Martin+et+al

//Cepaea nemoralis//, commonly known as the grove snail, is an air-breathing land snail and is the subject of the study in this investigation. They are one of the most common species of land snail in Europe and so very easy to locate and do a study on. //C. nemoralis// have a highly polymorphic shell pattern, of which each pattern can be distinguished relatively clearly from one another (unlike in other species), which is one reason why these snails were the chosen species of study. The shell pattern (number of bands and colour) of this particular snail is simply inherited and as mentioned before easily distinguishable from one another, which is crucial when collecting data to, overall, assess whether genetic drift, gene flow and/or selection are the cause of differences (if there is any) in frequency levels. Snails tend to not move far in their lifetime (an estimation of 20m), and so selecting a study site large enough to carry out the investigation is far easier than say selecting humans, who travel a great deal more, to different continents! Also due to their low lifespan, multiple generations can also be assessed. Finally, //C. nemoralis// are small species and thus easy to collect and observe. The sampling method involved a horizontal transect across two habitats, where six samples of snails were taken. A horizontal transect allows the control of altitude as a variable and thus it can be eliminated as a possible factor effecting the results. Woodland (the third type of habitat) was also eliminated purely due to lack of time, and as such only a limited number of samples could be taken. Removing woodland allowed replication of samples to occur in the other two habitats and thus a more detailed comparison could be taken. As mentioned, the sampling regime permits both habitats to be sampled three times allowing replication in the results hence increasing the reliability of the results. Comparisons between (and within) each habitat could then be carried out. Also, another key point to the sample method is that some of the samples are far enough away from each other so that the samples are independent reducing the effects of gene flow. From the sampling, the proportions of the different shell patterns will be analysed. Through this experiment and in creating the sampling regime, key principles have been enforced, for example, ensuring independent samples were taken through large enough distances between samples. Another lesson is to ensure that variables that are not part of the analysis should be controlled. Repetition and replication must be present in the sampling method to allow comparisons to occur. Standardising the shell pattern categories of the //C. nemoralis// amongst the group before collection of data is also necessary to reduce human error. The null hypothesis states that selection does not play a part in the variation of the frequency, just genetic drift and gene flow. To support this hypothesis; inconsistent differences between the populations would be observed, supporting the fact that selection does not play a role as there isn’t one specific phenotype that is beneficial for a specific habitat. The alternate hypothesis states that genetic drift, gene flow and selection all play a role in the phenotypic variations between snail populations. To support this hypothesis, (to detect selection) consistent differences between each habitat sample would be observed. Add names of group members
 * __Introduction__**