Morphological and phylogenomic investigation of Fistulifera cf. alcalina (Naviculales, Stauroneidaceae) from the Transbaikalia (Southern Siberia, Russia) with comments on evolution within the genus

The genus Fistulifera Lange-Bert. (Bacillariophyceae, Naviculales, Stauroneidaceae) currently comprises five valid species, including predominantly small-celled species. We isolated a strain belonging to Fistulifera from the coastal sediment samples of saline Lake Zun-Torey in the Daursky Biosphere Reserve, Transbaikalia, Russia. It was attributed to Fistulifera cf. alcalina based on the study of live cells and frustule morphology using light and scanning electron microscopy, and processed for whole-genome short-read sequencing. We have conducted a phylogenetic study of Fistulifera using single genetic markers (18S nrDNA, rbcL) as well as mitogenome and plastome data. Despite the morphological data, the genetic study, especially mitogenomic results, suggests an independent species status for our strain. Our results challenge the hypothesis of the existence of an ‘alkaline clade’ inside the Fistulifera genus. In contrast to previous studies, we propose an independent origin of earlier derived ‘alkaline’ lineages. Moreover, our data have confirmed that Fistulifera is a sister group of Proschkinia.