Species delimitation in the cyanolichen genus Rostania

Abstract

Background In this study, we investigate species limits in the cyanobacterial lichen genus Rostania (Collemataceae, Peltigerales, Lecanoromycetes). Four molecular markers (mtSSU rDNA, β-tubulin, MCM7, RPB2) were sequenced and analysed with two coalescent-based species delimitation methods: the Generalized Mixed Yule Coalescent model (GMYC) and a Bayesian species delimitation method (BPP) using a multispecies coalescence model (MSC), the latter with or without an a priori defined guide tree. Results Species delimitation analyses indicate the presence of eight strongly supported candidate species. Conclusive correlation between morphological/ecological characters and genetic delimitation could be found for six of these. Of the two additional candidate species, one is represented by a single sterile specimen and the other currently lacks morphological or ecological supporting evidence. Conclusions We conclude that Rostania includes a minimum of six species: R. ceranisca, R. multipunctata, R. occultata 1, R. occultata 2, R. occultata 3, and R. occultata 4,5,6. Three distinct Nostoc morphotypes occur in Rostania, and there is substantial correlation between these morphotypes and Rostania thallus morphology.

Thainema gen. nov. (Leptolyngbyaceae, Synechococcales): A new genus of simple trichal cyanobacteria isolated from a solar saltern environment in Thailand

“…However, the identification of many taxa within some cyanobacterial orders remains difficult, and further research is needed to better elucidate the relationships among their members. Although some approaches for species identification are rarely used for cyanobacteria, they are increasingly being used for algae and cyanolichens (e.g., [24,25]). Species delimitation analyses using tree-based and non-tree-based methods have enabled the identification of novel species, and are being utilized as a substantive concept in current systematics [26,27].…”

A revision of theRostania occultata(Collemataceae) complex in Fennoscandia

“…In our previous study (Košuthová et al 2020), we concluded through species delimitation analyses that the Rostania occultata complex consists of a minimum of four species, which we informally called R. occultata 1, R. occultata 2, R. occultata 3 and R. occultata 4,5,6. We tested and evaluated further potential candidate species within these informal species but found no distinct morphology, substratum ecology or geographical distribution to suggest that these genetically comparatively distinct but poorly sampled candidates should be treated as species.…”

“…Photobionts. Košuthová et al (2020) found a correlation between thallus morphology and the Nostoc morphotypes; species with granular thalli have Nostoc that produce either single cells or cells in small clusters (Fig. 1E), whereas species with lobate thalli have Nostoc with cells in short to long chains (Figs 2D & 4C).…”

“…Ascospores. The spores in the Rostania occultata species complex are often stated to be more or less cuboid (Degelius 1954;Jørgensen 2007;Košuthová et al 2019), but in reality they vary from ellipsoid-oblong to oblong with truncated ends, or almost cuboid (Košuthová et al 2020). They are often not easy to classify since immature spores of all species are first globose and then become ellipsoid to more edged.…”

“…Rostania occultata, a small, morphologically quite variable epiphytic taxon with more or less cuboid spores, is currently divided into two, somewhat vaguely delimited varieties (Degelius 1954;Perlmutter & Rivas Plata 2018). The genetic and morphological variation in R. occultata and the previously unnoticed variation in photobiont morphology spurred Košuthová et al (2020) to conduct a species delimitation study of Rostania s. str. using two coalescent-based methods.…”