Exploring Neotropical anuran parasites: a morphological, life cycle and phylogenetic study of Catadiscus marinholutzi (Trematoda: Diplodiscidae)

Abstract

Amphistome species belonging to the genus Catadiscus are poorly studied intestinal trematodes found primarily in Neotropical anurans. Herein, developmental stages of an amphistome species found during herpetological and malacological surveys in a temporary marsh pond from Brazil were subjected to morphological (light and scanning electron microscopy) and molecular analyses. Adult parasites recovered from anurans were identified as Catadiscus marinholutzi. Amphistome cercariae found in the planorbid snails Drepanotrema depressissimum and Drepanotrema lucidum from the same waterbody were used for experimental and molecular studies. Immature parasites, morphologically compatible with members of Catadiscus, were experimentally obtained in laboratory-reared tadpoles. Sequencing of a partial region of 28S rDNA gene of both adult and cercariae revealed 100% similarity between these developmental stages, confirming their conspecificity. Phylogenetic analyses were attempted for the first time to reveal the position of a species of Catadiscus in the superfamily Paramphistomoidea. Catadiscus marinholutzi falls in a virtual polytomy together with other paramphistomoids, which leaves its phylogenetic relationships within the group unclear. Moreover, the high genetic divergence to Diplodiscus spp. (10.06–10.84%) cast doubts on the placement of Catadiscus within Diplodiscidae. Hence the species composition of the Diplodiscidae should be re-evaluated in further studies using a broader spectrum of related taxa.

Keywords: Aamphibians; Brazil; Paramphistomoidea; cercariae; life cycle; phylogenetic relationships; snail; trematodes.

Graphical abstract

Fig. 1.

Catadiscus marinholutzi adult recovered from Leptodactylus podicipinus from Brazil: (A) Line drawing of a mature worm. (B) Body in ventral view of a haematoxylin-stained worm. (C) Details of pharynx with primary sacs (arrowhead). (D) Details of oesophageal bulb (arrowhead) and genital pore (arrow). (E) Details of the relative size of vitelline follicles (arrowhead) and eggs (asterisks). Scale bars: A, B = 200 μm; C, E = 50 μm, D = 100 μm.

Fig. 2.

SEMs of Catadiscus marinholutzi from Leptodactylus podicipinus. (A) Body in ventral view showing the genital pore. (B) Oral opening surrounded by undulated edges. (C) Details of the genital pore bearing a genital papillae. (D) Details of the median transversal constriction of acetabulum. Scale bars: A = 50 μm, B = 10 μm, C = 2 μm, D = 20 μm.

Fig. 3.

Line drawing of cercariae of Catadiscus marinholutzi found in Drepanotrema lucidum. (A) Whole view of cercaria. (B) Details of cercarial body. Scale bars: A = 100 μm, B = 25 μm.

Fig. 4.

Larval stages of Catadiscus marinholutzi found in Drepanotrema lucidum. (A) Whole-mount of the amphistome cercaria, ventral view. (B) Details of cercarial body. (C) Details of the constriction in the acetabulum of cercaria (arrowhead). (D) Recently encysted metacercaria and detail of the detachment of the tail from the body (asterisk). (E) Whole-mount of redia. (F) Details of anterior region of redia, evidencing the pharynx (arrowhead) and caecum (arrow). Scale bars: A, D, F = 100 μm; B, C = 50 μm. E = 200 μm.

Fig. 5.

BI phylogram based on partial 28S sequences of Catadiscus marinholutzi and selected members of the Paramphistomoidea. BI posterior probabilities and ML UFbootstrap support values are shown above nodes. Newly generated sequences are highlighted in bold. Parasitism in cold- and warm-blooded hosts are indicated by a black and a grey triangle, respectively. Branch length scale bar indicates the number of substitutions per site. CLA, Cladorchiidae; DIP, Diplodiscidae; GASTROD, Gastrodiscidae; GASTROT, Gastrothylacidae; MES, Mesometridae; MIC, Microscaphidiidae, OLV, Olveriidae; PAR, Paramphistomidae; ZYG, Zygocotylidae.