speciation - interesting

8/10/2019 Speciation - interesting

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Speciation


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Introduction

Species continue to evolve

Changes that occur within species

(microevolution) are easy to understand

Faster-running cheetahs

Colourful male songbirds

Larger brains in humans

But what factors lead to speciation- the

evolution of an entirely new species?


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What is a Species?

A species includes all members of a

population that can interbreed under natural

conditions

Some species are quite distinct based on their

morphology but some species are only

distinguished by genetic comparisons


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Modes of Speciation

New species can evolve many ways

Always includes the evolution of distinctfeatures that isolate the new species

reproductively, therefore genetically, from

other species


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Mechanisms of Reproductive Isolation

any biological factor that prevents the two

populations from interbreeding when living in

the same region.

Prezygotic mechanisms: prevents interspecies

mating and fertilization

Different breeding seasons, physical or

behavioural traits, habitat preferences or the

incompatibility of gametes


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any biological factor that prevents the two

populations from interbreeding when living in

the same region.

Postzygotic mechanisms: prevents maturation

and reproduction in offspring from

interspecies reproduction


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Prezygotic

Temporal Isolation: Species have different breeding

seasons.

Example: Western spotted skunks breed in the fall butthe Eastern species breeds in late winter

Western Eastern


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Eastern Western


Prezygotic

Behavioural Isolation: Species may have different

courtship or mating behaviours.

Example: Eastern meadowlark and westernmeadowlark are almost identical in everything,

except their courtship rituals and songs


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Mechanisms of Reproductive IsolationPrezygotic

Mechanical Isolation: Species may have reproductivestructures that are physically incompatible.

Example: Snails of the same species have reproductivestructures that align, but snails from two different

species part the other species


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Prezygotic

Ecological Isolation: very similar species may occupy

different habitats within a region

Example: The mountain bluebird lives at high elevations, whilethe eastern bluebird prefers lower elevations. The

mountain bluebird and eastern blue bird do not encounter

each other


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Prezygotic

Gametic isolation: male gametes may not be able to

recognize and fertilize an egg of a different species

Example: corals, clams and sea cucumbers release theirsperm and eggs into open water. The sperm

recognize the egg of their own species through

chemical markers on the egg surface.


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Mechanisms of Reproductive IsolationPostzygotic

Zygotic Mortality: mating and fertilization are possible,but genetic differences result in a zygote that is

unable to develop properly

Example: If you have sheep and goats on a farm, some

species of sheep and goat are able to mate, but the

zygote is not viable.


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Hybrid Inviability: a hybrid dies early in development,or lives to maturity but is not healthy and suffers an

early death.

Example: Some salamanders species may mate with

each other, but most of the offspring do not live to

adulthood, or if they do they are weak.


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Hybrid Infertility: The hybrid offspring mature intoadults but are infertile.

Example: A mule is bred from a female horse (left)and a male donkey (centre). Mules are physically

healthy but they are infertile.


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Allopatric Speciation

Most new species form when asingle species is separated into twogeographically isolated populations

Once physically separated,populations cannot share geneticinformation

Over many generations thepopulations will gradually becomeless alike

Mutations and genetic drift mayhave caused populations to change

Reproductive isolating mechanisms

may have developed


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Allopatric Speciation

Harriss antelope squirrelWhite-tailed antelopesquirrel


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Sympatric Speciation

The evolution of populationswithin the same geographic area

into separate species

Individuals within a population

become genetically isolated from

the larger population

speciation - interesting

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