The causes of behavioural handedness – Part 1: is it inherited?

Behavioural handedness is a part of everyday life that you probably don’t put much thought into. Roughly 90% of the population is right handed and prefer using their right hand for most manual tasks. As with most things handedness is not completely black and white and some prefer to use their non-dominant hand for some activities. Personally the only left thing about me is my political leaning. My left hand is useless and I favour my right for every task I can think of. As is common to right-handers, I also have a tendency to turn right upon entering a new environment. I share this behavioural bias with snail number 11714.

right handed boy
11714 at his starting position in a T-maze.

My masters project utilizes the pond snail Lymnaea stagnalis as a model organism to study the causes of behavioural handedness. This is a different species of snail to the famous Jeremy, although the snails I’m using for the second half of my project are also sinistral snails, featuring the exciting left coiling shell (as you can see in my next post).

Lymnaea stagnalis are a well-established organism for use in both brain lateralization studies and research into memory and learning. Like humans, pond snails exhibit behavioural handedness and when put into an adapted T Maze many snails will turn either left or right most of the time, with a majority seeming to favour turning left, just as a majority of humans favour using their right hand. Interestingly, this preference does not seem to be affected by the coiling direction of their shells.

My project focuses on trying to find where this bias comes from via two experiments: one focussing on the heritability of the preference and another exploring whether the preference can be learned. To see whether behavioural handedness is inherited in pond snails, a group of snails were taken from two wild sources (half from the pond of the house I grew up in and half from my supervisor’s allotment), kept in separate tanks in the lab and left to lay eggs. Those that had laid eggs were then observed in a T-maze for their innate turning preferences.

Max and snails
Three L. stagnalis taken from my home pond. Cat paw for scale.
observed boys
Three T-mazes of the twenty lined up for my first observations.

This was done last year before the Christmas break and since then the eggs of the F1 generation have all hatched. In fact, some of them did so while the parents were still being observed.

Snail with offspring
In this photo you can see some newly hatched L. stagnalis emerging next to their parent. A freshly laid egg mass can also be seen lower down.
Two of the offspring of snail 11707.

The second generation of snails are too small to observe at the moment as you can see above. In about a month’s time however, the F2 generation should be large enough to undergo the same observations as the first generation. A turning fraction and laterality index can then be calculated based on these observations for all the snails from both generations. The index will indicate the strength of each snail’s preference and a statistical analysis can then be performed to see how similar the preferences of the F2 generation are to their parents. If preferences are significantly similar this will indicate that the turning preference of pond snails has a genetic contribution.

Jeremy parents
Caught up in the project, the ghost of Jeremy looks back on memories of his own parents.

In the second part of my project, which I have recently started, I am exploring whether the innate turning preference of snails can be altered by training them to turn in a certain direction. To accomplish this, I have been given a group of inbred sinistral lab snails. I will talk about this part of my project in my next blog post.


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