Speciation is a Phylogeny process by which lineages split. -the evolutionary relationships among We should be able organisms to the reconstruct the history of these (millions of Time years) -the patterns of lineage branching produced splits (i.e., build an by the true evolutionary history evolutionary tree) Linnaean System Diversity: of Classification A Phylogenetic Framework I. Taxonomy II. Phenetics III. Cladistics Carl von Linné a.k.a. Linnaeus (1707-1778) Phenetics Taxonomy does not always reflect evolutionary history. • Grouping is based on phenotypic similarity • Does not distinguish the cause of similarities • Not widely used today because many Example: Example: Example: similarities are not due to common ancestry. Class Aves Kingdom Protista Class Reptilia 1 Convergent Evolution Cladistics • Emphasizes common ancestry (≠ similarity) • Distinguishes between two kinds of similarities: 1) similarity due to common ancestry 2) similarity due to convergent evolution • Most widely used approach to reconstructing phylogenies. Homology Bird feathers are made of keratin. a phenotype that is similar in two species because it was inherited from a common ancestor. fly wings ≠ bird wings Homoplasy a phenotype that is similar in two species because of convergent evolution. Insect wings are made of chiton. An Example of Cladistics Relate the following taxa: • Horse • Seal • Lion • House Cat Homoplasy 2 Data for Cladistic Analysis How to do a Cladistic Analysis * * Cat Lion Horse Seal Cat Lion Horse 1. Define a set of traits. Seal Lizard Trait Lizard 2. Analyze traits for homology. Retractable Claws 1 0 0 0 0 Pointed Molars 1 1 0 0 0 3. Assign phenotypic states to each taxon. Fusion of Wrist Bones 1 1 1 0 0 4. Determine ancestral phenotypic states Hair 1 1 1 1 0 for each trait (need an outgroup). Presence = 1 *Outgroup Presence = 1 Absence = 0 The Essence of Parsimony Data for Cladistic Analysis C A Lizard* Horse Cat Lion Seal Lizard* Horse Cat Lion Trait Seal Retractable Claws 1 0 0 0 0 B B Pointed Molars 1 1 0 0 0 Fusion of Wrist Bones 1 1 1 0 0 Hair 1 1 1 1 0 A A *Outgroup Presence = 1 Common Not Common Absence = 0 ? Are tigers more closely related to lizards? 3 Data for Cladistic Analysis Seal Lizard* Cat Lion Horse Seal Lizard* Cat Lion Horse Tiger Trait Tiger Retractable Claws 1 0 0 0 0 0 Pointed Molars 1 1 0 0 0 1 Fusion of Wrist Bones 1 1 1 0 0 1 Hair 1 1 1 1 0 1 Are tigers more closely related *Outgroup Presence = 1 to lizards? Absence = 0 Absence = 0 Parsimony says “NO” Which traits are meaningful? Today, we can also use genes to determine evolutionary relationships. Pleisiomorphies primitive traits (i.e., inherited) A molecule of DNA carries information about ancestry. Synapomorphies Informative shared derived traits The chemical structure of DNA can be used as traits Autapomorphies in a cladistic analysis. uniquely derived traits But how do we recognize homology from homoplasy? The Tree of Life • Genetically similar = closely related Example: Chimps and humans share >99% of their DNA code. • Genetically different = distantly related Example: Both humans and chimps share only 40% of their DNA with sponges. 4 Piecing together the Tree of Life Building the Tree of Life [Source: Bininda-Emonds, 2004, Trends in Ecology & Evolution 19: 315-322] But what traits do all organisms share? • All organisms possess a genes for RNA that helps make proteins (ribosomal RNA) • RNA is half as wide as DNA and much shorter. • The mutation of the ribosomal RNA gene is not too slow and not too fast. 5.