1. Institute of Biological Sciences, University of Wales, Aberystwyth, Ceredigion, SY23 3DD, Wales, U.K., Department of Computer Sciences, University of Wales, Aberystwyth, Ceredigion, SY23 3DB, Wales, U.K., and School of Biological and Biomedical Sciences, Glasgow Caledonian University, Cowcaddens Road, Glasgow, G4 0BA, Scotland, U.K.