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

Abstract

<i>Echinostoma paraensei</i>, described in Brazil at the end of the 1960s and used as a biological model for a range of studies, belongs to the ‘<i>revolutum</i>’ complex of <i>Echinostoma</i> comprising species with 37 collar spines. However, molecular data are available only for a few isolates maintained under laboratory conditions, with molecular prospecting based on specimens originating from naturally infected hosts virtually lacking. The present study describes <i>Echinostoma maldonadoi</i> Valadão, Alves & Pinto n. sp., a species cryptically related to <i>E. paraensei</i> found in Brazil. Larval stages (cercariae, metacercariae and rediae) of the new species were found in the physid snail <i>Stenophysa marmorata</i> in the State of Minas Gerais, Brazil, the same geographical area where <i>E. paraensei</i> was originally described. Adult parasites obtained experimentally in <i>Meriones unguiculatus</i> were used for morphological (optical microscopy) and molecular [28S, internal transcribed spacer (ITS), <i>nad</i>1 and <i>cox</i>1] characterization. The morphology of larval and adult parasites (most notable the small-sized dorsal spines in the head collar), associated with low (0–0.1%) molecular divergence for 28S gene or ITS region, and only moderate divergence for the mitochondrial <i>cox</i>1 gene (3.83%), might suggest that the newly collected specimens should be assigned to <i>E. paraensei</i>. However, higher genetic divergence (6.16–6.39%) was found in the mitochondrial <i>nad</i>1, revealing that it is a genetically distinct, cryptic lineage. In the most informative phylogenetic reconstruction, based on <i>nad</i>1, <i>E. maldonadoi</i> n. sp. exhibited a strongly supported sister relationship with <i>E</i>. <i>paraensei</i>, which may indicate a very recent speciation event giving rise to these 2 species.