An integrative description of Macrobiotus shonaicus sp. nov. (Tardigrada: Macrobiotidae) from Japan with notes on its phylogenetic position within the hufelandi group

Abstract

Tardigrade research in Japan dates back over 100 years, and to date, 167 species of this ecdysozoan phylum have been reported from the country. Of these species, the Macrobiotus hufelandi complex has been represented only by the nominal taxon of this group, Macrobiotus hufelandi. In this article, a new species of the hufelandi group from Japan, Macrobiotus shonaicus sp. nov., is described using integrative taxonomy. In addition to the detailed morphological and morphometric data, obtained using phase contrast light microscopy (PCM) and scanning electron microscopy (SEM), we provide DNA sequences of four molecular markers (both nuclear and mitochondrial). The new species belongs to the persimilis subgroup and is most similar to M. anemone from USA, M. naskreckii from Mozambique, and M. patagonicus from Argentina, but it can be easily distinguished from these species by the presence of thin flexible filaments on terminal discs of the egg process. By the latter character, the new species is most similar to M. paulinae and M. polypiformis, but it can be easily distinguished from them by having a solid egg surface between egg processes (i.e., without pores or reticulum). A phylogenetic analysis of available DNA sequences of the COI marker for the hufelandi group revealed that the new species clusters with the two other species that exhibit filaments on egg process discs (M. paulinae and M. polypiformis) and with two species that have entire egg processes modified into filaments (M. kristenseni and M. scoticus). All five species form a clade distinct from all other sequenced species of the hufelandi group with typical mushroom- or inverted goblet-shaped egg processes, which may suggest that the ancestor of the five species with atypical egg processes had a mutation allowing derivations from the mushroom or inverted chalice-like shape of egg processes.

Integrative description of Macrobiotus canaricus sp. nov. with notes on M. recens (Eutardigrada: Macrobiotidae)

“…Thus, it might be possible that increased sampling could reveal the presence of two further clades that differ by the egg process morphology. Nevertheless, our findings support the previous results that egg morphology seems to be evolving faster than animal morphology, which underlines the usefulness of chorion ornamentation in the delineation of closely related species (Guidetti et al 2013;Stec et al 2016aStec et al , 2017aStec et al , 2018a.…”

“…Recently, Stec et al (2018a) showed two well supported COI lineages within the M. hufelandi group: one clade grouping species with hufelandi-type egg processes in the shape of inverted goblets, and the other with modified egg process (conical processes or processes with filaments growing out of terminal discs). Thus, M. cf.…”

“…Nevertheless, regardless of the phylogenetic position of M. sapiens, the affinity of M. cf. recens with species exhibiting typical egg processes shows that the morphological criterion proposed by Stec et al (2018a) to distinguish the two clades is not Fig. 17.…”

Simultaneous Metabarcoding of Eukaryotes and Prokaryotes to Elucidate the Community Structures within Tardigrade Microhabitats

“…Armatimonadetes are a diverse group of Gram-negative bacteria found in numerous metagenomic samples, and their desiccation-tolerance or biological role in the moss environment is unknown. M. shonaicus can feed both on algae and rotifers in laboratory culture [24], and M. inceptum exclusively feeds on rotifers in laboratory conditions [42]; however, the contribution was positive for M. inceptum, whereas it was negative for M. shonaicus. Coupled with strong negative contributions of Fungi, Amoebozoa, and Acari, these data may suggest interspecies interaction preferences of M. shonaicus.…”

“…Xeric mosses, including Bryum argenteum [23], were sampled at the type locality of Macrobiotus shonaicus [24] in Otsuka-machi, Tsuruoka city, Japan (38 • 44 25" N, 139 • 48 26" E; 13 m asl) in June 2015, from the side of a concrete fence base approximately 10 cm from the ground (Figure 1). A total of 48 samples were collected at approximately 50 cm intervals, where the mosses were separated by a bare concrete surface.…”