Origin of Species - Chapter 24

Question 1

What Darwin said about speciation

Answer 1

“mystery of mysteries”

Darwin believed that the process of natural selection could explain the diversity of life, given enough time.

many definitions of speciation

Question 2

Speciation, microevolution, macroevolution

Answer 2

speciation - the process of splitting one species into 2 or more

microevolution - change in allele frequencies in a population

macroevolution - broad pattern of evolution above the species level

Question 3

Biological Species Concept

Answer 3

a definition of species that defines a species as a group that is able to produce healthy offspring with each other and can’t do so with other groups

Speciation in this definition depends on reproductive isolation

speciation has occured when populations become reproductively isolated

Question 4

Problems with Biological Species Concept

Answer 4

asexual organisms

extinct forms (what could they breed with? can’t determine)

species that hybridize

ring species

It’s difficult to apply this concept to the real world because many species that seem very different have gene flow betwen them.

Question 5

Why is ambiguity in speciation expected?

Answer 5

nature seldom conforms to neat categories

new species often evolve gradually

not one point in time that you can identify as the moment of speciation

Question 6

Reproductive isolating mechanisms

Prezygotic barriers to reproduction

Answer 6

prevent gene flow between populations

1. habitat isolation - different species living in different habitats, but the same area, will rarely (if ever) encounter each other
2. temporal isolation (gametes can’t mix between species who breed during different seasons)
3. behavioral isolation (courtship displays) - mate recognition doesn’t occur between speices with different mating rituals, so they won’t interbreed
4. mechanical isolation (irish wolfhound&chinese crested dogs) - morphological differences don’t allow successful mating
5. gametic incompatibility (esp. for ext. fert. need to separate plants) - sperm can’t fertilize egg of other species

Question 7

Mechanisms for reproductive isolation

Answer 7

allopatric speciation

sympatric speciation

Question 8

Prezygotic vs postzygotic barriers to genetic exchange

Answer 8

Prezygotic barriers stop fertilization from occuring

Postzygotic barriers contribute to reproductive isolation after a hybrid zygote is formed.

Question 9

Reproductive isolating mechanisms

Postzygotic barriers to reproduction

Answer 9

1. reduced hybrid viability - mix of hybrid genes hinder survival and development
2. reduced hybrid fertility - gametes don’t align and produce sterile offspring (no gene flow)
3. hybrid breakdown - hybrids are fertile, but their offspring are not.

Question 10

Morpohological Species Concept

Answer 10

Based on appearance

morph - shape

Linnaeus

concept relied on by paleontologists

Question 11

Problems with morphological species concept

Answer 11

cryptic (sibling) speices - virtually identical, but don’t interbreed

ecotypes - look different, but can interbreed

Question 12

Allopatric Speciation

Answer 12

most common among animals

occurs when two populations become geographically separated (size of geographic barrier depends on the speices ability to move about)

decreased by gene flow, can be fast (20 years worms at Woods)

Natural seleciton, genetic drift, mutation increase

1. populations become geographically isolated
2. isolation reduces gene flow (not interbreeding)
3. genetic divergence of 2 populations
4. eventually results in reproductive isolation (new speices!) (even if they come into contact again, they can’t interbreed)

Question 13

Which mechanisms of evolutionary change increase genetic divergence of isolated populations?

Which tend to prevent divergence?

Answer 13

increase: mutations, natural selection, sexual selection, genetic drift
decrease: gene flow

Question 14

Sympatric Speciation

Answer 14

speciation without geographical separation

Process: Polyploidy, habitat differntation, sexual selection. Once one of these occurs, a new species will arise if the mechanism contintues

Question 15

What factors can reduce gene flow to cause sympatric speciation?

Answer 15

Polyploidy, habitat differentiation, sexual selection

Question 16

Polyploidy

mechanism of sympatric speciation

Answer 16

ploidy = number of sets of chromosomes

results from an increase in chromosome nubmer

common in plants, rare in animals

instant speciation - because chromosomes can’t line up in meiosis (not same number)

results from non-disjunction of chromosomes during meiosis

Question 17

Autoploidy

Answer 17

unreduced gametes in meiosis (supposed to halve, but didn’t - doubles)

first documented by Hugo DeVries in primrose (several new species of primrose, bigger and larger)

Question 18

Alloploidy

Answer 18

hybridization follwed by non-disjunction

different species breeding then 1 has autoploidy error

2 rare events, but not necessarily in the same generation

event that initates: 2 different species interbreed, then hybrid reproducing asexually

Question 19

Hybrids have a low fitness reinforcement in hybrid zones - why unhealthy hybrids would cause selection for individuals that only mated with members of their own population?

