FORMATION OF NEW SPECIES

• Speciation- when over time, 2 populations become so different that they can no longer interbreed.

There are 3 steps to speciation

1. Separation

2. Adaptation

3. Division

1. Separation- portion of the population becomes isolated.

Example: canyon forms, mountain range, volcano, tsunami

For example, 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 some of 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 from their slimy nursery onto the lonely island. The two portions of the population, mainland and island, are now too far apart to reproduce with each other. At this point, speciation has not occurred—any fruit flies that got back to the mainland could mate and produce healthy offspring with the mainland flies.

2. Adaptation-as the environment changes, so may the population living there change and evolve separately to form separate species.

The populations diverge: Ecological conditions are slightly different on the island, and the island population evolves under different conditions and experiences different random events than the mainland population does. Color, shape, food preferences, and courtship displays change over the course of any generations of natural selection.

3. Division– over hundreds to thousands of generations, the 2 groups became so different that they were no longer the same species and could no longer interbreed.

So we meet again: When another storm reintroduces the island flies to the mainland, they will not readily mate with the mainland flies since they’ve evolved different courtship behaviors. The few that do mate with the mainland flies, produce inviable eggs because of other genetic differences between the two populations. The lineage has split now that genes cannot flow between the populations.

The Kaibab squirrel (right) became isolated in the Grand Canyon ~ 10,000 years ago. Features have gradually evolved that separate it from close relative, the Abert squirrel (left) .

Croatian Lizards

• Experiment: Scientists removed 5 pairs of insectivorous species to a new island habitat

• Old island habitat had very little plants – Lizard diet was 93% insects, 7% plants

• New island habitat had an abundance of plants

• After 40 years, the lizard diet was 36% insect and 64% plant

• In just a few decades the lizards have developed a completely new digestive structure, larger heads, and a harder bite, researchers say.

Galapagos tortoise• All subspecies of Galapagos tortoise evolved from a common ancestor that arrived from mainland South America about 6-12 million years ago.• A volcano formed the oldest Galapagos Island. Tortoises that arrived there colonized the island.• The distance between the islands prohibited much inter-breeding and resulted in independent evolution of the populations.

http://www.youtube.com/watch?v=yVqJ_mQazik

http://www.youtube.com/watch?v=8cn0kf8mhS4