Reading Cladograms Who is more closely related? Animals and fungi are more closely related than either is to plants.

Determining Evolutionary Relationships Fossils Morphology (homologous structures) Why can’t we use analogous structures? Molecular evidence (DNA, amino acids) Uses computer analysis

Cladogram Depiction of inferred evolutionary relationships among a set of species

Cladogram vs. Phylogenetic Tree Phylogenetic Trees are a type of cladogram Both show relationships between organisms Phylo Trees have branches that represent evolutionary time and amount of change

Important Terms

Relatedness Refers to recency of common ancestry Two species are closely related if their most recent common ancestor lived closer to the present More distantly related if their most recent common ancestor lived in the distant past Think of you + a cousin Who is your most recent common ancestor? Think of you + a second cousin Provides a basis for assertion that you are more closely related to your first than your second cousin

Evolutionary trees come in a variety of shapes- do not get distracted by this!

Shared derived characteristics: used to construct cladograms Outgroup: does not have anything in common with the other organisms

COMMON ERROR: reading across the tips COMMON ERROR: reading across the tips. A quick glance at Figure A might suggest that A and B are closely related because their labels are right next to each other. This shows that part of the evolutionary history that was shared by B and E was NOT shared by A and B.

COMMON ERROR: reading tips as ancestors COMMON ERROR: reading tips as ancestors. Remember that biologists never view one living species as the ancestor of another.

COMMON ERROR: not realizing that cladograms can rotate at the nodes and still show the same relationships. Think of these as mobiles.

Remember that nodes can rotate.

COMMON ERROR: assuming when a population evolved or how much gene change occurred in a linage. You can only do this if it is marked. Cannot assume that the wolf evolved more recently than the otter We DO know that the most recent common ancestor of the wolf and otter lived BEFORE the most recent common ancestor of the wolf and coyote

If you are told, or if you see a legend on the tree, THEN you can say that the length of the lines represents genetic change or that the line length indicates time. Genetic change: Comparing a homologous gene for development allows the lines to proportionally represent amounts of genetic change in each lineage. The fruit fly gene is used as an outgroup.

Branch lengths can represent time:

More Important Terms Clade: a group of organisms that includes a common ancestor and all the descendants of that ancestor Also called a monophyletic group

More Important Terms How to identify a clade: A piece of a larger tree that can be cut away from the root with a single cut If you need to 2 cuts to extract a set of taxa, the group is non-monophyletic

Monophyletic, paraphyletic, and polyphyletic groups An ancestral species and ALL of its descendants. An ancestral species and some of its descendants, but not all of them. Some of its members have different ancestors.

More Important Terms & Ideas Every living species has a unique “clade address”—the list of nested clades to which it can be assigned Trees are hypotheses. They can be changed with new discoveries!

Is a crocodile more similar to a lizard or a bird? Is a crocodile more related to a lizard or a bird? Which ancestor—the one at node one or node two—lived closer to the present? Note that birds and mammals both are endotherms, have 4-chambered hearts, and have insulating skin coverings, but they are not closely related. This is an example of convergent evolution.

References Baum, D.A., & Offner, S. (2008). Phylogenies and tree-thinking. The American Biology Teacher, 70(4), 222-229. Baum, D.A., DeWitt Smith, S., & Donovan, S.S. (2005). The tree-thinking challenge. Science, 310(979). doi: 10.1126/science.1117727