Anthea+Robyn+and+Becca's+Group

__Introduction__

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Polymorphism (Greek - many forms) is the occurrence of several distinct phenotypes within a single __species population [population or species' population]__ at the same time. Intra-specific colour differences __in insects[why are you talking about insects?]__ may occur as a result of environmental factors such as food type, temperature and humidity, or may be under genetic control. These colour polymorphisms may result in fitness differences through several mechanisms, including mate selection, camouflage from or warning to natural enemies, and heat absorption. (Nahrung and Allen 2005) ======

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 //Adalia Bipunctata// (two spotted ladybird) for example is __another species[apart from which?]__ containing abundant polymorphic __species [drafting wrong... the species ma be polymorphic, or it may contain polymorphic loci]__. Comparisons of //A.bipunctata// melanism in the industrial northwest of England with //Gonodontis bidentata// (Geometer moths) and //Biston Betularis// (Night-flying moths) shows that the pattern matches that of the less mobile //G.bidentata,// suggesting that the frequency of low melanic frequencies in isolated industrial towns cannot be explained by gene flow due to rarity of species migration (Muggleton, 1978). In Mikkola and Albrecht’s experiment, 1075 //A.bipunctata// beetles were collected as 12 samples over 3 days (August 4-6th) 92 were melanic, 54 were black with 4 red spots and 38 black with 6 red spots(Mikkola and Albrecht, 1988). As there is a low-level of melanism in Helsinki, differences cannot be via concept of thermal melanism, due to coast proximity, but the melanism is roughly the same as East Germany, North-West Netherlands and Southern London and half the level of Tallinn suggesting that melanism cannot be predicted on the basis of level of air pollution and geographical position. Though in the Gulf of Finland, melanism concentration in city areas suggests an industrial origin, as thermal selection and the “Heat island” effect does not account for melanic frequency distributions either (Mikkola and Albrecht, 1988). ======

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Therefore, polymorphism may be dependent on parameters such as mating systems or homozygous disadvantage; however geographical comparisons indicate that populations may react differently to the environmental conditions (Mikkola and Albrecht, 1988). ======

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Polymorphism is common in many species, including the //Cepaea// species that we will be studying. It has been estimated that ~90% of British populations of //C.hortensis// are polymorphic for shell phenotypes (Jones et al. 1977). Quite a lot is known about the genetic structure of //C.nemoralis// due to it being used as a ‘model organism’ and many of its inheritance patterns are almost identical to //C.hortensis// (Cook and Murray 1966). ======

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Genes controlling polymorphic phenotypes have been extensively studied and it is known that shell colour, lip colour and absence/presence of bands are all located together in a supergene, because of the close proximity of these genes, they usually have a very high degree of linkage but some recombination events have occasionally been recorded (Cain et al. 1960 & Fisher and Driver 1934). The number of bands is controlled by an allele at an unlinked locus. ======

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For our experiment we investigated shell colour and banding pattern. Dominant phenotypes of shell colour are Brown > Pink > Yellow. Of the banding patterns, un-banded > banded, and suppression of bands 1,2,4,5 or 1, 2 is dominant over unsuppressed. In other words, that means a 1 (centrally)-banded snail is dominant over a 5 banded, as is a 3 banded snail. ======

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In the case of the snails, we are looking to see if there is a relationship between what colour snails there are in the high-lands or low-lands. This could be down to genetic drift, selection or gene flow, or maybe a combination i.e. selection as a consequence of genetic drift. ======

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Natural selection , <span class="ontologytermlink" style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">genetic drift <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">, and <span class="ontologytermlink" style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">gene flow <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;"> are the <range type="comment" id="862919">mechanisms that cause changes in <span class="ontologytermlink" style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">allele <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;"> frequencies over time. When one or more of these forces are acting in a <span class="glossarytermlink" style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">population <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">, the population violates the Hardy-Weinberg assumptions, <range type="comment" id="311066">and <span class="ontologytermlink" style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">evolution <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;"> occurs. (Andrews 2010) <span class="messagebody" style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">The effects are more noticeable in __smaller populations, than larger populations, [surely that's just drift] __ where it can result in some alleles becoming more common, while others become less over time. ======

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<span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">Selection is a process in nature in which organisms that posses the most suitable phenotypes for a specific environment (desired traits) are more successful at reproducing and increase in number or frequency, and are therefore able to pass on their genotypic qualities to the next generations. These Traits that increase and organisms chances at reproducing and survival <range type="comment" id="774955">are more favoured than the less beneficial traits. ======

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<span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">The movement of <span class="glossarytermlink" style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">genes <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;"> into or out of a population is called gene flow; the movement may be due to <span class="glossarytermlink" style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">migration <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;"> of individual organisms that reproduce in their new populations, or to the movement of gametes. When natural selection and genetic drift are not present, gene flow leads to genetic homogeneity __within a population.[or did you mean between?]__ Limited gene flow, <span class="textexposedshow" style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">caused by geological events or barriers interrupting the movements of genes in a species population, <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;"> __promotes[no think it through logically, does it promote or allow?]__ population <span class="ontologytermlink" style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">divergence <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;"> via selection and drift, which leads to <span class="ontologytermlink" style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">speciation <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">. (Andrews 2010) ====== As several factors can influence the phenotypes observed in the snails that were sampled, the sampling regime needs to enable us to attribute the phenotypes to either drift, selection, gene flow, or sampling error. If a phenotype is common in one environment, it could be due to genetic drift. To show that this is due to selection, multiple repeats of the experiment must be carried out. To get significant repeats, these must be in similar environmental conditions which are sufficiently distanced to <range type="comment" id="501938">reduce the chance of gene flow. If the same phenotype is __still[still after what?]__ found to be common, it may suggest that that phenotype has been selected for in these conditions. We will count the number of snails found, their base colour and the number of bands upon their shells at sites with short grass and sparsely distributed scrubby patches at varying altitudes, thus keeping the environmental conditions the same but effectively eliminating the chance of gene flow.

