Question

Background: You are studying three populations of an endangered species of toad that used to be common in the California central valley. Global warming has caused this species to retreat to higher elevations in recent decades where it stays cooler; the toad used to be found throughout the valley, but is now restricted to the tops of three mountains. Sampling each population reveals that the toad population on each mountaintop is limited to a few hundred individuals, whereas historical records indicate that there used to be hundreds of thousands of toads in the central valley. You survey allozyme diversity at one locus on each of the three mountaintops. You find that each population is fixed for a different allele: the population on mountain #1 is fixed for the A1 allele, mountain #2 for the A2 allele, and mountain #3 for the A3 allele. The average number of baby toads born in each population is the same, and the environment on each mountaintop is similar as far as your data show.

Question: Explain why each population is fixed for a different allele.

Your answer:

Sentence 1: Describe the variability that was initially present in each of the populations.

Sentence 2: State which individuals had the highest fitness in a given population, or why fitness is not an issue if that is your conclusion.

Sentence 3: Explain what evolutionary force acted on the population(s), and why and how it acted.

Sentence 4: Describe how the populations evolved in response to their changing environment. Be as specific as you can (e.g., say “increased” or “decreased”, rather than just “changed”.)

Answer 1

Initially when the toads we occupying the central valley of california had three different populations which means that though  they belonged to the same community they had a slight difference amongst themselves which had been caused due to the mutations in their genomes, which caused variability within the species. These mutations may have been caused due to the changes in the geographical conditions of the places which they live , biotic and the abiotic factors of the particular ecosystem. In accordance to the theory of natural selection, the individual toads that had the highest fitness to survive through the process of changing climatic conditions have lived whereas the others that could not  sustain the climatic variations have been eliminated . The evolutionary change that had happened in this case is mutation that has caused a genetic drift to occur, this mutation has been adopted by the organisms in order to get through the process of natural selection. It is this process, that has made them to be colonised to various mountains according to the mutation that had taken place in their system. Natural selection phenomenon has been applied which has caused the thousands of toads to get reduced to hundreds in number.The populations have evolved in a variety of aspects to make them suitable for the climatic challenge that occured.  Moreover, the gene that helps them to resist to the climatic temperature fluctuations would have been increased to enable them to survive. The genes that are required for their survival in specific mountain tops would have also increased. In addition, the expression of the genes that enable the organisms to survive in the high altitudes would have also increased inorder to concentrate them on the mountain tops. The genes that make the organism susceptable to rising temperatures would have decresed.