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5 of 6 of my evolution unit. Image Credits: Biology (Campbell) 9th edition, copyright Pearson 2011, & The Internet. Provided under the terms of a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. By David Knuffke.

mariona vila

on 13 January 2014

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Transcript of Speciation

What is a specie?
Big Questions
Speciation = Reproductive Isolation
Species Barriers
Various mechanisms ("
") exist that prevent successful interspecies reproduction.
NOTE: "successful reproduction" = production of fertile offspring.

We can split these barriers into when they occur in relation to fertilization.
Prezygotic barriers
: Barriers prior to fertilization
Postzygotic barriers
: Barriers after fertilization
What is a species?

What is speciation?

How can evolutionary changes in a population lead to the production of new species?
A specie is defined as a group of organisms capable of interbreeding and producing fertile offspring
: Speciation is a lineage-splitting event that produces two or more separate species.

Series of evolutionary processes that result in the reproductive isolation of a population and create new species
Example of a process
The scene:
A population of wild fruit flies minding its own business on several bunches of rotting bananas, cheerfully laying their eggs in the mushy fruit...
Disaster strikes:

A hurricane washes the bananas and the immature fruit flies they contain out to sea.
The banana bunch eventually washes up on an island off the coast of the mainland.
The fruit flies mature and emerge onto the lonely island.
The two portions of the population, mainland and island, are now too far apart for gene flow to unite them.
IMPORTANT! At this point, speciation has not occurred—any fruit flies that got back to the island could mate and produce healthy offspring with the mainland flies.
The populations diverge:

The population of fruit flies from the island evolves under different circumstances than the mainland ones.
In consequence of that, the morphology, food preference and courtship displays change over the course of many generations of natural selection.
So we meet again:
When another strom introduces the islands flies to mainland, they will not readily mate with the mainland flies since they have evolved to different species.
The few that do mate with the mainland flies, produce inviable eggs beause of other genetic differences between the two populations.
IMPORTANT! The linage has split now that genes cannot flow between the populations.
Causes of Speciation
Geografic isolation
Reduction of gene flow
The process
= "other country"

A population is isolated from other populations because of geographic barriers.

If given enough time, and enough evolution, the populations will become reproductively isolated.
= "same country"

The populations remain in the same physical area, but become reproductively isolated from other populations because of other mechanisms.

A small population isolated at the edge of a larger population
Two different species of antelope squirrel, one for each rim of the grand canyon
The hybrid "Grolar Bear" offspring of a Polar bear and a Grizzly bear.
Modes of speciation
Thanks for your attention
Full transcript