A tetraploid freshwater snail (Planorbidae: Bulinus) in the highlands of Kenya

Abstract

Several levels of polyploidy are known in freshwater snails belonging to the Bulinus truncatus/tropicus complex. All are present in the highlands of Ethiopia, but only the tetraploid B. truncatus has been recorded from Kenya, living in the western lowlands. Observations are reported here on the chromosome number, shell, internal organs and egg-proteins of snails from 26 localities in the highlands of central Kenya; data are also given for B. truncatus from five localities in western Kenya. Diploid (2n = 36) and tetraploid (2n = 72) snails were obtained in central Kenya, the tetraploid being found only on the Kinangop Plateau (Aberdare Range) and Mau Escarpment at altitudes above 2400 m (7900 ft). There appeared to be no significant differences between diploid and tetraploid snails from the highlands in respect of morphological features or egg-proteins. However, the highland tetraploid differs from B. truncatus in characters of the shell, internal organs and egg-proteins and appears to have originated independently in the Kenyan highlands. Cytological examination of snails from Nairobi provided evidence that B. alluaudi (Dautzenberg), the oldest of five taxa belonging to the B. truncatus/tropicus complex and described from central Kenya, was originally described from diploid snails. Consequently, the appropriate name for the highland tetraploid is B. permembranacea (Preston).