6.1 Water Snakes in Lake Erie

When it comes to water snakes of Lake Erie, there are four major phenotypes to look at. Types A, B, and C live on the island, with type A being a stripe-less gray color and types B and C having a reduced number of stripes. Type D lives on the mainland, with it having a significantly higher number of stripes than those found on the island. Due to these trends, the percent of each phenotype found in the populations can be very informative as to the environment as well as the location. 

In Ontario, the mainland, the population consists of nearly 100% type D, where the high frequency of stripes assists in disguising the snakes in the leaf-ridden forest streams, working as camouflage as a survival mechanism adapted to the environment. While the peninsula is still a far majority of type D due to being attached to the mainland, you begin to see a slight mixture of the other phenotypes, likely due to migration from island to mainland. Kelleys Island and the Bass complex islands have a more even distribution of the phenotypes A, B, and C, with a largely reduced population in D. This is because these islands are apart from the mainland, leaving the population of D to be those who have migrated over, and are outnumbered for reproduction. The Middle and Pelee islands have a significantly high concentration of phenotype A, which is the stripe-less water snake. This indicates that the environment of these islands is likely rocky, so the water snakes evolved to have a gray exterior to help themselves blend in with their environment and increase their chances of survival. 

The major evolutionary consequence of migration within populations is that it causes increased genetic drift. If part of a population migrates away from the other part, they will begin to mutate and evolve independently causing an increase in variation. The longer these populations are apart, and the more genetic diversity grows, the greater the differences between populations will be to the point where there is a clear difference.