Reyda, F. B.; Marques, F. P. L. (2011). Diversification and Species Boundaries of Rhinebothrium (Cestoda; Rhinebothriidea) in South American Freshwater Stingrays (Batoidea; Potamotrygonidae). PLoS ONE. 6(8): e22604.
Diversification and Species Boundaries of Rhinebothrium (Cestoda; Rhinebothriidea) in South American Freshwater Stingrays (Batoidea; Potamotrygonidae)
PLoS ONE
6(8): e22604
Publication
Available for editors
Background: 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.
Methodology: Morphological 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.
Results: Morphological 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.
Significance: The 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.