Molecular characterization of the type species of Kyrtuthrix (Rivulariaceae, Cyanobacteriota) with comparison to Nunduva: Morphologically different but molecularly cryptic genera

TL;DR

This study compares the molecular and morphological characteristics of Kyrtuthrix and Nunduva, revealing they are distinct genera despite some molecular similarities.

Contribution

The paper provides molecular evidence that clarifies the taxonomic distinction between Kyrtuthrix and Nunduva.

Findings

Kyrtuthrix and Nunduva form sister clades when multiple genes are considered, supporting their classification as distinct genera.

The type species of Kyrtuthrix, K. dalmatica, is phylogenetically related to newly described Kyrtuthrix species.

Morphological differences between Kyrtuthrix and Nunduva do not align with molecular data alone.

Abstract

The euendolithic genus Kyrtuthrix was originally described in 1929 by A. Ercegović from the Dalmatian coast. Due to its isopolar filaments, Kyrtuthrix was classified within the cyanobacterial system as part of the family Scytonemataceae, even though trichomes tapering toward their ends represent a feature typical of the family Rivulariaceae. In the last decade, four new species of Kyrtuthrix have been described. Their sequences helped to establish Kyrtuthrix as belonging to the family Rivulariaceae. However, the new species demonstrated that Kyrtuthrix was not always euendolithic, as the new discoveries occurred on igneous rocks that were not susceptible to penetration by cyanobacteria. We were able to obtain sequences of the 16S rRNA gene, the 16S‐23S ITS rRNA region, the rpoC1 gene, and rbcLX gene for phylogenetic analyses of two classical species of Kyrtuthrix—the type species K. dalmatica collected from the Dalmatian coast and K. maculans collected from the Pacific coast of Peru. Our analyses revealed that both taxa were related to the newly described Kyrtuthrix species, although they were not clearly separated by molecular character sets from the more recently described Nunduva. A third Kyrtuthrix species from the coast of France was characterized by us during this study but was intermediate in morphological structure and phylogeny between K. dalmatica and K. maculans and not given a specific epithet. If we relied on the 16S rRNA gene sequence evidence, Nunduva would have been collapsed into the older genus Kyrtuthrix. However, using multiple gene evidence, they formed sister clades and, therefore, have been treated as distinct genera in this manuscript.

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