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Mus musculus domesticus; mitochondria; island colonization; inbred lines
Abstract:
Island colonizations are excellent models for studying early processes of
evolution. We found in a previous study on mice that had colonized the
sub-Antarctic Kerguelen Archipelago about 200 years ago that they were
derived from a single founder lineage and that this showed an unexpectedly
large number of new mutations in the mitochondrial D-loop. To assess
whether positive selection has played a role in the emergence of these variants,
we have obtained 16 full mitochondrial genome sequences from
these mice. For comparison, we have compiled 57 mitochondrial genome
sequences from laboratory inbred lines that became established about 100
years ago, also starting from a single founder lineage. We find that the
island mice and the laboratory lines show very similar mutation frequencies
and patterns. None of the patterns in the Kerguelen mice provides evidence
for positive selection. We conclude that nearly neutral evolutionary processes
that assume the presence of slightly deleterious variants can fully
explain the patterns. This supports the notion of time-dependency of molecular
evolution and provides a new calibration point. Based on the
observed mutation frequency, we calculate an average evolutionary rate of
0.23 substitutions per site per Myr for the earliest time frame of divergence,
which is about six times higher than the long-term rate of 0.037 substitutions
per site per Myr.
