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Interpreting Cladograms Notes 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) What is a Cladogram ● A diagram which shows ● Is not an evolutionary ___________ among tree, ___________show organisms. how ancestors are related ● Lines branching off other to descendants or how lines. The lines can be much they have changed traced back to where they branch off. These branching off points represent a hypothetical ancestor. Parts of a Cladogram Reading Cladograms ● Read like a family tree: show ________of shared ancestry between lineages. • When an ancestral lineage______: speciation is indicated due to the “arrival” of some new trait. Each lineage has unique ____to itself alone and traits that are shared with other lineages. each lineage has _______that are unique to that lineage and ancestors that are shared with other lineages — common ancestors. Quick Question #1 ●What is a_________? ● 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 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. Quick Question #2 ●What is an__________? ● A taxon outside of the group of interest. Outgroup All members of the group of interest are more closely related to each other than they are to the outgroup. Outgroups give you a sense of where on the bigger tree of life the main group of organisms falls. Quick Question #3 ●What is a_________? ● Species, family, or class 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 #4 ● 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. • __________can be compared across organisms • physical traits • genetic sequences • behavioral traits. BUT HOW DO WE CONSTRUCT A CLADOGRAM? ? 3 Alternative, mutually How Do We Choose exclusive Cladograms Between Them? INGROUP ORGANISMS Characters PP RD PC Fur/Mane No Yes Yes Yes Toes/Foot Many Toes One Hoof One Hoof One Hoof Wings No No Yes Yes Horn No No No Yes Eyes Yes Yes Yes Yes Tail Yes Yes Yes Yes Mouth Yes Yes Yes Yes Outgroup Primitive (ancestral) State Derived States INGROUP ORGANISMS Characters Outgroup PP RD PC Fur/Mane No Yes Yes Yes Toes/Foot Many Toes One Hoof One Hoof One Hoof Wings No No Yes Yes Horn No No No Yes Eyes Yes Yes Yes Yes Tail Yes Yes Yes Yes Mouth Yes Yes Yes Yes Derived character states 3 Steps found in only one organism Horn (evolutionary separate them from other transitions from organisms Wings ancestral → derived) to explain this tree Fur/Mane One Hoof Ancestral characters Eyes shared by all taxa link Tail organisms together Mouth Taxa Characters Outgroup RD PP PC Fur/Mane No Yes Yes Yes Toes/Foot Many Toes One Hoof One Hoof One Hoof Wings No Yes No Yes Loss of Wings Wings 4 Steps (with Wings wings developing convergently) Fur/Mane OR One Hoof Wings 4 Steps (with wings developing in ancestral pony, and lost in PP) Taxa Characters Outgroup PC PP RD Fur/Mane No Yes Yes Yes Toes/Foot Many Toes One Hoof One Hoof One Hoof Wings No Yes No Yes Loss of Wings Wings 4 Steps (with Wings wings developing convergently) Fur/Mane OR One Hoof Wings 4 Steps (with wings developing in ancestral pony, and lost in PP) 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 4 Steps.
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