Bio171-F08-lec25 - Lecture 25: Friday, October 31, 2008...

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Unformatted text preview: Lecture 25: Friday, October 31, 2008 Biology 171 Todays Topic: Phylogenetics and the Tree of Life Announcements Next Week in Discussion: Bacterial Diversity - Your Gut Flora Text Reading Lec 25: 2 nd ed: Chapter 26 (556-561) 3 rd ed: Chapter 27 (543-548) Lec 26: 2 nd ed: Chapter 26 (561-578) 3 rd ed: Chapter 27 (548-564) Speciation (concluded): Polyploidy Darwins Tree of Life Ancestral & Derived Characters Homology and Homoplasy Building Phylogenetic trees Formation of Prezygotic Reproductive Barriers Habitat Isolation Apple maggot flies mate on fruit of native hawthorne, where their larvae bore into the fruit. When apples were introduced into North America, some flies switched to mate on apple fruit. The populations diverged in sympatry due to reproductive isolation. Rhagoletis pomonella Maggot in apple Hawthorne tree Sea Urchin Gamete Recognition Proteins show high rates of evolution and may cause speciation if the sperm and egg receptors diverge so that gamete fusion is inhibited. Formation of Prezygotic Reproductive Barriers Gametic Isolation Formation of Prezygotic Reproductive Barriers Mechanical Isolation Like many insects, feas have very complex genitalia, especially in males. All the parts must properly Ft or stimulate the emale reproductive tract in order or mating to be successul. Many insect species can only be recognized morphologically based on dierences in their genitalia. Postzygotic Reproductive Barriers Hybrid Infertility The liger is a hybrid between a male lion and a female tiger. It looks like a giant lion with diffused stripes. Like tigers (and unlike lions), ligers like swimming. Ligers are typically sterile. Postzygotic Reproductive Barriers -Hybrid Infertility Sympatric speciation Via Polyploidy (increase in the number of complete sets of chromosomes) Very common in plants - less so in animals Can result in very rapid speciation 2 Basic modes: Auto- and Allo-Polyploidy Sympatric speciation by auto polyploidy in plants. The tetraploid offspring cannot backcross to the parent. One mechanism for allopolyploid speciation in plants. A hybrid of two different species is usually sterile because its chromosomes are not homologous and cannot pair during meiosis. However, such a hybrid may be able to reproduce asexually. This diagram traces one mechanism that can produce fertile hybrids (allopolyploids) as new species. The new species has a diploid chromosome number equal to the sum of the diploid chromosome numbers of the two parent species. Sympatric Speciation via Allo polyploidy Fig. 26.10 Allotetraploids of Tragopogon (goatsbeards) These fowers are native to Eurasia. 2 new allopolyploid species were spontaneously generated in the northwestern U.S. by hybridization events involving 3 introduced diploids....
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Bio171-F08-lec25 - Lecture 25: Friday, October 31, 2008...

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