Molecular population genetics
of adaptive color variation
Chaetodipus intermedius
Rock Pocket Mouse
Credit - Sean B. Carroll
Chaetodipus intermedius
Rock Pocket Mouse
“chocolate”
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“sandy”
Native to the southwestern United States
Burrow in soil close to or under rocks
Feed by gathering seeds
Favorite prey item for owls
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!
Predators have been effective.
• 99% of pocket
mice on lava
flows are
“chocolate”
• 99% of pocket
mice in the
non-volcanic
rocky regions
are “sandy”
Filled circles represent lava flows and open
circles are non-volcanic rocky regions.
The MC1R gene
determines color variation.
• “Sandy” mice have two
copies of the ancestral light
allele.
• “Chocolate” mice have
either one or two copies of
the mutant dark allele.
“chocolate”
OR
“sandy”
An advantageous mutation
• The soil in the lava flow areas is
richer in nutrients and supports
more vegetation.
• The “chocolate” mutant allele
is advantageous in these areas.
• The “sandy” allele is
disadvantageous in these areas.
• Natural selection acts to match
the pocket mouse coat color to
its habitat.
• Video