RANDOM AMPLIFIED POLYMORPHIC DNA (RAPD) MARKERS REVEAL CROSS-FERTILIZATION IN BIOMPHALARIA-GLABRATA (PULMONATA, BASOMMATOPHORA)

The freshwater, schistosome-transmitting snail, Biomphalaria glabrata is a simultaneous hermaphrodite which can reproduce by both cross-and self-fertilisation, but despite the medical importance of this species, little is known about the mating strategies adopted by wild-type individuals from natural populations. The identification of cross-fertilised progeny is a prerequisite for both evolutionary studies of the relative fitness of different reproductive strategies, and for the production of exclusively out crossed Fl populations for genetic mapping of biologically important phenotypes, most notably, resistance to schistosome infection. In this study, parents, offspring and 'synthetic offspring' (controls) from four families of B. glabrata recently derived from wild populations were analysed using the Random Amplified Polymorphic DNA (RAPD) assay. RAPDs were used because they reveal more genetic variation, require less tissue (juvenile snails were only 4-5 mm diameter) than protein electrophoresis, are less laborious than other molecular analyses, and do not require sequence data. Seven of the 19 arbitrary sequence, oligonucleotide primers used gave bands that were polymorophic between pairs of parent snails. Scoring the offspring for the presence/absence of these polymorphic bands showed that all the offspring tested were the products of cross-fertilisation. This study provides the first demonstration of the applicability of the RAPD technique to an analysis of fertilisation in wild-type B. glabrata.