Validating the systematic position of Plationus Segers, Murugan & Dumont, 1993 (Rotifera: Brachionidae) using sequences of the large subunit of the nuclear ribosomal DNA and of cytochrome C oxidase
Members of the family Brachionidae are free-living organisms that range in size from 170 to 250 microns. They comprise part of the zooplankton in freshwater and marine systems worldwide. Morphologically, members of the family are characterized by a single piece loricated body without furrows, grooves, sulci or dorsal head shields, and a malleate trophi. Differences in these structures have been traditionally used to recognize 217 species that are classified into seven genera. However, the validity of the species, Plationus patulus, P. patulus macracanthus P. polyacanthus, and P. felicitas have been confused because they were alternatively assigned in Brachionus or Platyias, when considering only morphological and ecological characters. Based on scanning electron microscope (SEM) images of the trophi, these taxa were assigned in a new genus, Plationus. In this study, we examined the systematic position of P. patulus and P. patulus macracanthus using DNA sequences of two genes: the cytochrome oxidase subunit 1 (cox1) and domains D2 and D3 of the large subunit of the nuclear ribosomal RNA (LSU). In addition, the cox1 and LSU sequences representing five genera of Brachionidae (Anuraeopsis, Brachionus, Keratella, Plationus, and Platyias) plus four species of three families from the order Ploima were used as the outgroup. The maximum likelihood (ML) analyses were conducted for each individual gene as well as for the combined (cox1 + LSU) data set. The ML tree from the combined data set yielded the family Brachionidae as a monophyletic group with weak bootstrap support (<50%). Five main clades in this tree had high (>85%) bootstrap support. The first clade was composed of three populations of P. patulus + P. patulus macracanthus. The second clade was composed of a single species of Platyias. The third clade was composed of six species of Brachionus. The fourth clade included a single species of the genus Anuraeopsis, and the fifth clade was composed of three species of the genus Keratella. The genetic divergence between Plationus and Platyias ranged from 18.4 to 19.2% for cox1, and from 4.5 to 4.9% for LSU, and between Brachionus and Plationus, it ranged from 16.9 to 23.1% (cox1), and from 7.3 to 9.1% (LSU). Morphological evidence, the amount of genetic divergence, the systematic position of Plationus within the family Brachionidae, and the position of Plationus as a sister group of Brachionus and Platyias support the validity of Plationus patulus and P. patulus macracanthus into the genus Plationus.
KeywordsPlationus Cox1 LSU Maximum likelihood Phylogeny
We thank Patricia de la Torre and Laura Márquez for their technical assistance on the sequencing of the plasmids. We are grateful to A. Bazinet, D. Ayres, and A. Y. Kawahara for their assistance in computational analyses. We are also grateful to S.S.S. Sarma and Nandini, S. for providing specimens of the genus Brachionus for this study. We also thank M. Ortega-Olivares and C. Serranía for their help in the field collection. Reyna-Fabián Miriam offers thanks to the Universidad Nacional Autónoma de México (UNAM) and to the program Doctorado en Ciencias Biomédicas, Instituto de Investigaciones Biomédicas and for the scholarship provided by Consejo Nacional de Ciencia y Tecnología (CONACYT- 203367). This research was supported by the Programa de Apoyo a Proyectos de Investigación e Inovación Tecnológica (PAPIIT No. IN230207), and the Consejo Nacional de Ciencia y Tecnología (CONACYT-No. 61334) to JPL, and PAPIIT-UNAM No. IN215709 and CONACYT-No. 102062 to MGV.
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