P10-Lecture 15-Speciation cont. Tree of Life- March 10

P10-Lecture 15-Speciation cont. Tree of Life- March 10 -...

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Unformatted text preview: Lecture 15: The Tree of Life Reconstructing Phylogeny s Organisms united by shared ancestry s Shared ancestry can be thought of as a Tree x Darwin's Metaphor s We can reconstruct this Tree! s Knowledge of the Tree of Life is very useful x In this course, and beyond Porifera . Cnidaria Ctenophora Platyhelminthes Rotifera Nematoda Mollusca Annelida Onychophora Arthropoda Ectoprocta Brachiopoda Echinodermata Hemichordata Chordata Analogous vs. Homologous traits Eyes evolved many t imes, including here and here "Tree Thinking" s Darwin described a "Great tree of Life" x Living species at the tips x Branches are groups of closely related species x Branch points are speciation events Problem: How can we reconstruct the tree of life (i.e. the history of life)? s Analysis of fossils Direct x Cons: Fragmentary, can be hard to interpret s Phylogenetic Analysis x Compare similarities of organisms x Pros: Reminder: What is a phylogeny? s The branches and connections on Darwin's tree of life. s Produced by two evolutionary events x Speciation x Origin of new T Hair I M E characteristics The essential question How are these animals related? Systematics Cladogram s A branching diagram depicting an estimate of the phylogeny. Cladistics determines the evolutionary relationships between living things based on Derived Similarity. s Derived Similarity Similarity x Single origin-an ancestral species & all the descendant species grouped together. x Implies close relationship! x Monophyletic groups = clade Hair = shared derived character which is unique to the clade. Hair Similarity s Convergent Similarity x Independent origins x Does not imply close relationship x Polyphyletic groups Similarity s Primitive Similarity x Single origin x Does not imply close relationship! x E.g. lizards and crocs lack feathers, but so did the ancestor of birds. x Paraphyletic groups x Not used in cladistics X Review of terms s Monophyletic groups- Clade x (e.g. mammals) Common ancestor and all descendants x United by shared derived similarity x Synapomorphies s Polyphyletic groups (e.g. birds+bats) x Do not share a unique common ancestor x United by convergent similarity (analogous) s Paraphyletic groups (e.g. "reptiles") x Do not share a unique common ancestor x United by primitive similarity Phylogenetic analysis (Cladistic Methods) s Goal - Monophyletic groups x Accurately describe relationships s Problem: How can we distinguish derived similarity (which is informative) from convergent and primitive similarity (which are not)? Phylogenetic analysis (Cladistic Methods) s Willi Hennig - 1950, 1966 s Two principle techniques for reconstructing phylogeny: x Outgroup analysis x Parsimony Outgroup Analysis Distinguishing derived from primitive similarity Outgroup Analysis Distinguishing derived from primitive similarity Outgroup Analysis Distinguishing derived from primitive similarity Outgroup Ingroup ? Primitive or derived? Cold-bloodedness? 4 limb walking? Fully divided heart? Outgroup Analysis of Dinosaurs See also Fig.27.4 Parsimony s The cladogram requiring the fewest evolutionary changes is (usually) preferred s Why? Uses the simplest explanation for the distribution of characters x Not necessarily the true phylogeny x A reasonable and explicit goal x See Fig. 27.3 Parsimony s The cladogram requiring the fewest evolutionary changes is (usually) preferred ? Does this work? Parsimony s The cladogram requiring the fewest evolutionary changes is (usually) preferred s Suppose we know the relationships (the phylogeny) of these animals Mono-, poly, or paraphyletic? s What makes these animals look similar? Mono-, poly, or paraphyletic? s What about this? s What makes these animals look similar? Mono-, poly, or paraphyletic? s What about this? s What makes these animals look similar? What have we learned? s Phylogeny vs. Cladogram s Derived vs. Convergent vs. Primitive similarity s Monophyletic vs. Polyphyletic vs. Paraphyletic groups (examples) s Monophyletic groups recognized using: xOutgroup analysis xParsimony Which two are closest relatives? A A and B? A and C? B and C? B C 1. 2. 3. ...
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This note was uploaded on 05/11/2010 for the course BIOLOGY 105 taught by Professor Richard during the Spring '10 term at George Mason.

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