Molecular analyses reveal high species diversity of trematodes in a sub-Arctic lake

Abstract

To identify trematode diversity and life-cycles in the sub-Arctic Lake Takvatn, Norway, we characterised 120 trematode isolates from mollusc first intermediate hosts, metacercariae from second intermediate host fishes and invertebrates, and adults from fish and invertebrate definitive hosts, using molecular techniques. Phylogenies based on nuclear and/or mtDNA revealed high species richness (24 species or species-level genetic lineages) and uncovered trematode diversity (16 putative new species) from five families typical in lake ecosystems (Allocreadiidae, Diplostomidae, Plagiorchiidae, Schistosomatidae and Strigeidae). Sampling potential invertebrate hosts allowed matching of sequence data for different stages, thus achieving molecular elucidation of trematode life-cycles and exploration of host-parasite interactions. Phylogenetic analyses also helped identify three major mollusc intermediate hosts (Radix balthica, Pisidium casertanum and Sphaerium sp.) in the lake. Our findings increase the known trematode diversity at the sub-Arctic Lake Takvatn, showing that digenean diversity is high in this otherwise depauperate sub-Arctic freshwater ecosystem and indicating that sub-Arctic and Arctic ecosystems may be characterised by unique trematode assemblages.

A fine‐scale phylogenetic assessment of digenean trematodes in central Alberta reveals we have yet to uncover their total diversity

“…Other lineage splits seen within Diplostomum baeri and Tylodelphys sp. 2 have previously been described (Soldánová et al, 2017) and are further supported with our phylogeny.…”

“…For an ecoregion that has previously been considered speciespoor (Hoberg, Galbreath, Cook, Kutz, & Polley, 2012), sub-Arctic lake ecosystems have presented a surprising amount of trematode diversity from recent surveys. From one lake in Norway, on the 69th parallel, 24 different trematode species were recovered, representing seven different, common families from lakes in the Northern hemisphere (e.g., Strigeidae, Diplostomidae, Schistosomatidae, Echinostomatidae, Notocotylidae, Plagiorchiidae; Soldánová et al, 2017). Though further South, between the 54th and 52nd parallel, our study is still considered within the sub-Arctic region and has uncovered a range of 3-38 trematode species representing 3-8 families, each, among six lakes (the lower end, from Pigeon Lake and Lac La Nonne, was only sampled in 1 year as opposed to 3 years for the other lakes).…”

“…A final nucleotide alignment ( nad1 ) of 73 sequences was 386 bp long and included 31 unknown sequences from this study and all available species with significant overlap in the same region from GenBank. As in Soldánová et al (), among others, Isthmiophora melis () was used as an out‐group.…”

“…Traditionally, taxonomic descriptions of trematodes are from morphological traits of adult worm stages derived from vertebrate hosts, as their most prominent features are fully developed and measurable, contrasting the less developed features of the larval stages (Schell, 1985). With the onset of molecular barcoding, not only have we realized the problems of cryptic morphology and the need for multiple lines of evidence for species delineation, but that for trematodes, we can now use larval stages to delineate species (Detwiler et al, 2010(Detwiler et al, , 2012Georgieva, Selbach et al, 2013;Gordy, Locke, Rawlings, Lapierre, & Hanington, 2017;Locke, Mclaughlin et al, 2010;Schwelm, Soldánová, Vyhlídalová, Sures, & Selbach, 2018;Soldánová et al, 2017). This is advantageous in that it is considerably easier to collect larvae from snail, first-intermediate hosts.…”

Seasonal dietary shifts enhance parasite transmission to lake salmonids during ice cover

“…The taxa Crepidostomum spp. comprise at least four different species that are transmitted thought insect larvae and/or amphipods (Soldánová et al, 2017). If some species of Crepidostomum only use insect larvae as intermediate host (see Marcogliese, Goater, & Esch, 1990), these may have higher prevalence during summer when the feeding on insect prey is high, while the prevalence of those transmitted through amphipods may increase toward winter, consequently explaining the lack of seasonality in Crepidostomum ssp.…”