Speciation

Speciation The formation of a new species from pre-existing species.

What is a species? A population of physically similar organisms that can interbreed and produce fertile offspring fertile= able to produce more offspring Are these spiders the same species? Happy Face Spiders – although different are the same species

Same Species? Horse + Donkey = Mule + = Horse + Donkey = Mule Mules are sterile – unable to reproduce Conclusion: Horses and Donkeys are different species Chromosomes are similar enough to produce offspring but too different to produce a fertile offspring

Limits to Species Definition Impossible to test reproductive compatibility of extinct organisms Some organisms reproduce asexually- they don’t interbreed bacteria-reproduce asexually by binary fission bacteria produced by binary fission are genetically identical to one another

How do species form? Speciation requires isolation 2 parts of a population that interbreed are prevented from interbreeding

Two Types of Isolation Geographic – A physical barrier separates formerly interbreeding members of a population Example- Desert Pupfish 13 species of small fish in Southwest US.

Geographic Isolation Continued Area was once covered in a large lake during the last ice age -ice age ended – lake dried up -small populations of pupfish were isolated in small spring fed lakes- - lakes selected different phenotypes – led to new species

Reproductive Isolation Behavioral or physical differences that prevent members of a population from interbreeding

Reproductive Isolation Wood Frogs and Leopard frogs very closely related, but different mating calls and mating times prevent interbreeding

Reproductive Isolation continued Eastern and Western Meadow Larks-nearly identical,only hybridize at the edge of their range

Genetic drift

How do we track speciation?