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Polymorphism of //Cephaea nemoralis//

//Cepaea nemoralis// or the brown-lipped snail or grove snail is a common species of terrestrial snail in Europe. The grove snail has a highly variable phenotype; the shell of the snail can be yellow, brown or pink in hue and can also be unbanded or have many or few bands. Polymorphism is the variation of phenotypes within the same species, the polymorphism of //C. nemoralis// is representative of its genetics; the gene controlling shell colour forms a supergene with the genes for banded/unbanded, band pigmentation and lip colour. (Jones et al, 1977) The obvious polymorphism of the snail makes it appealing to study in terms of evolutionary genetics. The ease in which one can genetically classify a snail from its appearance is one of the reasons that we chose to study //C. nemoralis//. The visible polymorphism of the snail also makes it easy to study the effect that ecology can have on genetic variation within and between populations. This experiment has been designed to study the effect that different habitats have on the phenotype of //Cepaea nemoralis//.. Cain et al. (1950) found that environment is closely related to shell colour and banding pattern, for example the yellow coloured snails were more prevalent in green environments and un-banded snails were more common in the uniform environments. Our study aims to confirm that different habitats incur different selection pressures, resulting in the variation of phenotypes across the different habitats. There are many different aspects within a habitat that could be acting as selection pressures on a population of grove snails. For example, visual selection from predation by the song thrush or climatic selection across different altitudes or under varying amounts of cover. The study was conducted in a nature reserve in Buckinghamshire; this area was chosen due to its diverse number of habitats ranging from woodland through shrubs and bushes to open grassland. We chose to obtain samples from the most dramatically different habitats, so we sampled populations in woodland and grassland. Samples were taken at least 20 metre intervals in order to prevent sampling error by pseudo-replication. Hurlbert (1984), defined pseudo-replication as //"...a particular combination of experimental design (or sampling) and statistical analysis which is inappropriate for testing the hypothesis of interest."// This insured that the populations were isolated enough from each other to be considered separate populations and that our results would be appropriate for testing our hypothesis. Temperature affects the morph distribution of //C. nemoralis// (Jones et al, 2013) and temperature is influenced by altitude. Although temperature may vary between the covered woodland and open grassland, we took samples from similar altitudes to prevent this having any further effect on the temperature and influencing the results. We are examining the difference in phenotypic frequencies between woodland and grassland to assess whether the different selection pressures in a habitat can influence the phenotype frequency of the population in that habitat. We are expecting to find a difference in phenotype frequencies between habitats due to selection pressures from predation. We expect the populations to have a high frequency of snails with an advantageous phenotype that camouflages them against the background of their habitat. Alternatively we may find that there is no significant difference between populations and that natural selection is not influencing the phenotype frequency in populations of //C. nemoralis.//

//Heredity// (1950) 4, 275–294; doi:10.1038/hdy.1950.22 Selection in the polymorphic land snail //Cepaea nemoralis// A J Cain [|1] and P M Sheppard [|1] Department of Zoology and Comparative Anatomy, University of Oxford Received 31 January 1950. Hurlbert SH (1984). Pseudoreplication and the design of ecological field experiments. //Ecol Monogr// 54(2):187–211.

Polymorphism in Cepaea: A Problem with Too Many Solutions? J. S. Jones, B. H. Leith and P. Rawlings //Annual Review of Ecology and Systematics//, Vol. 8, (1977), pp. 109-143

Robert A. D. Cameron and Laurence M. Cook Habitat and the shell polymorphism of //Cepaea nemoralis// (L.): interrogating the Evolution Megalab database J. Mollus. Stud. (2012) 78 (2): 179-184 first published online January 4, 2012 doi:10.1093/mollus/eyr052