Phylogeny.pdf

PHYLOGENY & MODERN TAXONOMY  Recall: Taxonomy - the classification, identification and naming of organisms - aims to group organisms according to a set of criteria (ex. how closely related they are to each other) - Classifying a species by kingdom, phylum, and so on, is like placi...

PHYLOGENY & MODERN TAXONOMY  Recall: Taxonomy - the classification, identification and naming of organisms - aims to group organisms according to a set of criteria (ex. how closely related they are to each other) - Classifying a species by kingdom, phylum, and so on, is like placing students in a large school system. First a student might be identified by school, then by specific The leopard shares many characteristics with the grade, and finally as a unique individual lion—which belongs to the same genus—but far fewer characteristics with snails, sponges, or by name. earthworms, though they are all members of the animal kingdom. The Theory of Evolution All living things are descended from a common ancestor in the same way that family members are related to each other through a common ancestor. Phylogeny (“evolutionary tree”) - the study of the evolutionary relatedness between, and among, species (entire populations of individuals) - these relationships are similar to a large family tree, but instead of tracing relationships between family members, phylogeny tracks relationships between entire species - Really similar to a family tree except we’re looking at a whole species These relationships can be presented in a: Phylogenetic tree (sometimes called cladograms) - a branching diagram used to show evolutionary relationships between different species or groups - hypothesized genealogy traced back to the last common ancestor (i.e., the most recent) through hierarchical (from general to specific), dichotomous branching  Phylogenetic Tree/Cladogram Feathers Lungs Gizzard Jaws Lamprey Antelope X X Sea Bass X Bald Eagle X X X X Alligator X X X  Phylogenetic Tree/Cladogram Feathers Lungs Gizzard Jaws Lamprey Antelope X X Sea Bass X Bald Eagle X X X X Alligator X X X  Phylogenetic Tree/Cladogram Feathers Lungs Gizzard Jaws Lamprey Antelope X X Sea Bass X Bald Eagle X X X X Alligator X X X  Phylogenetic Tree/Cladogram Feathers Lungs Gizzard Jaws Lamprey Antelope X X Sea Bass X Bald Eagle X X X X Alligator X X X  Phylogenetic Tree/Cladogram Feathers Lungs Gizzard Jaws Lamprey Antelope X X Sea Bass X Bald Eagle X X X X Alligator X X X  Phylogenetic Tree/Cladogram Feathers Lungs Gizzard Jaws Lamprey Antelope X X Sea Bass X Bald Eagle X X X X Alligator X X X  Phylogenetic Tree/Cladogram Feathers Lungs Gizzard Jaws Lamprey Antelope X X Sea Bass X Bald Eagle X X X X Alligator X X X  Phylogenetic Tree/Cladogram Feathers Lungs Gizzard Jaws -- Feathers Lamprey Antelope X X Sea Bass X Bald Eagle X X X X Alligator X X X How to read a phylogenetic tree: Present Most recent common ancestor species to B & C Nodes – branch point, Past speciation event Most recent common ancestor species to A, B & C Clade - a taxonomic group that includes a single common ancestor and all its descendants - each evolutionary branch in a phylogenetic tree - Example: 2 clades exist in this tree Leopards and house cats compose a branch of two species that share a common ancestor. A larger branch that also includes wolves has a common ancestor that would have lived longer ago Small clades – small number of species than the ancestor of leopards and house cats. that share a very recent common ancestor Large clades – includes all species that share a common distant ancestor Common ancestor species  Other Examples: How many clades are in this figure? This cladogram shows how derived characters can be used to identify clades among certain vertebrates (animals with backbones). All the species shown here share a common ancestor that had a backbone. (Each clade is actually defined by several derived characters, not just one.) Review: 1. How many clades are represented in this tree? 2. Which characteristic is located the “furthest back in time”? 3. Which characteristic links the living reptiles and living amphibians? 4. Are living reptiles more closely related to birds or mammals? Why? 5. Where is the most common ancestor located of all the species? REVIEW -- 2 types of taxonomy: 1) Traditional classification (taxonomic tradition) - hierarchical classification system by Linnaeus - groups species primarily by observed morphological (physical) characteristics 2) Phylogenetic analyses (cladistic hypotheses) - “modern taxonomy” - organisms are grouped based on evolutionary relatedness/pathways (not taxonomic ranks) Note: Taxonomic groups often reflect true clades, so both methods are valid. In a phylogenetic tree, each branch point represents a common ancestor of the species above that point. In this diagram, the branches are labeled to reinforce how taxonomy reflects the branching pattern of evolution.