Calcification by marine organisms can be drastically affected by ocean acidification (OA) due to a reduced availability of calcium carbonate in seawater. Planktonic gastropods (pteropods and heteropods) are believed to be among the most vulnerable organisms to OA as they live at the ocean surface and build thin shells of aragonite. Shelled pteropods have received considerable attention and are reported to decrease calcification rates and experience shell dissolution under high CO2 conditions. Shelled heteropods have received much less attention, but are expected to be equally vulnerable. However, the vulnerability of planktonic gastropods is based on short-term exposures to extreme OA conditions. The aim of the proposed project is to study the evolution of calcification in planktonic gastropods and assess its evolutionary potential under OA. Planktonic gastropods build shells through a biomineralization process, controlled at the molecular level, but the genes underlying this process are unknown. Using shell proteomics will enable to identify for the first time the biomineralization genes in pteropod and heteropod species. Next, these genes will be used to understand how biomineralization evolved in the two independent plankton groups over long and short timescales. Over long timescales will include building solid macro-evolutionary frameworks using fossil-calibrated phylogenomic trees and analysis of the evolution of biomineralization genes. Over short timescales will involve studies at the population-level by measuring gene expression under past, present and future concentrations of CO2. The proposed action will allow the discovery of new molecular markers to investigate the impacts of OA. Combining macro- with micro-evolutionary approaches will shed light on the processes that drive diversity and evolution of calcification in planktonic gastropods and will allow more realistic predictions of the consequences of global change on marine calcifiers.
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