Migration and Water Snakes

 


Stripes = D  — for mainland
Reduced striping = B and C
Stripeless, gray color = A  — for island

In Ontario, which in this graph means further into the mainland, the only phenotype recorded is that of         snakes characterized by complete stripes. In the peninsular mainland, the strong stripe phenotype is still very prominent and most popular, but the other phenotypes, reducing stripe pattern and no stripe pattern at all, are present in low numbers. On Kelleys Island, the reduced stripe pattern is most common, while the strong stripe and no stripe at all are low but at the same number. It is noted that Kelleys Island is one of the islands closest to the mainland. The Bass complex Islands have more no stripe phenotypes while the stripe phenotype is lowest in number. Finally, the Middle & Pelee Islands have the largest number of completely no stripe phenotype snakes. The general pattern that emerges is that the further away from the mainland, the less snakes that have stripes and the more snakes that have no stripes. The closer to the mainland, the more likely the snakes are to have stronger pattern of stripes. 

The snakes from the mainland can travel a distance to the peninsular islands or the closer islands and spread their numbers there. That is why these places have the highest number of this phenotype at these places. The peninsular island and islands close to the mainland have numbers of lesser stripe phenotype snakes because the more common no stripe snakes on the very far islands can travel near. The fact that there is not total speciation, that there is not a dichotomy of striped or not striped snakes, means there is migration between the two phenotypes. This has likely caused the reduced, but not totally eradicated, stripe phenotype of snake which are more popular in the middling islands. As to evolutionary consequences of migration for populations, migration introduces variation into populations. Greater variation means a better chance for a trait that is beneficial for the organism and will be selected for. Additionally, migration slows down speciation. Because the no stripes and ‘yes’ stripes snakes are migrating between the islands and the mainland, they can still reproduce with one another and maintain the features and genetic material required for them to continue to breed. If there were no migration between the mainland and island snakes, speciation would likely result; the snake populations would become adapted to their local environments. Their traits would likely change significantly enough to better suit their environment and significantly enough that they would not be able to breed with one another.


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