Biology [[Classification, Selection and Evolution]]Species and Speciation

Speciation: The production of new species

What is a species?
A species is a group of organisms with similar morphological, physiological, biochemical and behavioural features, which can interbreed to produce fertile offspring and are reproductively isolated from other species.

Morphiological: Structural features
Physiological: Way the body works
Biochemical: sequence of bases in DNA.

For Example: Donkeys and Horses.
*Donkeys look and work like other donkeys and can breed with donkeys to produce donkeys. This concludes that all Donkeys are of the same species.
* Donkeys can breed with Horses, which are similar.
* These produce Mules
*Mules cannot breed, so they are infertile (they are a dead end)
* The conclusion is that Donkeys and Horses are not the same species.

This test is not always possible, as the organisms may be dead, museum specimens or fossils, both of the same sex, or perhaps even the biologist does not have the time or the equipment necesary. Some organisms will not breed in captivity, or may be immature and unable to breed. For these reason, it is rare to test this.

Biologists rely on morphiological, physiological, biochemical and behavioural differences to decide whether or not two specimens are of the same species.

To produce a new species, then two groups of the same speices must become reproductivly isolated from each other. This takes time, so experiments are impossible. The evidence is circumstantial.

[[Allopatric Speciation]]

Geographical Isolation

Suggested by the fact that many islands have their unique species. There are species in the Galapagos and Hawaiian Islands found only there.

This type of isolation requires a barrier to prevent the species from mixing.
e.g. Water

For Example: Hawaiian Birds

*Birds arrive on Island, perhaps blown by a storm
*They are seperated from their species by the ocean
*Selection pressures on the island are different from those on the mainland
*The group interbred
*Different Alleles were selected
*Over time, the morphiological, Physiological, biochemical features became so different the species could no longer interbreed
* A new species had evolved.

Other barriers:
Dense forest cut down to leave "islands" of forest will isolate groups of species.

Allopatric = different places

[[Sympatric Speciation]]

A new species arises without the original population being seperated by a geological barrier

The most common way by which this can happen is through Polyploidy

A polyploid organism is one with more than two complete sets of chromosomes in its cell. This can happen if meiosis goes wrong when gametes are being formed and a gamete ends up with two sets of chromosomes. If two such gametes form then the zygote gets for sets of chromosomes instead of one = tetraploid

Tetraploids formed like this are sterile. All four chromosomes try to pair up in meiosis one and get confused, so it is difficult for the cell to divide by meisos and produce new gametes

The organism will still be able to grow and reproduce asexually, as mitosis can still occur. This happens in plants, but rarely in animals

This type of polyploidy is called autopolyploid as all four sets of chromosomes are from the same species. If two sets of chromosomes are from one species, and two sets from another, then it is alloploid. Meiosis happens more easily in an alloploid than an autoploid.