Speciation How does a population evolve into separate species? Adapted from: Evolution 101: Reproductive Isolation. University of California Museum of Paleontology,

What is Geographic Isolation? One population of organisms separated into two smaller populations by a physical barrier. One population of organisms separated into two smaller populations by a physical barrier. Human modification of the environment can also cause geographic isolation of populations. Human modification of the environment can also cause geographic isolation of populations. Types of Geographic Barriers: Mountains Mountains Bodies of water Bodies of water Deserts Deserts Valleys Valleys Shopping malls Shopping malls Large expressways Large expressways

The Scene A population of wild fruit flies were minding its own business, cheerfully laying their eggs in a bunch of mushy bananas when… A population of wild fruit flies were minding its own business, cheerfully laying their eggs in a bunch of mushy bananas when…

Disaster Strikes! A hurricane washes the bananas carrying the immature fruit flies out to sea. A hurricane washes the bananas carrying the immature fruit flies out to sea. The banana bunch eventually washes up on an island off the coast of the mainland. The banana bunch eventually washes up on an island off the coast of the mainland. The fruit flies emerge from their slimy nursery and explore their new island home. The fruit flies emerge from their slimy nursery and explore their new island home.

Selective Pressures Ecological conditions on this island were different than on the mainland. Different fruits were abundant on this island. How will the fruit flies survive?

Survival of the Fittest Selective pressures favored those fruit flies that preferred mangos. Selective pressures favored those fruit flies that preferred mangos. Hanging around the mangos, these flies had greater chances of finding mates and passing their “fit” genes to their offspring. Hanging around the mangos, these flies had greater chances of finding mates and passing their “fit” genes to their offspring.

They Meet Again! When another storm reintroduces the island flies to the mainland, they do not readily mate with the mainland flies because of different food preferences and courtship behaviors. When another storm reintroduces the island flies to the mainland, they do not readily mate with the mainland flies because of different food preferences and courtship behaviors.

The Populations Diverge The island fruit flies experienced random mutations and different selection pressures. The island fruit flies experienced random mutations and different selection pressures. Morphology, food preferences, and courtship displays change over the course of many generations of natural selection Morphology, food preferences, and courtship displays change over the course of many generations of natural selection

Speciation Occurs The few that do mate with mainland flies, produce eggs that are not viable due to other genetic differences between the two populations from random mutations and genetic shuffling. The few that do mate with mainland flies, produce eggs that are not viable due to other genetic differences between the two populations from random mutations and genetic shuffling. Since genes cannot flow between the populations, they are now considered two separate species! Since genes cannot flow between the populations, they are now considered two separate species!

So What Exactly Happened? Geographic isolation began the speciation process, genetic changes are necessary to complete the process. Geographic isolation began the speciation process, genetic changes are necessary to complete the process. Selection pressures favored flies that preferred mangos. These flies mated with each other. Selection pressures favored flies that preferred mangos. These flies mated with each other. Random mutations and genetic shuffling added further variations to the island population. Random mutations and genetic shuffling added further variations to the island population. Over many generations, the island and mainland populations diverged and became separate species. Over many generations, the island and mainland populations diverged and became separate species.

Adaptive Radiation Darwin's finches are an excellent example of the way in which species' gene pools have adapted in order for long term survival via their offspring. Darwin's finches are an excellent example of the way in which species' gene pools have adapted in order for long term survival via their offspring. Darwin's Finches illustrate the way the finch has adapted to take advantage of feeding in different ecological niches. Darwin's Finches illustrate the way the finch has adapted to take advantage of feeding in different ecological niches. Their beaks have evolved over time to be best suited to their function. Their beaks have evolved over time to be best suited to their function.

The End!