Week 2: Phylogeny and Evolutionary History

Question 1

What is Linnaean taxonomy?

Answer 1

arranged organisms in hierarchical classification.

Question 2

What is phylogenetic systematics?

Answer 2

classify organisms according to evolutionary history.

Question 3

What is phylogeny?

Answer 3

branching relationships of populations as they give rise to multiple descendant populations over evolutionary time.

Question 4

What are characters?

Answer 4

any observable characteristics of organisms.

Question 5

What are traits? Why are they critical to phylogeny?

Answer 5

specific values of a character (ie. brown fur). Traits are critical to phylogeny because 1) use observations of traits to infer patterns of ancestry - represent as a phylogenetic tree. 2) By mapping additional traits onto phylogeny already created, we can study sequence and timing of evolutionary events.

Question 6

What is parsimony?

Answer 6

the relationships that requires the smallest number of character changes is most likely to be correct.

Question 7

What is an outgroup?

Answer 7

is a taxon related to the groups of interest but branched off earlier in history.

Question 8

What is a sister taxa?

Answer 8

derived from same node

Question 9

What is a polytomy?

Answer 9

a node with more than two branches - relationships between are uncertain.

Question 10

What is a monophyletic group?

Answer 10

taxonomic group consisting of all descendants of most common ancestor and no other members.

Question 11

What is a clade?

Answer 11

represents a group of species that share a single recent common ancestor.

Question 12

What is a polyphyletic group?

Answer 12

is not a monophyletic group - do not represent proper evolutionary clades - most are no longer used in modern systematics.

Question 13

What is a paraphyletic group?

Answer 13

contains groups most common ancestor but not all its descendants.

Question 14

What are rooted vs. unrooted trees?

Answer 14

Rooted trees - common lineage. Unrooted trees - do not indicate direction of time - branch tips represent more recent species than those represented by interior nodes - correspond to rooted trees. If unrooted tree has k branches - there are k corresponding rooted trees.

Question 15

What are the differences between cladograms, phylograms and chronograms?

Answer 15

Trees without different branch lengths are cladograms and trees with are phylograms. Trees in which branch lengths represent actual time are chronograms.

Question 16

What is a homologous trait?

Answer 16

found on 2+ species because they have inherited them from ancestor.

Question 17

What is an analogous trait?

Answer 17

shared by 2+ species - not because of common descent - because of some other evolutionary process (usually natural selection) has independently fashioned similar traits in each species

Question 18

What is divergent evolution?

Answer 18

closely related populations diverge because natural selection operates differently on each of them.

Question 19

What is convergent evolution? And an example?

Answer 19

2 or more populations become more similar because they are exposed to similar selective conditions. aposematic coloration in frogs - bright warning colors. Aposematic coloration and toxicity are polyphyletic - caused by convergent evolution

Question 20

What is a derived trait?

Answer 20

derived from ancestor

Question 21

What is a synapomorphy?

Answer 21

shared derived trait - help uncover evolutionary relationships.

Question 22

What is a homoplasy?

Answer 22

An analogous trait is homoplasy - trait similar in 2+ species but was not present in a common ancestor - can be misleading when constructing evolutionary tree.

Question 23

What is a symplesiomorphy?

Answer 23

Symplesiomorphy - very recently derived and is not shared

Question 24

How should you avoid being confused when making phylogenetic trees?

Answer 24

To avoid being confused 1. pick traits likely to be synapomorphies rather than symplesiomorphies. 2. Use a large number of characters. 3. Use an outgroup - one with known evolutionary relationship to the taxon we are studying - by using multiple - better estimate the polarity - order of appearance of traits using.

Question 25

How do we combat misleading phylogenies derived from morphological characteristics>

Answer 25

Phylogenies derived from morphological characteristics can be misleading - especially when multiple characters have undergone convergent evolution. Now, use DNA sequencing to combat this.

Question 26

What is beneficial about adding traits to preexisting phylogenetic tree?

Answer 26

When traits are placed on a preexisting phylogenetic tree - hypotheses about when traits evolved and which traits may be shared among which groups of relatives.

Question 27

What are vestigial traits and 3 explanations for them?

Answer 27

Vestigial traits - have no known current function but appear to have been important in past. 3 explanations: 1) trait is not costly to organism - natural selection does not act against it. 2) There is some natural selection against it or it would have been lost. 3) the trait has some function that we have not identified - making it not vestigial. Can help us find evolutionary relationships.