Snakes of the same species live on both the mainland and on the island. However, snakes on the mainland typically show to be completely or semi-banded, while those found on the island are mostly without bands. The non-banded snakes on the island seem to blend better with their surroundings. Yet, the banding phenotype still shows presence in the population due to snakes swimming across from the mainland. Describe how migration and natural selection operate in a population of water snakes living on islands in Lake Erie. What is the combined effect of these processes on the water snake population? How does the actual situation compare to the model with respect to the predicted equilibrium allele frequency for bands? (based off of ch6 and 7 of evolutionary analysis 5th edition)
Added by Mason W.
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Migration: Snakes from the mainland, which are typically banded or semi-banded, swim across to the island. This introduces the banded phenotype into the island population. Show more…
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Below are the results of the experiment that we discussed in class regarding banding patterns on snakes in Lake Erie. Researchers determined the percentage of snakes that were banded in mainland Ohio and on three separate islands in Lake Erie (Pelee, North Bass, and Kelley's Islands). What did researchers conclude based on these results? Banded Unbanded Pelee Island North Bass Island Middle Bass Island Rattlesnake Island Middle Island South Bass Island Kelley's Island Banded Unbanded Ohio Banded Unbanded Gene flow from the mainland snake populations to the island snake populations is likely preventing the island snakes from adapting to the environment on the islands. Genetic drift is causing allele frequencies to change on the islands through the founder effect. The island snakes are a different species than the mainland snakes. Frequency-dependent selection is occurring that is preventing the banded snakes from predominating on the islands. A new allele was recently created in the population of mainland snakes that makes all the snakes have a banded pattern.
Matthew S.
Natural selection acts (through predation) against banded water snakes on certain Lake Erie islands, favoring the uniformly light-colored snakes. The banded form is very common on the nearby mainland. Yet, banded snakes are maintained in the island populations and not eliminated completely. This is probably due to mutation, low genetic and natural selection. Genetic drift will tend to increase genetic variability both within and between populations. The Hardy-Weinberg equilibrium represents an idealized, evolution-free population in which the allele frequencies and genotype frequencies will not change over time. In order for this to happen, five conditions must be met: there must be no mutation; there must be no gene flow between populations; the populations must be very large; mating must be random; and there must be no natural selection. If any of these conditions were violated, genetic change, thus evolution, would occur in the populations of subsequent generations. Suppose that only one condition were violated, that the population was very small. In this situation, the evolution would probably be due to mutation, migration, genetic drift, natural selection, or all of the above. The gene pool is the total number of copies of an allele for a specific gene in a population. The Hardy-Weinberg principle is a model of population genetics that shows that evolution will occur if all of the conditions of the principle are met. It is also a model of population genetics that describes how evolution occurs in nature. Both the first and third answers are correct.
Adi S.
Recall the banded snake example we covered during our gene flow lecture. The current fitness of banded water snakes on islands in Lake Erie is estimated to be approximately 0.7. If their fitness was much lower, say 0.2, what would we expect to happen to the amount of gene flow between the mainland and island populations? It would decrease since fewer banded snakes would survive long enough to reproduce on the islands. It would remain the same. It would increase since the banded snakes that do survive will have a large relative importance. It would decrease since fewer banded snakes would leave the mainland for the islands.
Md.Daniyal A.
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