Darwinian Snail Lab Report

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Darwinian Snails: Introduction

The flat periwinkle is a small snail that lives on seaweeds growing on rocky shores in New England (McRae 2016). The scientific name of the periwinkle snail is Littorina obtusata. They were first introduced to the Atlantic Coast during the 19th century. These snails are known mainly for a morphological trait, the variation of shell thickness within the population. Several studies have been done already to study the evolution of the periwinkle snails shell thickness. Seeley (1986) found that introducing crabs to a population of L. obtusata demonstrated a classic example of Darwinian selection. The snails with a smaller shell thickness were selected against and were not able to survive and reproduce. Therefore,
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The periwinkle snails were eaten by their predator, the European Green Crab, and were observed on how their shell thickness evolved from before the European Green Crabs were released into the population and after the Crabs had already had several meals of the snails. It was hypothesized that after the European Green Crabs were released into the population, the snails with a smaller shell thickness (1-2 mm) would not be able to survive due to them being “unfit” for the environment, being that they were more likely to be eaten by the crabs because it required less energy to eat snails with a smaller shell thickness. Whereas, snails with a thicker shell would be able to survive and reproduce, being that they were less likely to be eaten by the crabs. This is a phenomenon known as survival of the …show more content…
Variation within the population is a crucial requirement in order for natural selection to occur. In the first part of this exercise, there was no variation in the population. This factor was used to simulate if the snails shell thickness would evolve. It was hypothesized that if there was no variation in the population, the shell thickness would remain the same after the crabs had several meals because variation must be present in order for evolution to occur. In the second part, inheritance was tested, and the snails had shell thicknesses that were not heritable. It was hypothesized that the snails shell thickness would not involve because the shell thickness was not inherited. In the third part of this exercise, selection was tested, the snails were not selected against when they were eaten, instead they were eaten at random. It was hypothesized that the snails shell thickness distribution would not change due to the snails being eaten at random because they were not being selected as to which snails were considered more fit for the

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