J'adore+les+escargots*

Group members: Sam Windross Morgan Vondee Jaynita Patel Sara Khan Raj Piraveen Rajaratnam

__Introduction __

Polymorphism is essentially a condition where different phenotypes exist in the same population of a species; on a genetic level it is where many alleles are at the same locus of a chromosome in a population (1). When new alleles arrive in a population through mutation, a number of forces are involved in either fixing them (in the population) or causing them to be lost completely. These forces are gene flow, genetic drift and natural selection. The investigation studies whether natural selection and genetic drift or genetic drift alone is responsible for the polymorphism exhibited in the snail species //Cepaea nemoralis//; the phenotypic polymorphism that will be studied is the banding and colours of the //C. nemoralis// snail shell. //Cepaea nemoralis //, commonly known as the brown-lipped snail or the banded wood snail, was discovered by Linnaeus in 1758. The snails are native to Western Europe but are generally distributed in North America and Central and Western Europe, and are commonly found in urban areas, but can also be found in woodland, shrubland and grassland areas (1). //Cepaea nemoralis// are studied due to their varied phenotypes such as different shell colours and different banding patterns. They are preferable to study because they only move up to approximately 30 meters in their lifetime, compared to humans, who have a greater ability to travel (high rates of gene flow) as well as a greater spread across the planet. //C. nemoralis// have a short life span meaning that the phenotypes of several generations can be analysed. To identify the effects of Natural Selection, Genetic Drift and Gene Flow within a population, //C. nemoralis// will be our organism of choice. The sampling strategy involves taking samples along a transect from shrub habitat and grassland; these samples will be taken on the same altitude. By ensuring the same altitude for each sampling area we will control factors caused by varied elevation such as temperature. The samples will be around 20 meters apart allowing us to attain a large snail sample that is representative of the population, <range type="comment" id="388247952_4">as well as reduce the possibility of gene flow between the different areas.</range id="388247952_4"> <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">If we were to determine that polymorphism of //C. nemoralis// was due to natural selection we would observe a phenotype that has a significantly higher frequency in one type of habitat than another. If the intensity of genetic drift was greater than selection on the population of snails, we will expect to see <range type="comment" id="388247952_5">random phenotypic frequencies across the different habitats, also there would be smaller differences in the frequency of polymorphs between populations (2). </range id="388247952_5">Whether a pattern indicating natural selection or genetic drift (as the cause of polymorphism) is identified several replicate samples will be taken to ensure the consistency of the observation. <range type="comment" id="388247952_6">A chi squared test will be used to assess the significance of the results.</range id="388247952_6">

<span style="background-color: white; font-family: 'Times New Roman',serif; font-size: 12pt;">In this investigation the null hypothesis is that polymorphism of Cepaea nemoralis in grass land and shrubs is not due to natural selection, but genetic drift and gene flow. The alternative hypothesis is that polymorphism of Cepaea nemoralis <span style="background-color: white; font-family: 'Times New Roman',serif; font-size: 12pt;">in grassland and shrubs is due to natural selection in the majority of cases, with genetic drift and gene flow being minor influences. <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">We hope as stated in our hypothesis t<range type="comment" id="388247952_7">o see how selection acts w</range id="388247952_7">ithin the snail population as opposed to that of drift and gene flow, by observing consistent phenotypic frequency variations between the two habitats of shrub and grass land.


 * 1) <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">1. <span style="background-color: white; font-family: 'Times New Roman',serif; font-size: 12pt;">Jones, J.S., Leith, B.H., Rawlings, P. 1977. Polymorphism in Cepaea: a problem with too many solutions? // Ann. Rev. Ecol. Syst // . ** 8 ** :109-143.
 * 2) <span style="font-family: 'Times New Roman',serif; font-size: 12pt;">2. Barton, N.H., Briggs, D.E.G., Eisen, J.A., Goldstein, D.B., Patel, N.H. 2007. Evolution. Cold spring Harbor Laboratory press. New York, united states of America.