Diversification and Species Boundaries of Rhinebothrium (Cestoda; Rhinebothriidea) in South American Freshwater Stingrays (Batoidea; Potamotrygonidae)

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.

A new genus of rhinebothriidean cestodes from batoid elasmobranchs, with the description of five new species and two new combinations

“…Such a relatively relaxed pattern of host specificity contrasts a widely demonstrated pattern of strict host specificity in rhinebothriideans and other elasmobranch cestodes in which cestode species typically occur in only a single host species. This is termed an oioxenous level of host specificity (sensu Euzet and Combes 1980) and has been demonstrated in many (Williams 1964, Caira and Jensen 2001, Jensen 2005, Tyler 2006, Ruhnke et al 2015 but not all (Palm andCaira 2008, Reyda andMarques 2011) elasmobranch cestode species.…”

“…This has also been done in species of other rhinebothriidean genera, such as Rhinebothrium (see Reyda and Marques 2011). Considering the importance of bothridial septa in defining species of Stillabothrium and given that septa can vary in their visibility (e.g.…”

Rhinebothrium jaimei sp. n. (Eucestoda: Rhinebothriidea: Rhinebothriidae): a new species from Neotropical freshwater stingrays (Potamotrygonidae)

“…Our knowledge of the diversity Rhinebothrium inhabiting potamotrygonids remained stationary for more than three decades until Reyda (2008) recognised R. copianullum Reyda, 2008 in Paratrygon aiereba (Müller et Henle) from Boca Manu, Rio Madre de Dios, Amazon Basin, Peru. It was later found in other locations and host species throughout the Amazon Basin (Reyda and Marques 2011).…”

“…After more than a century of taxonomic history, the genus is represented by 44 valid species (Healy 2006, Reyda 2008, Reyda and Marques 2011, Menoret and Ivanov 2011 that are parasites of most families of batoids (e.g. Arhynchobatidae, Dasyatidae, Myliobatidae, Potamotrygonidae, Rhinobatidae, Rhynchobatidae, Urolophidae, Urotrygonidae and Zanobatidae) from all over the world (see Caira et al 2012).…”

“…Shortly after, this species was considered a junior synonym of R. paratrygoni by Reyda and Marques (2011) in their most recent review of the Neotropical freshwater lineages of Rhinebothrium. In their review, Reyda and Marques (2011) described two additional species of Rhinebothrium from potamotrygonids: R. brooksi Reyda et Marques, 2011 in Paratrygon aiereba and Potamotrygon orbignyi (Castelnau) from the Rio Negro and Rio Xingú, Amazon Basin, Brazil, and R. fulbrighti Reyda et Marques, 2011 in P. orbignyi and in an undescribed species of Potamotrygon from Bahía de Marajó, lower Amazon region, and from the lower Rio Tapajós, Brazil. Finally, Menoret and Ivanov (2011) described R. corbatai Menoret et Ivanov, 2011 andR.…”