BIOL 329 Lecture Notes - Lecture 31: Heterozygote Advantage, Warble Fly, Omnivore
6 May 2018
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Lect 31
Lighter color reindeer calves have higher intensity of warble fly larvae. This is associated with a decrease
in body mass and may hence influence subsequent fitness of the animals – light deer is
disadvantageous.
Unexpected advantages of whiteness in horses: tabanid (horse) flies are less attracted to white horses
because the flies use polarizing light to detect their prey. White horses are less detected by flies.
In the Rockies – where there are black bears and grizzlies, there are several incidences of cinnamon
bears – a black bear coat mutation.
Ursus americanus kermodei: young bear held captive in Beacon Hill from 1920s-50s.
Bears become stained from tannin colored creeks. Black mother is heterozygous and produces white
cub (mated with black or white bear). Genetic: black is fully dominant to white coat color. Mutation at
the melanocortin 1 receptor gene. Mother-cub combination suggests random mating.
Potential explanations:
A) Glacial relict? Camouflage to sneak up on prey. Possible but low probability.
B) Neutral mutation that increased due to geographical isolation. Evidence for neutrality? Color trends
do not confer survival advantage because black bear has few natural enemies. Not advantageous for an
omnivore. Unlogged sanctuaries are not needed for preservation of the Kermode bear.
Neutral mutation in a large population – unlikely to persist over time if neutral. BUT these are small
populations. The common allele goes to fixation (monomorphism).
As populations get smaller, they are much more likely to be monomorphic. If there is heterozygosity
when the population is small the trait must not be neutral. Gribbell Island – total 50 bears. 30% of
these are white.
B) Neutral mutation and isolation... possible but unlikely.
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Document Summary
Lighter color reindeer calves have higher intensity of warble fly larvae. This is associated with a decrease in body mass and may hence influence subsequent fitness of the animals light deer is disadvantageous. Unexpected advantages of whiteness in horses: tabanid (horse) flies are less attracted to white horses because the flies use polarizing light to detect their prey. In the rockies where there are black bears and grizzlies, there are several incidences of cinnamon bears a black bear coat mutation. Ursus americanus kermodei: young bear held captive in beacon hill from 1920s-50s. Black mother is heterozygous and produces white cub (mated with black or white bear). Genetic: black is fully dominant to white coat color. Possible but low probability: neutral mutation that increased due to geographical isolation. Color trends do not confer survival advantage because black bear has few natural enemies. Unlogged sanctuaries are not needed for preservation of the kermode bear.
