Cork, 7-13 September 1996

Littorinids are one of the very few molluscan families with a sufficient following among researchers that they merit their very own symposia. This was the fifth in a series (which began in London in 1986, and has since been held in Sweden, Wales and France), and was organized by Ruth O'Riordan and Gavin Burnell at University College, Cork. The meeting attracted no less than 60 participants, and had a truly international representation, from 18 countries. As on two previous occasions, the proceedings of the meeting will be published as a refereed volume of Developments in Hydrobiology (the remaining volume was published in 1992 by the Malacological Society).

From the European perspective, one of the major areas of interest continues to be the `rough periwinkles'. On the one hand, traditional anatomical and allozyme studies have mostly supported the concept of three distinct species (Littorina saxatilis, L. arcana, L compressa - formerly L. nigrolineata), which all show parallel ecotypic variation in shell form in similar microhabitats. On the other, detailed examination of gene flow on a local scale has revealed barriers to interbreeding between `ecotypes' suggesting that L. neglecta, L. saxatils `H' and `M' forms, and L. tenebrosa, might each be reproductively isolated at least on some shores.

The formal naming scheme is of much less importance than the recognition of this system as a fascinating example of the processes of evolutionary divergence, and a model for sympatric speciation. A collaborative, EU-funded, research project is now underway in Leeds, Galway and Brussels, led by John Grahame, Peter Mill, Betty Gosling and Thierry Backeljau, which will examine this system over a wide geographical area and using various genetic techniques. In this team, Craig Wilding showed the preliminary results of his analysis of random-amplified polymorphic DNA (RAPDs) of rough periwinkles in Yorkshire, and plans to sequence specific nuclear and mitochondrial genes, while Ian Wilson described an approach using allozyme frequencies on the west coast of Ireland. The continuing saga of Littorina neglecta (no longer aptly named) has spawned numerous papers, theses and research careers over the past 20 years. During the course of a long coach ride home from the conference excursion to Killarney, the saga was irreverently set to music to create a malacological version of a rubgy song. By popular demand, this was performed again during the Irish banquet that evening, in the splendid surroundings of Blackrock Castle.

Modern DNA technology is also being applied to other groups of littorinids. In some cases the evolutionary relationships deduced from morphology and from mitochondrial DNA sequences are similar, as in the small, ancient, tropical genus, Tectarius. However there are about 50 species in the largest littorinid genus, Nodilittorina, which appears to have speciated recently; Peter Clarke explained how only DNA sequence data has the potential to resolve the phylogeny of this group. A new biochemical approach was described by Thierry Backeljau, whose team are using electrophoretic techniques to study phylogenetic patterns in the variation of myoglobin in the radular muscles of littorinids.

Much of the fascination with littorinids has been inspired by their extraordinary variation in shell shape and colour, and this continues to be a fruitful area of research. Increasingly, it is understood that shell shape and sculpture are the result not only of genotype, but also of ecophenotypic effects. By means of elegant transplantations between microhabitats in the Abrolhos Islands, Michael Johnson showed how faster growth produces flatter shell shape in the Australian littorinid Bembicium. Equally impressive is the contrast between striate and nodulose shells of Littorina striata in the Azores, described by Hans de Wolf, which may prove to be another case of phenotypic plasticity. In recent years shell colour variation has been curiously neglected. Anette Ekendahl has tested ideas that birds exert visual selection on the polymorphic L. saxatilis, by releasing samples of snails of known colour frequencies on the feeding grounds of knots in Iceland. In a different approach to the explanation of colour polymorphism, Sergei Sergievsky described correlations between colour frequencies and environmental salinity in the White Sea.

In many gastropods, the radula has been widely used as a taxonomic character. Unfortunately, radulae of littorinids often show as much intraspecific variation as their shells, precluding their use in species-level systematics. The causes of radular variation have not been investigated until now. Dianna Padilla described a remarkable series of experiments on species of Lacuna from the northwestern coast of the United States, showing that blunt tooth cusps were induced by rearing on seagrass, and pointed cusps on kelp. This again emphasizes the extraordinary phenotypic plasticity of littorinids. Similar effects should perhaps be considered in studies of other gastropod groups. Dawn Dittman has quantified the morphology of radular teeth, and used a recent phylogeny of Littorina species to investigate patterns of evolution of tooth form.

A more applied aspect of littorinid biology is the use of Littorina littorea as an indicator of tributyl tin (TBT) pollution. Previously, it had been thought that this winkle was insensitive to the masculinizing effects of the pollutant, but studies in both Germany and Ireland have now found that it shows intersex abnormalities at higher TBT concentrations than Nucella lapillus, extending the range over which biological monitoring by gastropods can be used (Jorg Oehlmann, Barbara Bauer, Pio Fioroni and others).

Following the Littorinid Symposium, there was a workshop on the aquaculture of marine gastropods, mainly abalone (Haliotis species). The edible winkle Littorina littorea is widely collected for food in Ireland and exported to Europe; although it is not yet cultured commercially, there was an interesting discussion of the practicalities of harvesting, maintaining and marketing this species, and Gavin Burnell described the development of a pelleted food supply for winkles kept in enclosures on the shore.

This short report cannot cover the entire range of talks and posters that were contributed at the Symposium. In addition to those mentioned, there were presentations on population biology, ecophysiology, reproductive biology, mating behaviour and parasitology. Monodonta and Nucella were also declared honorary littorinids for the duration of the meeting, to accommodate studies of other intertidal gastropods with similar ecology. There was even a report on the European `terrestrial winkle' (Pomatias elegans) by Elizabeth Platts, who memorably described a novel means of assessing its osmoregulatory abilities - undeniably bold, but highly subjective!

In the past the great majority of littorinid research has been carried out on a few European species, so it was good to hear several papers on tropical species, belonging to the genera Nodilittorina, Littoraria and Tectarius. To encourage a less Euro-centric view of the littorinid world, and hopefully increase participation by American malacologists, it was agreed that the Sixth Littorinid Symposium should be held in Jamaica in July, 1999. This will be organised by Bob McMahon and Joe Britton. There will be laboratory facilities and the opportunity for fieldwork with one of the most diverse littorinid faunas in the world, all in a desirable holiday location... To be added to the mailing list for details of this meeting, please contact Bob (Email: McMa...@uta.edu).

David Reid

David Reid, Peter Mill and John Grahame searching for the elusive Littorina neglecta among the barnacles at Mizen Head, County Cork