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?

1837 “The most important diagram in biology” Steve Jones 2009

What is a phylogenetic tree? 1859

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

3

Which of the four phylogenies shown below is false given the larger phylogeny above? 4

If you were to add a trout to the phylogeny shown above, where would its lineage attach to the rest of the tree? 5

Part 2 How to infer shared ancestry

Which of the five letters in the phylogeny above corresponds to the most recent common ancestor of a mushroom and a sponge? 6

Part 3 How to interpret relationships

According to the phylogeny shown above, which of the following statements is true? AA green alga is more closely related to a red alga than to a moss. BA green alga is more closely related to a moss than to a red alga. CA green alga is equally related to a red alga and a moss. DA green alga is related to a red alga, but is not related to a moss. 7

According to the phylogeny shown above, which of the following statements is true? AA crocodile is more closely related to a lizard than to a bird. BA crocodile is more closely related to a bird than to a lizard. CA crocodile is equally related to a lizard and a bird. DA crocodile is related to a lizard, but is not related to a bird. 8

According to the phylogeny shown above, which of the following statements is true? AA seal is more closely related to a horse than to a whale. BA seal is more closely related to a whale than to a horse. CA seal is equally related to a horse and a whale. DA seal is related to a whale, but is not related to a horse. 9

Part 4 How to infer evolutionary change

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? ALong tail, ear flaps, external testes and fixed claws BShort tail, no ear flaps, external testes and fixed claws CShort tail, no ear flaps, abdominal testes and fixed claws DShort tail, ear flaps, abdominal testes and fixed claws ELong tail, ear flaps, abdominal testes and retractable claws 10

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? ALepidodendron DPsilotum BClubmoss EFern COak 11

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 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

An example

Links Tree thinking challenge Downloadable graphic image of the tree of life