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

Each branch point Represents the divergence of two species Leopard Domestic cat Common ancestor

“Deeper” branch points Represent progressively greater amounts of divergence Leopard Domestic cat Common ancestor Wolf

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