Lecture 5: Ecology and Evolution

Reading:  Economy of Nature, pp. 414-416.

Examples of directional selection and directional evolution:

	antibiotic resistance evolution in gonorrhea, TB, Salmonella, Shigella
	pesticide resistance evolution in malaria mosquitos (Anopheles), boll weevils
	herbicide resistance evolution in agricultural weeds

Example of stabilizing selection and stabilizing evolution:

sickle cell hemoglobin and malaria resistance in humans

Example of disruptive selection and disruptive evolution:

Adaptations are products of evolution by natural selection.

	Adaptations are features of an organism that enable it to confront the Hostile Forces of Nature.
	The functions of adaptations are survival and reproduction.

Does Natural Selection have a goal? No, selection does not have a specific goal.

	Selection acts on the phenotypic variation that is present, the best of the alternatives available is the phenotype that is most successful.
	The best alternative phenotype depends entirely on the Hostile Forces of Nature at a given place and time and the other phenotypes that are present.

Example of Evolution and Natural Selection

Industrial Melanism, Cryptic Coloration, and Environmental Change

Organism: Peppered Moth, Biston betularia

Variation in wing and body color and color pattern (see Ricklefs, 1996, p 383).

Light color morph: white or light tan color wings and body with dark markings (spots and irregular lines, somewhat like pepper sprinkled on paper).

Dark color morph: dark brown or black body and wings (melanistic form).

This variation has a genetic component and involves a single gene. Spontaneous mutation in both directions occurs at low frequency, so dark morph parents rarely produce light morph offspring and light morph parents rarely produce dark morph offspring.

In pre-industrial England, the light morph dominates in the collections of natural historians, and tree trunk (natural perches for this moth species) are covered with lichens making the perches light in color.

Based on extensive natural history collections made in Manchester, England:

1848 first dark morph specimens captured in Manchester area.

1895 collections consist of 98% dark morph

During this same time, pollution from coal burning (industrial revolution) was killing lichens on tree and covering tree trunks with soot.

1937 E.B. Ford proposed that differential predation on dimorphic moths depends on the color of the perches.

1950 H.B.D. Kettlewell performed experiments to test the hypothesis that the change in moth color morphs was due to natural selection (differential predation).

 

Hypothesis: Cryptic (camouflaged) moths will be at lower predation risk than non-cryptic moths.

Environment (Perch Color)
	Polluted (Dark Perch)	Non-Polluted (Light Perch)
Dark Morph	More Cryptic Lower Predation Risk	Less Cryptic Higher Predation Risk
Light Morph	Less Cryptic Higher Predation Risk	More Cryptic Lower Predation Risk

 

Prediction: Birds take non-cryptic morphs more frequently than the cryptic morphs.

Predation on Moths by Birds
	Light Morph	Dark Morph
Polluted Forest	43 (74%)	15 (26%)
Non-Polluted Forest	26 (14%)	164 (86%)

Hypothesis: Cryptic (camouflaged) moths will survive longer in nature than non-cryptic moths.

Prediction: When both moth morphs are marked and released in nature, the more cryptic morph will be more readily recaptured than will the less cryptic morph.

A given trait may be an adaptation in one environment and not in another.

Mutation keeps reintroducing the rare color morph in all populations.

Natural Selection does not have a goal.

Differential survival and reproduction simply occurs among the individuals in a given population. The outcome of selection depends on the specific environment at a given place and time, and the phenotypes present in a given population.

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