Rep isolating mechanism evolution final

PRESENTATION TOPIC: Reproductive Isolating mechanism

Submitted to: Madam Hakim BibiSubmitted by: Farhat Bano

Contents:

What is Speciation? What is Reproductive Isolation? Isolating mechanisms & Types Prezygotic isolating mechanisms Postzygotic isolating mechanisms Examples

https://en.wikipedia.org/wiki/Species

What is specie?

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.

Diversity of species

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?

www.biodiversity.ru/coastlearn/bio-eng/boxes/specdiv.html

https://en.wikipedia.org/wiki/Speciation

Evolution of Species (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.

https://en.wikipedia.org/wiki/Speciation

Speciation & 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.

https://www.britannica.com/science/reproductive-isolation

Reproductive Isolation is the driving force behind Speciation

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


Species

Barriers


Species

Barriers

Pre-zygotic Post-zygoticGeographical


Species

Barriers


Reproductive Isolation

Gene flow


Species

Barriers


Reproductive

IsolationGene flow

Speciation SlowFast

http://www.bio.miami.edu/dana/dox/reproductive_isolation.html

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.


Isolating mechanisms

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.


Pre-Zygotic Barriers

“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.


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.

Water-dwelling Thamnophis

Terrestrial Thamnophis


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. (February/April)

Bishop pine


Cont..

Example Red and black sea urchins live in the same location, but release their gametes at different times of the year.


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 righthanded spirals.


al

Mechanical incompatibility in snail


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.


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 theirmates. Over 2000 species of fireflies are isolated based on the patterns of flashes


CONT..

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


Courtship ritual of blue-footed boobies


Postmating Isolating Mechanisms

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 reproducePostmating isolating mechanisms include:1. Hybrid inviability2. Hybrid infertility3. Hybrid breakdown


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


Hybrid Inviability

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.


Hybrid Sterility

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) Sterile

K


Hybrid breakdown

In this, First generation (F1) hybrids are viable and fertile, but further hybrid generations (F2 and backcrosses) may be inviable or sterile.


Rep isolation & Speciation of Darwin’s Finches

Speciation in the Galapagos finches occurred by: Founding a new population: A small population of finches migrates to a different island

Geographic isolation: Finches don’t usually fly over open water, so stayed on

own island (separate gene pool) Changes in the new population’s gene pool: Adapted to new environment to be more fit


Cont..

Reproductive isolation: Differences in phenotypes and mating rituals may turn

different finches off to one another Continued Evolution: Process repeats and over many generations, it produced the

13 different finch species

http://slideplayer.com/slide/5801510/

Example

Populations begin to diverge when gene flow between them is restricted. Geographic isolation is often the first step in allopatric speciation.

Examples: Galapagos finches and tortoises, Asian elephants, and the following experiment by Diane Dodd in 1989.

Conclusion:

These results are consistent with the idea that geographic isolation or reproductive isolation is an important step for speciation events.

Science

Rep isolating mechanism evolution final