Echinostoma chankensis nom. nov., other Echinostoma spp. and Isthmiophora hortensis in East Asia: morphology, molecular data and phylogeny within Echinostomatidae

Abstract

Abstract

A new cryptic species of Echinostoma (Trematoda: Echinostomatidae) closely related to Echinostoma paraensei found in Brazil

“…In the present study, we reinforce the limitations of ribosomal nuclear DNA for the distinction of closely related species (the new taxon could not be recognized using this dataset) and found only moderate nucleotide divergence (3.83%) using cox1 between the sister taxa E. maldonadoi n. sp. and E. paraensei, much lower than the 6.3-13.7% and 7.3-16.8% interspecific values reported by Morgan and Blair (1998b) and Izrailskaia et al (2021), respectively. These different values may just be biased by the paucity of cox1 sequences for Echinostoma spp., leaving just a few sequences of closely related sister taxa to be compared.…”

“…For this reason, most taxonomic surveys on Echinostoma provided nad1 sequences (Georgieva et al, 2014(Georgieva et al, , 2017Faltýnková et al, 2015;Pantoja et al, 2021). However, Izrailskaia et al (2021) argued that cox1 may be more informative than nad1 and might solve more confidently taxonomic problems within the Echinostomatidae.…”

“…Our understanding of the species diversity of the genus Echinostoma has been improved by integrating molecular and morphological approaches to better delimit species boundaries and consequently address more accurately questions concerning host use, geographical distribution and life cycle (Georgieva et al ., 2013 , 2014 ; Faltýnková et al ., 2015 ; Izrailskaia et al ., 2021 ; Valadão et al ., 2022 ). A number of studies stressed the presence of several cryptic lineages within the ‘ revolutum ’ species complex of Echinostoma , mostly from the Holarctic realm (Detwiler et al ., 2010 , 2012 ; Georgieva et al ., 2014 ; Izrailskaia et al ., 2021 ), which presented challenges either for identification of known taxa or the proposal of new taxa with no morphological differential trait to report. Even though cryptic diversity is more common among trematodes than other groups of parasitic helminths (Pérez-Ponce de León and Poulin, 2018 ), some of the cryptic evolutionary independent lineages found in previous studies of Echinostoma spp.…”

“…The utility of the most densely sampled nuclear ribosomal genetic regions, 28S and ITS, and mitochondrial protein-coding genes, cox1 and nad 1, were evaluated in molecular phylogenetic studies (Morgan and Blair, 1998 a , 1998 b ; Georgieva et al ., 2014 ; Izrailskaia et al ., 2021 ). While all of them agree that mitochondrial genes should be the first choice for barcoding species of Echinostoma in the ‘ revolutum ’ group, as nuclear ribosomal genes may not provide enough phylogenetic signal to differentiate closely related species, they differ concerning which mitochondrial marker is more informative.…”

“…In the last decades, the use of molecular tools has revealed the existence of numerous independent evolutionary lineages of Echinostoma, usually referred to as cryptic species, but also has helped to unravel the correct identity of previously known taxa, some of them described as new (Detwiler et al, 2010;Georgieva et al, 2013Georgieva et al, , 2014Georgieva et al, , 2017Faltýnková et al, 2015;Izrailskaia et al, 2021;Valadão et al, 2022). These recent advances have contributed to a better knowledge of the species composition and the distribution of these parasites and have generated evidence on their biogeography, evolution and radiation.…”