Snail+Snatchers+-+Introduction

// Cepaea nemoralis, // commonly known as the Grove snail or the brown-lipped snail, has been extensively studied by evolutionary geneticists, due to their shell colour and banding polymorphism. These hermaphroditic land snails are easily identifiable due to their characteristic shell colours (brown, pink or yellow) and unique banding pattern (0, 1, 2, 3, 4 or 5 bands). The qualities directly correspond to their genotype; allowing the mapping of allelic combination to be made from phenotypic observational analysis alone. A study could not take place on humans for example, because there are many genes and factors that contribute towards their outward appearance [not true for all human traits, eye colour for example ] .Because of this, it becomes considerably more difficult to directly observe and attribute various phenotypes to their correct allele. Good first para Aside from this, other factors which make //C. nemoralis// ideal animal models in the study of evolution and genetic drift include; short migration distances, causing variation over a short [small areas, or short scales] geographical area, extensive population genetics data paralleled only by that of //Homo// //sapiens// (Jones et. al., 1977), and their presence in a wide range of habitats. This therefore enables us to examine the interplay between stochastic processes such as genetic drift, gene flow’s homogenizing role and natural selection on morph frequency. This this what... don't start sentences with 'This' alone. Use 'This understanding' or 'These principles' can then be interpreted and applied in the study of other living organisms including humans. In this study we aim to explain the geographic distribution of //C. nemoralis// morph frequency within the Chiltern hills; an environment consisting of woodland, grassland and shrubs. Our experimental model focuses on distinguishing between genetic drift, natural selection, and gene flow all of which can influence morph frequency. Two sets of shrubs spaced far apart, each set containing two shrubs roughly equal in size, will be chosen. [ Use present and past in the intro, not future. You are writing up after the experiments were done] Two sets at a relatively high altitude and another two sets at a lower altitude. The relatively large distance between the sets within the same environment and between the differing altitudes should reduce the possibility of gene flow between populations. If one of the sets in the same environment is __a product of a genetic bottleneck population, [explain better] __ this will be identifiable as the second set further away will have a dissimilar phenotypic frequency. Having two sets spaced apart __allows for comparison of morph frequency in the same area to ensure it is uniform throughout__. __ [explain better] __ If our findings show substantial morph frequency differences between high and low altitude this would suggest environment to be having a selective influence. However, if morph frequency was not significantly different between the populations at low and high altitudes then this may indicate that stochastic processes such as genetic drift have greater influence __ [logic seems wrong, stochastic processes produce differences don't they??] __ . Two 4m x 4m areas of open grassland at high altitude and another two at low altitude will also be looked at. This is to see if any morphological frequency (or any differences between frequencies) __found within shrubs at a particular altitude is also true for open grassland.__ __ [explain better] __ __ We would expect a different morph frequency from that of shrubs to be a cause of selection (e.g. predation) or bottleneck populations. If difference is due to selection, the difference should be seen in all open land. If it is simply a bottleneck population, the other open lands should have different morph frequencies to it. __ __ [explain better- try, if diferences were due to drift or other stochastic processes, we would expect to observe...., if they were due to selection ...] __ Past research in the frequency distribution of //C. nemoralis// morphs __has compounded more hypotheses rather than affirmative conclusions__ (Jones et. al., 1977). [over written - and use of fancy terms has entirely obscured the meaning], One theory suggests darker snails; brown in particular, __to be__ [are] more common within woodlands due to the obvious camouflage benefits it brings and thus protection from predators. On the other hand, another __premise implicates__ [over written - and misuse of 'premise' I think you mean hypothesis, look up the difference] climate as a major factor in the appearance of differing allelic frequencies, proposing that brown and pink snails heat up more quickly than the lighter coloured yellow snails and are therefore protected from any excessive solar radiation through being in woodlands and the shade tall vegetation provides. However, other __hypothetically derived factors__ [phrase imprecise and overblown, use plain english] such as ‘disruptive selection’, ‘frequency-dependent selection’, ‘density-dependent selection’ or a combination of the above may be at work. __Discretely__ __discriminated__ among all these hypotheses is the __emphasis__ [what do you mean] of frequency distribution correlated with a certain change in environment. It is therefore important to allocate environment specific sampling sites in the experimental procedure in order to __substantiate the current study’s hypothesis with__ past research.
 * Group Members: **
 * Amy Donninson, Emmanuel Escobar Gonzalez, Nira De La Vega Gallarado, Pippasha Khan, Samuel Wigmore-Sykes, Sivappriyan Nagarajah * **

all of the underlined sections in the last para are overblown, or misuse terms.

A decent first attempt.

Word Count: 702 References: Jones et al. (1977) //Polymorphism in Cepaea: A Problem with Too Many Solutions?// Ann Rev Ecol Syst 8:109-143.


 * Discussion: **
 * Group Members: **
 * Amy Donninson, Emmanuel Escobar Gonzalez, Nira De La Vega Gallarado, Pippasha Khan, Samuel Wigmore-Sykes, Sivappriyan Nagarajah * **

Despite our chi square values suggesting there is no significant difference in morph frequency between high and low altitude, sampling error cannot be ruled out. Further, because a chi-square test only gives a rough estimate of confidence, a more precise statistical test could provide differing results. The experiment should have been repeated with several sets of shrubs spaced apart at a predetermined minimum distance, on different days, with all weather conditions recorded. This would have enabled a larger sample size; thus increasing the reliability and accuracy of any data collected.

Our chi square value for shell size also indicates no significant difference between sites at differing altitudes. However this does not necessarily mean natural selection plays no influence on shell size. It may once again be a product of sampling error combined with the use of a crude measuring device - a calliper would have been far more suitable.

Furthermore the weather was not favourable; the lack of rainy conditions preferred by live snails may explain why the majority of our data was restricted to dead adults or juveniles. In the ‘open land’ sites, the influence of nearby shrubs and the possible migration of snails were not considered. If a repeat experiment were to be carried out then, in perfect conditions, all open land sites should be a minimum distance away from surrounding shrubs. Additionally, the habitat areas studied were not entirely free from disruption with dog walkers and other groups studying the area. This could explain presence of shells in clusters at one particular location within a shrub. Data from such sites in future should be viewed with caution and usage avoided if possible.

Our categories could have been widened to collect more data and potentially allow greater inferences. For instance including cause of death (predation or natural) would allow the investigation of how distinct selection pressures (e.g. predation) affect each of the various phenotypes to be carried out.

The identification of an orange shell in a shrub relatively close to the woodland area suggests that the process of gene flow may be occurring. This is because orange heterozygotes are the products of interbreeding between brown snails (thought to be confined to the woodland) and pink snails. A category to record such rare alleles combined with cause of death may allow for “frequency dependant selection” to be tested.

Word Count: 389