Transcript Methods of Speciation

SPECIATION
Key Concepts: Isolation and reduced gene flow
Biological Species Concept: (Ernst Mayr, 1942) Members of a
species successfully interbreed and produce fertile offspring.
They are reproductively isolated from other species. Gene
flow occurs only between members of the same species.
Their reproductive isolation can be in the form of pre-zygotic
factors (those things that prevent mating in the first place) or
post-zygotic factors (those things that happen after mating)
Problems with the BCS:
What about asexually reproducing organsims?
What about single sex organisms (ex. Killifish) ?
What about species that hybridize?
Other species concepts;
Recognition concept: members of a species recognize each other as
potential mates and interbreed.
Morphological concept: Members of a species resemble one another and
interbreed.
Phylogenetic Concept: Members of a species are the smallest set or
organisms sharing a common ancestor and DNA lineage. Phenotypic
variation matters less than DNA variation.
Ecological Concept: Members of a species interbreed and occupy the
same ecological niche.
Methods of Speciation
How New Species May Arise
Allopatric Speciation
“Different Country Speciation”
In this case, members of a population become
geographically isolated from each other and thus
have very little or no gene flow between them.
Mutations arise in the separated population and
natural selection happens and over time this
population becomes reproductively isolated from the
original one.
Often thought to be important to populations
isolated on islands or by significant geological events.
- iguanas blown onto an island by a storm
- -squirrels in the Grand Canyon
- -fruit fly maltose vs sucrose
- -ring species salamanders
Sympatric Speciation
“Same Country”
No geographical barrier is needed in this model
Members of the population remain in contact with each
other but gene flow becomes reduced between some
members of the population
How could this happen?
Habitat selection (apples vs hawthorns)
Polyploidy in plants
Sexual selection in fish (cichlids in Lake Malawi)