Activity and weight loss in relation to solar radiation in the polymorphic land snail Cepaea nemoralis

Abstract

Shell spectral reflectance, activity and weight loss in the land snail Cepaea nemoralis were examined to test whether solar radiation has different effects on the behavioural and physiological responses of different morphs. A uniform area from the empty shells of different morphs was cut and a spectrophotometer was used to measure the spectral reflectance at wavelengths from 220 nm to 800 nm. Snails were put into cages made of mesh hardware cloth, and their activities were observed from dawn onwards on two hot, dry days. Weight loss of snails under shade and under direct sunlight was also measured.The results show that unbanded morphs reflect more light than five‐banded ones, but the yellow morphs reflect only a little more than pink morphs. Five‐banded morphs became inactive more quickly than unbanded ones from dawn onwards, but the differences in activity patterns were not significant between pink and yellow morphs. There are significant differences in percent weight loss between snails placed under direct sunlight and under shade. The weight loss of different morphs under shade was not statistically different. But when exposed to sunlight, five‐banded morphs lost more weight than pink and yellow unbanded morphs.Because of their lower reflectance of solar radiation, the five‐banded morphs are, in a hot, arid climate, at a selective disadvantage compared to unbanded morphs. However, they can avoid such selective disadvantage by actively seeking a shaded area, as all other morphs do in the field. Such behavioural habitat selection could help the maintenance of genetic polymorphisms in natural populations.