1/17/2016 Speciation: 4 Types of Speciation | Evolution

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Speciation: 4 Types ofSpeciation | Evolutionby Puja Mondal Evolution

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Speciation is the formation of one or more new species

from an existing species.

A species is a collection of demes. The deme is a group of

populations with common gene pool.

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Types of Speciation:

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Speciation is of following types.

1. Allopatric Speciation (alios— other, patria—native land):

In this type of species formation, a part of the population

becomes geographically isolated from the main popula-

tion. The population becomes entirely separated and

finally constitutes a new species. Thus geographic

isolation brings about allopatric speciation. An

important example of this type of speciation is

formation of Darwin’s finches that formed separate

species in the Galapagos Islands (Fig. 7.55A).

2. Sympatric Speciation (sym— together, patria— native land):

In this type of species formation, a small segment of the

original population becomes isolated reproductively. As

the isolating mechanism comes into force, a new

subspecies emerges. In due course of time a new species

is formed. Thus sympatric speciation is the formation of

species within a single population without geographical

isolation. The reproductive isolation brings about

sympatric speciation (Fig. 7.55B).

3. Parapatric Speciation:

It separates adjacent population. Parapatric speciation

takes place when a population of a species enters a new

niche or habitat. It occurs only at the edge of the parent

species range. Although there is no physical barrier

between these populations, yet the occupancy of a new

niche results as a barrier to gene flow between the

population of new niche. Two species are produced due

to reproductive isolation from single one. Such type of

speciation is found in flightless grasshoppers, smails and

annual plants.

1/17/2016 Speciation: 4 Types of Speciation | Evolution

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4. Quantum Speciation:

It is the rapid and abrupt mode of species formation.

Grant (1971) defined quantum speciation “the budding

off a new and very different daughter species from a

semi-isolated peripheral population of the ancestral

species”. This type of speciation is based on the

observation of H.L. Carson on Drosophila inhabiting

Hawaii Island.

The quantum speciation is a sudden and rapid

speciation. It does not produce subspecies or

intermediate stage. Genetic drift or chance plays a major

role in quantum speciation.

Factors Influencing Speciation:

Following factors influence the speciation:

(i) Mutation

(ii) Recombination

(iii) Natural selection

(iv) Hybridization

1/17/2016 Speciation: 4 Types of Speciation | Evolution

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(v) Genetic drift

(vi) Polyploidy (to be described) and

(vii) Isolation.

Polyploidy:

Increase in number of chromosomes or chromosome

sets is called polyploidy. Polyploidy does not occur

commonly in animals. The additional chromosomes in

animals are mostly lethal. However, polyploidy occurs

commonly in plants. Polyploidy has played an important

role in plant evolution.

There are many common polyploidy plants. Tobacco is a

polyploidy that evolved by the hybridization of two

smaller species. In wheat, there are species with 14, 28

and 42 chromosomes. Different varieties of wheat have

been obtained by polyploidy.

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