Systematics “Systematics is the study of biological diversity and its origins. It focuses on understanding evolutionary relationships among organisms, Study of: species, higher taxa, or other biological entities, • the kinds and diversity of organisms such as genes, and the evolution of the (http://www.msnbc.msn.com/id/11114156/) properties of taxa including intrinsic traits, ecological interactions, and geographic • the relationships among them distributions. An important part of systematics is the development of methods for various aspects • taxonomy and systems of classification of phylogenetic inference and biological nomenclature/classification.” -Systematic Biology editorial board 1 2 Effigia okeeffeae Archosaur - 210 my Harpymimus okladnikovi Dinosaur - 120 my 3 4 Phylogenetic Tree or cladogram • Topology Cow • Hypothesis Horse Gecko Salamander Time 5 6 1 Nodes Internal Terminal Time Branch Branch or Tip Taxon (pl. Taxa) Cladogenesis Anagenesis 7 8 Rotation of branches No change in topology Gecko Cow Cow Horse Horse Gecko Salamander Salamander 9 10 New topology Cow Cow Horse Gecko Gecko Horse Salamander Salamander • Monophyletic group • Natural group • Clade 11 12 2 Cow Cow Horse Horse Gecko Gecko Salamander Salamander Herps The gecko is the sister taxon to the Paraphyletic group mammals in this tree. 13 14 Steps in phylogenetic analysis Steps in phylogenetic analysis Step 1. Select characters for Step 1. Select characters for analysis and make data matrix. analysis and make data matrix. Step 2. Select method and search Step 2. Select method and search for the best tree. for the best tree. 15 16 Characters must be homologous (i.e., similar Character – any heritable attribute of an organism because of decent from a common ancestor). Character state – any observed variation of a given character 17 18 3 1 2 3 4 Steps in phylogenetic analysis V F L H Cow 1 1 1 1 Step 1. Select characters for analysis and make data matrix. Horse 1 1 1 0 Step 2. Select method and search Gecko 1 0 0 0 for the best tree. Salamander 1 0 0 0 Data matrix 19 20 Fur or Maximum parsimony (Cladistics) Lactation Cow • Simpler explanations are preferred over more complex ones. Horse • Chooses the tree with the fewest evolutionary steps as best estimate of phylogeny. Gecko • Minimizes confusing effects of homoplasy (convergent or analogous characters) Salamander Apomorphy – derived character state Synapomorphy – shared derived character state 21 22 Horns Cow Cow Vertebrae Horse Horse Gecko Gecko Salamander Plesiomorphy - ancestral character state Salamander Symplesiomorphy – shared ancestral character state Autapomorphy – unshared derived character state 23 24 4 Fur Horns Fur Horns Lactation Lactation Cow Cow Vertebrae Vertebrae Horse Horse Gecko Gecko Salamander Salamander Alternate character mapping method 4 step tree 25 26 c c h h h h s s No. taxa No. rooted trees g s c g s g g c 21 c c h h g g g g 33 h s c s s h s c 415 c c s s s s g g 5105 h g c h c 10 3 X 107 g h h c c c 50 3 X 1077 g h s h g g 1000 4 X 102,864 s s h The 15 possible trees for 4 taxa 27 28 Fur Horns Horns Fur Lactation Lactation Cow Cow Vertebrae Vertebrae Gecko Horse Horse Gecko Salamander Salamander 6 step tree 4 step tree 29 30 5 Fur Horns 1 2 3 4 5 Lactation V F L H C Cow Cow 1 1 1 1 1 Vertebrae Horse 1 1 1 0 0 Horse Gecko 1 0 0 0 1 Gecko Salamander 1 0 0 0 0 Salamander Data matrix Brown color 6 step tree 31 Homoplasy 32 A brief history The Outgroup of Systematics • Used to “root” the phylogenetic tree Phylogeny –a • Differentiate shared, ancestral character states branching diagram from shared, derived ones representing the evolutionary relationships or history of genes, species or other taxa. Kennedy (1929) 33 34 Willi Hennig 35 36 6 Today’s Goals 1. Construct a phylogeny of vertebrates using the “vertebrate example” data set 2. Construct a phylogeny for eight primate species using skulls in the lab. David Swofford FSU 37 38 Using Mesquite Analysis of phylogeny & character evolution 39 7.