Another plea for ‘best practice’ in molecular approaches to trematode systematics: Diplostomum sp. clade Q identified as Diplostomum baeri Dubois, 1937 in Europe

Abstract

DNA sequence data became an integral part of species characterization and identification. Still, specimens associated with a particular DNA sequence must be identified by the use of traditional morphology-based analysis and correct linking of sequence and identification must be ensured. Only a small part of DNA sequences of the genus Diplostomum (Diplostomidae) is based on adult isolates which are essential for accurate identification. In this study, we provide species identification with an aid of morphological and molecular (cox1, ITS-5.8S-ITS2 and 28S) characterization of adults of Diplostomum baeri Dubois, 1937 from naturally infected Larus canus Linnaeus in Karelia, Russia. Furthermore, we reveal that the DNA sequences of our isolates of D. baeri are identical with those of the lineage Diplostomum sp. clade Q , while other sequences labelled as the ‘D. baeri’ complex do not represent lineages of D. baeri. Our new material of cercariae from Radix balthica (Linnaeus) in Ireland is also linked to Diplostomum sp. clade Q. We reveal that D. baeri is widely distributed in Europe; as first intermediate hosts lymnaeid snails (Radix auricularia (Linnaeus), R. balthica) are used; metacercariae occur in eye lens of cyprinid fishes. In light of the convoluted taxonomy of D. baeri and other Diplostomum spp., we extend the recommendations of Blasco-Costa et al. (2016, Systematic Parasitology 93, 295–306) for the ‘best practice’ in molecular approaches to trematode systematics. The current study is another step in elucidating the species spectrum of Diplostomum based on integrative taxonomy with well-described morphology of adults linked to sequences.

Species complexes and life cycles of digenetic trematodes from the family Derogenidae

“…The main reasons are: (1) lack of faunistic data in many regions; (2) phenotypic variation; (3) the existence of cryptic or just hardly distinguishable species; and (4) the complex life cycles (Cribb, 2016). Happily, an integrative approach incorporating molecular genetics and modern morphological methods applied to different life-cycle stages gives the opportunity to bring the research on the digenean diversity to a new level (Georgieva et al ., 2013; Gilardoni et al ., 2020; Gonchar and Galaktionov, 2021; Huston et al ., 2021; Faltýnková et al ., 2022). This approach has been barely used for one of the most widespread digenean taxa parasitizing fish – the superfamily Hemiuroidea.…”

Diplostomum cf. vanelli Yamaguti, 1935 (Trematoda: Diplostomidae Poirier, 1886): Morpho-Molecular Data and Life Cycle

“…At the same time, the nucleotide sequence of trematode from this study was identical to samples KR269765 and MZ314171, designated as D. spathaceum. However, data on morphology are presented only for D. baeri [23]. Faltynkova and co-authors [23] have noted that due to weak morphological differences between Diplostomum species, erroneous species identification is possible.…”

“…However, data on morphology are presented only for D. baeri [23]. Faltynkova and co-authors [23] have noted that due to weak morphological differences between Diplostomum species, erroneous species identification is possible. For correct species determination, an integrated approach is required, namely, the combination of both nucleotide sequences and the morphology of the worm from which these sequences were obtained.…”

Resurrection of Diplostomum numericum Niewiadomska, 1988 (Digenea, Diplostomatoidea: Diplostomidae) Based on Novel Molecular Data from the Type-Host

“…The identity of the newly generated sequences was checked with the Basic Local Alignment Search Tool (BLASTn) (www.ncbi.nih.gov/BLAST/, accessed on 15 January 2023 ). The novel sequences were aligned with those of 172 representatives of the genus Diplostomum (Table S1; [10,12,15,[17][18][19][20][21][22][23][24][33][34][35][39][40][41][42][43][44][45][46][47][48]) in MEGA v. 10 [38] and trimmed to the shortest length, 384 nt. The nomenclature of Diplostomum spp.…”

“…The nomenclature of Diplostomum spp. followed the latest studies [22][23][24]35]. The cox1 sequence for Tylodelphys clavata (Nordmann, 1832) (JX986909) was used as an outgroup (Table S1; [15]).…”