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Seminar: Mon 2014-11-03 15:15
Lunch room Soliden 3
University of Cologne
Clonal interference and recombination on epistatic fitness landscapes
The evolutionary dynamics of large microbial populations is governed by the interference between multiple clones arising from different beneficial mutations, which compete for fixation in the absence of recombination or horizontal gene transfer. The resulting slowdown of adaptation compared to recombining populations is known as the Fisher-Muller effect, and can be precisely quantified at least for simple situations where beneficial mutations combine multiplicatively. In the present talk I will focus on the implications of clonal interference for the adaptation on rugged fitness landscapes characterized by sign epistasis and multiple fitness peaks. A primary consequence of the coexistence of multiple clones is a bias towards mutations of large effect, which makes adaptation greedy and hence more deterministic, as has been observed in microbial evolution experiments. However, with increasing population size this mechanism is superseded by the increased frequency of fitness valley crossings by multiple mutations, leading to a non-monotonic dependence of a posteriori evolutionary predictability on mutation supply. In the presence of genetic exchange between individuals the existence of multiple fitness peaks implies that the advantage of recombination expected from the Fisher-Muller effect becomes strictly transitory, because the long-time dynamics is dominated by trapping at local fitness maxima, which is strongly enhanced by recombination. A permanent advantage of recombination can arise if the fitness landscape changes on a time scale that is shorter than the typical trapping time.