This document introduces phylogenetic trees and how to read them. It explains that phylogenetic trees show the evolutionary relationships among organisms and depict their shared ancestry over time. Key parts of phylogenetic trees are identified, including terminal taxa, internal and terminal branches, internal nodes, and the root node. The document emphasizes that phylogenetic trees are simplifications of the complex process of evolution and speciation over long periods of time. It also notes that rotating branches on a tree does not change the relatedness shown, only the appearance.

1. Introduction to Phylogeny:
Reading Phylogenetic
Trees
“Nothing in biology makes sense except in
the light of evolution”
T.H. Dobzhansky (1973)
Dr. Rachel Mackelprang

2. Introduction to phylogeny
•Phylogeny is a description of the evolutionary
history of relationships among organisms
•Portrayed in a diagram called a phylogenetic tree
•The Tree of Life refers to the concept that all living
organisms are related to one another through shared
ancestry

3. Phylogeny was central to Darwin’s work on natural
selection
“I think” tree
First published tree
On the Origin of Species

4. How to read a
phylogenetic
tree

5. How to read a
phylogenetic
tree
This is the common ancestor to all
groups on the tree. It is called the
root

6. How to read a
phylogenetic
tree
This is the common ancestor to all
groups on the tree. It is called the
root
The splits in the branches are
called nodes and indicate a
division of one lineage into two.

7. How to read a
phylogenetic
tree
This is the common ancestor to all
groups on the tree. It is called the
root
The splits in the branches are
called nodes and indicate a
division of one lineage into two.
The positions of the
notes on the time
scale indicate the
times of the
corresponding
species event

8. Phylogenetic trees are simplifications of species
evolution

9. Phylogenetic trees are simplifications of species
evolution

10. Phylogenetic trees are simplifications of species
evolution
Speciation is the
process whereby one
species gives rise to two
descent species
If B and C are species
descended from A, then
the branching (splitting)
point represents the
speciation event

11. Phylogenetic trees are simplifications of species
evolution
Draw simplified branches

12. Phylogenetic trees are simplifications of species
evolution
Remove the complex
backboneA
B
C

13. Phylogenetic trees are simplifications of species
evolution
Now imagine the
process occurring at a
larger time scale.
Phylogenies are the
result of multiple
speciation events over
long periods of time
A
B
C
D
E

14. Phylogenetic trees are simplifications of species
evolution
Now imagine the
process occurring at a
larger time scale.
Phylogenies are the
result of multiple
speciation events over
long periods of time
A
B
C
D
E

15. Phylogenetic trees are simplifications of species
evolution
Remove the complex
backbone
A
B
C
D
E

16. Horizontal tree

17. Vertical tree

18. Parts of a phylogenetic tree
A phylogeny of taxa a-h

19. Parts of a phylogenetic tree
A phylogeny of taxa a-h
Terminal (or tip) taxa

20. Parts of a phylogenetic tree
A phylogeny of taxa a-h
Terminal (or tip) taxa Terminal branches

21. Parts of a phylogenetic tree
A phylogeny of taxa a-h
Terminal (or tip) taxa Terminal branches
Internal nodes

22. Parts of a phylogenetic tree
A phylogeny of taxa a-h
Terminal (or tip) taxa Terminal branches
Internal nodes Internal branches

23. Parts of a phylogenetic tree
A phylogeny of taxa a-h
Terminal (or tip) taxa Terminal branches
Internal nodes Internal branches
Root node

24. Branch rotation

25. Branch rotation
Rotation around the node that connects h and g

26. Branch rotation
“Order” left-to-right has no meaning on a vertical
tree

27. Branch rotation
After rotation the tree has the same meaning

28. Questions of relatedness
Both trees say the same thing. g and h share a more
recent common ancestor with each other than either
does with f Present
Past

29. Questions of relatedness
Both trees say the same thing. g and h share a more
recent common ancestor with each other than either
does with f Present
Past
Relative
relatedness of
taxa is a question
of how recently
they share
common ancestry

30. Kahoot
Take out your smart phone, tablet, or laptop
Go to kahoot.it

31. Kahoot question 1
a b c d e f g h abcdefgh
Do both of these trees show the same information?

32. Kahoot question 2
a b c d e f g h a b c d e f g h
Do both of these trees show the same information?

33. Kahoot question 3
a b c d e f g h a b c d e fgh
Do both of these trees show the same information?

34. Kahoot question 4
Is taxon e more closely related to d or to h?
Recall: Relative
relatedness of
taxa is a question
of how recently
they share
common ancestry

35. Kahoot question 5
Is taxon d more closely related to c or to f?
Recall: Relative
relatedness of
taxa is a question
of how recently
they share
common ancestry