Local adaptation in the presence of gene flow in Patagonian and Antarctic Nacella limpets

• Main Author: Pöhlmann, Kevin
• Format: Thesis
• Language: unknown
• Published: 2011
• Subjects: Antarctic; The Antarctic; Antarctic Peninsula; Drake Passage; Nacella; Antarc*; Antarctica
• Online Access: https://epic.awi.de/id/eprint/26117/; https://epic.awi.de/id/eprint/26117/1/Kevin_P%C3%B6hlmann_Dissertation.pdf; https://hdl.handle.net/10013/epic.39069; https://hdl.handle.net/10013/epic.39069.d001

The classical belief that speciation needs geographical isolation has raised the question how the huge amount of biodiversity can be explained in an open environment like the ocean that is characterized by the absence of strict barriers to gene flow over large geographical scales. Many theoretical approaches have contested that classical belief showing how speciation can take place in the background of gene flow rendering natural selection as a potent evolutionary force. However, most of the empirical population genetic studies aiming at speciation processes apply neutral molecular markers which do not respond to selective forces and therefore do not allow for statements on the actual roles of selection causing ecologically based barriers to gene flow. The present study‘s superordinate aim was to reconstruct the evolutionary history of South American and Antarctic patellogastropods of the genus Nacella. The central aspects of the thesis were the investigation of the actual roles of gene flow barriers and natural selection in processes causing speciation and population divergence. In order to fulfill this task a wide range of markers, both neutrally evolving and under selection, was applied to reveal gene flow patterns and local adaptation. The ACC is one of the most prominent physical barriers in the ocean. Its origin around 35 Ma before present should therefore be reflected in the timing of the divergence of Nacella. Molecular dating approaches carried out in this thesis with three different nuclear and mitochondrial genes (COI, 16S, 18S) revealed the timing of speciation of Nacella to be much younger than the proposed onset of the ACC (~ 10 Ma). Gene flow must, therefore, have been possible after the ACC had already been fully established until the Miocene 10 Ma ago. This time coincides with the second major cooling of Antarctica that led to the glaciation of the Antarctic Peninsula and most likely increased the selection for physiological and genetic adaptation on both sides of the Drake Passage. The present ...