Tree thinking in scholarship biology
Rob Cruickshank
Department of Ecology
Lincoln University
“Just as beginning students in geography
need to be taught how to read maps, so
beginning students in biology should be
taught how to read trees and to understand
what trees communicate”
Robert O’Hara 1997
What is a phylogenetic tree?
What is a phylogenetic tree?
What is a phylogenetic tree?
“The most
important
diagram in
biology”
Steve Jones
2009
1837
What is a phylogenetic tree?
1859
Variations on a theme
Variations on a theme
Variations on a theme
Variations on a theme
Variations on a theme
Variations on a theme
These trees are identical
Which tree is different?
1
Part 1
How to read a phylogeny
Which of the four phylogenies shown below depicts a
different pattern of relationships to the others?
2
Which of the four phylogenies shown below depicts a
different pattern of relationships to the others?
3
4
Which of the four phylogenies shown below is false given
the larger phylogeny above?
5
If you were to add a trout to the phylogeny shown above,
where would its lineage attach to the rest of the tree?
Part 2
How to infer shared ancestry
6
Which of the five letters in the phylogeny above
corresponds to the most recent common ancestor of a
mushroom and a sponge?
Part 3
How to interpret relationships
7
According to the phylogeny shown above, which of the
following statements is true?
A A green alga is more closely related to a red alga than
to a moss.
B A green alga is more closely related to a moss than to a
red alga.
C A green alga is equally related to a red alga and a moss.
D A green alga is related to a red alga, but is not related
to a moss.
8
According to the phylogeny shown above, which of the
following statements is true?
A A crocodile is more closely related to a lizard than to a
bird.
B A crocodile is more closely related to a bird than to a
lizard.
C A crocodile is equally related to a lizard and a bird.
D A crocodile is related to a lizard, but is not related to a
bird.
9
According to the phylogeny shown above, which of the
following statements is true?
A A seal is more closely related to a horse than to a
whale.
B A seal is more closely related to a whale than to a
horse.
C A seal is equally related to a horse and a whale.
D A seal is related to a whale, but is not related to a
horse.
Part 4
How to infer evolutionary change
10
In the phylogeny shown above, assume that the ancestor had a
long tail, ear flaps, external testes and fixed claws. Assuming all
evolutionary changes are shown, what traits do sea lions have?
A Long tail, ear flaps, external testes and fixed claws
B Short tail, no ear flaps, external testes and fixed claws
C Short tail, no ear flaps, abdominal testes and fixed claws
D Short tail, ear flaps, abdominal testes and fixed claws
E Long tail, ear flaps, abdominal testes and retractable claws
11
In the phylogeny shown above, assume that the ancestor was not a
tree and did not have leaves or seeds. Assuming all evolutionary
changes are shown, which of the tips is a tree without leaves?
A Lepidodendron
B Clubmoss
C Oak
D Psilotum
E Fern
Part 5
Common mistakes
and how to avoid them
Living organisms are not primitive
“It is absurd to talk of
one animal being
higher than another”
Charles Darwin 1837
Living organisms are not primitive
Living organisms are not primitive
Living organisms are not ancestors
Humans are not
descended from
chimpanzees, rather
humans and
chimpanzees share a
common ancestor
that was neither a
human nor a
chimpanzee
Lineages are not basal
Lineages are not basal
Lineages are not basal
Lineages are not basal
Lineages are not basal
An example
Links
Tree thinking challenge
http://www.tree-thinking.org/publications.html#science310
Downloadable graphic image of the tree of life
http://www.zo.utexas.edu/faculty/antisense/downloadfilestol.html