How the colour in snail shell pattern may influence snail’s personality.

In a recent article published in BioRxiv, the open access preprint repository for paper in biology, researchers from CNRS, France (Univ Rennes, INRA and ECOBIO) are trying to understand a puzzling issue: how do behavorial phenotypes, ie personalities, of snails correlate with their shell’s phenotype, ie colour and morphology, and with their environment?

More generally, the authors are interested in the questions of individual variations in species and links between morphology and behaviour. Inevitably, one can make unconscious comparisons with human individuals. In the non-human animal kingdom, talking about personalities might seem natural for pets like dogs or horses.  Studying the personalities of snails is definitively an unusual view.

The authors focused on snails from the species Cepaea nemoralis, which are abundant and exhibit large variations in shell phenotypes. In this species, snails with shells of light colour absorb better the heat and therefore have a low body temperature and a higher water content: they are better suited for hot climates. In opposition, snails with shells of darker colours are better suited for cold climates.

In addition, shells that have light background colour but dark bands contain more pigments (the melanins) and are more resistant to crushing.

Finally it is know since the late 1990’s that the shells colours likely influence the snail’s behaviour through its ability to cope with temperature. (These observations were made after experiments  consisting in painting snail’s shells!)

Based on these past results, the authors thus formulated the following hypotheses:

  • Risk-taking behaviour, i.e. exploration and boldness, are repeatable and common in snails
  • Exploration and high activity increases with the temperature of the snails through their metabolisms, therefore snails with light coloured shells are expected to be more active.
  • The downside of boldness (risk taking) is predation, therefore vulnerable snails are likely to be less risk-taking, i.e. the snails with shells containing less dark bands.

To verify their hypotheses, the authors collected 360 snails in a wet marsh environment in France in two areas: one with lots of protective tree, and another one with less trees. They collected the snails, tagged each individual, and put them in winter-like dormancy for a few months before releasing them in boxes where the experiments were conducted: upon providing them with food, they look at the snails activity at different temperatures, simulated predation, and looked at the speed of the snails to collect the food.

As a result, the authors found that:

  • heavily-banded snails were slower to explore their environment
  • snails with light shells not containing bands were bolder
  • personal traits in the snails were repeatable
  • the original landscape were the snails were collected did not influence much
  • the speed of exploration  of the snails increased with the temperature.

It was thus concluded from the study that there are links between shell phenotype and behaviour, but these correlations would also demand for genetic confirmation.

One last note about the study: there was an ethical statement, although it was written that is not officially required.