Periwinkles and parasites: the occurrence and phenotypic effects of parasites inLittorina saxatilisandL. arcanain northeastern England

Abstract

Littorina saxatilis is a common intertidal gastropod on shores of the North Atlantic, and an 24 important study species for evolutionary investigations. Its congener L. arcana is much less 25 widely distributed, but both species are common at Old Peak, Yorkshire, UK. The parasite 26 profiles of L. saxatilis and L. arcana from this shore were determined histologically, revealing 27 a ciliated protist, Protophrya ovicola, an unidentified apicomplexan (present in <1% L. 28 saxatilis) and three trematode parasites tentatively assigned to Renicola sp., Microphallus 29 similis and M. pygmaeus. The profile data include prevalence information and associated 30 histology. Protophrya ovicola associated predominantly with the wave ecotype of L. saxatilis 31 (65%) rather than the crab ecotype (16%). Microphallus similis occurred at a higher 32 prevalence in the L. arcana population (38%) in comparison with the L. saxatilis population 33 (11%). Overall, there appeared to be a lower prevalence of trematodes in the high-shore L. 34 saxatilis. By modelling occurrence of individual parasites and shell morphometrics, an 35 assessment of parasite-associated morphological change was conducted. We conclude that 36 parasitism appeared not to cause shell-shape change, but rather that snails of a certain shell 37 shape were more likely to display infection. Records of parasites in L. saxatilis and L. arcana 38 are briefly reviewed, showing that the diversity of parasites reported here is relatively low.