Lec25_Speciation2_HO 2010 - BioEE 2780 Evolutionary Biology...

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BioEE 2780 Fall 2010 Evolutionary Biology Today’s lecturer: Mike Webster Speciation II: Extrinsic Isolation and Variations on the Theme Readings: Textbook chapter 16 This lecture focuses mostly on the outside forces that cause populations to diverge (and sometimes but not always split into separate species). We also will consider some variations on the classic allopatric speciation model. A. Reproductive barriers are a key component of the speciation process • Reproductive barriers cause genetic isolation and prevent gene flow between populations • Genetic isolation allows independent evolutionary trajectories, allowing populations to diverge B. What is the nature of reproductive barriers? • Extrinsic (geographical/environmental) • Mountains, rivers, oceans, deserts, etc. • Physical separation prevents gene flow • Intrinsic (biological/organismal) • Habitat specialization, mating preferences, hybrid incompatibilities, etc. • Evolutionary divergence prevents gene flow C. Secondary Hybrid Zones Form when differentiated populations come into secondary contact What happens after secondary contact depends on… 1.the amount of dispersal into and out of the hybrid zone 2.the pattern and intensity of selection on hybrids relative to the two parental populations
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This note was uploaded on 12/29/2010 for the course BIOEE 1780 at Cornell University (Engineering School).

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Lec25_Speciation2_HO 2010 - BioEE 2780 Evolutionary Biology...

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