Shell colour polymorphism of the Negev desert landsnail, Trochoidea seetzeni: the importance of temperature and predation

Trochoidea seetzeni in the Negev desert of Israel has two colour morphs, white and brown. We tested whether there is an adaptive mechanism maintaining this colour polymorphism. We measured internal body temperatures of white and brown snails at different heights above the ground in summer and winter. Neither colour morph has an apparent thermoregulatory advantage in either season. Brown snails are more cryptic. However, we found that their rodent predators chose, if any colour, more brown snails than expected by chance. However, apostatic selection, for which we did not directly test, may or may not be operating. There may be no adaptive advantage to being brown over white (or vice versa). The colour polymorphism in T. seetzeni must be maintained either through an external selection form other than temperature or predation, or through a random genetic process, or apostatic selection.