Feeding strategy and habitat choice in Littorina saxatilis (Gastropoda: Prosobranchia) and their role in the origin and maintenance of a sympatric polymorphism

Abstract A remarkable adaptive polymorphism occurs in L. saxatilis on exposed rocky shores in Galicia (NW Spain), where two conspecific morphs (Ridged and Banded, and Smooth and Unbanded) can be found associated with different shore levels. These two morphs overlap in the mid shore, and in spite of hybridization they retain their distinct phenotypes. This is partially caused by an adaptive response of each morph to different microhabitats as well as a partial prezygotic reproductive isolation between them. We investigated the diet and microhabitat preference of these two morphs and hybrids to check their possible contribution to the origin and maintenance of the present polymorphism. The diversity and abundance of species in the gut content was studied in separate individuals of these morphs from different shore levels, microhabitats and localities. The most frequent taxa present in the gut content of all morphs were diatoms, mainly Grammatophora and Navicula (about 50% of total gut content). Twelve other...