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Part 6.1: The One-Island Model of Migration and Water Snakes in Lake Erie

Module 6.1 Evolutionary Mechanism II - Migration, Genetic Drift, Migration, and Non-Random Mating

Blog #1 - How migration affects the polymorphisms in snakes 

Observed phenotype distributions in mainland and water snakes

Migration is the movement of alleles between populations with geographic variation which is also known as gene flow. The one-island model of migration suggests that the impact of migration is greater on smaller populations (island) than larger populations (mainland). This occurs due to the smaller genetic diversity in the population. 

Figure 1: Migration Image

Figure 2: Image of the islands in Lake Erie 

Phenotype D: striped phenotype (provides camouflages in the leaf litter of forest streams)
Phenotypes B & C: Reduced stripping 
Phenotype A: Gray Color phenotype or stripless phenotype (adaptive on islands)

Figure 3: Data on the frequency of different phenotypes on various mainland and island snake populations 

Mainland Snakes: 

Ontario - Most common phenotype: D
  • Phenotype A: Gray Color phenotype or stripless phenotype 0%
  • Phenotypes B: Reduced stripping 0%
  • Phenotype C: stripless phenotype 0%
  • Phenotype D: striped phenotype 100%
Ontario snake population shows that migration is NOT acting on its populations as 100% of its snakes express the same (striped) phenotype. 

Penisular Mainland - Most common phenotype: D
    • Phenotype A: Gray Color phenotype  or stripless phenotype~7%
    • Phenotypes B: Reduced stripping ~3%
    • Phenotype C: Reduced stripping 10%
    • Phenotype D: striped phenotype 80%
    While the peninsular mainland exhibits more genetic diversity, phenotype D (80%) is still very prominent among the population 

    Water Snakes:

    Evolutionary forces needed to act on water snakes to increase their fitness on islands and to preserve their ability to camouflage - this resulted in three additional phenotypes. 

    Kelleys Islands - Most common phenotype: B & C
      • Phenotype A: Gray Color phenotype or stripless phenotype 10%
      • Phenotypes B: Reduced stripping 30%
      • Phenotype C: Reduced stripping 50%
      • Phenotype D: striped phenotype 10%
      The water snakes in the Kelleys Islands, the majority of the snakes exhibited a reduced stripping phenotype (B/C). However, striped phenotype (mostly observed in the mainland) was found in the island suggesting migration occurring within the population.  

      Bass complex Islands - Most common phenotype: A & B
        • Phenotype A: Gray Color phenotype or stripless phenotype 38%
        • Phenotypes B: Reduced stripping 39%
        • Phenotype C: Reduced stripping 19%
        • Phenotype D: striped phenotype 4%
        In the Bass Complex Islands exhibited a low striped phenotype. Other phenotypes were more prominent in the population that increased fitness of the snakes however, no phenotype was availbile in the population more than 50%. This may suggest that migration of snakes from the midland could affect the phenotypic expression. 

        Middle and Pelee Islands- Most common phenotype: A
          • Phenotype A: Gray Color phenotype or stripless phenotype 64%
          • Phenotypes B: Reduced stripping 19%
          • Phenotype C: Reduced stripping 14%
          • Phenotype D: striped phenotype 4%
          The Middle and Pelee Islands has genetic diversity however phenotype A was most common on the population. This suggests that the snakes adapted on the island. Additionally, the striped phenotypes was low which may suggest migration of mainland snakes to the Middle and Pelee Islands may be very little. 

          Ontario snake population shows that migration is NOT acting on its populations as 100% of its snakes express the same (striped) phenotype. The one-island model of migration suggests that the impact of migration would be greater on the island than on the mainland due to the fact that the island contains a smaller population. Based on all the island and mainland data (except for Ontario) prove that the impact on migration is greater among island populations than mainland populations. One limitation this data has is the inconsistency of N which may skew the results. 

          *All information was based on BIOL 520 class material.

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