Evolution – Formation of New Species

What is a species?

Biological species concept - groups of interbreeding natural populations that are reproductively isolated from other such groups.

(not quite clear cut... There are problems with this definition, but it’s the best we have…)

Evolution – Formation of New Species

Organisms that look alike may be different species

Organisms that look very different may be considered the same species

Evolution – Formation of New SpeciesOrganisms from different species may be able to to interbreed

Some organisms like bacteria simply do not interbreed...

Evolution – Formation of New Species

Sometimes, the transition from one species to the next is not clear cut

Evolution – Formation of New Species

Speciation depends on two factors:

1. Isolation of populations

2. Genetic divergence

Evolution – Formation of New SpeciesMechanisms

Speciation can occur through allopatric or sympatric means.

Evolution – Formation of New SpeciesMechanisms

Speciation can occur through allopatric or sympatric means.

Evolution – Formation of New SpeciesMechanisms

Speciation can occur through allopatric or sympatric means.

In allopatric speciation, genetic flow is reduced through geographic isolation

In sympatric speciation, genetic flow is reduced through ecological isolation orchromosomal aberrations

(Chromosomal aberrations are more common in plants because they can self fertilize)

Evolution – Formation of New SpeciesMechanisms

Speciation occurs over space and time!

Using the fossil record, we can see creation of new species over time,as well as changes in individual species over time

Note that changes and formations of new species is not a constant process over time – Why?

Evolution – Formation of New SpeciesMechanisms

Adaptive Radiation – one species gives rise to many... occurs when populations of a single species invade a variety of new habitats and evolve in response to the differing environmental pressures in those habitats.

Evolution – Formation of New SpeciesMechanisms

Mechanisms for reproductive isolation (a general overview):

Pre-mating Isolation -

1. Geographic isolation

2. Ecological isolation

3. Temporal isolation

4. Behavioral isolation

5. Mechanical incompatibility

Post-mating Isolation -

1. Gametic Incompatibility

2. Hybrid inviablity

3. Hybrid infertility

Evolution – Formation of New SpeciesMechanisms

New species are always formed, while others go extinct. Over 99.9% of all speciesthat have ever existed are now extinct!!

Major causes of extinction:

1. Competition among species

2. Introduction of new predators or parasites

3. Destruction (or rapid change) of habitat