Speciation and Reproductive Isolation

Question 1

Biological Species Concept (BSC)

Answer 1

species are groups of interbreeding natural populations that are reproductively isolated from other such groups

• groups of populations that can exchange genes (actually or potentially)
• produce fertile offspring
• reproductively isolated from other such groups
• as long as two forms interbreed, they cannot diverge
• if two forms DO NOT interbreed, they each can develop different adaptations

Question 2

Pre-Zygotic Isolation

Answer 2

union of egg and sperm never occurs because gametes never encounter one another

Question 3

Post-Zygotic Isolation

Answer 3

egg and sperm encounter one another but the zygote is either not viable or gives rise to individuals that cannot reproduce or have very low fitness

Question 4

Zygote

Answer 4

cells formed by the union of male (a sperm) and a female (an ovum) sex cells

Question 5

Pre-Zygotic Mechanisms for Reproductive Isolation

Answer 5

1. ) Geographic Isolation (allopatric speciation)
2. ) Gametic Isolation
3. ) Mechanical Isolation
4. ) Temporal
5. ) Behavioral
6. ) Ecological Preferences and Mating Isolation

Question 6

Geographic Isolation (allopatric speciation)

Answer 6

existences of a geographic barrier

• complete geographic isolation

Question 7

Gametic Isolation

Answer 7

occurs when incompatibility in gametes (egg and sperm) do NOT permit fertilization

• i.e. differences in number of chromosomes or chemical signals

Question 8

Mechanical Isolation

Answer 8

simply put, male “parts” don’t fit female “parts”

• i.e. dragonflies, beetles, bush babies, flowering plants and specificity in their pollinators

Question 9

Temporal Isolation

Answer 9

inter-species differences in timing of reproduction

• could be considered sympatriotic because there’s no geographic isolation
• i.e. cicadas

Question 10

Behavioral Isolation

Answer 10

can occur when mating displays and courtship rituals become intertwined with reproductive act

• mating rituals, displays, songs, etc.

Question 11

Ecological Preferences and Mating Isolation

Answer 11

occurs when environmental preferences reduces the frequency of interbreeding

• i.e. apple maggots

Question 12

Post-Zygotic Mechanisms for Reproductive Isolation

Answer 12

1. ) Zygote Morality
2. ) Hybrid Inviability
3. ) Hybrid Sterility
4. ) Low Hybrid Fitness (survivorship)

Question 13

Zygote Morality

Answer 13

occurs when a successfully fertilized egg begins process of development but the zygote is not viable and fails to complete development

Question 14

Hybrid Inviability

Answer 14

occurs when gametes fuse, development progresses, but offspring cannot survive to adulthood

• i.e. occasional cross between Rana Pipiens and Rana Sylvatica offspring lasts only a few days

Question 15

Hybrid Sterility

Answer 15

occurs when gametes fuse, development progresses and offspring survive to adulthood but they themselves cannot reproduce

• i.e. the Zorse

Question 16

Low Hybrid Fitness (survivorship)

Answer 16

occurs when gametes fuse, development progresses and offspring survive to adulthood and can produce offspring but have very low fitness in the wild

• i.e. dog-wolf hybrids

Question 17

3 Geographic Models of Speciation

Answer 17

1. ) Allopatry
2. ) Parapatry
3. ) Sympatry

Question 18

Allopatry

Answer 18

occurs when populations become completely, physically separated from one another by geographic barriers

• i.e. isolation on islands (Darwin’s finches)

Question 19

Parapatry

Answer 19

separated not by geographical areas but an extreme change in habitat

i.e. grass adapting to rivers with heavy metals whereas the grass in clean rivers don’t need to

Question 20

Sympatry

Answer 20

occurs when there is no spatial separation but reproductive isolation occurs

Question 21

Ring Species (Parapatry)

Answer 21

two populations that do not interbreed are living in the same region but they are connected by a geographic ring of population that do interbreed

Question 22

How do geographically isolated populations diverge?

Answer 22

1. ) Natural selection adjusts population to local environments
2. ) Genetic Drift (mutations)

Question 23

Allopatric Model for Speciation (how geographically isolated populations diverge)

Answer 23

1. ) a single contiguous population in a homogeneous environment
2. ) differentiation of environment and migration to a new environment increases phenotypic variation
3. ) Founder Effect plus adaptation to local environments results in genetic divergence in geographically isolated peripheral populations
4. ) some of these isolated subspecies differentiate with respect to genetic and chromosomal changes that control reproductive isolation mechanisms
5. ) changes with the environment permit geographically isolated populations to overlap with parent species

Question 24

Genetic Drifts (how geographically isolated populations diverge)

Answer 24

all left to chance; unpredictable fluctuations in allele frequencies

• more effective in small populations (sampling errors)

Question 25

Bottleneck Effect

Answer 25

the large population decreases in size and their survivors lack diversity

• i.e. Florida panthers

Question 26

Founder Effect

Answer 26

when a few individuals of group separate from a large population and establish a new one

• genetic diversity within the main population is conserved
• i.e. the Amish population