Can include morphological traits eg color structures

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Can include: Morphological traits (e.g. color, structures) Biochemical traits (e.g. DNA, proteins) Behavioral traits A character can be any trait that varies among species and offers information about the relationship of those species
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11 Homology: similarity that results from inheritance of characters from a common ancestor Homology: similarity that results from inheritance of characters from a common ancestor
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12 Homology: similarity that results from inheritance of characters from a common ancestor Species 1 CATC--CCCCAAAGTCTGCAGCATGTTTTTCGGCAAGGACC Species 2 CATCAGCCCCGAAGTCTGAAGCATGTTTTTCGGCAAGGACC Species 3 CATCAGCCCCAAAGTCTGAAGCATGTTTTT----AAGGACC Species 4 CATCAGCCCCAAAGTCTGCAGCATGTTTTTCGGCAAGGACC Homology: similarity that results from inheritance of characters from a common ancestor
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13 Phylogenetics: the science of reconstructing evolutionary trees Lecture Outline 1. Tree Anatomy 2. Characters & Homology 3. Reconstructing Trees 1. Cladistic analysis 2. Homoplasy & Parsimony The logic of tree reconstruction Intuitively, we expect more closely related species to share more similarities But do all characters offer the same information?
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14 The logic of tree reconstruction Intuitively, we expect more closely related species to share more similarities But do all characters offer the same information? NO some homologous characters have more phylogenetic signal than others Assumptions of Cladistic Methods: 1. Taxa are related by descent from a common ancestor 2. Relationships can be reflected in a tree 3. Only shared derived traits identify monophyletic groups
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15 Synapomorphy: A shared derived character Shared: occurs in two or more taxa Non-shared: occurs only in one taxon Derived : differing from the ancestor Cladistic phylogenies are based ONLY on synapomorphies Cladistic Terminology: Cladistics: Only certain types of homologous characters are useful for inferring trees: Synapomorphies (shared derived characters)
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16 Cladistics: Only certain types of homologous characters are useful for inferring trees: Synapomorphies (shared derived characters) Cladistics: Only certain types of homologous characters are useful for inferring trees: Synapomorphies (shared derived characters)
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17 Synapomorphies are evidence of relationship because they define monophyletic groups How to tell if a character is derived or ancestral? The OUTGROUP COMPARISON • Choose an OUTGROUP known (on the basis of other evidence) to be OUTSIDE the group of interest • Character states present in the outgroup are assumed to be ancestral • Character states present only in the ingroup are potentially synapomorphies out ingroup
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