lecture17F06 - Examples of natural and sexual selection:...

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Examples of natural and sexual selection: Guppies ( Poecillia reticulata ) are small tropical American fish that have become good examples of microevolution because 1. Spectacular success in artificial selection. 2. Observations on the interaction of natural and artificial selection “in the field” (nature). 3. Experimental replication of natural and artificial selection in the lab. 4. Experimental studies on the interaction of natural and artificial selection “in the field” (nature). 5. Color and other variation is largely genetic.
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From Dr. K. Hughes web site at UIUC. The three guppies in the middle are females, which show no pronounced color variation. The males on either side are representative of the enormous variation in this species - effectively all male have a different appearance. This is an example of hypervariability for a morphological (anatomical) trait.
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Domesticated guppies artificial selection
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Guppies from a river in Trinidad: Upstream of rapids that block migration of large predators. Downstream , with strong predators.
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Field observation: male size and coloration differs even in the same stream, and seems to be related to the presence or absence of predators of adult guppies. Can this observation be acted upon with experiments? Above falls, predators only of baby guppies (killifish). Below falls, predators of adult guppies (pike cichlid). Natural selection (+ sexual selection)
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Yes . Lab experiments (in above ground swimming pools in a greenhouse at Princeton) showed that the amount of color on male guppies increases due to sexual selection - females prefer to mate with brightly colored males, populations evolve to have brighter males. Adding killifish (prey only on baby guppies) does not affect the increase in male brightness. But adding a pike cichlid to a pool results in the fish evolving back to the appearance of “below-falls” fish - dull colored males - natural selection because of predators. Can this experiment be done “in the field”?
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Yes! Small streams can be found (in Trinidad) which do not have guppies or pike cichlids (although even the smallest streams have killifish) Moving guppies from a “below-falls” population (dull males) to an “empty stream” results in males evolving to be brighter. This has been replicated several times. The reverse experiment is harder to set up, but has been
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This note was uploaded on 04/07/2008 for the course IB 201 taught by Professor Hughes/berlocher during the Spring '07 term at University of Illinois at Urbana–Champaign.

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lecture17F06 - Examples of natural and sexual selection:...

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