rep isolating mechanism evolution final
TRANSCRIPT
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
https://www.britannica.com/science/reproductive-isolation
Species
Barriers
https://www.britannica.com/science/reproductive-isolation
Species
Barriers
Pre-zygotic Post-zygoticGeographical
https://www.britannica.com/science/reproductive-isolation
Species
Barriers
Pre-zygotic Post-zygoticGeographical
Reproductive Isolation
Gene flow
https://www.britannica.com/science/reproductive-isolation
Species
Barriers
Pre-zygotic Post-zygoticGeographical
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.
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
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.
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
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.
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
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
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
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
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
Cont..
Example Red and black sea urchins live in the same location, but release their gametes at different times of the year.
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
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.
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
al
Mechanical incompatibility in snail
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
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.
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
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
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
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
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
Courtship ritual of blue-footed boobies
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
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
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
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
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
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.
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
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
http://www.bio.miami.edu/dana/dox/reproductive_isolation.html
Hybrid breakdown
In this, First generation (F1) hybrids are viable and fertile, but further hybrid generations (F2 and backcrosses) may be inviable or sterile.
https://www.britannica.com/science/reproductive-isolation
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
https://www.britannica.com/science/reproductive-isolation
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.