Speciation

Question 1

Define speciation.

Answer 1

The process by which one species becomes two species.

Question 1

Define the morphological species concept.

Answer 1

Species are groups of individuals that share morphological characteristics in common.

Question 2

Describe the biological species concept.

Answer 2

Species are groups of actually or potentially interbreeding populations, which are reproductively isolated from other groups

Question 3

Who developed the biological species concept?

Answer 3

Theodosious Dobzhansky & Ernst Mayr

Question 4

What are the three types of reproductive isolation?

Answer 4

Premating
Post-mating, pre-zygotic
Post-zyogtic

Question 5

What is meant by premating as a type of reproductive isolation?

Answer 5

Different breeding/flowering times;
Incompatible sex organs
Prevents copulation

Question 6

What is post-mating, pre-zygotic reproductive isolation?

Answer 6

Mating but not fertilization

Question 7

What is post-zygotic reproductive isolation?

Answer 7

Offspring die or are infertile.

Question 8

Describe the phylogenetic species concept.

Answer 8

A cluster of organisms that form a monophyletic clade.

Question 9

What are the two steps to determining a species using the phylogenetic species concept?

Answer 9

o Estimating phylogeny
o Determining “groups”

Question 10

Describe the pros of the morphological species concept (3).

Answer 10

• Easy, anyone can do it
• Doesn’t require expensive genetics
• Objective criteria

Question 11

Describe the cons of the morphological species concept (4).

Answer 11

• Inaccurate, in part because what traits do you measure?
• Variation within species
• Cryptic species
• Convergent evolution

Question 12

Describe the pros of the biological species concept (3).

Answer 12

• Objective definition
• Experimentally testable
• Based on the biology of organisms

Question 13

Describe the cons of the biological species concept (3).

Answer 13

• Not always practical or ethical
• Infertility is not absolute
• Doesn’t work with everything (e.g., asexual species like bacteria)

Question 14

Describe the pros of the phylogenetic species concept (3).

Answer 14

• Applicable to any group of organisms
• Reflects evolutionary history
• Objective

Question 15

Describe the cons of the phylogenetic species concept (5).

Answer 15

• Expensive and time consuming
• Doesn’t necessarily reflect biology of species and mating
• Genes vary in rates of evolution
• Which gene?
• Might not be able to recognize different species

Question 16

What are the three general types of speciation?

Answer 16

Allopatric
Parapatric
Sympatric

Question 17

Describe allopatric speciation.

Answer 17

o Occurs when a single population of the same species is geographically separated into two or more populations by a geographical barrier
o Through time the separated populations diverge into separate species

Question 18

What two mechanisms lead to the divergence of species in allopatric speciation?

Answer 18

Genetic drift
Natural selection

Question 19

What are the two types of allopatric speciation?

Answer 19

Vicariance
Dispersal

Question 20

Describe vicariance allopatric speciation.

Answer 20

Occurs when a single population of the same species is split into two by a new geographical barrier and through time the separated populations diverge into separate species

Question 21

What are the mechanisms for vicariance?

Answer 21

 Randomly mating population
 Separated by a barrier – NO GENE FLOW
 Divergence in isolation: Natural selection and genetic drift

Question 22

Give examples of vicariance speciation discussed in class (2).

Answer 22

 Chimps -> bonobos via Congo River
 Abert squirrel -> Kaibab squirrel via Grand Canyon

Question 23

What is believed to be the most important mechanism of speciation?

Answer 23

Dispersal (allopatric speciation)

Question 23

Describe the dispersal form of allopatric speciation.

Answer 23

o Occurs when populations of the same species are geographically separated from each other because some individuals disperse away from the parent population

Question 23

Describe the mechanism of allopatric speciation via dispersal.

Answer 23

 Randomly mating population  Some individuals migrate away – NO GENE FLOW  Divergence in isolation: Natural selection and genetic drift

Question 24

Give an example of allopatric speciation via dispersal discussed in class.

Answer 24

Darwin's finches

Question 25

Describe parapatric speciation.

Answer 25

o Occurs when a single population diverges into two species at its geographic extremes without a physical barrier

Question 26

Describe sympatric speciation.

Answer 26

Occurs when a single population of one species splits into two species without any geographical barrier or separation

Question 27

Describe the mechanism of sympatric speciation.

Answer 27

 Randomly mating population  Strong potential for GENE FLOW  Populations diverge to be reproductively isolated

Question 28

Give an example of sympatric speciation discussed in class.

Answer 28

Apple maggot fly (Hawthornes and apples, different development time)

Question 29

What did Coyne and Orr 2004 establish about sympatric speciation? (4)

Answer 29

 Largely overlapping geographic ranges  Speciation must be complete  Must be sister species  “…history of the groups must make the existence of an allopatric phase very unlikely”

Question 30

Why is sympatric speciation likely to be rare?

Answer 30

The conditions for sympatric speciation are restrictive

Question 31

Within sexual populations, when is sympatric speciation only likely? (2)

Answer 31

When there is strong divergent selection for a population to adapt to two resources, AND When there is simultaneous selection for positive assortative mating

Question 32

Explain why some species have more lineages than others and provide an example.

Answer 32

 Number of species is a function of diversification rate and age of lineage  Some species diversify very quickly over time (e.g., birds) and thus have more lineages

Question 33

How is diversification rate calculated?

Answer 33

Diversification rate = speciation rate – extinction rate

Question 34

Provide the three explanations for why some geographic regions have more species than others.

Answer 34

1. High rates of speciation 2. Low rates of extinctions 3. The area is older, and has accumulated more species through time