Lec 29 A - BIS2B Fall 2009(Keen Lecture 29 Speciation III...

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BIS2B Fall 2009 (Keen) Lecture 29 . Speciation III 18 November Examples of speciation; hybridization and ring species Students should be able to: Give examples of allopatric, parapatric and sympatric speciation including relevant forms of reproductive isolation and situations that favor positive assortative mating Explain how hybrid zones and ring species arise Discuss ways in which hybrid zones and ring species pose problems for biological pigeon-holes (species descriptions)
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Vicariant Geographic Isolation • The rise of the Isthmus of Panama (3-5 MYA) shut off gene flow between the Pacific Ocean & Caribbean Sea Assume that the formation of the Isthmus did divide the two taxa. We see many different shrimp species on each side of the Isthmus. Could a cladogram help us find out whether the species formed before or after the Isthmus split the ancestor? Carib Carib Pacific Pacific OR Carib Pacific Carib Pacific !"#$%%&"' )&" !"#$%%&"' )&" *"+$,$+ -+&"' -+&"' Explain the patterns
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Species are distributed throughout the ocean; there may be more than one species present species present before split are isolated Pacific species Caribbean species
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*"+$,$+." *"+$,$+. *"+$,$+ / *"+$,$+0 *"+$,$+1 *"+$,$+2 *"+$,$+ 3 *"+$,$+4" *"+$,$+4 *"+$,$+4 !"#$%%&"'. !"#$%%&"'0 !"#$%%&"'/ !"#$%%&"'/" !"#$%%&"' 1 !"#$%%&"'2 !"#$%%&"'3 !"#$%%&"'4 5$+"#$"'6 7"889:"6#$+; <:&+$"6$9' $' <'"::$'= <>#$?: we don’t know the branch order here { all lineage splits when there was one open ocean basin } Lineage splits after the Isthmus
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5 evolutionary changes Branch lengths may represent different things: they may only specify the order of branching (divergence) they may be scaled for the length of time since divergence they may specify the number of base pair changes for a particular DNA sequence 10 evolutionary changes
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*"+$,$+ ."
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