The Effect Of Crab Predation On Snail Shell Synthesis

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Evolution by natural selection and predator induced phenotypic plasticity are mechanisms that have been proposed to describe the effect of crab predation on snail shell thickness. Biologist Robin Seeley hypothesized that the periwinkle populations of New England evolved by natural selection as the European green crab was introduced to the area (Seeley, 1986). The three requirements for evolution by natural selection are that there is variation among a population, the variation is partly hereditary, and certain variants are able to survive to reproduce at higher rates than others. Once these three conditions are met, it is believed that the snail population will evolve toward thicker shells. A simulation was used to model the distribution of …show more content…
One population composed of only thick shells showed the distribution of shell thickness to shift towards the center and snails with the thickest shell were not present. Nevertheless, the variation in shell thickness in the populations after the simulation depended on the variation present in the parent generation, indicating heritability. Therefore, the second requirement of evolution by natural selection was met by both the original crab infested and crab-free …show more content…
For the majority of the tanks, the variation in shell thickness matched that of the parent generation. The fourth tank which was initially composed of the thickest shells, were not as prevalent after the simulation. A possible explanation for the shift toward slightly thinner shell thickness is because of mutation that allows for additional shell thickness to appear among the population. Another explanation is that possessing a thick shell is expensive in terms of energy costs. Other studies have found that thinner shells are favored when crab predators are absent because they are less expensive to produce and allow the snails to experience rapid growth (Palmer, 1985). Due to the lack of predation in this case, there was no need to maintain a thicker sized shell and over time slightly thinner shells became more

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