Shell shape and shell thickness of the intertidal snail Littorina obtusata has c

Question

Shell shape and shell thickness of the intertidal snail Littorina obtusata has changed markedly between 1871 and 1984 in northern New England. Shells collected prior to 1900 were tall with thin walls, whereas shells collected in 1982-84 were short with thick walls. An intertidal crab, Carcinus maenas, which preys on obtusata was not abundant in northern New England until around 1900. Field and laboratory experiments have shown that the tall, thin-walled form of L. obtusata, which can still be found in some areas, is more vulnerable to predation by Carcinus than is the low-spired form of L. obtusata.

Has evolution by natural selection occurred in L. obtusata populations? Why or why not? In your answer be sure to explain the basic elements required for natural selection and if you need to assume anything be sure to list your assumption.

Be sure to include proper grammar, sentence structure, and scientific format. Define the elements required for natural selection, relate these principles to the observations in this study, and list your assumptions.

Explanation / Answer

Evolution basically means development which is a slow stage process that depends on adaptation to different environments. If an organism is adapting to a new environment then it will be reflected in its genes and that is passed on to its generations.

We have evolved from bacteria, which is because of evolutionary changes that resulted billions of years ago. Each and every organism of the Earth is interconnected and thats why we have such huge biodiversity.

Changes are continuously happening to evolve better and better. So environmental factors play a major role in evolution.

Natural selection is based on the fact that individuals which can survive and reproduce at any given environment is the most fit. Hence, all the individuals in a population selected by natural selection will be most fit which can pass on its traits to next generation to increase the population size.

Adaptation to new environment or to any given environment, the changes need to be at the genetic level where mutation occurs. A change or mutation brings about a new trait which can adapt to new environment. Hence, natural selection preserves that trait or genetic variation by selecting that best fit individual from other non-adaptable traits. And, it can directly means that it preserves more genetic variation or traits which are called survival of the fittest.

In this case, natural selection has occured because shells which are short and thick are naturally selected trait in order to protect themselves (Littorina obtusata) from the predator (Carcinus maenas). Until 1900, the predator was not abundant so, Littorina obtusata had shells which are thin and tall (predator problem was less). But after 1900, predator problem was prominent, therefore in order to protect, new traits (thick and short) were developed.

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