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Phylogeny and Systematics Chapter 26: (Making “Trees of Life”) Macroevolution • studies focus on change that occurs at or above the level of species ▫ The origin of taxonomic groups higher than species level How does this occur? • Evolution of new traits (novelties) • mass extinctions • Open adaptive zones (divergent evolution) • Currently, scientists use ▫ Morphological, biochemical, and molecular comparisons to infer evolutionary relationships Obtained through fossil studies, DNA technology and current organisms Phylogeny What is phylogeny? • The evolutionary history of a group • Systematics attempts to reconstruct phylogeny, by analyzing evolutionary relatedness. ▫ Use morphological and biochemical similarities • Molecular systematics uses DNA, RNA and proteins to infer evolutionary relatedness. • Different tools are used to reconstruct phylogenies called phylogentic trees. Molecular systematics Systematics • Uses evidence from fossil record and existing organisms to reconstruct phylogeny (Linneaus) • Binomial nomenclature Genus species keeps identity of organism universal ▫ Other taxa used to classify Domain, Kingdom, Phylum, Class, Order, Family, Genus, species Taxonomy Linnaeus ordered division of organisms into categories based on a set of characteristics used to assess similarities and differences Linking Classification and Phylogeny Species Panthera Figure 25.9 Order Family Panthera Mephitis Canis Canis Lutra lutra pardus mephitis familiaris lupus (European (leopard) (striped skunk) (domestic dog) (wolf) otter) Genus • Systematists depict evolutionary relationships In branching phylogenetic trees Felidae Mephitis Lutra Mustelidae Carnivora Canis Canidae • Each branch point ▫ Represents the divergence of two species Leopard Domestic cat Common ancestor • “Deeper” branch points ▫ Represent progressively greater amounts of divergence Wolf Leopard Common ancestor Domestic cat Cladistics • Cladogram is a tree with two way branch points • Each branch point represents divergence from common ancestor • Each branch is called a clade • Clades ▫ Can be nested within larger clades, but not all groupings or organisms qualify as clades • 3 types of groupings ▫ Monophyletic ▫ Polyphyletic ▫ Paraphyletic Different Types of Clades • Monophyletic = single ancestor gave rise to all species in the taxon; ONLY valid clade • Polyphyletic = includes numerous types of organisms that lack a common ancestor; not a valid clade • Paraphyletic = a grouping that consists of an ancestral species and some, but not all, of the descendants; not a valid clade Clades Grouping 1 Monophyletic Grouping 2 Paraphyletic Grouping 3 Polyphyletic Let’s practice… Making “Trees”: Morphological & molecular homologies • similarities based on shared ancestries ▫ bone structure ▫ DNA sequences • beware of analogous structures convergent evolution Not all Similarities Represent Common Ancestry • Homologous structures indicate shared common ancestry ▫ Homologous structures are therefore evidence of divergent evolution • Analogous structures are similar in function but not in evolutionary history ▫ Analogous structures are evidence of convergent evolution • It is not always easy to sort homologous from analogous structures • RECALL… • Convergent evolution occurs when similar environmental pressures and natural selection ▫ Produce similar (analogous) adaptations in organisms from different evolutionary lineages Marsupial Eutherian (placental) Making Evolutionary Life Trees: Illustrating Phylogeny • 1. Cladistics = ▫ sorts homologous from analogous structures ▫ sorts primitive and shared derived characteristics ▫ Makes cladograms The Universal Tree of Life • The tree of life is divided into three great clades called domains: ▫ Bacteria, Archaea, and Eukarya Billion years ago Bacteria Eukarya Archaea 0 4 Symbiosis of chloroplast ancestor with ancestor of green plants 1 3 Symbiosis of mitochondrial ancestor with ancestor of eukaryotes 2 Possible fusion of bacterium and archaean, yielding ancestor of eukaryotic cells 1 Last common ancestor of all living things 4 2 3 2 3 1 Origin of life Figure 25.18 4 • A shared primitive character ▫ a homologous structure that is shared by all groups we are trying to define • A shared derived character ▫ A new evolutionary trait unique to a particular clade(s) ▫ Making Cladograms Activity A Cladogram What is the shared primitive characteristic? Notochord 65.5 251 Mesozoic Millions of years ago 542 Paleozoic Proterozoic • In a phylogram ▫ The length of a branch in a cladogram reflects the number of genetic changes that have taken place in a particular DNA or RNA sequence in that lineage ▫ Involves timing cladograms do NOT! Cenozoic Phylograms