO2 by the surface ocean changes seawater carbonate chemistry leading to increased carbon availability and a lowered pH. This pro­cess, called ocean acidification, has become a well studied threat to many marine organisms. While numerous studies have shown physiological effects of ocean acidification, the potential for rapid evolutionary changes has been widely neglected. Considering the short generation time of unicel­lular algae, this group lends itself for testing the evolutionary potential to respond to projected future ocean changes. Starting from freshly isolated strains of the calcifying microal­gae Emiliania huxleyi we designed replicated laboratory selection experiments with several hundred generations under ambient and predicted future COlevels. We test for adaptation by measuring growth rate as Darwinian fitness proxy and calcification and organic carbon production rates as biogeochemically relevant phenotypic traits. This approach provides first insights into the role of rapid evolution for modu­lating the physiological response of key phytoplankton species in a high CO2 ocean.

 

 

Is the adaptive potential of Emiliania huxleyi constrained by previous adaptation to ocean acidification?

Lothar Miersch

The coccolithophore Emiliania huxleyi is a globally distributed phytoplankton species with a key role in marine primary production and biogeochemical cycles. Predicted future responses to a rapidly changing ocean have long been exclusively based on short-term studies. Only recently evolutionary adaptation to a single selection pressure (ocean acidification) has been demonstrated by Lohbeck et al. (2012). We now aim to investigate adaptation to multiple selection pressures, e.g. ocean acidification and rising temperature.

Populations adapted for 1500 generations to high CO2 will be exposed to increased temperature as additional selection pressure. Temperature will be increased until the algae show responses of temperature stress.

Further, a new selection line with both selection pressures starting at the same time (co-occurring vs. time-shifted) will be established. After approximately 500 additional generations under the double-selection regime a reciprocal assay experiment will be performed to test for adaptation. Growth rate will serve as a fitness proxy, while the production of particulate inorganic and organic carbon will be used to determine phenotypes.. Additionally, RNA and DNA samples will be taken to evaluate the genetic background.

The outcome may be influenced by two major factors: sign epistasis and standing genetic variation. We plan to develop different assay scenarios to disentangle these factors.

The work is supervised by Thorsten Reusch & Ulf Riebesell.

 

 

 

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