Speciation

Question 1

What are the two speciation scenarios

Answer 1

anagenesis

cladogenesis

Question 2

What does anagenesis explains

Answer 2

explains the continuity of life

Question 3

What does cladogenesis explains

Answer 3

explains the diversification of life

Question 4

What is anagenesis

Answer 4

replacement of one species by another, following an adaptive genetic transformation

Question 5

What is cladogenesis

Answer 5

Emergence of two (or more) species from one pre-existing species. This ancestral species could e.g. have been separated geographically

Question 6

What are the 4 models of speciation

Answer 6

allopatric
sympatric
parapatric
peripatric

Question 7

What is allopatric speciation

Answer 7

Classical model
Populations of a single species become geographically isolated e.g. due to separation of continents, ice age refuges etc.
This creates reproductively isolated gene pools, with independent evolution

Question 8

What is sympatric speciation

Answer 8

the evolution of a new species from a surviving ancestral species while both continue to inhabit the same geographic region.

Question 9

What is parapatric speciation

Answer 9

when a smaller population is isolated, usually at the periphery of a larger group, and becomes differentiated to the point of becoming a new species.

Question 10

What is peripatric speciaition

Answer 10

a mode of speciation in which a new species is formed from an isolated peripheral population

Question 11

What are the two levels of reproductive isolation

Answer 11

Pre-zygotic isolation – e.g. mate choice

Post-zygotic – e.g. hybrid sterility

Question 12

What is reproductive isolation

Answer 12

When species have diverged and changed genetically

Question 13

what does pre-zygotic isolation include

Answer 13

includes differences in:
Ecology, behaviour, time of reproduction, gametic incompatibility, differences in pollinators (in plants), sexual isolation

Question 14

Which mode of isolation if more fitness efficient and why

Answer 14

pre-zygotic
No gametes or zygotes are wasted
Hence, pre-zygotic isolation is more likely to evolve (eventually) in sympatric species > reinforcement

Question 15

When is hybrid sterility more common

Answer 15

Haldane noted that hybrid sterility is more common in the heterospecific sex
XY males in mammals
Females in butterflies and birds

Question 16

Why is is hybrid sterility more common in the heterospecific sex

Answer 16

Dominance theory
Incompatibility is caused by (partially) recessive alleles
These alleles become fully expressed in XY individuals
Faster evolution of sterility in males
Spermatogenesis might be more easily upset than oogenesis

Question 17

When does post-zygotic isolation occurs and why

Answer 17

Post-zygotic isolation occurs when hybrids are unfit. This can be because of:
Differences in ploidy levels
Differences in number of chromosomes, or chromosome arrangements
Incompatible alleles
(latter most important esp. in animals)

Question 18

When can sexual selection drive speciation

Answer 18

Fisher’s ‘runaway process’ can occur when a male trait differentiates and it becomes correlated (linked) to a female preference gene

Question 19

Explain the process of fisher’s runaway selection creating a new species

Answer 19

Certain females prefer males with exaggerated traits
If preference and male traits are heritable
Then daughters and sons inherit these genes (i.e. traits and preferences)
This sub-group of individuals may become genetically isolated

Question 20

Which group of species tend to be more species rich

Answer 20

promiscuous - Bigger role of sexual selection, which could drive speciation
sexual dimorphic

Question 21

When does reinforcement occur

Answer 21

When two initially allopatric differentiated populations come into secondary contact, producing inferior hybrids. Selection favours those who can avoid mating with individuals who are dissimilar, encouraging speciation

Question 22

example of evidence for reinforcement

Answer 22

Males of some sibling-species of Mbuna cichlids from Lake Malawi can have overlapping territories
Hybrids can be easily made in the lab
However, these hybrid males are recognised by the males of both parental types and have difficulty establishing territories

Question 23

What is reinforcement

Answer 23

Reinforcement is a process of speciation where natural selection increases the reproductive isolation (further divided to pre-zygotic isolation and post-zygotic isolation) between two populations of species

Question 24

What is the hypothesis of differential fusions

Answer 24

This hypothesis states that of the many species have historically come into contact with one another, the only ones that persist in sympatry (and thus are seen today) are species with strong mating discrimination. On the other hand, species lacking strong mating discrimination are assumed to have fused while in contact, forming one distinct species (introgression)

Question 25

What is the Dobzhansky-Muller model

Answer 25

Dobzhansky-Muller Model is a scientific explanation of why natural selection influences speciation in such a way that when hybridization occurs between species, the resulting offspring is genetically incompatible with other members of its species of origin.

Question 26

when does the Dobzhansky-Muller model occur

Answer 26

when you have negative interactions between genes of two differentiated population that have undergone mutations and now are back in sympatry and the hybrids are now incompatible .

Question 27

What are the 3 types of balancing selection

Answer 27

Overdomince/ Heterozygote advantage
 frequency-dependent
selection
 selection
varying in space and time

Question 28

example of frequency-dependent selection

Answer 28

Balancing selection maintaining sex ration in populations with the X/Y sex chromosome system

Question 29

how can we detect balancing selection

Answer 29

from looking at nearby neutral sites - BS maintains diversity at the selected sites themselves , whilst increasing diversity at closely linked neutral sites. Regions of genome close to a site under balancing selection, which rarely recombine with the selected site(s), will have common ancestors longer ago than other regions (longer coalescence times),