SREL Reprint #2027




Intraspecific and Interspecific Patterns of AllozymeVariation Among Species of Biomphalaria Preston, 1910 (Gastropoda: Planorbidae)


1Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802, U.S.A.;
2Department of Biology, University of New Mexico, Albuquerque, NM 87131, U.S.A


Freshwater snails in the genus Biomphalaria transmit Schistosoma mansoni, a causative agent of human schistosomiasis in Africa and the Neotropical region. Twenty-five populations representing 1 1 species of Biomphalaria from both Africa and the Neotropical region were examined using starch gel electrophoresis for 22 loci. The percentage of polymorphic loci observed per population varied from 4.5 to 63.6%, with a mean of 28.7%; observed heterozygositv levels varied from 0.002 to 0.1 26, with an average of 0.052. Observed heterozygosity and polymorphism values fell within the range of values reported in previous studies of the genus, but observed heterozygosity in most cases was less than expected under Hardy-Weinberg equilibrium. The genetic variance was partitioned among species, populations and individuals using hierarchical G-statistics. For all of the populations considered together, the variance among species was 58.4/o, among populations within species 24.9%, and among individuals within a population 16.7%. When only the Neotropical species were considered, the percentages of the total variance attributable to variation among species, among populations within species, and among individuals were 18.1%, 29.2% and 52.7'Y., respectively. For the African species, 27.8% of the variance was among species, 42.3% among populations, and 29.9% among individuals. lntraspecific Roger's genetic distances ranged from O.01 to 0.38, and interspecific distances from 0.1 to 0.84. Nei's unbiased distances ranged from 0.00 to 0.44 within a nominal species, and from 0.02 to 1.82 between species. Non-metric multidimensional scaling of Rogers'distances revealed a clear separation of African species from Neotropical species and of the Neotropical species from each other. The African species formed overlapping clusters.

Key Words-Biomphalaria; Planorbidae; Gastropoda; ramshorn snails, Schistosoma mansoni; allozymes; population variation; systematics.

SREL Reprint #2027

Bandoni, S.M., M. Mulvey, and E.S. Loker. 1995. Intraspecific and interspecific patterns of allozyme variation among species of Biomphalaria Preston, 1910 (Gastropoda: Planorbidae). Biochemical Systematics and Ecology 23:593-616.


To request a reprint