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Taxonomy To sort organisms into species To classify species into higher taxonomic levels A taxon is a taxonomic unit at any level; for example “Mammalia” is a taxon at the Class level (taxa = plural)
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Taxonomy Species that appear to be closely related are grouped into the same genus (e.g., the leopard Panthera pardus; African lion Panthera leo; Tiger Panthera tigris) Similar genus are grouped into the same family, and so on…
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Domain Kingdom Phylum Subphylum Class Order Family Genus Species Diversification
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Taxonomy Classification system Domain Eukarya KingdomAnimalia PhylumChordata ClassMammalia OrderPrimates FamilyHominidae GenusHomo speciessapiens
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Taxonomy The taxonomic system was developed by Linnaeus in the 1750’s Binomial (two part) system; Genus species The scientific name includes the species name Example: Homo sapiens or H. sapiens No 2 organisms can have the same scientific name and this name is the same everywhere in the world!
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Taxonomy Scientific names are descriptive May describe unique characteristic, region where species is found, etc. Example: Humpback whale Megaptera novaeangliae –Magas = large –Pteron = wing –Novas = new –Angaliae = England
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Taxonomy Common names can be deceiving… http://www.koala.net/media http://www.ticam.utexas.edu/images/grizzly.jpg “bear” “dolphin”
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Taxonomy Scientific names may change over time Many hierarchies are being re-examined based on results of molecular analysis Linnaean taxonomy does not take into account evolutionary relationships Enter phylogeny and systematics…
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Systematics The reconstruction and study of evolutionary relationships Phylogeny – an evolutionary tree; species grouped by how long they’ve shared a common ancestor Evidence for determining these relationships must come from shared homolagous characteristics
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Phylogeny The evolutionary history of a group is presented graphically in phylogenetic trees In a phylogenetic tree: –Time goes from the bottom up –Read from bottom up, not left to right –Branch length = number of changes –Depicts evolutionary relationships!
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Time
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Remember: Read from the bottom up; not left to right!
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These three versions convey the same information (phylogenies depict evolutionary relationships) Node 1: common ancestor of human and chimp Node 2: c.a. of human, chimp, and gorilla
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Phylogenetic trees reflect hierarchical classification of taxonomic groups
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Phylogeny Systematists prefer monophyletic taxa Monophyletic – a single ancestor gave rise to all species in that taxon (and to no species in any other taxa); “single tribe” A monophyletic group consists of a common ancestor and all its descendants
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Monophyletic group Monophyletic group (indicated in pink) consists of most recent common ancestor and all of its descendents Common ancestor: “Archosaur”
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Paraphyletic group Paraphyletic group (indicated by pink) consists of the most recent common ancestor and some (not all) of the descendents 1 descendent, the hawk, is excluded
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Polyphyletic group Polyphyletic group (indicated in pink) does NOT contain the most recent common ancestor Birds and bats can be included because of morphological similarities (convergent evolution)
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Monophyletic versus Paraphyletic and Polyphyletic groups
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Old classification system for plants New classification system for plants
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Phylogeny What evidence is used to reconstruct phylogeny? –Comparative anatomy –Morphology –Embryology –Protein comparisons –DNA comparisons Problems of homology versus analogy
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Phylogeny Homology (homologous structures) – likeness due to common ancestor Analogy (analogous structures) – also known as “homoplasy”; likeness due to convergent evolution; functional constraint Analogous structures are the result of separate evolution
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Comparative Biology Elongated canine teeth (saber teeth) evolved separately in different groups of carnivores
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Cladistics Cladistics – only shared derived characters are used in determining evolutionary relationships Homoplasy (analogy) complicates cladistic analysis Species that share a common ancestor constitute a clade (a monophyletic group is a clade) Clades are hypotheses, just as phylogenetic trees are
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Time clade
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Cladistics Principle of parsimony – favors the hypothesis that requires the fewest assumptions (the phylogeny that requires the fewest evolutionary events is the best hypothesis) Simplest is best (Occam’s Razor)
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Parsimony and Homoplasy Placement of frogs as closely related to salamanders requires that tail loss (in adults) evolved twice (homoplasy); if frogs are closely related to gorillas, then tail loss evolved once, but would also have to lose amniotic membrane and hair
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Ancestral versus Derived characters Ancestral – dates back to common ancestor (found in common ancestor and all its descendents) Derived – feature of distinct taxon Hair is a shared derived feature of mammals, but so is a backbone; the presence of a backbone cannot help us distinguish mammals from other vertebrates The presence of backbone is a shared ancestral feature (also present in amphibians and reptiles)
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Recommended Reading Dictionary of Word Roots and Combining Forms; Donald J. Borror Best $15 you can spend Compiled from Greek, Latin and other languages, with special reference to biological terms and scientific names
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