Bulinus on Aldabra and the subfamily Bulininae in the Indian Ocean area

Abstract

The molluscan family Planorbidae is widely distributed throughout the temperate and tropical regions of the world. The subfamily Bulininae includes two genera only, Bulinus which is confined to the Ethiopian zoogeographical region, the Mediterranean area, the Middle East and some islands in the Western Indian Ocean, and Indoplanorbis which is common throughout India and Southeast Asia and also occurs on Socotra. These snails have been the subject of particularly intense study because of their importance as intermediate hosts for blood-flukes of the genus Schistosoma parasitic in man and domestic animals. The presence of a species of Bulinus on Aldabra is interesting because of the relative rarity of freshwater molluscs on atolls and also because it has served as a focus for drawing together the results of recent investigations into the distribution, relationships and intermediate host capacity of bulinids in the Indian Ocean area. This area has presented a number of problems in the interpretation of patterns of schistosomiasis transmission and most of these problems stem from misunderstandings about the taxonomy of the host snails and their parasites. Many of the misunderstandings have arisen from the paucity and unreliable nature of morphological criteria for taxonomic studies in basommatophoran snails and these have now been supplemented by cytogenetic, biochemical and immunological information. The methods used include paper chromatography of bodysurface mucus (Wright 1964), electrophoresis of egg proteins on cellulose acetate (Wright & Ross 1965, 1966), starch-gel electrophoresis of digestive-gland enzymes (Wright, File & Ross 1966; Wright & File 1968), Ouchterlony plate gel diffusion and agar-gel immuno-electrophoresis of egg proteins using antisera prepared in rabbits, and colcimid blocking of mitotic metaphase chromosome figures in developing embryos.