Team+Gastropoda

Team Gastropoda comprises of the following individuals:

Stephanie Chan*

Stuttee Mehra

Kishan Patel

Arran Hamlet

Lauren Tithecott

Light green: Tree, Dark green: Shrub, Brown: Grass


 * Introduction **

Hypothesis: A change in habitat will lead to a significant difference in the frequency of phenotypes, due to selection over genetic drift.

Our null hypothesis is that there will be no significant difference between the effects of selection and genetic drift on the frequency of phenotypes.

//Cepaea nemoralis// is a terrestrial creature of the mollusca family, chosen for study due to its sedentary nature, 20m in a generation, and its diverse polymorphic traits. The use of this snail species, as opposed to humans, is due primarily to their visual display of their phenotype on their shells. This allows for the identification of phenotype both pre and post death. This lack of movement also leads to sub-populations in geographically close proximity displaying a variety of phenotypes.

If there is a significant difference in frequency of phenotypes between the habitats then selection is the primary force acting upon the snails. However, if there is no notable difference between phenotypes overall in separate habitats, then genetic drift is a greater force than selection. 


 * Method **

We shall be conducting a horizontal line transect across a consistent altitude as this eliminates the confounding variables associated with altitude differences: temperature, wind exposure and humidity.

<span style="font-family: Verdana,Geneva,sans-serif;">Snail shell colour will be clarified before the field exercise and any disparities between samplers will be decided between us. Habitats will also be defined pre field exerecise.

<span style="font-family: Verdana,Geneva,sans-serif;">We are sampling across 6 sites over 2 different habitats, trees and grass, along the line transect. We are only sampling 2 habitats due to time constraints. The sampling will be bias to select tree habitats and grass, this is done to make sure we get sample populations from only the designated areas. The habitats will also be located away from pedestrian footpaths as this would reduce the amount of snails located. The allocation of these sites will be <range type="comment" id="372232212_2">placed at least 20m away from each other in an attempt to not sample the same sub-populations. 3 sampling sites will be allocated to each habitat. A sampling site will be approximately 5x5m.

<span style="font-family: Verdana,Geneva,sans-serif;">A chi squared test will be employed to distinguish whether the results are due to the effects of sampling error or are significant findings. Chi squared is also used in lieu of other tests as we are comparing two samples with discrete variables. <span style="font-family: Verdana,Geneva,sans-serif;"></range id="372232212_2">

<span style="font-family: Verdana,Geneva,sans-serif;">**Advantages**

<span style="font-family: Verdana,Geneva,sans-serif;">One advantage of this method is its control of confounding variables. By controlling height we are controlling humidity, temperature, moisture and wind exposure. This will lead to a greater ecological validity in our results, and due to the strict control of variables, a greater degree of replication. Which will be evident in the consistency of phenotype ratios between our sample sites.


 * <span style="font-family: Verdana,Geneva,sans-serif;">Disadvantages **

<span style="font-family: Verdana,Geneva,sans-serif;">Due to time and economical constraints we are limited to taking 6 samples, in two habitats, at a single small site in England. This may mean that our sub-populations could actually be part of the same population and gene flow occurs regularly between these. <range type="comment" id="372232212_4">If this is the case, then we would not see any indication of habitat's effect on selection and so the phenotypes between areas would not show any consistency. </range id="372232212_4">