A molecular phylogenetic appraisal of the acanthostomines Acanthostomum and Timoniella and their position within Cryptogonimidae (Trematoda: Opisthorchioidea).

Andrés Martínez-Aquino,M Leopoldina Aguirre-Macedo,Victor M Vidal-Martínez

doi:10.7717/peerj.4158

Abstract

The phylogenetic position of three taxa from two trematode genera, belonging to the subfamily Acanthostominae (Opisthorchioidea: Cryptogonimidae), were analysed using partial 28S ribosomal DNA (Domains 1–2) and internal transcribed spacers (ITS1–5.8S–ITS2). Bayesian inference and Maximum likelihood analyses of combined 28S rDNA and ITS1 + 5.8S + ITS2 sequences indicated the monophyly of the genus Acanthostomum (A. cf. americanum and A. burminis) and paraphyly of the Acanthostominae. These phylogenetic relationships were consistent in analyses of 28S alone and concatenated 28S + ITS1 + 5.8S + ITS2 sequences analyses. Based on molecular phylogenetic analyses, the subfamily Acanthostominae is therefore a paraphyletic taxon, in contrast with previous classifications based on morphological data. Phylogenetic patterns of host specificity inferred from adult stages of other cryptogonimid taxa are also well supported. However, analyses using additional genera and species are necessary to support the phylogenetic inferences from this study. Our molecular phylogenetic reconstruction linked two larval stages of A. cf. americanum cercariae and metacercariae. Here, we present the evolutionary and ecological implications of parasitic infections in freshwater and brackish environments.

Highlights

36 bi-directional partial 28S and ITS1-5.8S-ITS2 sequences were obtained from three individual cercariae and three individual metacercariae from A. cf. americanum, as well as three individual metacercariae from T. cf. loossi, O. mayae, and C. cichlasomae (Table 1)
The partial 28S rDNA sequence fragment consisted of 881 base-pairs for the cercariae and metacercariae of A. cf. americanum; 880 bp in T. cf. loossi, 871 bp in O. mayae, and 870 bp in C. cichlasomae
The phylogenetic trees obtained from Bayesian inference (BI) and Maximum likelihood analyses (ML) analyses, inferred from the 28S and concatenated dataset, identified the phylogenetic position of the acanthostomines A. cf. americanum and T. cf. loossi, and illustrate different intergeneric relationships among cryptogonimids

Summary

Introduction

The Cryptogonimidae Ward, 1917, is a speciose family (≥370 species), consisting of 93 genera associated with the intestine or pyloric caeca of marine and freshwater teleosts, reptiles and occasionally amphibians around the world (Miller & Cribb, 2008a; Miller & Cribb, 2013; Miller et al, 2009; Miller et al, 2010a; Miller et al, 2010b; Cribb & Gibson, 2017; Tkach & Bush, 2010; Fernandes et al, 2013). The criteria for the subfamily Acanthostominae, as recognized by Brooks & Holcman (1993), was based on six characters: (1) a terminal oral sucker; (2) a body armed with single row of spines; (3) a preacetabular pit; (4) a genital pore not in preacetabular pit; (5) a seminal vesicle coiled posteriorly; and (6) a sucker-like gonotyl. Based on these criteria, the acanthostomine trematodes include five genera: Timoniella Rebecq, 1960; Proctocaecum Baught, 1957; Gymnatrema Morozov, 1955; Caimanicola Freitas and Lent, 1938; and Acanthostomum Looss, 1899 (Brooks, 2004). Miller & Cribb (2008a) were not convinced by the morphological characteristics that were used to justify subfamily-level divisions in Cryptogonimidae, because several subfamilies were separated by few, and often trivial, characters. Miller & Cribb (2008a) recognized that the phylogenetic analyses of acanthostomines by Brooks (1980) could be used to infer intergeneric relationships between cryptogonimids

Methods

Results

Conclusion