ACTIVITY 97: ORIGIN OF THE SPECIES

97: ORIGIN OF THE SPECIES Challenge  What role do mutations play in natural selection? Useful Vocabulary: Mutations Speciation

When the DNA within a species becomes SO different (mutations) that it can no longer reproduce successfully, speciation is said to occur. Speciation – The divergence, or branching, of one species into 2 distinct species.

EXAMPLE OF SPECIATION: The scene: 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 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 for gene flow to unite them. 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.

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

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.

ANTICIPATION GUIDE 1)Complete the before column in the anticipation guide as best as you can. 2)Tape or Glue the anticipation guide into your Science Journals.

PROCEDURE While you read the information, be sure to complete each Stopping to Think Question in your notebooks (In complete sentences)

STOPPING TO THINK 1 Physical Features likely to be a result of genetic differences Physical features that may not be a result of genetics, but as a result of some other factor from birth to adulthood Physical features that might be a result of both genetic and other factors Hair color Eye color Skin color Height Amputations Burns Tattoos Piercings Scars Skin tone Intelligence Personality Weight Muscles

STOPPING TO THINK 2 a.A mutation in a puppy that would be neither helpful or harmful would be different colored eyes b.A mutation in a puppy that could be harmful could be missing a leg.

STOPPING TO THINK 3 You can NOT choose your traits. Your genes are passed to you by your parents at conception. These traits are INHERITED and not Acquired.

STOPPING TO THINK 4 I would disagree with my friend. The Total number of mutations in the Galapagos Finches would have exceeded 14. It is also unlikely that one mutation will prevent 2 populations from interbreeding, or change their breeding habits enough that they no longer try.

ANALYSIS #1 Mutations are not always helpful Since mutation occur randomly, many or most of them are either harmful or neither helpful OR harmful. In addition, whether a mutation is helpful is relative to the particular environment. In general, if a mutation becomes common in a population, it must have been helpful, or advantageous, for that population.

ANALYSIS #2 Originally there was just one species of cichlid. A cichlid was born with a mutation that allowed it to withstand colder water. When there was a shortage of food, this cichlid could survive on different food that then other cichlids because it could go deeper in the lake It survived, reproduced, and passed on its traits to its offspring. Over time, there were 2 types of cichlids. One spent most time in deeper levels. The two types interbreed less and less. Eventually as a result of accumulated mutations, the 2 types of species could no longer interbreed. At this point they become 2 different species.

ANALYSIS #3 Bacteria must evolve faster, since their populations go through so many more cycles of reproduction within equivalent time periods In fact, bacteria are far more capable of surviving sudden environmental changes than slower reproducing species such as humans and other complex species This helps to explain Antibiotic Resistance!