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Abstract

Ecological factors exert a range of effects on the dynamics of the evolutionary
process. A particularly marked effect comes from population structure,
which can affect the probability that new mutations reach fixation. Our interest
is in population structures, such as those depicted by ‘star graphs’, that amplify
the effects of selection by further increasing the fixation probability of advantageous
mutants and decreasing the fixation probability of disadvantageous
mutants. The fact that star graphs increase the fixation probability of beneficial
mutations has lead to the conclusion that evolution proceeds more rapidly in
star-structured populations, compared with mixed (unstructured) populations.
Here, we show that the effects of population structure on the rate of evolution
are more complex and subtle than previously recognized and drawattention to
the importance of fixation time. By comparing population structures that
amplify selection with other population structures, both analytically and
numerically, we show that evolution can slow down substantially even in
populations where selection is amplified