Lecture 9: Speciation

Question 1

What is a population?

Answer 1

Group of individuals from same species living in same area

Question 2

What is gene flow?

Answer 2

Movement of genes (alleles) among populations due to migration of individuals

Question 3

What is a species?

Answer 3

Group of interbreeding individuals that can produce viable and fertile offspring

Question 4

How do we determine if two organisms are members of the same species?

Answer 4

Take two organisms and see if they produce viable offspring

If they can, declare them the same species

Question 5

What is speciation?

Answer 5

Reduction/elimination of gene flow among populations due to evolution of reproductive barriers

Question 6

What are reproductive barriers?

Answer 6

Behaviors, physiological states, genetic makeup that prevent successful production of viable offspring

Question 7

What is the fate of most lineages?

Answer 7

Extinction

Question 8

What is panmixia?

Answer 8

Random mating among members of a population

Question 9

What does sympatric mean?

Answer 9

“Same land”

Two populations overlap completely

No gene flow restriction

Allows cross mating

100% gene flow between populations

Question 10

Panmixia occurs in ________.

Answer 10

Sympatric speciation

Question 11

What does parapatric mean?

Answer 11

Populations are adjacent to each other but no overlap

No panmixia

Some gene flow at hybrid zones

Question 12

What does allopatric mean?

Answer 12

“Different land”

Not adjacent and no overlap

Completely separated by geographic barrier

0% gene flow between populations

Question 13

How did Darwin think speciation worked?

Answer 13

• Believed sympatric was main form of speciation

•

Question 14

In _______ speciation, an ancestral population splits into two species without any geographic isolation

Answer 14

Sympatric

Question 15

Describe the process of allopatric speciation.

Answer 15

1. One population fragments into two populations (e.g., due to vicariance event)
2. Isolated populations diverge (through mutation and natural selection) in mating characteristics (genetics, physiological, morphological, behavioral)
3. Incompatible mating characteristics prevent production of viable/fertile offspring between members of two populations (reproductive barriers)
4. According to Biological Species Concept, a new species has formed

Question 17

Evolutionary theory implies that life evolved (and continues to evolve) randomly, or by chance

Answer 17

Things evolved but selection (non random process)

Question 18

Evolution results in progress; organisms are always getting better through evolution

Answer 18

Population adapt to local environment/conditions

Question 19

Individual organisms can evolve during a single lifespan.

Answer 19

Evolution takes generations

Question 20

Because evolution is slow, humans cannot influence it

Answer 20

Through genetic engineering and artificial selection

Question 21

Genetic drift only occurs in small populations

Answer 21

Occurs in both small and large populations

Has higher rate of influence on smaller populations

Question 22

Natural selection is not operating on humans currently

Answer 22

E.g., stabilizing selection of newborn skull sizes

Question 23

Natural selection involves organisms trying to adapt

Answer 23

Theology (nothing theological about evolution)

Question 24

The fittest organisms in a population are those that are strongest, healthiest, fastest, etc.

Answer 24

Fittest organisms create greatest number of offspring

Question 25

Natural selection is about survival of the very fittest individuals in a population

Answer 25

Natural selection does not equal survival of the fittest

Question 26

All traits of organisms are adaptations

Answer 26

Many traits evolve by drift

Question 27

Each trait is influenced by one Mendelian locus

Answer 27

Traits are polygenic (influenced by multiple loci simultaneously)

Question 28

What are prezygotic barriers? List and explain the different types.

Answer 28

Prezygotic barriers - prevent formation of zygote 1. Behavioral isolation - males perform species-species courtshsips recognized by females that belong to same species 2. Mechanical isolation - incompatible reproductive organs 3. Gametic isolation - mating attempt successful, but gametes are incompatible (no gene flow between species)

Question 29

What are postzygotic barriers? List and explain the different types.

Answer 29

• Postzygotic barriers - 1. Reduced hybrid viability/fertility

Question 30

Bottleneckint is most likely to occur during _______ speciation.

Answer 30

Peripatric

Question 31

Strong diversifying selection is a key part of _______ speciation.

Answer 31

Sympatric

Question 32

How do we know when speciation is complete?

Answer 32

when two populations of a species have diverged so much genetically that they can no longer interbreed and produce viable, fertile offspring

Question 33

Malaria resistance allele and Duffy antigen

Answer 33

DUFFY antigen: - Portal of entry into red blood cells - More susceptible to plasmodium than if you lacked them - Malaria parasites P. vivax and P. knowlesi exploit Duffy antigen receptor on RBCs - Almost 100% Africans who live in Malaria infested regions are Duffy negative (=natural selection) - Most Europeans Duffy positive ~20% Americans with African ancestry are Duffy positive ~12% Afro-Caribbeans are Duffy positive ~75% Clombians with African ancestry are Duffy positive - Duffy positive alleles increased in population with recent African ancestry (Result of gene flow)

Question 34

_______ = brake pedal on divergence.

Answer 34

Gene flow

Question 35

Full divergence = _________. Slow down divergence = _________.

Answer 35

No gene flow; add a lot of gene flow

Question 36

Compare the process of allopatric, peripatric, parapatric, and sympatric speciation.

Answer 36

Allopatric: * Original population - 100% gene flow * Initial step of speciation - barrier formation (vicariance event); physical barrier prevents gene flow * Evolution of reproductive isolation * New distinct species after * Amount of gene flow during speciation: none Peripatric: * Initial step of speciation - founder event (single pregnant female found in population) --> Gene flow is zero Newly founded tiny population --> Initial population is small Populations evolved by genetic drift --> Bottleneck event * Evolution of reproductive isolation: mating characteristics diverge and distinct species evolve *Amount of gene flow: none Parapatric: * Little gene flow (slows speciation) Sympatric: * Disruptive selection - no intermediates; only extremes * Among of gene flow during speciation: a lot * Homogenizes population

Question 37

How does allopatric speciation begin?

Answer 37

Vicariance event Fragmentation of initial population into 2 populations

Question 38

What is the second fasted speciation process?

Answer 38

Allopatric speciation

Question 39

What are two terms important for peripatric (island) speciations

Answer 39

1. Founder event: few individuals from large panmitic population colonize an island of small isolated patch on land 2. Founder effect: small initial population >> very rapid evolution by random genetic drift >> fixation of rare variants

Question 40

What are the issues with biological species concept?

Answer 40

1. Reproductive isolation may not be the only force maintaining species integrity 2. Interspecific hybridization 3. Difficult to apply concept to populations that are geographically separated in nature 4. Many species that do not hybridize in the wild will do so in captivity 5. Many organisms are asexual 6. Possible that different processes maintain species identity in different organisms

Question 41

Explain the ecological species concept.

Answer 41

* Each species adapted to its environment * Distinctions among species maintained by disruptive selection * Hybrids are quickly eliminated from gene pool * Strong selection overwhelms gene flow