Host-switching between distantly related host species offers rare insight into how parasites overcome compatibility barriers and initiate evolutionary divergence. Microphallus pseudopygmaeus is exceptional among digeneans in its ability to infect gastropods from two distantly related subclasses, Vetigastropoda and Caenogastropoda. This study aimed to test the hypothesis about the species status of M. pseudopygmaeus and clarify its host range. We obtained partial sequences of the cox1 gene, 28S rDNA and ITS2 for M. pseudopygmaeus from nine host species, including Margarites spp. (Vetigastropoda). The data on the conservative and variable markers, phylogenetic and barcoding gap analyses, supported the unity of the species and its broad specificity to the first intermediate hosts. The cox1-based haplotype network revealed host-associated genetic divergence, particularly in isolates from Margarites spp. and Cryptonatica affinis. This pattern may result from localized circulation of the parasite in the regions where certain host species, such as Margarites spp., dominate in the absence of periwinkles, creating ecological conditions that could promote reproductive isolation and incipient speciation. This work opens up the prospects of using M. pseudopygmaeus as a model for studying host-switching and speciation in parasites.
Sokolova et al. (Thu,) studied this question.