Answer 19

unhealthy hybrids are going to cause selection for individuals that only mate with their own population because these offspring will likely survive, whereas the unhealthy hybrids will not survive long enough to produce more offspring or the offspring will also be unhealthy, so theis will reinforce reproductive barriers

Question 20

“mystery of mysteries”

Darwin believed that the process of natural selection could explain the diversity of life, given enough time.

many definitions of speciation

Answer 20

What Darwin said about speciation

Question 21

speciation - the process of splitting one species into 2 or more

microevolution - change in allele frequencies in a population

macroevolution - broad pattern of evolution above the species level

Answer 21

Speciation, microevolution, macroevolution

Question 22

a definition of species that defines a species as a group that is able to produce healthy offspring with each other and can’t do so with other groups

Speciation in this definition depends on reproductive isolation

speciation has occured when populations become reproductively isolated

Answer 22

Biological Species Concept

Question 23

asexual organisms

extinct forms (what could they breed with? can’t determine)

species that hybridize

ring species

It’s difficult to apply this concept to the real world because many species that seem very different have gene flow betwen them.

Answer 23

Problems with Biological Species Concept

Question 24

nature seldom conforms to neat categories

new species often evolve gradually

not one point in time that you can identify as the moment of speciation

Answer 24

Why is ambiguity in speciation expected?

Question 25

prevent gene flow between populations

1. habitat isolation - different species living in different habitats, but the same area, will rarely (if ever) encounter each other
2. temporal isolation (gametes can’t mix between species who breed during different seasons)
3. behavioral isolation (courtship displays) - mate recognition doesn’t occur between speices with different mating rituals, so they won’t interbreed
4. mechanical isolation (irish wolfhound&chinese crested dogs) - morphological differences don’t allow successful mating
5. gametic incompatibility (esp. for ext. fert. need to separate plants) - sperm can’t fertilize egg of other species

Answer 25

Reproductive isolating mechanisms

Prezygotic barriers to reproduction

Question 26

allopatric speciation

sympatric speciation

Answer 26

Mechanisms for reproductive isolation

Question 27

Prezygotic barriers stop fertilization from occuring

Postzygotic barriers contribute to reproductive isolation after a hybrid zygote is formed.

Answer 27

Prezygotic vs postzygotic barriers to genetic exchange

Question 28

1. reduced hybrid viability - mix of hybrid genes hinder survival and development
2. reduced hybrid fertility - gametes don’t align and produce sterile offspring (no gene flow)
3. hybrid breakdown - hybrids are fertile, but their offspring are not.

Answer 28

Reproductive isolating mechanisms

Postzygotic barriers to reproduction

Question 29

Based on appearance

morph - shape

Linnaeus

concept relied on by paleontologists

Answer 29

Morpohological Species Concept

Question 30

cryptic (sibling) speices - virtually identical, but don’t interbreed

ecotypes - look different, but can interbreed

Answer 30

Problems with morphological species concept

Question 31

most common among animals

occurs when two populations become geographically separated (size of geographic barrier depends on the speices ability to move about)

decreased by gene flow, can be fast (20 years worms at Woods)

Natural seleciton, genetic drift, mutation increase

1. populations become geographically isolated
2. isolation reduces gene flow (not interbreeding)
3. genetic divergence of 2 populations
4. eventually results in reproductive isolation (new speices!) (even if they come into contact again, they can’t interbreed)

Answer 31

Allopatric Speciation

Question 32

increase: mutations, natural selection, sexual selection, genetic drift
decrease: gene flow

Answer 32

Which mechanisms of evolutionary change increase genetic divergence of isolated populations?

Which tend to prevent divergence?

Question 33

speciation without geographical separation

Process: Polyploidy, habitat differntation, sexual selection. Once one of these occurs, a new species will arise if the mechanism contintues

Answer 33

Sympatric Speciation

Question 34

Polyploidy, habitat differentiation, sexual selection

Answer 34

What factors can reduce gene flow to cause sympatric speciation?

Question 35

ploidy = number of sets of chromosomes

results from an increase in chromosome nubmer

common in plants, rare in animals

instant speciation - because chromosomes can’t line up in meiosis (not same number)

results from non-disjunction of chromosomes during meiosis

Answer 35

Polyploidy

mechanism of sympatric speciation

Question 36

unreduced gametes in meiosis (supposed to halve, but didn’t - doubles)

first documented by Hugo DeVries in primrose (several new species of primrose, bigger and larger)

Answer 36

Autoploidy

Question 37

hybridization follwed by non-disjunction

different species breeding then 1 has autoploidy error

2 rare events, but not necessarily in the same generation

event that initates: 2 different species interbreed, then hybrid reproducing asexually

Answer 37

Alloploidy

Question 38

unhealthy hybrids are going to cause selection for individuals that only mate with their own population because these offspring will likely survive, whereas the unhealthy hybrids will not survive long enough to produce more offspring or the offspring will also be unhealthy, so theis will reinforce reproductive barriers

Answer 38

Hybrids have a low fitness reinforcement in hybrid zones - why unhealthy hybrids would cause selection for individuals that only mated with members of their own population?