GroSnail+Snatchersup+3


 * Eric Boateng
 * Ollie Britton
 * Alex Laybourn*
 * Sophie Nash
 * Jamil Razzaque

__ Null Hypothesis __

Our results will show no significant differences in frequencies of polymorphisms between habitats; we will not be able to conclusively distinguish selection from genetic drift.

__ Alternate Hypothesis __

There will be a significant difference in the frequency of polymorphisms in each habitat. Woodland __ C.nemoralis __ are expected to show higher frequencies of darker snails, due to visual predation, than scrub. This finding will be consistent across our samples in similar habitats, reducing the likelihood that Genetic Drift (chance) is solely responsible for the frequency of polymorphisms.

__ Sampling Strategy __

__ Revised Strategy __

We shall be performing 1 interrupted transect, with samples taken in 2 of the 3 habitats (woodland & scrub). Each habitat will be sampled at the same  elevation on the site, as above.  The sampling areas will be at least 20 m apart, reducing gene flow between micro-populations. In addition to standardising our criteria for polymorphisms (colour/shell bands etc.) we shall also be standardising the effort put into each sample area, using the same number of people searching an area for a set amount of time.

__ Strengths of This Design __

As there are marked differences between habitats (eg. shade, background colour) selection for polymorphisms in each habitat could vary greatly. Each habitat will be sampled at the same elevation, reducing the variables amongst samples of the same habitat type. The interrupted transect is easy to replicate should no samples be found in any 1 site. Our method & results are standardised, facilitating collaboration with another group performing an interrupted transect at the same elevation. As samples will be isolated by at least 20 m distance, the likelihood of gene flow between samples is reduced. As we are standardising not just measuring criteria, but also effort we will reduce bias resulting from intense searching of 1 area & barely searching another.

__ Weaknesses of This Design __

We will only be sampling two habitats, woodland & scrub, neglecting grassland. Differences seen may be due to another variable we cannot account for, but the snails are aware of (increased access to calcium carbonate or prevailing winds, for example).