Snail+Snatchers+-+Revised


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

__ 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.

__ 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.

__ Revised Strategy __



We shall be performing 1 interrupted transect, with samples taken in 2 of the 3 habitats (scrub & woodland). Each habitat will be sampled at the same  elevation on the site, as above.  The sampling areas will be at least 20 m apart. 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 __

There are marked differences between habitats (eg. shade, background colour), therefore selection for polymorphisms in each habitat could vary greatly. Each habitat will be sampled at the same elevation, reducing the differences 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 also performing an interrupted transect at the same elevation. In this case, we shall obtain samples of the grassland habitat. 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 shall be neglecting the grassland habitat. Differences observed between different habitats may have nothing to do with the variables we are controlling (gene flow, elevation), but other biotic or abiotic features only the snails are aware of such as availability of calcium carbonate or drainage, for example.