Phylogeny and Systematics LECTURE 33 Making Trees of

Phylogeny and Systematics LECTURE #33 (Making “Trees of Life”) Honors Biology Ms. Day

Evolutionary Classification • Phylogeny = the study of evolutionary relationships • Biologists now group organisms into categories that represent evolutionary descent (and not just physical similarities) • How would you classify a hyena? • Would you group it with cats or dogs? Photo credit flickr: ibeatty

• Currently, scientists use ▫ Morphological, biochemical (ex: DNA), and molecular comparisons to infer evolutionary relationships Obtained through fossil studies, DNA technology and current organisms

Why do you arrange shared histories? • Uses evidence from ▫ fossil record ▫ Anatomy of existing organisms ▫ DNA/amino acid sequences (proteins) • Use branching “trees” to reflect phylogeny and place groups of closer related organisms into clades ▫ Clade= group of closely related species

• A cladogram ▫ a picture (“tree”) of shared characteristics among groups of different organisms • A clade within a cladogram ▫ a group of species that includes an ancestral species & all its descendants • Cladistics ▫ the study of resemblances among clades

Taxonomy An ordered division of organisms grouped into categories based on a set of characteristics used to assess similarities and differences

Linking Classification and Phylogeny Species Genus Family Order Panthera pardus (leopard) Panthera Felidae Mephitis mephitis (striped skunk) Lutra lutra (European otter) Lutra Mephitis Mustelidae Carnivora Canis familiaris (domestic dog) Canis Canidae Canis lupus (wolf)

• 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 ▫ Can be nested within larger clades

Making “Trees” • similarities based on shared ancestries ▫ bone structure ▫ DNA sequences • beware of analogous structures SAME function DIFFERENT development (opposite of homologous structures) This is a result of convergent evolution http: //ccl. northwestern. edu/simevolution/o bonu/cladograms/Open-This-File. swf

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

How do we differentiate between homologous and analogous structures? • Compare embryonic development of the structures in question • Compare macromolecules along with anatomical features called comparative molecular biochemistry.

Making “Trees” (Con’t) • A shared primitive character ▫ A structure that is shared by all groups we are trying to define • A shared derived character ▫ A new evolved trait unique to a particular clade(s)

What is the shared primitive characteristic? Notochord