BIOL3045 Lecture Notes - Lecture 5: Bush Rat, Reaction Norm, Genetic Drift

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Animal Ecological Physiology BIOL3045 460381099
Lecture 5: Adaptation.
Heritable changes in phenotype that results from natural selection and increase fitness of an
organism in a particular environment.
It is one response to environmental variation.
Adaptation can be attributed to : fitness of an individual, through reproductive output and
passing on of an allele; natural selection where there is a change in genetic variability. This can
either be stabilizing or directional.
There is no “reaction norm” for a whole species as individuals within them may differ. These
differences are attributed to the following:
Adaptation of reaction norms Selection
Animals distributed across different climate gradients. Different selection pressures in each
different environment.
Creates new reaction norms, with optimum temperatures moving up or down.
Eventually, if one population is separated into a different climate, reproduction isolation with
occur and form two different species (speciation).
Example: Darwin’s Finches were relocated to different environments, with different selection
pressures. This shifts performance curves and leads to speciation.
Adaptation of reaction norms Genetic drift
Decreased gene transfer resulting from increased distances between populations. This forms
greater genetic difference between the populations. Genetically isolated populations may be
different without differences in selection pressures, so can’t always conclude that differences in
populations are due to selection.
Two species comparison
To show adaptation, compare species living I different environments.
Example: Carp and bream live in water with low oxygen and high oxygen concentration,
respectively. Shows that fish adapted to hypoxia can extract oxygen from water at lower oxygen
concentration.
Read: Garland, T. jr. and Adolph, S. C. 1994. Why not to do two-
species comparative studies: limitations on inferring
adaptation. Physiol. Zool. 67, 797-828.
What are the problems with 2 species comparisons? There is a problem with 2 species
comparisons, as these conflate species differences with environmental differences. You should,
rather, consider replicates of the same species (different populations) found in isolated
(different environments).
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Document Summary

Lecture 5: adaptation: heritable changes in phenotype that results from natural selection and increase fitness of an organism in a particular environment. It is one response to environmental variation: adaptation can be attributed to : fitness of an individual, through reproductive output and passing on of an allele; natural selection where there is a change in genetic variability. This can either be stabilizing or directional: there is (cid:374)o (cid:862)reactio(cid:374) (cid:374)or(cid:373)(cid:863) for a (cid:449)hole species as i(cid:374)di(cid:448)iduals (cid:449)ithi(cid:374) the(cid:373) (cid:373)ay differ. Adaptation of reaction norms selection: animals distributed across different climate gradients. This shifts performance curves and leads to speciation. Adaptation of reaction norms genetic drift: decreased gene transfer resulting from increased distances between populations. This forms greater genetic difference between the populations. Genetically isolated populations may be different without differences in selection pressures, so ca(cid:374)"t al(cid:449)ays co(cid:374)clude that differe(cid:374)ces i(cid:374) populations are due to selection.

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