DNA barcodes show cryptic diversity and a potential physiological basis for host specificity among Diplostomoidea (Platyhelminthes: Digenea) parasitizing freshwater fishes in the St. Lawrence River, Canada

Abstract

Diplostomoid metacercariae parasitize freshwater fishes worldwide and cannot be identified to species based on morphology. In this study, sequences of the barcode region of cytochrome c oxidase subunit 1 (CO1) were used to discriminate species in 1088 diplostomoids, most of which were metacercariae from fish collected in the St. Lawrence River, Canada. Forty-seven diplostomoid species were detected, representing a large increase in known diversity. Most species suggested by CO1 sequences were supported by sequences of internal transcribed spacer (ITS) of rDNA and host and tissue specificity. Three lines of evidence indicate that physiological incompatibility between host and parasite is a more important determinant of host specificity than ecological separation of hosts and parasites in this important group of freshwater fish pathogens. First, nearly all diplostomoid species residing outside the lens of the eyes of fish are highly host specific, while all species that occur inside the lens are generalists. This can be plausibly explained by a physiological mechanism, namely the lack of an effective immune response in the lens. Second, the distribution of diplostomoid species among fish taxa reflected the phylogenetic relationships of host species rather than their ecological similarities. Third, the same patterns of host specificity were observed in separate, ecologically distinctive fish communities.

Diversity, specificity and speciation in larval Diplostomidae (Platyhelminthes: Digenea) in the eyes of freshwater fish, as revealed by DNA barcodes

“…The larger ML analysis indicated that D. ardeae may belong to a genus other than Diplostomum, Tylodelphys or Austrodiplostomum, and that Tylodelphys may be paraphyletic, as Austrodiplostomum is nested within it. A CO1 sequence (HM064650) from a specimen formerly identified only to family (Locke et al, 2010b) fell within the Diplostomum clade, and is thus considered a member of the genus (Diplostomum sp. 11).…”

An updated look at the uneven distribution of cryptic diversity among parasitic helminths

“…When correcting for study effort and accounting for other confounding variables, cryptic species do not appear to be more frequent among parasitic than free-living taxa (Poulin & Pérez-Ponce de León, 2017). Yet cryptic parasite species are reported with increasing frequency; this is a consequence of genetic methods having become standard practice for parasite identification, and often being used deliberately to prospect for cryptic diversity (Blouin, 2002;Locke et al, 2010;Rosas-Valdez et al, 2011;Razo-Mendivil et al, 2015). For parasitologists, there are serious implications: the occurrence of cryptic parasite species can greatly complicate parasite taxonomy, bias estimates of host specificity and undermine our efforts to control parasitic diseases (Poulin & Keeney, 2008; Pérez-Ponce de León & Nadler, 2010;Nadler & Pérez-Ponce de León, 2011).…”

A review on the molecular characterization of digenean parasites using molecular markers with special reference to ITS region

“…of 47 studies, 11 expressing variations in ITS-1 region, 20 in ITS-2 region and 16 in both ITS-1 and ITS-2 region. Apart from ITS region, mitochondrial genes like COI, NDI (Caffara et al, 2014;Heneberg et al, 2014;Locke et al, 2011) etc. are also included to corroborate the fi ndings.…”

“…Locke et al (2010a) studied the barcode region of COI and ITS sequences to differentiate species of diplostomoids from fi shes in St. Lawrence River, Canada. 47 species of diplostomoids were noticed and COI sequences analysis was supported by ITS region data.…”

“…In general COI region was advanced than commonly used ITS region for species differentiation. Locke et al (2011) studied the distribution of adult and larval parasites Apharyngostrigea cornu, Hysteromorpha triloba and Alaria mustelae from fi sh, frogs, birds and mammals of North America using COI and ITS region sequences. The sequences of all adult parasites of defi nitive hosts matched with meta and meso-cercari-ae of fi sh and frogs.…”