Global molecular diversity of the zoonotic tapeworm Spirometra mansoni (Cobbold, 1883) (Cestoda: Diphyllobothriidea)

Abstract

Spirometra mansoni is a zoonotic tapeworm with a global distribution; however, its population-level genetic structure and phylogeographic patterns remain poorly understood. Robust phylogeographic inference is essential to understand diversification and the geographical structuring of its mitochondrial diversity. We analysed three datasets of newly generated and publicly available mitochondrial cox1 sequences differing in length: a short-fragment alignment (303 bp; n = 319), a full-length dataset (1556 bp; n = 101) and a length-matched subset extracted from the full-length sequences (303 bp; n = 101). Phylogenetic, haplotype network and population genetic analyses were performed to assess the effect of fragment length on phylogeographic inference. Haplotype network analyses revealed extensive haplotype sharing between Asian and North American isolates, whereas European isolates formed a distinct, low-diversity clade recovered in both the 303 bp and 1556 bp networks. No consistent clustering by host species or developmental stage was detected. Short-fragment datasets were dominated by a few widespread haplotypes, whereas full-length cox1 dataset resolved a higher number of closely related, often geographically restricted haplotypes. At the pooled level, the combination of high haplotype diversity, low nucleotide diversity and significantly negative Fu's Fs values indicates an excess of rare haplotypes consistent with recent demographic expansion, although regional analyses showed this signal to be confined to the Asian lineage in the full-length dataset. A key methodological finding is that the 303 bp partial cox1 fragment underestimates haplotype diversity compared to full-length cox1 for the same isolates. Phylogeographic inference in Spirometra therefore requires complete cox1 sequences combined with broader, geographically balanced sampling, particularly from Africa, South America and Europe.

Keywords: Genetics; Phylogeography; Population; Sparganosis; Spirometrosis; Zoonoses; cox1.