Post on 16-Dec-2015
transcript
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)
Interpreting Cladograms Notes
Reading Cladograms
• 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.
Read like a family tree: show patterns of shared ancestry between lineages.
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?
Outgroup
(Not an Ancestor, but a Stand-in to represent the Ancestral Condition)
PP RD PCFur/Mane No Yes Yes YesToes/Foot Many Toes One Hoof One Hoof One HoofWings No No Yes YesHorn No No No YesEyes Yes Yes Yes YesTail Yes Yes Yes YesMouth Yes Yes Yes Yes
Primitive (ancestral) State Derived States
CharactersINGROUP ORGANISMS
Outgroup PP RD PCFur/Mane No Yes Yes YesToes/Foot Many Toes One Hoof One Hoof One HoofWings No No Yes YesHorn No No No YesEyes Yes Yes Yes YesTail Yes Yes Yes YesMouth Yes Yes Yes Yes
CharactersINGROUP ORGANISMS
Fur/ManeOne Hoof
Wings
Horn
EyesTailMouth
Ancestral characters shared by all taxa link organisms together
Derived character states found in only one organism separate them from other organisms
3 Steps (evolutionary transitions from ancestral derived) to explain this tree
Outgroup PPRD PCFur/Mane No YesYes YesToes/Foot Many Toes One HoofOne Hoof One HoofWings No NoYes Yes
CharactersTaxa
Fur/ManeOne Hoof
Wings
Wings4 Steps (with wings developing convergently)
Wings
Loss of Wings
4 Steps (with wings developing in ancestral pony, and lost in PP)
OR
Outgroup PP RDPCFur/Mane No Yes YesYesToes/Foot Many Toes One Hoof One HoofOne HoofWings No No YesYes
CharactersTaxa
Fur/ManeOne Hoof
Wings
Wings4 Steps (with wings developing convergently)
Wings
Loss of Wings
4 Steps (with wings developing in ancestral pony, and lost in PP)
OR
3 Steps
4 Steps
4 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?