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lecture outlines for posting13

lecture outlines for posting13 - Lecture 13 EEB 13 21...

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Lecture 13 - EEB 13 - 21 February 2008 Dr. Hespenheide Speciation - process of speciation – must occur - if migration stopped altogether by a barrier migration migration barrier deme 1 deme 2 deme 3  deme n then demes accumulate differences then demes - may not interbreed if brought back together; i.e., - they have become reproductively isolated biological species concept (Mayr) - species are - actually/potentially interbreeding demes - reproductively isolated from other demes - What does it mean to be reproductively isolated? - if not, then hybridization - mating between different species (Mayr, p. 171) [vs. Mendel’s sense of mating between true-breeding genotypes] rare in nature, because of… reproductive isolation [text, p.170f] - two kinds 1. mating occurs but hybrids don’t survive or can’t reproduce – - example: mules - sterile hybrid of horse and donkey (both in genus Equus ) - the parent species have different karyotypes, so meiosis is unsuccessful in making gametes because chromosomes can’t pair up = postmating (“postzygotic”) reproductive isolation 2. mating doesn’t occur - - individuals don’t recognize members of other species as potential mates – not “attractive” because of sexual selection, or - occur in different habitats or reproduce at different times of year = premating (“prezygotic”) reproductive isolation
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note : bsc does not apply to all organisms asexual reproduction (Mayr: “agamospecies”) = clones - no interbreeding; each individual a separate “species” (example: blackberries and related “berries”) other organisms with extreme/different genetic systems – plants (oak trees) that show extensive hybridization without loss of fertility in
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lecture outlines for posting13 - Lecture 13 EEB 13 21...

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