Postmating - gene exchange (e.g., bird songs and plumage...

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Postmating isolating mechanisms inhibit or prevent interspecific crosses gametic mortality (sperm transferred but does not fertilize eggs). zygote mortality (egg is fertilized but zygote dies). hybrid inviability (F1 hybrid has reduced viability: incomplete development). hybrid sterility (F1 hybrid viable but sterile) e.g., mule Premating isolation prevents wasting of gametes : highly susceptible to improvement by natural selection. Damselflies: character displacement of wing spot density. Rapid speciation events often involve behavioral isolation: Hawaiian Drosophila: hundreds of species in the past several million years. Postmating isolation does not prevent the wasting of gametes and its improvement by natural selection is indirect. Isolating mechanisms may work in concert; if one breaks down, another will prevent
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Unformatted text preview: gene exchange (e.g., bird songs and plumage patterns). This issue of the opportunity for selection to act on pre- vs. postmating isolating mechanisms is important in the discussion of Reinforcement in the next lecture. Breakdown of isolating mechanisms will lead to hybridization (crickets in eastern North America hybridize in a hybrid zone along the Appalachian ridge). Are hybridizing "species" really species? If the hybrids backcross to either type, introgression can occur ("the incorporation of genes from one species into the gene pool of another species"). Many examples of hybridization in both plants and animals. Often referred to as semispecies , i.e., not complete species....
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This note was uploaded on 11/06/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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