POPULATION DIFFERENCES IN BEHAVIOR AND MORPHOLOGY IN THE SNAIL LITTORINA-SAXATILIS - PHENOTYPIC PLASTICITY OR GENETIC DIFFERENTIATION

The ovoviviparous Littorina saxatilis (Olivi) can be found in many int ertidal habitats. Winkles From different habitats have different morph ologies and behaviours, which are usually argued to reflect adaptation s. Whether the different forms are caused by genetic differentiation o r due to phenotypic plasticity is, however, less discussed. Our aim wa s to document morphological and behavioural differences among one expo sed rock population, one sheltered boulder population, and one mud fla t population, and we reared offspring in a common laboratory environme nt to see if the differences persisted. We used principal component an alysis (PCA), based on 19 measurements, to compare size and shape diff erences. We also used PCA and linear regression to study allometry and compare growth trajectories. Behavioural differences were studied in three laboratory trials. Littorina saxatilis From the rock were relati vely small, had small aperture lips, thin shells, blunt spires, and wi de columellae. They preferred to stay in cracks and to be above the wa ter surface, and they quickly emerged out of their shells after distur bance. L. saxatilis from the boulder shore were relatively large, had large lips, thick shells, pointed spires, and narrow columellae. They preferred open surfaces, submergence, and after disturbance they slowl y emerged out of the shell. L. saxatilis from the mud flat were relati vely small, had small lips, thin shells, pointed spires, and narrow co lumellae and most behaved similarly to the boulder shore snails. Altho ugh less pronounced, most of these morphological and behavioural diffe rences persisted in the snails that we reared in the common environmen t. This indicates some genetic differentiation. All groups grew allome trically, and most groups differed in growth trajectories. Despite sim ilar ages, the reared females were generally larger than the real ed m ales, indicating higher growth rate in females. Sexual maturation seem ed to be reached at a certain size rather than at a certain age. Theor ies predict genetic differentiation in intertidal snail species with l ow dispersal, but some investigations show results that contradict the theories, while others agree with them. Our study confirms the predic tion that L. saxatilis should be genetically differentiated.