Phylogenies Depict ancestor and descendent relationships among organisms based on homology These evolutionary relationships are represented by cladograms branching diagrams that organize those relationships ID: 547948
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Slide1
Big Ideas: Phylogenies Depict ancestor and descendent relationships among organisms based on homologyThese evolutionary relationships are represented by cladograms, branching diagrams that organize those relationships
Interpreting CladogramsSlide2
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. Slide3
Reading Cladogram: Identifying CladesUsing a cladogram, it is easy to tell if a group of lineages forms a clade, a group that includes a common ancestor and all the descendants (living and extinct) of that ancestor.
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)Slide4
Quick Question
Looking at the image to the right:
Which of the boxes in the figure depict a clade (if any)? Why?Slide5
Reading Cladograms: CladesClades are nested within one another they form a nested hierarchy. A clade may include many thousands of species or just a few.Slide6
Interpreting CladogramsCladograms can be misinterpreted. They do not imply that some organisms are more "advanced" than others.When reading a cladogram, it is important to keep three things in mindSlide7
(mis)Interpreting Cladograms: OneEvolution produces a pattern of relationships among lineages that is tree-like, i.e. branching.Evolution does not produce step-wise relationships of one taxa becoming another and so on.Slide8
(mis)Interpreting Cladograms: TwoWe tend to read phylogenies from left to right, just as we read text. Please note, however, that there is NO correlation between a cladogram from reading left to right and "advancement“ or “progression”.Slide9
(mis)Interpreting Cladograms: ThreeFor 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:Slide10
Quick Question
This is a
cladogram
of vertebrates.
What do you think are represented by the red lines? Slide11
Creation of CladogramsGiven 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
traitsgenetic sequencesbehavioral
traits.Slide12
?
BUT
HOW
DO WE CONSTRUCT A CLADOGRAM?Slide13
3 Alternative,
m
utually exclusive
Cladograms
How Do We Choose Between Them?Slide14
Outgroup
(Not an Ancestor, but a Stand-in to represent the Ancestral Condition)
PP
RD
CE
Fur/Mane
NoYesYesYesToes/FootMany Toes
One HoofOne HoofOne HoofWings
No
NoYes
Yes
Horn
No
No
No
Yes
Eyes
Yes
Yes
Yes
Yes
Tail
Yes
Yes
Yes
Yes
Mouth
Yes
Yes
Yes
Yes
Primitive (ancestral) State
Derived States
Characters
INGROUP ORGANISMSSlide15
Outgroup
PP
RD
CE
Fur/Mane
No
YesYesYesToes/FootMany Toes
One HoofOne HoofOne 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
Characters
INGROUP ORGANISMS
Fur/Mane
One Hoof
Wings
Horn
Eyes
Tail
Mouth
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 treeSlide16
Outgroup
PP
RD
CE
Fur/Mane
No
YesYesYesToes/FootMany Toes
One HoofOne HoofOne Hoof
Wings
No
No
Yes
Yes
Characters
Taxa
Fur/Mane
One Hoof
Wings
Wings
4 Steps (with wings developing
convergently
)
Wings
Loss of Wings
4 Steps (with wings developing in ancestral pony, and lost in PP)
ORSlide17
Outgroup
PP
RD
CE
Fur/Mane
No
YesYesYesToes/FootMany Toes
One HoofOne HoofOne Hoof
Wings
No
No
Yes
Yes
Characters
Taxa
Fur/Mane
One Hoof
Wings
Wings
4 Steps (with wings developing
convergently
)
Wings
Loss of Wings
4 Steps (with wings developing in ancestral pony, and lost in PP)
ORSlide18
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?Slide19
Lets build a
Chocolate
Cladogram
!