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Flashcards in Speciation Deck (29)
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What are the two speciation scenarios



What does anagenesis explains

explains the continuity of life


What does cladogenesis explains

explains the diversification of life


What is anagenesis

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


What is cladogenesis

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


What are the 4 models of speciation



What is allopatric speciation

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


What is sympatric speciation

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


What is parapatric speciation

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.


What is peripatric speciaition

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


What are the two levels of reproductive isolation

Pre-zygotic isolation – e.g. mate choice
Post-zygotic – e.g. hybrid sterility


What is reproductive isolation

When species have diverged and changed genetically


what does pre-zygotic isolation include

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


Which mode of isolation if more fitness efficient and why

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


When is hybrid sterility more common

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


Why is is hybrid sterility more common in the heterospecific sex

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


When does post-zygotic isolation occurs and why

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)


When can sexual selection drive speciation

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


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

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


Which group of species tend to be more species rich

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


When does reinforcement occur

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


example of evidence for reinforcement

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


What is reinforcement

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


What is the hypothesis of differential fusions

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)


What is the Dobzhansky-Muller model

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.


when does the Dobzhansky-Muller model occur

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 .


What are the 3 types of balancing selection

Overdomince/ Heterozygote advantage
varying in space and time


example of frequency-dependent selection

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


how can we detect balancing selection

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),