Speciation - Types of speciation (Allopatric, peripatric, parapatric, sympatric) - kinds of different species .docx

Notes on topic "Speciation" - Evolution and Principles of Systematics
*Speciation - Example
*Types of speciation: Allopatric speciation, Peripatric Speciation, Parapatric Speciation, Sympatric Speciation
* Kinds of Different Species: Allopatric species, Microspecies, Subspecies, Sibling species, Monotypic species, Polytypic species

1. Speciation
Definition: “Speciation is the process of formation of new species from
existing populations.”
Speciation occurs when a group within a species separates from other members
of its species and develops its own unique characteristics.
The demands of a different environment or the characteristics of the members of
the new group will differentiate the new species from their ancestors.
Example: An example of speciation is the Galápagos finch. Different species of these
birds live on different islands in the Galápagos archipelago, located in the Pacific Ocean
off South America. The finches are isolated from one another by the ocean. Over
millions of years, each species of finch developed a unique beak that is especially
adapted to the kinds of food it eats. Some finches have large, blunt beaks that can crack
the hard shells of nuts and seeds. Other finches have long, thin beaks that can probe
into cactus flowers without the bird being poked by the cactus spines. Still other finches
have medium-size beaks that can catch and grasp insects. Because they are isolated, the
birds don’t breed with one another and have therefore developed into unique species
with unique characteristics.
Types of Speciation
There are four main types of speciation: allopatric, peripatric, parapatric, and sympatric.

2. 1. Allopatric Speciation
In allopatric speciation, organisms of an ancestral species evolve into two or more
descendant species after a period of physical separation caused by a geographic barrier,
such as a mountain range, rockslide, or river.
Once the groups are reproductively isolated, they may undergo genetic divergence.
That is, they may gradually become more and more different in their genetic makeup
and heritable features over many generations.
If the reproductive barriers that have arisen are strong—effectively preventing gene
flow—the groups will keep evolving along separate paths. That is, they won't exchange
genes with one another even if the geographical barrier is removed. At this point, the
groups can be considered separate species.
Example: squirrels and the Grand Canyon
The Grand Canyon (Arizona, United States) was gradually carved
out by the Colorado River over millions of years. Before it formed,
only one species of squirrel inhabited the area. As the canyon got
deeper over time, it became increasingly difficult for squirrels to
travel between the north and south sides.
Eventually, the canyon became too deep for the squirrels to cross
and a subgroup of squirrels became isolated on each side.
Because the squirrels on the north and south sides were
reproductively isolated from one another due to the deep canyon
barrier, they eventually diverged into different species.

3. 2. Peripatric Speciation
Peripatric speciation is a form of allopatric speciation that occurs when populations that
have become isolated have very few individuals. Within the small sub-population,
organisms which are able to survive within the new environment may carry genes that
were rare within the main population but that cause a slight variation to behavior or
morphology. Through repeated matings, the frequency of these, once rare, genes
increases within the small population. Over time, the characteristic that was determined
by the gene becomes fixed within the population, leading to an isolated species that is
evolutionarily distinct from the main population.
An example of peripatric speciation occurred with the London Underground mosquito.
This species broke off from the main species to the London Underground. They have
different behaviours and can breed all year round unlike its ancestor species which
hibernates in winter.
3. Parapatric Speciation
This is a type of allopatric speciation in which the species are not formed by any physical
barrier. Instead, they are beside each other. This occurs by an extreme change in the
habitat. Though the individuals in these areas can interbreed, they develop different
characteristics and lifestyles.
One example of parapatric speciation is the Tennessee cave salamander which exists
both in surface and cave-dwelling varieties. The migration between these two species
allows for some gene flow, producing hybrids, but they are able to remain two distinct
species.
4. Sympatric Speciation
Sympatric speciation occurs when there are no physical barriers preventing any
members of a species from mating with another, and all members are in close proximity
to one another. A new species, perhaps based on a different food source or
characteristic, seems to develop spontaneously. The theory is that some individuals
become dependent on certain aspects of an environment—such as shelter or food
sources—while others do not.
A possible example of sympatric speciation is the apple maggot, an insect that lays its
eggs inside the fruit of an apple, causing it to rot. As the apple falls from the tree, the

4. maggots dig in the ground before emerging as flies several months later. The apple
maggot originally laid its eggs in the fruit of a relative of the apple—a fruit called a
hawthorn. After apples were introduced to North America in the 19th century, a type of
maggot developed that only lays its eggs in apples. The original hawthorn species still
only lays its eggs in hawthorns. The two types of maggots are not different species yet,
but many scientists believe they are undergoing the process of sympatric speciation.
Kinds of Different Species
Allopatric species
The two or more related species that have distinct geographical ranges are called
allopatric species. Examples of such species are Indian lion and African lion.
Microspecies
Those species in which variations are very less are called microspecies. They reproduce
asexually, so they have very less variation.

5. Subspecies
In biological classification, subspecies is a rank below species, used for populations that
live in different areas and vary in size, shape, or other physical characteristics
(morphology), but that can successfully interbreed. Not all species have subspecies, but
for those that do there must be at least two. Subspecies is abbreviated subsp. or ssp.
Sibling species
Members of species which are morphologically similar but reproductively isolated are
known as sibling species i.e. they cannot interbreed among themselves.
Sibling species is one taxonomic species (because these members have similar
morphology) but they are different biological species (because they cannot interbreed).
Examples are Drosophila persimilis and D. pseudoobscura.
Monotypic species
When a genus includes a single species but does not include any subspecies, e.g.,
Vampyroteuthis, a vampire squid which is a single monotypic genus and also contains a
single species, V. infernalis (monotypic species).
Polytypic species
When a species contains two or more subspecies, it is called polytypic species. Examples
are tiger, Panthera tigris which has several subspecies; such as –
i.Indian tiger, Panthera tigris tigris
ii.the Chinese tiger, Panthera tigris amoyensis
iii.the Siberian tiger, Panthera tigris altaica
iv.the Javan tiger, Panthera tigris sondaica