The Macrobiotus ariekammensis species complex provides evidence for parallel evolution of claw elongation in macrobiotid tardigrades

• Published in: Zoological Journal of the Linnean Society
• Main Authors: Stec, Daniel, Vončina, Katarzyna, Møbjerg Kristensen, Reinhardt, Michalczyk, Łukasz
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press (OUP) 2022
• Subjects: Arctic
• Online Access: http://dx.doi.org/10.1093/zoolinnean/zlab101; https://academic.oup.com/zoolinnean/article-pdf/195/4/1067/53928889/zlab101.pdf

Abstract The recent integrative revision of the family Macrobiotidae demonstrated monophyly of the genus Macrobiotus and its complex, mosaic morphological evolution. Here, we analyse three Macrobiotus populations that exhibit extraordinary claw morphology characterized by elongated primary branches. Two of these populations, from the Arctic, were initially classified as Macrobiotus ariekammensis, but detailed integrative analyses resulted in splitting them into two subspecies: Macrobiotus ariekammensis ariekammensis and Macrobiotus ariekammensis groenlandicus subsp. nov.. The third population was Macrobiotus kirghizicus from Kyrgyzstan. Given the unusual phenotype of the above-mentioned taxa, we tested whether they constitute a distinct lineage in the family Macrobiotidae and could be delineated as a new genus. Although the phylogenetic investigation showed that the three taxa form a monophyletic group, the clade is nested in the genus Macrobiotus. Therefore, despite their morphological distinctiveness, a new genus cannot be established and we group these taxa in the Macrobiotus ariekammensis species complex instead. The complex includes the three above-mentioned taxa and Macrobiotus ramoli, which is included based on morphological characters. Moreover, our results provide evidence for rapid parallel evolution of long claws in macrobiotid tardigrades inhabiting cold and icy environments. Finally, we discuss the validity of the recent suppression of the genus Xerobiotus, which gathers macrobiotids with reduced claws.