Role of ambient wavelength, shell size and pigmentation intensity in the heating of Mediterranean Theba pisana (Eupulmonata: Helicidae)
ABSTRACT Theba pisana is a polymorphic land snail widely used in ecophysiological research on the biological significance of solar irradiation. We investigated whether, taking size into account, differently pigmented morphs of a Mediterranean population of T. pisana influence the snails’ heating under different wavelengths. We used a laboratory set-up comprising light-emitting diodes emitting visible light of defined wavelengths and quantified shell heating using high-resolution thermography. Shell pigmentation was quantified densitometrically. There were significant effects of both shell size and light wavelength, such that small snails heated more than large ones over 15 min, and blue light (470 nm) raised temperature more than green light (525 nm). Pigmentation alone did not show significance, but a trend towards higher temperature with increasing pigmentation was evident. Despite the observed significances and trends, we could only explain at most 4.67% of variation in shell heating by multiple regression modelling. However, the light intensity used in this experiment was low and the pigmentation intensity of the shells varied, at most, by a factor of 2. This suggests the actual temperature of a snail depends not only on the tested variables, but also on the multifactorial action of a number of unknown, perhaps intrinsic physiological parameters.