Ch 23: Systematics, Phylogenies, & Comparative Biology

Question 0

Phylogeny

Answer 0

-Hypothesis about patterns of relationships among species

Question 1

Systematics

Answer 1

- The reconstruction and study of 
   evolutionary relationships.
-Biologists group organisms
based on shared characteristics & newer molecular sequence data.
        -since fossil records are not 
         complete scientists rely on 
         other types of evidence to 
         determine evolutionary 
         relationships.

Question 2

Cladogram

Answer 2

• A tree of similarities and differences between species

- Depicts a hypothesis of evolutionary relationships

Question 3

Branching Tree

Answer 3

Darwin: all species come from a single common ancestor; history can be depicted as a branching tree.

Question 4

Problem W/ Phylogeny based on similarities.

Answer 4

• Similarity may not accurately predict evolutionary relationships
• Rates of evolution vary
• Evolution may not be unidirectional
• Evolution is not always divergent

Question 5

Convergent Evolution

Answer 5

Similar characteristics not derived from common ancestry

Question 6

Derived characteristic

Answer 6

Similarity that is inherited from the most recent common ancestor of an entire group.

Question 7

Ancestral characteristics

Answer 7

Similarities that arose prior to the common ancestor of the group.

Question 8

Synapomorphies

Answer 8

• Derived characters shared by clade members

- In cladistics, only shared derived characteristics are considered informative about evolutionary relationships

Question 9

Cladistic Method

Answer 9

• Requires that character variation be identified as ancestral or derived.
• Characters can be any aspect of the phenotype including morphology, physiology, behavior, and DNA

Question 10

Character States

Answer 10

• Presents vs. absence
• Example: character “teeth” in amniote vertebrates have two states: present in most mammals and reptiles, and absent in birds and turtles

Question 11

Outgroup Comparison

Answer 11

Usually avail fossils don’t rep most recent common ancestor:
outgroup comparison used to assign character polarity.

Outgroup:
- A species/group of species, but 
  not member of group studied.
- When group studied shows 
  multi. character states, & 1 is 
  shown by outgroup, state is 
  ancestral and others are 
  derived.
- Outgroup species do not always 
  exhibit the ancestral condition.

Question 12

Clade

Answer 12

Species that share a common ancestor- shown by the having shared derived characters.

Question 13

Plesiomorphies

Answer 13

Ancestral character states.

Question 14

Symplesiomorphies

Answer 14

• Shared ancestral states (shared plesiomorphies)
• reflect character states inherited from distant ancestor. Do not imply that species exhibiting state are closely related

Question 15

Homoplasy

Answer 15

A shared character state that has not been inherited from a common ancestor.

Question 16

Evolutionary reversal

Answer 16

Return to ancestral state

Question 17

Principle of Parsimony

Answer 17

Systematists rely on this principle which favors the hypothesis that requires the fewest assumptions.
-The Cladogram that requires the fewest number of evolutionary changes is favored

Question 18

Classification

Answer 18

How we place species and higher groups I to the taxonomic hierarchy.

Question 19

Monophyletic Group

Answer 19

Includes most recent common ancestor of group and all it’s descendants.

Question 20

Paraphyletic Group

Answer 20

Includes most recent common ancestor. But not all descendants.

Question 21

Polyphyletic Group

Answer 21

Does not include most recent common ancestor of group.

Question 22

Phylogenetic Species Concept

Answer 22

Species is a pop or set of pops characterized by one or more shared derived characters
   - Controversial: "splitting" - will 
     lead to recognition of even 
     slightly diff pops as distinct 
     species.

Question 23

Phylogenetic Analysis

Answer 23

Determines homologous vs analogous

Question 24

Analogous Structures

Answer 24

Similar function due to similar selection pressure, but are not homoplastic (not the same structure).