Nuclear Intron Sequence Variation of the Bulinus globosus Complex (Mollusca: Planorbidae): Implications for Molecular Systematic Analyses

Urinary schistosomiasis is caused by the blood fluke <i>Schistosoma haematobium</i>, which is predominantly found in Africa. The freshwater snail <i>Bulinus globosus</i> is its main intermediate host. The species that make up the <i>B. globosus</i> group are genetically complex, and their taxonomic status remains controversial. Genetic variation, heterozygosity, and DNA recombination in <i>B. globosus</i> were examined using the mitochondrial cytochrome c oxidase subunit 1 (<i>COI</i>) and the intron 3 region of the arginine kinase gene (AkInt3). A total of 81 <i>B. globosus</i> snails were collected from three different localities in Kwale County, Kenya. Genomic diversity, heterozygosity, DNA recombination, and haplotype network were calculated using AkInt3 sequences. Low polymorphism in the <i>COI</i> sequence divided <i>B. globosus</i> into six haplotypes (C1-C6). However, AkInt3 sequencing studies showed high polymorphisms, classifying 81 <i>B. globosus</i> snails into 44 haplotypes (H1-H44). These haplotypes were separated into three haplogroups (I-III). AkInt3 sequence heterozygosity was also found. DNA recombination haplotypes between haplogroups were commonly found in heterozygous samples. AkInt3 sequence studies showed high levels of genetic polymorphism and heterozygosity, supporting its use as a genetic marker for elucidating the population genetics of <i>B. globosus</i>. Furthermore, our study showed that <i>B. globosus</i> populations in Kenya form a "species complex".