Tuesday, 5 June 2012

Beginning of Snail Experiments

When I was an undergraduate my final year research project was on plant nutrition.

I had wanted the project to be on animal behaviour as that was what I was most interested in while studying. However as almost all of the animal behaviour projects had gone to Zoology students the only projects left for those who were on a straight Biology course were ones involving plants.

Luckily for me my dissertation tutor understood that the project I had been assigned was not my first choice. As a result we altered to project to involve some element of animal behaviour specifically looking at the effect of nutrient concentration on wheat desirability to common garden snails. This was given the more impressive sounding title of ‘testing the resource availability hypothesis using winter wheat and garden snails’ when I wrote up my findings for submission. Unfortunately while I found that the snails preferred the wheat grown in the higher nutrient concentration the test plants didn’t show a significant growth difference (difference in dry mass).

One quirk of my research has always stuck with me though. Early on in the project I tried running my preference trials using multiple snails at once for expedience. This was quickly abandoned as the snails would crawl on top of each other and bigger snails would drag smaller ones to one side. This meant that I couldn’t be certain that the snails were making individual choices in which wheat plants they were choosing. The main effect this had on me as a 20 year old student was to increase my experimentation time as I had to test each snail individually.

I spent a lot of the autumn and early winter in an experimental greenhouse watching snails deciding the direction they were going to move in.

Over the intervening years I have always wondered whether the behaviour the snails showed in a group could be replicated. If it could then why the snails did this? Was it a way of making the group of snails too big for a potential predator? Would the smaller snail release the group below it if attacked? Or was it a one off behaviour which has no behavioural benefit?

After many years of never having time to test this I finally made time and decided to observe what happened when I replicated having snails in a group together. A quick peruse around the garden found 5 garden snails – 1 large one, 3 medium sized ones and 1 small snail. As ever the snails were found in small groups under the rims of flower pots.

Annoyingly after a few trials the ‘piggy back’ behaviour I remembered seemed not to be occurring. Instead what seemed to be happening was that the snails just crawled over each other if they were in the way and then moved off.

Slightly perturbed that my interesting snail behaviour seemed to be a one off I decided to look at what was happening when the snails were on top of each other and if this was affected by their size.
I began to notice that the smaller snail when crawling on top of the larger ones didn’t affect the larger snails at all. As a result they carried on moving and dragged the smaller snail away with them. The smaller snail after less than a minute of ‘hitching a ride’ then disembarked off the larger snail and moved away in a different direction.

For the larger snails when they crawled on top of each other the one on top actually stopped the one below from moving. Often the snail on the bottom was starting to get their head out to move. Being crawled on by a larger snail seems to stop them getting ready to move off. This has the effect of delaying them in getting to shelter.

Also whilst the smaller snail seemed to always move away from the larger snails – possibly to avoid predation as it would be less conspicuous than the larger snail. The larger snails followed each other and stuck close together. This could be in order to reduce the chance of them getting predated on. Much like colonial birds living together to remove the chance of their chicks being the ones eaten.

In order to fully describe what is occurring I will further investigate the following;

  1. 1.       Do smaller snails consistently move away from the larger ones if climbing on has occurred?
  2. 2.       Do the similar sized snails consistently follow each other if climbing on has occurred?
  3. 3.       Does climbing on a competitor snail always affect their ability to begin moving to shelter?

It would also be worth cleaning the area between trials so that previous snail tracks are not present so they cannot be affecting the direction the snails are taking. 

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