Molecular systematics of some North American species of Diplostomum (Digenea) based on rDNA-sequence data and comparisons with European congeners

Abstract

The systematics of Diplostomum species, common intestinal parasites of piscivorous birds, has long been problematic, owing to phenotypic plasticity and the paucity of morphological features that are often subject to age-and host-induced variation. We sequenced the ITS1-5.8S-ITS2 regions of the rDNA from adult Diplostomum huronense, Diplostomum indistinctum, and Diplostomum baeri obtained from experimentally infected ring-bill gulls (Larus delawarensis) and compared them with partial ITS1 sequences from several species of Diplostomum in GenBank. The three North American species were distinguishable on the basis of ITS sequences. Sequences from D. huronense differed from those of D. indistinctum at 12 sites in ITS1 and 4 sites in ITS2, supporting morphological and morphometric data that indicate the two are distinct species. Sequences of D. huronense and D. indistinctum differed from those of D. baeri at 27 and 24 sites, respectively, in ITS1 and 15 and 12 sites, respectively, in ITS2. Phylogenetic analysis of partial ITS1 sequences revealed that the North American and European species of Diplostomum formed separate groups, with the former being basal to the latter. The results indicated that D. huronense and D. indistinctum from North America are distinct from Diplostomum spathaceum and other similar species from Europe. Furthermore, sequences from specimens identified as D. baeri from North America differed from those of D. baeri from Europe by 3.8% in ITS1 (23 sites). While morphologically similar, the two are not conspecific. Sequences of the North American species have been deposited in GenBank (AY 123042-123044).Résumé : La systématique des espèces de Diplostomum, parasites intestinaux communs des oiseaux piscivores, a toujours été problématique à cause de leur plasticité phénotypique et de la rareté des caractères morphologiques qui sont souvent soumis à des variations dues à l'âge et à l'hôte. Nous avons procédé au séquençage des régions ITS1-5.8S-ITS2 du gène d'ADNr de Diplostomum huronense, de Diplostomum indistinctum et Diplostomum baeri adultes provenant de goélands à bec cerclé (Larus delawarensis) infectés expérimentalement et nous avons comparé les séquences obtenues à des séquences partielles d'ITS1 de plusieurs espèces de Diplostomum de la banque génétique GenBank. Les trois espèces nord-américaines se distinguent par les séquences de leurs ITS. Les séquences de D. huronense diffèrent de celles de D. indistinctum à 12 sites sur ITS1 et à 4 sites sur ITS2, ce qui corrobore les données morphologiques et morphométriques qui indiquent qu'il s'agit de deux espèces distinctes. Les séquences de D. huronense et de D. indistinctum diffèrent de celles de D. baeri à 27 et 24 sites sur ITS1 et à 15 et 12 sites sur ITS2, respectivement. L'analyse phylogénétique des séquences partielles D'ITS1 a révélé que les espèces nord-américaines et européennes de Diplostomum forment deux groupes distincts, le premier groupe étant plus ancien. Les résultats indiquent que D. huronense et D. indistinctum d'Amérique du Nord so...

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

“…Sequences can clarify whether morphological heterogeneity represents interspecific (BlascoCosta et al, 2014;Faltý nková et al, 2014;Pérez-del-Olmo et al, 2014) or intraspecific variation among metacercariae (Cavaleiro et al, 2012;Otachi et al, 2015). Molecular links to adults from avian definitive hosts are usually needed to identify, rather than merely discriminate, species of metacercariae (Galazzo et al, 2002;Locke et al, 2010aLocke et al, , 2011Georgieva et al, 2013;Pérez-delOlmo et al, 2014). However, even when sequences are obtained from adult diplostomids, often not all species detected in surveys of metacercariae are resolved (Galazzo et al, 2002;Georgieva et al, 2013;Pérez-del-Olmo et al, 2014).…”

“…Molecular links to adults from avian definitive hosts are usually needed to identify, rather than merely discriminate, species of metacercariae (Galazzo et al, 2002;Locke et al, 2010aLocke et al, , 2011Georgieva et al, 2013;Pérez-delOlmo et al, 2014). However, even when sequences are obtained from adult diplostomids, often not all species detected in surveys of metacercariae are resolved (Galazzo et al, 2002;Georgieva et al, 2013;Pérez-del-Olmo et al, 2014). The result is a sequence database dominated by unidentified, provisional species, many of which have been distinguished primarily through DNA sequence analysis.…”

“…For example, provisional, molecular delineations of diplostomid species have revealed compositional differences (Rellstab et al, 2011) and evidence of interspecific interactions among metacercarial communities in fish eyes (Désilets et al, 2013). In other ecological field studies, diplostomids in fish eyes are often pooled into genera (e.g., Marcogliese et al, 2006), even when local species are known from prior molecular taxonomic work (Galazzo et al, 2002). Pooling metacercariae in this manner can change the factors implicated in, and reduce variance explained by, ecological analysis of parasite communities .…”

“…Contrary to what Gibson (1996) expected based on the mobility and distribution of their avian hosts, none of the genetically distinguished Diplostomum spp. are common to both the Nearctic and Palearctic (Galazzo et al, 2002;Locke et al, 2010a;Cavaleiro et al, 2012;Georgieva et al, 2013). Intriguingly, it appears this biogeographic partition results mainly from two waves of Nearctic to Palearctic colonisation, one in the lens clade, the other in the clade of non-lens species (BlascoCosta et al, 2014).…”

Morphological and molecular characterization of Posthodiplostomum sp. (Digenea: Diplostomidae) metacercaria in the muscles of snakeheads (Channa punctata) from Manipur, India

“…Piscivorous birds, mainly herons (Ardeidae), are definitive host for the parasite in Eurasia (Skrjabin, 1964;Yamaguti, 1971). Molecular characterization of larval and adult forms of various diplostomid taxa utilizing data from rDNA markers has proven to be useful in supplementing their morphology-based identification (Galazzo et al, 2002;Niewiadomska & Laskowski, 2002;Criscione et al, 2005;Nguyen et al, 2012;Zhao et al, 2012). The mitochondrial cytochrome oxidase 1 (mtCO1) gene has also been largely utilized as a tool in molecular discrimination of digenean species (Nolan & Cribb, 2005;Olson & Tkach, 2005).…”