Origin of SpeciesBy Meen NO.12 Pizza NO.26 MEP M.6/11

Yasothonpittayakom School

Presented to T.Anna Cao

Origin of speciesSpecies, In biological terms, it is an individual

belonging to a population whose members have common characteristics as well as the potential to interbreed with one another to produce viable offspring, but who cannot successfully interbreed with members of other species.

Reproductive Barriers Separate SpeciesEach species is genetically isolated by other

such population by reproductive barriersAny factor that prevent two species from

producing viable, fertile hybrids is a reproductive barriers that maintains the integrity of a species. There are prezygotic and postzygotic barriers

Reproductive Barriers Separate Species

Prezygotic Barriers

Habitat Isolation

Behavioural Isolation

Temporal Isolation

Postzygotic Barriers

Reduced Hybrid Viability

Reduced Hybrid fertility

Hybrid Breakdown

Prezygotic Barriers

Habitat Isolation is where sepecies occupying the same geographic area live in separate habitats.

Habitat Isolation can be a result of habitat destruction by human activities. The endangered damselfy Coenagrion mercuriale is the key component of the European freshwater ecosystem.

Prezygotic Barriers• Behavioural Isolation

sepecies that process unique, exclusive mating signals and display certain courtship rituals are separated by what is known as Behavioural Isolation

Example of Behavioural Isolation is the courtship rituals performed by blue-footed boobies. Part of the rituals calls for male to ‘high-step’, displaying the blue feet that is characteristic of the species

Prezygotic BarriersTemporal Isolation

Two sepecies that breed at different times of the day, different seasons or different years are separate by temporal isolationExample is the periodical

cicada Magicicada septendecim, which spends most of its life in several

juvenile stages underground.

Postzygotic Barriers• Reduced Hybrid Viability

After the formation of a zygote, genetic incompatibility between two species may abort the development of the hybrid at some embryonic stage,or produce frail offspring in cases where hybrid development is complete.

Example, frog genus Rana, of which several species live in the same regions and habitats and occasionally hybridise

Postzygotic Barriers• Hybrid Breakdown

In cases where mating takes place across species, the hybrid survives but with very low fitness. This prevents gene flow between species.

Example of this can be seen in cotton plant

Postzygotic Barriers• Reduced Hybrid fertility

Even when the hybrid of two species successfully mate and produce vigorous offspring, reduced hybrid fertility or hybrid sterility occurs where by the hybrid offspring are completely or largely sterile.

Example, the mule is a robust but sterile hybrid between a horse and a donkey

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