Gaya Snail foot strength project

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An unexpected correlation between snail foot strength and body size on Pulau Beach, Gaya Island

The glueing technique

It is generally accepted that abiotic factors have a significant influence on both the geographic range of a species and its morphological evolution. Another important factor that impacts a species' range is competition for limited resources with other similar species. On Gaya Island, 5km off the coast of Borneo, the coexistence of two gastropod groups with distinct shell morphologies but similar foot morphologies on two different beach habitats provides an opportunity to investigate possible intraspecific micro-evolution. The presence of a third gastropod morphology that occurs on only one of the beach habitats with the other two morphotypes provides an opportunity to investigate interspecific habitat specialization. Two questions then arise from this natural occurrence. Is there quantifiable variation on foot strength within the same morphotype of gastropod at two distinctly different habitats? Has competition between similar gastropods driven variation among foot strength between different snail morphotypes at the same location? With these questions in mind, this study investigates the difference in foot strength of three distinct morphologies of gastropods and how that variation may be correlated with their environment and/or overall body size. We hypothesize that within the two morphotypes found at both shore locations, the population found at the high-energy wave action shore will have greater foot strength in comparison to the population on the low-energy wave action shore. We also hypothesize that the morphology found only at the high-energy shore will have a greater foot strength than the two morphologies found at both the high energy and low-energy shores.

Ten snails of three different morphologies were collected from the high-energy shore. Ten snails of two of those morphologies were then also collected at the low-energy shore. Rubber bands were attached to each snail with super-glue. The strength of the foot was calculated using the difference between two specific vertical height measures: the initial attached snail and taut rubber band height and the height at which the rubber band was pulled to detached the snail. Measurements were taken once the snail was firmly attached to the measuring rock for a specific time period. The resting height was subtracted from the snail detach height to determine the distance the rubber band was stretched. This distance was then interpreted as representative of foot strength. Each individual was tested multiple times and the mean distance was calculated. The foot length and total shell length were also recored to correct for size-induced strength differences and to determine the correlation between overall size and foot strength.

Snail Measurements

The data was than analyzed using the statistical analysis platform R. Both correlation tests and linear regression models were used to generate results. The results indicated that there was no significant difference in foot strength within the same morphotype at different shore locations. There was also no significant difference between morphotype foot strength at the same location. The null hypotheses were not subsequently rejected. However, the correlation tests revealed that body size and foot strength were strongly correlated in snails that inhabit the high-energy wave shore, while there was no correlation between overall snail body size and foot strength in snails that inhabit the low-energy wave shore. It is possible that for the snails which inhabit the high-energy shore, the foot muscle is strengthened by continuous pressure from the waves in relation to how long the snail has been exposed to the harsh environment. As a result, the older snails, and thus the larger snails, who have been subjected to the high-energy environment for longer may exhibit stronger foot strength. This proposed gradient of increasing foot strength with time exposed to a high-energy wave environment could produce a strong correlation between overall body size and foot strength.

P-Values of Correlation at the different shore habitats
While unexpected, these results suggest further studies are needed to investigate the mechanisms underlying such a correlation.
Correlation Between Size and Foot Strength in Rock Spiral Morphotype
Lack of Correlation Between Size and Foot Strength in Beach Spiral Morphotype