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

Abstract

Echinostoma paraensei, described in Brazil at the end of the 1960s and used as a biological model for a range of studies, belongs to the ‘revolutum’ complex of Echinostoma 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 Echinostoma maldonadoi Valadão, Alves & Pinto n. sp., a species cryptically related to E. paraensei found in Brazil. Larval stages (cercariae, metacercariae and rediae) of the new species were found in the physid snail Stenophysa marmorata in the State of Minas Gerais, Brazil, the same geographical area where E. paraensei was originally described. Adult parasites obtained experimentally in Meriones unguiculatus were used for morphological (optical microscopy) and molecular [28S, internal transcribed spacer (ITS), nad1 and cox1] 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 cox1 gene (3.83%), might suggest that the newly collected specimens should be assigned to E. paraensei. However, higher genetic divergence (6.16–6.39%) was found in the mitochondrial nad1, revealing that it is a genetically distinct, cryptic lineage. In the most informative phylogenetic reconstruction, based on nad1, E. maldonadoi n. sp. exhibited a strongly supported sister relationship with E. paraensei, which may indicate a very recent speciation event giving rise to these 2 species.

Keywords: Brazil; Echinostoma; cryptic species; integrative taxonomy; phylogeny.

Graphical abstract

Fig. 1.

Echinostoma maldonadoi n. sp. line drawings of the holotype. (A) Whole view. (B) Detail of cephalic collar. (C) Detail of genital complex. Scale bars: A: 1 mm; B, C: 250 μm.

Fig. 2.

Micrographs of Echinostoma maldonadoi n. sp. (A) Whole view of a carmine-stained paratype. (B) Detail of angular (*) and lateral (#) spines. (C) Detail of dorsal spines (+). (D) Detail of the cirrus sac. (E) Eggs obtained in feces. Scale bars: A: 1 mm; B, C, E: 50 μm; D: 100 μm.

Fig. 3.

Echinostoma maldonadoi n. sp. larval stages found in Stenophysa marmorata from Brazil. (A) Redia. (B) Cercaria. (C) Detail of the body of cercaria. (D) Detail of anterior end. (E) Metacercaria. Scale bars: A: 200 μm; B: 100 μm; C, E: 50 μm; D: 20 μm.

Fig. 4.

Phylogenetic relationship between Echinostoma maldonadoi n. sp. (in bold) and other 37-collar-spined Echinostoma species inferred from sequences of 28S rDNA (1051 bp; nucleotide substitution model: HKY + G) (A) and of internal transcribed spacer (ITS) (1001 bp; nucleotide substitution model: K2 + G) (B) based on maximum likelihood (ML) and Bayesian inference (BI) analyses. Nodal support is indicated as ML/BI; values <0.70 (BI) and <70 (ML) are indicated by a dash.

Fig. 5.

Phylogenetic relationship between Echinostoma maldonadoi n. sp. (in bold) and other 37-collar-spined Echinostoma species inferred from sequences of cox1 mtDNA (366 bp; nucleotide substitution model: HKY + I) (A) and of nad1 (438 bp; nucleotide substitution model: HKY + G + I) (B) based on maximum likelihood (ML) and Bayesian inference (BI) analyses. Nodal support is indicated as ML/BI; values <0.70 (BI) and <70 (ML) are indicated by a dash.