__We will then complete the Chi Squared test on the different height groups to see if we can group these results together in comparison.[not the issue, the test is to see if differences are small enough to be attributed to sampling error]__ Our hypothesis is that natural selection has stronger influence on the phenotypic frequency of the snails at each site rather than genetic drift <range type="comment" id="34242">and also that gene flow is occurring between populations but that Natural selection is predominant.

__References:__

Andrews, C. A. (2010) Natural Selection, Genetic Drift, and Gene Flow Do Not Act in Isolation in Natural Populations. Nature Education Knowledge 1(10) :5

Cain, A. J., King, J. M. B., Sheppard, P. M. (1960). New data on the genetics of polymorphism in the snail //Cepaea nemoralis// L. Genetics Vol 45 pp 393-411

Cook, L. M., Murray, J. J. (1966). New information on the inheritance of polymorphic characters in //Cepaea hortensis// Journal of Heredity Vol 57 pp 245-47 American Genetics Association

Fisher, R. A. & Diver, C. (1934) Crossing over in the land snail //Cepaea nemoralis// L. Nature Vol 133, pp 834.

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

Mikkola, K., and Albrecht, A., (1988). The melanism of //Adalia Bipunctata// around the Gulf of Finland as an industrial phenomenon. //Annals of Zoology Fennici,// 25, pp. 177-185.

Muggleton, J., (1978). Selection against the melanic morphs of //Adalia Bipunctata// (two-spot ladybird): a review and some new data. //Heredity,// 40(2), pp. 269-280.

<span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">Nahrung H F, Allen G R (2005) Maintenance of colour polymorphism in the leaf beetle //Chrysophtharta agricola// (Chapuis) Journal of Natural History, 2005, vol. 39, no. 1, pp. 79-90(12) Taylor & Francis

<span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">Word Count 1,002

__<span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">Contributors __ <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">Hazel Hewitt <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">Ailis Carmody <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">Becca Cullen <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">Robyn Crowther <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">Rebecca Benneworth <span style="font-family: 'Calibri','sans-serif'; font-size: 14.6667px;">Anthea McLaughlin-Brown

__Discussion__

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We applied a chi-squared test to our results, comparing brown/pink shell colour against yellow. We had to combine brown and pink shell colours because we found very few brown shells and chi squared tests work best with larger categories. For high ground, our χ 2 = 3.01, for mid ground χ 2 = 1.164 and low ground χ 2 = 0.1339. At one degree of freedom and 5% confidence limits, the c2 value is 3.84. None of our results are larger than this, therefore we cannot provisionally reject our null hypothesis. ======

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From our observed results, there are more 3-5 banded snails in high ground than 0-2 banded snails, 37 compared to 10. Also, in low ground there are more 3-5 banded snails than 0-2 banded snails, 24 compared with 4. As snails with more bands are able to heat up quicker, due to efficient absorption of radiation, they are more active and are hence found in higher, sunny areas. This is called the “Heat island” effect, in which the proportion of banded snails increases with increasing temperature. Another hypothesis could be that due to the lower temperature at the bottom of the hill compared to the top, snails need more bands for efficient absorption of radiation in regions of low sunshine, a thermal mechanism of evolution (Mikkola & Albrecht, 1982)1. ====== As in each location the differences in the frequencies of brown/pink shells compared with yellow shells was not significant it could be said that altitude does not provides a significant selective pressure on snail shell colour, or that the differences in altitude were not great enough to produce a significant difference. The investigation may be improved by sampling snails at altitudes that are further apart. If this produced significant results it would need to be repeated a number of times over different environments to establish whether the differences could be due to selection.

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Our data is reliable and there aren’t any overly large numbers found that are disproportionate to the rest of the findings. There are however a few zero counts, this affects the chi squared values and even through compiling our parameters we could not get rid of some of the zeros. These zeros could have arisen through us missing snails that were well hidden or through misjudging the colour or number of bands on the shell, as this is subjective to the persons view. Also as our subjects are live animals or at least were live animals they will not be spread evenly throughout our chosen sites. ======

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We took several simple steps to ensure that our data was reliable. We split into pairs and were designated specific areas, to avoid over-lapping so that we wouldn’t be counting and recording the same snails more than once. Furthermore, one person was in charge of recording while the other found the snails, once again reducing the chances of counting the same snails more than once. We also made sure that we put the snails back exactly where we found them, so as not to corrupt the data for other groups. However, there were cases when we came across clumps of snails, abandoned incorrectly by previous groups. This may have had an effect on our data making it less reliable. ====== __References__

__ Word Count __ – 538
**__Contributors__** Hazel Hewitt* Rebecca Benneworth Anthea McLaughlin-Brown Becca Cullen Ailis Carmody Robyn Crowther