Groupx+24

Joanne Afulukwe, Ofonime Ebong, Hannah Osman, Clarissa Gardner, Jumana Baz, Manish Mistry

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=**__Introduction:__**= We are studying the evolutionary forces that maintain polymorphism within the species //Cepaea Nemoralis// at Monk's Riseborough. Also known as the grove snail or brown-lipped snail, this is a land snail found commonly in Europe. It is a model organism for evolutionary study as its shell banding is directly related to one genetic factor, from which great diversity can arise based on certain environmental factors. The differences in patterns of shells, helps to identify genetically different individuals. The following properties can be used to indicate polymorphism.

Bands can range in number from 0 to 5 on a shell and the arrangements can vary greatly, in terms of fusion of nearby bands and strength of pigmentation. This suggests many phenotypes within the population. To support this, background colours of the shell also exhibit many varieties of colour, including: yellow pink and brown. Additionally these also vary in shades and strengths of pigmentation colours, which can also be superimposed on each other. These phenotypes are expressed by a supergene, a collection of genes on the same chromosome (Jones et al. 1977).

Selection comes in forms both visual and climactic. For example, previous studies indicate that lighter coloured snails are more often found in grassland areas in comparison to darker coloured snails, which were mostly found in woodland areas. This study aims to measure the effects of gene flow, genetic drift and forms of natural selection on the polymorphisms of //C. Nemoralis// byfocussing specifically on whether light intensity has a significant effect on the shell polymorphism of this species.

By sampling snails from a number of different environments we will come to a conclusion on whether the snails we sample in the lighter grassland areas have a higher frequency of snails with lighter coloured shells, and conversely in the darker woodland areas.

It is to be expected that differences in phenotypes will be based on location and environment due to a selection pressure. Where there is little variation in terms of shell patterns we can expect genetic drift to be acting on that allele, reducing genetic variation. Where there is a similarity between two isolated groups, in terms of patterns we can attribute this to gene flow. <range type="comment" id="530465262_9">Using these ideas we can proceed to identify the main driving force behind polymorphism for this species (Jones et al. 1977).</range id="530465262_9">

REFERENCES

Jones, J.S., Leitch, B.H., Rawlings, P. 1977. Polymorphism in Cepaea : A Problem with Too Many Solutions? Ann Rev Ecol Syst. **8**, 109-143