What is Speciation ?

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Crimean state medical University named after
S. I. Georgievsky
Georgievsky
Submitted to Anna Zukhova
Submitted by Ajay Sharma

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Contents
01
What is Speciation ?
Contents
02
What is Reproductive Isolation ?
Contents
03
Isolation mechanism & types :• Prezygotic isolation mechanism
• Postzygotic isolation mechanism
Contents
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Example

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A population or group of populations whose members have the ability
to interbreed with one another under natural condition and produce
fertile offspring and reproductively isolated from other species.
In biology, a species is the basic unit of classification and a taxonomic
rank of an organism, as well as a unit of biodiversity. A species is
often defined as the largest group of organisms in which any two
individuals of the appropriate sexes or mating types can produce
fertile offspring, typically by sexual reproduction.

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The diversity of species on Earth is simply
astounding. Scientists have identified about
two million species and still do not know how
many species inhabit Earth. Scientists
estimate as many as 30 million species may
inhabit Earth.
So, the big question is how did so many
species form?

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Speciation
Speciation = formation of new species
Speciation occurs when members of similar populations no
longer interbreed to produce fertile offspring within their natural
environment
It occurs when groups in a species become reproductively
isolated and diverge
A single species can generate multiple species
HENCE IT LEAD TO A NEW IDEAS ABOUT EVOLUTION
Speciation is the origin of new species.
Speciation increases our planet’s biological diversity.
Therefore, speciation is an important part of the theory of
evolution.
Many scientist have different ideas about it.

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Reproductive Isolation
The existence of biological factors (barriers) that prevent two individuals of a
species from mating and producing viable and fertile offspring
A new species will form when reproductive isolation occurs
The mechanisms of reproductive isolation are a collection of evolutionary
mechanisms, behaviours and physiological processes critical for speciation.
They prevent members of different species from producing offspring, or ensure
that any offspring are sterile. These barriers maintain the integrity of a species by
reducing gene flow between related species

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Geographical Isolation
Geographical isolation occurs when populations cannot
mate because of physical barriers
Geographically separated populations aren’t
necessarily distinct species.
Example: Northern Spotted Owl and Mexican Spotted
Owl.

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Isolation mechanism
Isolating mechanisms prevent interbreeding and maintain
reproductive isolation.
Isolating mechanisms can be divide in to two different
types.
Isolating mechanisms that occur before fertilization are
called Prezygotic isolating mechanisms.
Isolating mechanisms that occur after fertilization are
called postzygotic isolating mechanisms.

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PRE-ZYGOTAIC BARRIER
Pre-zygotic barriers are obstacles that are present before
an egg can be fertilized.
A zygote is an egg that has been fertilized by a sperm
Premating isolating mechanisms include:
1) Ecological isolation.
2) Temporal isolation.
3) Behavioral isolation.
4) Mechanical incompatibility.
5) Gametic isolation

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Ecological isolation
Ecological isolation occurs when potential mates
never meet because they live in different
habitats.
Ex. The mountain bluebird lives at high elevation
while the eastern bluebird prefers low elevation

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Temporal isolation
Temporal isolation occurs when species can’t mate
because they breed at different times of year.
Ex: The Monterey Pine and the Bishop pine have
different pollination periods.
Example Red and black sea urchins live in the same
location, but release their gametes at different times of
the year.

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Mechanical incompatibility
Mechanical incompatibility occurs when species cannot
mate because their reproductive structures are
incompatible
Closely related species may attempt to mate but fail
because they are anatomically incompatible and
transfer of sperm is not possible
In animals with internal fertilization, male and female
sexual organs may not fit together
EX. snails of species whose shells have left handed
spirals may be unable to successfully copulate with
snails whose shells have right handed spirals

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GAMETIC ISOLATION
Sperm of one species may not survive internal
environment of female reproductive tract in another
species
For fertilization to occur, the sperm must reach the
ovum. For this to happen they usually attract each
other through chemical means, but the chemicals might
vary from one specie to another. In this case gametes
won’t recognise each other and fertilization won’t take
place.

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Behavioral isolation
Behavioral isolation occurs when species can’t mate
because patterns of courtship may be different to the
extent that sexual union is not achieved
Ex: Fireflies produce patterns of flashes that attract
their mates. Over 2000 species of fireflies are isolated
based on the patterns of flashes
Members of the two species will not mate with each
other because they use different songs to attract
mates. Eastern meadowlarks will not respond to
western meadowlark songs, and vice versa.
Example: Eastern and Western Meadowlarks

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POSTMATING ISOLATING MECHANISM
Isolating mechanisms which operate after fertilization
Prevents hybrid zygotes from developing into viable,
fertile adults
There are three likely cases that will occur to ensure
that the hybrid does not reproduce Postmating isolating
mechanisms include:
1. Hybrid inviability
2. Hybrid infertility
3. Hybrid breakdown

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HYBRID INVIABILITY
The term 'hybrid' refers to the offspring between two different species and 'inviability' refers to
an organism that does not thrive. In hybrid inviability, mating occurs and a hybrid is produced,
but Hybrid very weak and can’t live outside the uterus.
Ex. Several species of the frog live in the same habitats but hybrids do not complete
development
If Sheep and goats mate then Hybrid zygotes Die before birth
The creation of an unsuccessful hybrid is also a form of post- zygotic barrier.

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ABNORMALITIES
Species mate and hybrid is viable but sterile.
If chromosome numbers are different, meiosis cannot
produce normal gametes
EX. Male donkey x Female horse Mule Mules: Healthy
(viable)

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Conclusion(1)The reproductive isolation is quite difficult in human
because of the invention of different medium of transport.
(2)It can be seen in animals but it is rare in human as
human beings can travel to any place to
reproduce.(3)WHO says no to gene edited babies.

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