Groupx+6

Tanya Deol Reina Sng Mala Sabharwal Hadley Hall Safiyyah Sheikh Gemma Hampshire
 * Group members:**

__**Revised Draft Diagram (week 3)**__

__**Final Draft Diagram:**__


 * Null Hypothesis:** There will be no significant difference between the observed phenotypes relating to shell colour and number of bands on the shells of the snails sampled


 * Alternative Hypothesis**: There will be a significant difference between the observed phenotypes relating to shell colour and number of bands on the shells of the snails sampled.


 * Method/Logic:**

Our plan is to collect snail samples from 6 locations spanning grassland and shrub land areas. Each of the sampling areas will 5m x 5m in order to ensure that we get a sufficient sample size to carry out the statistical analysis.

We will attempt to keep the altitude the same throughout the sampling in order to keep factors such as humidity, wind exposure and temperature constant. We appreciate that the altitude may be slightly lower in the middle section but we will try to minimise the differences but we won’t know how great the difference will be until we see the site itself.

We chose to only sample the Grassland and Shrub land as we felt the difference in habitat and predators between the snails living in the shrub and in the woodland would be too great to compare as it would add another variable to the study.

We choose to collect the samples in 3 groups: 1 and 2, 3 and 4 and 5. Each sample in a group will be taken at a distance of 10m apart. We chose to keep the distance between the two samples relatively small in order to observe the affects that gene flow might have.


 * __ Introduction: __**

The genus Cepaea consists of pairs of sibling species: Cepaea nemoralis and Cepaea hortensis. Cepaea nemoralis is a species of snail originating from Western Europe, which can be found in a multitude of geographic locations such as wetlands, dunes, farming lands and mountains (Jones, et al., 1977). C. nemoralis has a preference towards warmer microclimates and generally survive better, conserving water more efficiently in hot dry conditions. Despite this, such habitats demonstrate the wide range of temperatures, altitudes, climates, wind exposure, and moisture the species is able to tolerate.

The study of polymorphism has been ongoing in various organisms. There has been much debate between the scientific community whether these differences are due to the processes of natural selection, gene flow or simply the random processes of evolution by genetic drift. In the case of C. nemoralis, this species is recognised as “one of the most polymorphic members of the European fauna” (Jones, et al., 1977). The variation in traits such as shell colour, the number of bands, as well as lip colour, all allow for the notion of the supergene. As a result, this species is ideal for studying polymorphic traits because the phenotype directly represents the genotype. This is important because these physical traits are representative of specific habitats. Therefore, by examining physical traits such as shell colour and banding pattern, the polymorphic nature of a specific locus can be extrapolated.

The polymorphism at a specific loci of the “supergene” seen in Cepaea nemoralis was studied to determine if there is a correlation between coloration and banding patterns as well as habitat altitude. The “supergene” is also found in the sister species Cepaea hortensis.

Genetic polymorphism supports diversity within a population, it expands over multiple generations because no form in the species will have leverage over the others with regards to natural selection. In the case of C. nemoralis, there are various snail forms with the presence of yellow, brown and pink coloured shells. These three different types of snails also have an alternate number of bands on their shell ranging from zero to five bands.

Because there are many geographical factors that contribute to the phenotypic frequency of Cepaea nemoralis at each location, it can be very difficult to attribute the variation to a specific factor. Furthermore, there are several influential factors such as pH or predation that difficult for human detection, resulting in them often going unnoticed.

The null hypothesis is that <range type="comment" id="530473030_9">there will be no significant statistical difference </range id="530473030_9">between the phenotypic frequency of Cepaea nemoralis within shrubland along a varying altitude and any observed difference would be due to sampling variation. <range type="comment" id="530473030_10">The alternative hypothesis is that there will be a significant statistical difference between phenotypic frequency of Cepaea nemoralis within shrubland along a varying altitude.</range id="530473030_10">


 * __Final Diagram of experimental design:__**

__** Experimental Design: **__

Samples of C. Nemoralis were collected from six locations of shrubland along a declining altitude. Each of the sampling areas were 5m x 5m in order to ensure that a sufficient sample size was obtained to carry out the statistical analysis. Each sample area was measured 5m apart from the next. The distance was kept small between the six samples in order to observe the effects that gene flow might have.

The field that that the samples were collected from contains three different habitats: woodland, grassland and shrubland. However, only the shrubland habitats were sampled. These habitats were sampled along a declining altitude in an attempt to increase the statistical power of our results by focusing on reducing the number of variables while repeating the same habitat. This means that any statistical variation could be attributed to the change in altitude, rather than a change in habitat. By decreasing altitude consistently throughout the sampling, it can be determined if factors such as humidity, wind exposure and temperature might play a significant role in phenotype frequency.

There are several similarities between the two sister species found at this location. Specific characteristics of Cepaea nemoralis such as an absence of a hole in the base of the shell and a dark band on the lip of the shell were recognised in order to ensure that the correct species was collected and data accurately reflected the phenotypic frequency of Cepaea nemoralis.

= Bibliography = Jones, J., Leith, B. & Rawlings, P., 1977. Polymorphism In Cepaea: A Problem with Too Many Solutions, London: Annual Review Ecology Systems.