Department of Evolutionary Genetics, Max-Planck-Institute for Evolutionary Biology, 24306 Plön, Germany, Institue for Neuro- and Bioinformatics, Lübeck University, 23562 Lübeck, Germany and Mathematical Stochastics, Mathematical Institute, Freiburg University, Germany Department of Evolutionary Genetics, Max-Planck-Institute for Evolutionary Biology, 24306 Plön, Germany, Institue for Neuro- and Bioinformatics, Lübeck University, 23562 Lübeck, Germany and Mathematical Stochastics, Mathematical Institute, Freiburg University, Germany.