Building Cladograms

Question 1

Cladogram

Answer 1

def: A diagram representing the hypothetical relationship between a group of organisms

Question 2

why do we use Cladistics?

Answer 2

We use cladistics to
1. classify organisms based on their evolutionary history
2. Results in a HYPOTHESIS of evolutionary relationships that have predictive power
A visual representation of this relationship is a cladogram

Question 3

Branch

Answer 3

The arm of the cladogram, representing an evolutionary lineage

Question 4

Scaled tree

Answer 4

Branch lengths are proportional to the number of changes in the DNA which occur between species on that branch

Question 5

Unscaled tree

Answer 5

• branch lengths are not proportional

- (We mainly deal with these trees)

Question 6

Ancestral trait

Answer 6

-older trait

Question 7

Derived trait

Answer 7

-newer trait
-Character can be gained or lost, but must be changed from the ancestral trait
-Absent in the last common ancestor of the group being considered
(Relationship of traits is always relative to the particular group being considered)

Question 8

Apomorphy

Answer 8

-An evolutionary novelty that is different from the plesiomorphy
-derived trait, de novo mutations
(again, a relative term)

Question 9

Synapomorphy

Answer 9

• type of apomorphy

- Apomorphy shared across several species in a group

Question 10

Autapomorphy

Answer 10

• type of apomorphy
• An apomorphy that arises in a single lineage
• Useful for species identification, not as useful for building trees.

Question 11

Homoplasy

Answer 11

• type of apomorphy
• An apomorphy shared by more than one species in the group being assessed, but not present in the last common ancestor
• ex. wings in birds and bats
• Bad when making a cladogram

Question 12

Plesiomorphy

Answer 12

• The ancestral trait(s) in a cladogram

- Plesiomorphies reveal nothing about relationships

Question 13

Monophyletic

Answer 13

-group containing all descendants of a single common ancestor
= clade
-when making a cladogram, monophyletic groups should be defined based on the occurrence of synaptomorphies

Question 14

Paraphyletic

Answer 14

-group containing all descends of a single common ancestor, however where one or more of the monophyletic groups have been removed

Question 15

Polyphyletic

Answer 15

• group not descended from a common ancestor

- convergent evolution

Question 16

Clade

Answer 16

monophyletic group

Question 17

Ingroup

Answer 17

all taxa being considered/grouped in your analysis

Question 18

Outgroup

Answer 18

related taxa outside your group

• NOT the last common ancestor
• It also descended from the last common ancestor, but bery unrelated to all other taxa in the ingroup

Question 19

Sister group

Answer 19

groups that are each other’s closest relative

Question 20

Internal node

Answer 20

hypothetical last common ancestor of all resulting species

Question 21

Terminal node

Answer 21

most recent species of the evolutionary ine

Question 22

Polarity

Answer 22

• Outgroup determines character polarity

- which characters are to be classified as plesiomorphic and which characters are to be classified as apomorphic

Question 23

Characters

Answer 23

1

Question 24

Binary characters

Answer 24

present and absent

Question 25

Multistate characters

Answer 25

when characters have multiple apomorphic states

Question 26

Parsimony principle

Answer 26

you should always choose the simplest scientific explanation that fits the evidence
(if you hear hoofbeats think horses, not zebras)

Question 27

Consensus tree

Answer 27

Single tree that shows information that is common to all or most of the multiple equally parsimonious trees

Question 28

Strict consensus tree

Answer 28

Shows only information in ALL equally parsimonious trees

-can result in polytomy

Question 29

Polytomy

Answer 29

Nodes with more than two branches arising at the same point

Question 30

Majority rules tree

Answer 30

Shows information common to a specified percentage (ie. 50%, 70%) of the multiple equally parsimonious trees

Question 31

Tree length

Answer 31

the number os steps (character state changes) on tree

• directly related to character numbers: more characters = longer tree
• A longer tree is not necessarily worse than one made with a different character size

Question 32

Consistency index

Answer 32

Measure of homoplasy on a tree
-Ideally each character state arises once - no homoplasy
minimum steps/actual steps

Question 33

Bootstrap support

Answer 33

High bootstrap value = branch is strongly supported by characters

• strong support = multiple apomorphies with no homoplasy
• not as strong = single apomorphies, homoplasious characters states, weak character states (maybe qualitative such as behaviour)

Question 34

Which tree is preferable?

Answer 34

-more reliable characters
better fit to other data - molecular, ecological, behavioural, zoogeographic
-one tree may be more in line with existing classification