Mating system of Biomphalaria sudanica, a vector of Schistosoma mansoni

Abstract

Biomphalaria snails are intermediate hosts for schistosome parasites, which cause morbidity and mortality in humans worldwide. We aimed to determine the mating system of Biomphalaria sudanica, a hermaphroditic vector of schistosomiasis in the African Great Lakes, with the goal of informing the design of genetic studies such as linkage mapping to improve genome assembly and genetic association studies to identify snail resistance genes. To determine the relative rates of outcrossing versus selfing, we assayed the progeny of experimental crosses of snails in the laboratory using a PCR and restriction enzyme digest to determine snail genotype and parentage. Out of 7 experimental crosses and 56 total offspring assayed, 100% were derived from outcrossing rather than inbreeding. These results indicate that B. sudanica is primarily an outcrossing species, although previous work has shown that this species retains the capability of self-fertilization.

Graphical abstract

Experimental design to determine the mating system of paired snails. Snails with a single nucleotide polymorphism in the superoxide dismutase 1 (SOD1) gene were paired together and allowed to reproduce. The resulting offspring were assessed via PCR amplification of SOD1 followed by restriction enzyme digest with HaeIII, which cuts fragments with “C” at the cut site, but not those with “T”. Fragment number and size were assessed by agarose gel electrophoresis. Heterozygotes are derived from cross-fertilization while homozygotes are derived from self-fertilization. Created in BioRender. Steinauer, M. (2025) https://BioRender.com/j83q904.

Highlights

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  Snails of the genus Biomphalaria are vectors for Schistosoma mansoni.

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  While all snails of the genus are hermaphroditic, species differ in whether they primarily outcross or self-fertilize.

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  A PCR and restriction enzyme digestion were designed to determine mating strategies in laboratory crosses of B. sudanica.

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  All 56 offspring from 7 families were produced via outcrossing and none via self-fertilization.

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  Results will inform the design of genetic association studies and the development of snail-based control measures.