Groupx+12

__**MEMBERS:**__ Maliha Chowdhury Tahiya Mahmood Fatima Bhatti Wardah Ahson Rachael Lazaroo Alysha Aizai Azan

__**SNAIL BUSTERS' SAMPLING DESIGN**__

Fig 1. Sampling design highlighting the locations where we will be collecting //Cepaea nemoralis//

__Key:__ 1). Deep woodland 2). Intermediate woodland / grassland 3). Distant woodland 4). Distant bushes 5). Intermediate grassland / bushes 6). Deep bushes

Independent variable: Distance Constant variable: Altitude and habitat Dependant variable: Snail shell colour and band numbers (snail polymorphisms)

We will be observing the shell colour and the number of bands of //Cepaea nemoralis,// by collecting 30 individuals from each 15m squared location.

We will be taking 3 samples from 2 different habitats (6 locations in total). In each habitat we will take one sample deep within the habitat (control), another intermediate between the habitat and open grassland (close), and a last sample from a distant population. We feel this will enable us to evaluate as close as possible whether gene flow or selection are taking place.

If we take the woodlands as an example, we will compare populations 1 and 2 to see if gene flow occurs, and then compare 1 and 3 to see if selection occurs. We will do the same for the bushes habitat ( 4, 5 and 6 ).

Null Hypothesis: In the same habitat, there is not a significant difference in snail polymorphisms in the distant population compared to the closer populations. Alternative Hypothesis: In the same habitat, there is a significant difference in snail polymorphisms in the distant population compared to the closer populations.


 * __SAMPLING DESIGN 2__**



__Key:__ 1). Woodland A 2). Woodland B 3). Woodland C  4). Grassland A 5). Grassland B  6). Grassland C

Independent variable: Distance Constant variable: Altitude and habitat Dependant variable: Snail shell colour and band numbers (snail polymorphisms)

We will be observing the shell colour and the number of bands of //Cepaea nemoralis,// by collecting 30 individuals from each 15m squared location.

We will be taking 3 samples from 2 different habitats (6 locations in total). In each habitat we will take two samples deep within the habitat (for replication purposes) and one distant location within the same habitat. We feel this will enable us to evaluate as close as possible whether gene flow or selection are taking place.

In each habitat, we will compare populations A and B to see if gene flow occurs, and then compare A and C to see if selection occurs.

To avoid pseudo-replication samples A and B from each habitat will have a distance of 40 metres between them.

We have chosen to limit the number of variables so that our results are more accurate and reliable.

Null Hypothesis: In the same habitat, there is not a significant difference in snail polymorphisms in the distant population compared to the closer populations.

Alternative Hypothesis: In the same habitat, there is a significant difference in snail polymorphisms in the distant population compared to the closer populations.

__**INTRODUCTION**__

//Cepaea nemoralis,// one of the most abundant species of terrestrial molluscs in Europe, found in habitats as variable as coastline dunes, hedgerow, grassland and woodland. Having been originally introduced into south-eastern Poland, where it currently thrives, it has migrated to cover areas as vast as Southern Scandinavia to the Iberian Peninsula. In the nineteenth century it has also been introduced to North America.

Polymorphism is defined as ‘the occurrence of more than one kind or form of organisms of the same species that exist together in one locality’ (Biology Online, 2014). The shell polymorphisms in //C. nemoralis// vary in colour (yellow, pink or brown) and numbers of bands, ranging from 0 to 5. It is a model organism for studying the forces of selection vs. genetic drift and gene flow. With its genetic make-up being directly represented in its shell phenotype it allows researchers to easily identify an individual’s genotype. An individual can conveniently be classified by what the researcher observes without the need for complex DNA analysis to determine its genetic constitution. //Cepaea hortensis// is the sibling species of //Cepaea nemorali//s. The only phenotypic variation between the two is an obvious brown apertural lip around the opening of the shell in //C.nemoralis// and the presence of a white lip (not easily identifiable) in //C.hortensis//.

Previous studies have highlighted the problem of identifying a single evolutionary force responsible for the observable snail polymorphisms. Jones et al. (1977) concluded that there are at least 8 evolutionary forces acting on //C.nemoralis//. Jones and colleagues studied populations in the Pyrenees. Researchers before them had each championed a different mechanism when looking at this species. Jones and colleagues identified that it was in fact an interaction of multiple pressures acting on the species which accounted for the variety and distribution which they found.

In this study we analysed the snail polymorphisms present within different habitats of //Cepaea nemoralis// in the Pulpit Hill nature reserve in Monks Risborough, Buckinghamshire at the foothills of the Chilterns. By looking at populations from different habitats we can establish whether selection is occurring. We also included distance as a variable allowing us to establish whether genetic drift was a major factor. The habitats we chose to study were bushes and woodland as we felt this would give a good interpretation of evolutionary processes acting on the populations.

The purpose of this investigation is to determine whether, within the same habitat, there is or is not a significant difference in snail polymorphisms in the distant populations compared to the closer populations. Therefore, this allows us to, as accurately as possible; ascertain how //C.nemoralis// is genetically evolving.

__**References:**__ 1). Jones, J. S., Leith, B. H. and Rawlings, P. (1977). Polymorphism in Cepaea: A Problem with Too Many Solutions? //Annual Review of Ecology and Systematic.// Vol. 8, pp. 109-143. 2). Biology Online (2014). //Polymorphism// [online]. [|www.biology-online.org/dictionary/Polymorphism]. Accessed 11/11/2014.