Observations on shell morphology, enzymes and random amplified polymorphic DNA (RAPD) in Bulinus Africanus group snails (Gastropoda: Planorbidae) in zanzibar

The taxonomic status of Bulinus globosus and B. nasutus as separate species remains unclear, especially in areas of East Africa where their distribution overlaps. In order to throw further light on this question, a study was carried out on snails collected from the islands Unguja and Pemba, collectively known as Zanzibar, which lie in the Indian Ocean close to mainland Africa. In total, 169 snails from 22 sample sites were characterised by three methods: morphometric analysis of 15 shell measurements, enzyme analysis involving three enzyme systems and analysis with random amplified polymorphic DNA (RAPD). Enzyme analyses indicated that both B. nasutus and B. globosus were present on each island and their distribution was allopatric. Shell variation was considerable but did not clearly differentiate these taxa. Similarly, RAPD analysis indicated substantial genetic variation within and between samples; more often than not, no two RAPD profiles were identical within the sample. On Pemba, B. globosus is more widely dispersed than B. nasutus which is confined to the eastern coast of the central region. On Unguja, B. globosus is found in more northern areas than B. nasutus.