Interpreting Cladograms Notes INTERPRETING CLADOGRAMS BIG IDEA PHYLOGENIES

Interpreting Cladograms Notes INTERPRETING CLADOGRAMS BIG IDEA: PHYLOGENIES DEPICT ANCESTOR AND DESCENDENT RELATIONSHIPS AMONG ORGANISMS BASED ON HOMOLOGY THESE EVOLUTIONARY RELATIONSHIPS ARE REPRESENTED BY DIAGRAMS CALLED CLADOGRAMS (BRANCHING DIAGRAMS THAT ORGANIZE RELATIONSHIPS)

Reading Cladograms � Read like a family tree: show patterns of shared ancestry between lineages. • When an ancestral lineage splits: speciation is indicated due to the “arrival” of some new trait. Each lineage has unique traits to itself alone and traits that are shared with other lineages. each lineage has ancestors that are unique to that lineage and ancestors that are shared with other lineages — common ancestors.

Quick Question #1 �What is our definition of a clade? �(look back to zoology notes #1 if you cannot remember) �A group that includes a common ancestor and all the descendants (living and extinct) of that ancestor.

Reading Cladogram: Identifying Clades �Using a cladogram, it is easy to tell if a group of lineages forms a clade. � Imagine clipping a single branch off the phylogeny all of the organisms on that pruned branch make up a clade So everything in the pink circle is a clade (common ancestor and all descendants)

Quick Question #2 �Looking at the image to the right: �Is the green box a clade? �The blue? �The pink? �The orange?

Reading Cladograms: Clades �Clades are nested within one another they form a nested hierarchy. �A clade may include many thousands of species or just a few.

Interpreting Cladograms �it's easy to misinterpret cladograms as implying that some organisms are more "advanced" than others �however, cladograms don't imply this at all. �when reading a cladogram, it is important to keep three things in mind

(mis)Interpreting Cladograms: One �Evolution produces a pattern of relationships among lineages that is tree-like, not ladder-like.

(mis)Interpreting Cladograms: Two �Just because we tend to read phylogenies from left to right, there is no correlation with level of "advancement. "

(mis)Interpreting Cladograms: Three �For any speciation event on a phylogeny, the choice of which lineage goes to the right and which goes to the left is arbitrary. The following phylogenies are equivalent:

Interpreting Phylogenies: Human Example � The points described above cause the most problems when it comes to human evolution. � It is important to remember that: Humans did not evolve from chimpanzees. Humans and chimpanzees are evolutionary cousins and share a recent common ancestor that was neither chimpanzee nor human. Humans are not "higher" or "more evolved" than other living lineages. Since our lineages split, humans and chimpanzees have each evolved traits unique to their own lineages.

Quick Question #3 �What is this called? �What do you think the red lines represent? �

Creation of Cladograms �Given a set of observations, phylogenetic analysis seeks to find the simplest branching relationships between organisms to depict their evolution. �Heritable traits possessed by organisms, characters, are used to compare the organisms being studied. • Characters can be compared across organisms • physical traits • genetic sequences • behavioral traits.

BUT HOW DO WE CONSTRUCT A CLADOGRAM? ?

3 Alternative, mutually exclusive Cladograms How Do We Choose Between Them?

INGROUP ORGANISMS Characters PP RD PC Fur/Mane No Yes Yes Toes/Foot Many Toes One Hoof Wings No No Yes Horn No No No Yes Yes (Not an Ancestor, but a Eyes Yes Stand-in to represent the Yes Tail. Ancestral Condition) Yes Mouth Yes Outgroup Primitive (ancestral) State Yes Derived States

Characters Fur/Mane Toes/Foot Wings Horn Eyes Tail Mouth Outgroup No Many Toes No No Yes Yes 3 Steps (evolutionary transitions from ancestral derived) to explain this tree INGROUP ORGANISMS PP Yes One Hoof No No Yes Yes RD Yes One Hoof Yes No Yes Yes Derived character states found in only one organism separate them from other organisms PC Yes One Hoof Yes Yes Yes Horn Wings Fur/Mane One Hoof Ancestral characters shared by all taxa link organisms together Eyes Tail Mouth

Characters Fur/Mane Toes/Foot Wings Outgroup No Many Toes No RD Taxa Yes One Hoof No Loss of Wings 4 Steps (with wings developing convergently) OR 4 Steps (with wings developing in ancestral pony, and lost in PP) PP PC Yes One Hoof Yes Wings Fur/Mane One Hoof Wings

Characters Fur/Mane Toes/Foot Wings Outgroup No Many Toes No PC Taxa Yes One Hoof No Loss of Wings 4 Steps (with wings developing convergently) OR 4 Steps (with wings developing in ancestral pony, and lost in PP) PP RD Yes One Hoof Yes Wings Fur/Mane One Hoof Wings

3 Steps The preferred cladogram is the simplest! (Least number of assumptions) So, which cladogram is the best description of the evolution of these little ponies? 4 Steps