Abstract
BackgroundNeotropical freshwater stingrays (Batoidea: Potamotrygonidae) host a diverse parasite fauna, including cestodes. Both cestodes and their stingray hosts are marine-derived, but the taxonomy of this host/parasite system is poorly understood.MethodologyMorphological and molecular (Cytochrome oxidase I) data were used to investigate diversity in freshwater lineages of the cestode genus Rhinebothrium Linton, 1890. Results were based on a phylogenetic hypothesis for 74 COI sequences and morphological analysis of over 400 specimens. Cestodes studied were obtained from 888 individual potamotrygonids, representing 14 recognized and 18 potentially undescribed species from most river systems of South America.ResultsMorphological species boundaries were based mainly on microthrix characters observed with scanning electron microscopy, and were supported by COI data. Four species were recognized, including two redescribed (Rhinebothrium copianullum and R. paratrygoni), and two newly described (R. brooksi n. sp. and R. fulbrighti n. sp.). Rhinebothrium paranaensis Menoret & Ivanov, 2009 is considered a junior synonym of R. paratrygoni because the morphological features of the two species overlap substantially. The diagnosis of Rhinebothrium Linton, 1890 is emended to accommodate the presence of marginal longitudinal septa observed in R. copianullum and R. brooksi n. sp. Patterns of host specificity and distribution ranged from use of few host species in few river basins, to use of as many as eight host species in multiple river basins.SignificanceThe level of intra-specific morphological variation observed in features such as total length and number of proglottids is unparalleled among other elasmobranch cestodes. This is attributed to the large representation of host and biogeographical samples. It is unclear whether the intra-specific morphological variation observed is unique to this freshwater system. Nonetheless, caution is urged when using morphological discontinuities to delimit elasmobranch cestode species because the amount of variation encountered is highly dependent on sample size and/or biogeographical representation.
Highlights
The context The central unit for taxonomy and systematics is the species, and assigning populations unequivocally to species is essential for a meaningful reference system of biological information [1,2]
The diagnosis of Rhinebothrium Linton, 1890 is emended to accommodate the presence of marginal longitudinal septa observed in R. copianullum and R. brooksi n. sp
Given the low taxonomic representation for marine species of Rhinebothrium and the use of a single locus to infer a species tree, we find that it is premature to discuss the phylogenetic relationships among all lineages of this genus
Summary
The context The central unit for taxonomy and systematics is the species, and assigning populations unequivocally to species is essential for a meaningful reference system of biological information [1,2]. Definitions, and delineations have been contentiously debated for decades ([14,15] among many others), the recognition of species boundaries is primarily influenced by the method used to delimit species [16]. Integrative and pluralistic approaches to species delineation in which data are acquired and synthesized from different and independent sources in conjunction with appropriate methods of extracting information from the data gathered (see [2,17]) have the potential to enhance species discovery and our understanding of biological diversity. Neotropical freshwater stingrays (Batoidea: Potamotrygonidae) host a diverse parasite fauna, including cestodes. Both cestodes and their stingray hosts are marine-derived, but the taxonomy of this host/parasite system is poorly understood
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