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SYSTEMATICS The reconstruction and study of evolutionary relationships.

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1 SYSTEMATICS The reconstruction and study of evolutionary relationships

2 Taxonomy Two main objectives: –to sort out organisms into species –to classify species into higher taxonomic levels Species that appear to be closely related are grouped into the same genus. the leopard, Panthera pardus, belongs to a genus that includes the African lion (Panthera leo) and the tiger (Panthera tigris). Taxon = a named taxonomic unit at any level; (taxa = plural) –ex: Mammalia is a taxon at the Class level

3 TAXONOMY taxonomic system developed by Linnaeus in the 18th century –binomial = Genus species –classification system Domain Eukarya KingdomAnimalia PhylumChordata ClassMammalia OrderPrimates FamilyHominidae GenusHomo speciessapiens

4 Domain Eukarya Kingdom Animalia Phylum Chordata Subphylum Vertebrata Class Mammalia Order Rodentia Family Sciuridae Genus Sciurus Species Sciurus carolinensis Sciurus carolinensis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Did King Phillip Come Over For Great Sex?

5 5 Limitations of the Linnean System Many hierarchies are being re-examined based on the results of molecular analysis -Linnaean taxonomy does not take into account evolutionary relationships -The phylogenetic and systematic revolution is underway

6 PHYLOGENY Hypothesis of the evolutionary history of a group represented by pictures: phylogenetic trees –time goes from the bottom up –read from bottom up, NOT LEFT TO RIGHT –branch length = the number of changes

7 Fig Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Variations of a Cladogram GibbonHumanChimpGorillaOrangutanGibbonOrangutanGorillaHumanChimp Human Gorilla Orangutan Gibbon Version 1 Version 2 b.a. Version 3 Reproduced by kind permission of the Syndics of Cambridge University Library, Darwins Notebook B, Tree of Life Sketch, p. 36 from DAR.121 D312

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11 11 Phylogenies depict evolutionary relationships

12 Phylogenetic trees reflect the hierarchical classification of taxonomic groups nested within more inclusive groups. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 25.8

13 Approaches to Constructing Phylogenies Cladistics –uses shared derived characteristics (synapomorphies) to classify organisms –Not shared ancestral characteristics (symplesiomorphies) –not overall similarity Because evolution is not steady paced, not unidirectional, may be convergent

14 14 Examples of ancestral versus derived characters Presence of hair is a synapomorphy (shared derived feature) of mammals Presence of lungs in mammals is a symplesiomorphy (an ancestral feature); also present in amphibians and reptiles Cladistics

15 Building Cladograms Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Traits: Organism JawsLungs Amniotic Membrane HairNo TailBipedalLampreySharkSalamanderLizardTigerGorillaHuman Lamprey Shark Salamander Lizard Tiger Gorilla Human Jaws Lungs Amniotic membrane Hair Tail loss Bipedal a.b.

16 Can also use molecular data Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. G Site Species A Species B Species C Species D Outgroup DNA Sequence ATATCCGTAT ACAGCCGCAT ACATCGGTGG GCATAGTGT OutgroupSpecies BSpecies DSpecies ASpecies C Homologous evolutionary changes Homoplastic evolutionary changes 2:TC 4:T 8:T G C 10:TG 8:TC 9:A 6:C G G 5:CA 1:AG GCATAGGCGT

17 PHYLOGENY systematists prefer monophyletic taxa –a single ancestor gave rise to all species in that taxon and to no species in any other taxa

18 18 Monophyletic Group Systematics and Classification

19 19 Paraphyletic Group Systematics and Classification

20 20 Polyphyletic Group Systematics and Classification

21 21 Old plant classification system Systematics and Classification

22 22 New plant classification system Systematics and Classification

23 Evidence used to reconstruct phylogenies Comparative anatomy, morphology, embryology, etc. –problems of homology vs homoplasy (analogy) homology = likeness due to common ancestry homoplasy or analogy = likeness due to convergent evolution

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27 Fig Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Monotremes Marsupials Placentals Phylogeny of Mammals Carnivores Felines Nimravids Saber-toothed cat Hyenas Civets Mongooses Saber-toothed nimravid Phylogeny of Carnivores How many times have saber teeth evolved in mammals? Hypothesis: Saber teeth are homologous and have only evolved once in mammals (or, conversely, saber teeth are convergent and have evolved multiple times in mammals). Phylogenic Analysis: Examine the distribution of saber teeth on a phylogeny of mammals, and use parsimony to infer the history of saber tooth evolution (note that not all branches within marsupials and placentals are shown on the phylogeny). Result: Saber teeth have evolved at least three times in mammals: once within marsupials, once in felines, and at least once in a group of now-extinct cat-like carnivores alled nimravids. Interpretation: Note that it is possible that saber teeth evolved twice in nimravids, but another possibility that requires the same number of evolutionary changes (and thus is equally parsimonious) is that saber teeth evolved only once in the ancestor of nimravids and then were subsequently lost in one group of nimravids. (Note that for clarity, not all branches within marsupials and placentals are shown in this illustration.) Saber-toothed marsupial Bears, seals, weasels, canids, and raccoons Saber-toothed nimravid SCIENTIFIC THINKING Question:

28 Evidence used to reconstruct phylogenies Protein comparisons DNA comparisons –DNA-DNA hybridization, restriction mapping, DNA sequencing

29 29 A Cladogram: DNA Can Have Homoplastic Molecular Data

30 Character Mapping Once you have a phylogeny you can trace the evolution of characters or traits in that group use the rules of parsimony –the simplest is the best

31 Parental Care Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a.b. a: Image #5789, photo by D. Finnin/American Museum of Natural History; b: © Roger De La Harpe/Animals Animals

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33 33 Parsimony and Homoplasy

34 Classification System

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36 Archaea Chromalveolates Rhizaria Archaeplastida Excavata Amoebozoa Opisthokonta Eubacteria Excavata (organisms lacking typical mitochondria) Chromalveolata (organisms with chloroplasts obtained through secondary endosymbiosis) Archaeplastida (organisms with chloroplasts for photosynthesis) Rhizaria (organisms with slender pseudopods used for movement) Amoebozoans (organisms with blunt pseudopods used for movement) Opisthokonts (fungi, animal ancestors, and animals) Six Supergroups Within Eukarya

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38 38 Grouping Organisms Carl Woese proposed a six-kingdom system Prokaryotes Eukaryotes

39 KINGDOMS Monera = Archaebacteria & Eubacteria –prokaryotic Protista –eukaryotic Plantae –eukaryotic, multicellular, autotrophic, cell walls Fungi –eukaryotic, multicellular, heterotrophic, cell walls Animalia –eukaryotic, multicellular, heterotrophic, no cell walls


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