Snails show their true colours: rate of evolutionary divergence in the shell colour polymorphism of Cepaea nemoralis

Abstract

The shell colour polymorphism in the land snail Cepaea nemoralis is maintained by environmentally variable light intensity and predation. Previous work showed that divergence in colour polymorphism between habitat pairs of open and closed areas increased with age of the habitat. However, that study was limited to a time span of 80 years (27 snail generations). Here, we investigate shell colour divergence over habitat pair ages of 95 to 325 years. We did find an increase in evolutionary divergence of colour polymorphism with increasing age, however equilibrium could not be determined. This is possibly due to the evolutionary effect of camouflage working in opposite direction to light intensity in certain locations, consequently clouding the results. Therefore, camouflage might also be an important factor to take into account in the search for the evolutionary equilibrium of colour polymorphism in Cepaea nemoralis.