Not Caloneis egena: morphological description and complete plastid and mitochondrial genomes of Caloneis paraegena sp. nov. from the Gulf of Tomini, Indonesia

Abstract

Introduction: Caloneis egena is a species of diatom originally described from Campeche Bay (Mexico) that is regarded as cosmopolitan, with several reports from the Pacific region. Methods: A strain of diatom from the genus Caloneis was isolated from the Gulf of Tomini, Sulawesi (Indonesia). It was subjected to an integrated approach combining microscopy, genomic analyses, and phylogeny. Results: Although looking similar to C. egena, the strain from Tomini was found to be a new species, hereby described as Caloneis paraegena sp. nov. The complete mitochondrial and plastid genomes were sequenced and annotated and represent the first organellar genomes made available for the genus Caloneis. The multigene phylogeny inferred from these results positions C. paraegena as sister to a clade that associates Caloneis fontinalis, Caloneis silicula and Caloneis lewisii. Discussion: A survey of the literature dedicated to C. egena led to questioning its distribution, suggesting that records from the Pacific region might in fact represent C. paraegena based on morphology. Because of the absence of molecular reference for C. egena, the exact relationship between these two species remains to be verified. A new species of diatoms, Caloneis paraegena sp. nov. is proposed. Although looking similar to C. egena, integrative analyses combining light and scanning electron microscopy provided evidence of morphological discrepancies between C. paraegena and the type of material of C. egena from Campeche Bay (Mexico), prompting its description as a new species. In the meantime, greater similarities were found between C. paraegena and other specimens reported from the Pacific region and ascribed to C. egena, suggesting that the previously assessed cosmopolitanism should be revised. A genome-skimming approach resulted in the retrieval of the complete 34,065 bp mitochondrial genome and the 136,121 bp plastid genome, which represent the first organellar genomes sequenced for the genus Caloneis. The multigene phylogeny inferred from these results positions C. paraegena as sister to a clade that associates Caloneis fontinalis, Caloneis silicula and Caloneis lewisii, but because of the absence of molecular reference for C. egena, the exact relationship between these two species remains to be verified.