Groupx+5

Sumeera Ahmad, Remi Maeda,Thomas Burt, Sarrah Moeen, Louise Fu

Balancing selection- natural selection that maintains variation longer than expected from genetic drift alone. Genetic drift- in a finite population, loss of genetic variation due to random sampling of gametes at each generation. Allele- an alternative from of a gene. Polymorphism - includes one of two or more variants of a particular DNA sequence. Variation at a single base pair.
 * KEY WORDS:**

We will be collecting 30 snails in each sampling location, all at ground level but varying altitudes. This will help identify if altitude is a factor contributing to polymorphism. Sampling locations have been spread out into different micro-habitats within the main habitat, with a few located on the perimeter of certain habitats to see how/if mixed conditions affect polymorphism. At each site, sampling will be kept in an area of 5m X 5m.
 * NULL HYPOTHESIS**: There will be no significant differences in the frequency of the phenotypes (shell colour and number of bands) of the snails sampled in different habitats across varying altitudes.
 * ALTERNATIVE HYPOTHESIS**: There will be significant differences in the frequency of the phenotypes (shell colour and number of bands) of the snails sampled in different habitats across varying altitudes.
 * METHOD / REASONING**:

Improved version


We have decided to do a transect across the habitat, as opposed to our previous idea to random sample in the various micro-habitats. This is to minimise the number of variables affecting our sampling, as it is assumed the altitude won't be changing dramatically, or enough to affect the polymorphism of the snails. The sample size is still 30 and is still going across the different micro-habitats identified in the main habitat, being: deep woods, on the perimeter of the woods and grassland, in the hedgerow/bushes, open grassland, on the perimeter of hedgerow/bushes and grassland, and the other side of the woods. This will help in identifying the different conditions that affect snail polymorphism. Along the line transect, samples will be taken from within a 5m X 5m area, and the distance marked.
 * METHOD / REASONING:**

LAST IMPROVEMENT

We have now modified our experiment as shown in the diagram above. After performing further background research, we’ve found that altitude plays an important role as it is related to climate. In the Jones et al. paper, it was mentioned in depth that altitude can have an effect on polymorphism. However, simply adding the altitude variable into our experiment would increase the amount of difficulty in the experiment and may lead to us collecting unreliable results. So we decided to take out the hedgerow habitat and only perform sampling in the woodlands and grasslands (as we believe this should show the greatest variation). As for sample size, we are still collecting 30 snails per site to ensure we obtain reliable/replicable data. In addition, we will be observing each individual snail as a group to avoid experimental bias in order to have valid results.
 * METHOD / REASONING:**

**__ Investigating the mechanisms that affect polymorphism in the Grove snail //Cepaea nemoralis.// __** The aim of this investigation is to determine whether selection alone governs the polymorphism of the shell colour of //Cepaea nemoralis,// or if other ‍‍mechanisms such as gene flow and genetic drift, play a more central role‍‍. ‍‍Polymorphism involves a variation at a single base pair, or variants of a specific DNA sequence, leading to alternative phenotypes within a species and thus increasing population diversity.The different phenotypes are often neutral regarding natural selection, so can be preserved over many generations.‍‍ This investigation is based on previous works of Jones, Leith and Rawlings [1], whereby an investigation was carried out to explain polymorphism in the snail species //Cepaea//. Shell colour and banding was observed over differing altitudes and a selection of environments including open grasslands and woodlands.

The grove snail, //Cepaea nemoralis// is a cross fertilizing hermaphrodite, common in Western Europe as well as in Britain. Being extremely polymorphic and slow moving, it is an ideal species to study as we can see the effects of many mechanisms ‍‍acting upon several generations‍‍. [1] ‍‍A supergene‍‍ gives rise to polymorphism by controlling shell colour, pigmentation and presence or absence of bands; giving rise to pink, brown or yellow shells with bands between 0-5. [1]

During our experiment, we hope to collect data that will help identify‍‍ the source of polymorphism. ‍‍The collated data will allow us to carry out statistical analysis, i.e. chi squared test and contingency tables will allow us to find differences. This investigation is carried out at Pulpit hill, Monk’s Riseborough in an isolated area based on a hill with open grassland, shrubbery and surrounding woodland. Our final experimental design focuses on repetition of two main environments; open grassland and woodland, with samples of 30 being collected at a low and high altitude. This will allow us to investigate the effects of habitat conditions and altitude on shell polymorphism. To test for evidence showing effects of gene flow, our experimental design includes sample collection at the transition from grassland to woodland.

From our own knowledge and information gathered from Jones et al research paper, we came to the prediction that lighter (yellow and pink) shells with fewer bands will be found at higher altitude, and darker (brown) shells with more bands, will be most frequent at lower altitudes. This is because lighter shells will be favoured higher up due to more exposure to sunlight, and darker shells will help absorb energy in the less exposed woodlands. Regarding the two different habitats, we expect to see a higher proportion of banded and light snails in the open grassland, where camouflage will play a factor in predator avoidance; with darker and no/ less banded shells in the woodlands. In addition, we predict a phenotypic gradient along the transition between grassland and woodland. [1] Results from the tables and Chi squared test will lead us to accept or decline the null hypothesis. Our Null hypothesis states that there will be ‍‍no significant differences in the frequency of phenotypes‍‍ (shell colour and number of bands) of the snails sampled in different habitats across varying altitudes.

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1) [|__Jones et al 1977 . Ann Rev Ecol Syst 8:109-143 Polymorphism in Cepaea: A Problem with Too Many Solutions?__]