Group+100


 * Group members:**
 * Nikara Abylkassimova
 * Sara Zohny
 * Sophie Randall
 * Aikaterini Liarelli
 * Paula Muresan
 * Ekaterina Kapitonova*


 * Sampling design**

//Null hypothesis:// snail shell colours and banding patterns will not show variation in different sampling areas due to selective pressures. //Alternative Hypothesis//: snail shell colours and banding patterns will vary in different sampling areas due to selective pressures. 


 * Introduction **

The grove snail, //Cepaea nemoralis//, is one of the most common land snails in Europe and is found in a wide range of habitats including urban areas, gardens, parks, woodlands, plains, highlands, and dunes. It is a good model organism for population genetics studies because it displays its genotype on its shell, allowing a rapid genotypic survey. //C. nemoralis// takes approximately two years from hatching to becoming sexually mature, with a life span of seven to eight years. This, combined with its slow movement – a grove snail will typically only travel a distance of 10 meters in two years – allows observation of a population’s genetic patterns in a small field. The most common shell colours in //C. nemoralis// are pink, yellow, and brown, and shell banding patterns can display between 0 and 5 bands. Variation in shell colour and banding pattern in a population could be due to genetic drift, selection, or a combination of both. A field study can be carried out to determine which of the above factors affect genotypes in a //C. nemoralis// population. The Monks Risborough nature reserve was chosen for the field study because it is located on chalk downland, so calcium is abundant. There are large populations of several snail species on the nature reserve because they can easily build their calcium carbonate shells. The field has a variety of environments and terrains: there are areas of open grass, woodland, and shrub, at different elevations. Due to time constraints only six population samples could be recorded, so a sampling design was devised to represent different environments while minimizing pseudoreplication. Pseudoreplication occurs when there are not enough replicates per treatment and prevents accurate estimation of variability, without which statistical inferences cannot be made. The six populations sampled were located in woodland, open grass, and shrub, at both high and low elevations (see Figure 1). //Fig. 1: Sampling diagram of the sites chosen//

There are three main possible explanations of the genotypic data observed: sampling variation, where results vary due to chance and random sampling, genetic drift, which may explain some or all of the variation observed, or genetic drift and selection combined. It is assumed that sampling variation and genetic drift are always present, so the experiment will investigate the role of selection in the population’s genotypes. A χ² test of the raw data will be carried out to determine whether or not the variation observed is due to sampling variation. If the result of the test is significant, sampling variation can be eliminated as the most likely cause of the observed genotype variation. The results expected if the null hypothesis is accepted are that snail shell colours and banding patterns will not show variation in different sampling areas due to selective pressures. The expected results if the null hypothesis is rejected and the alternative hypothesis is accepted are that snail shell colours and banding patterns will vary in different sampling areas due to selective pressures.