Macrobiotus persimilis‑polonicus

Bertolani, Roberto, Cesari, Michele, Giovannini, Ilaria, Rebecchi, Lorena, Guidetti, Roberto, Kaczmarek, Łukasz & Pilato, Giovanni, 2023, The Macrobiotus persimilis-polonicus complex (Eutardigrada, Macrobiotidae), another example of problematic species identification, with the description of four new species, Organisms Diversity & Evolution (New York, N. Y.) 23 (2), pp. 329-368 : 344-345

A Macrobiotus persimilis‑polonicus complex

All the new species here described, based on molecular and/ or morphological data, belong to a group of species with very homogeneous morphology of animals and eggs and are very similar to M. persimilis and M. polonicus . Therefore, we have defined this group as the persimilis-polonicus complex. All the species of this complex are characterized by: first macroplacoid deeply constricted in the middle, indented lunules on the hind legs, eggs of the persimilis type, and males (if present) with a lateral gibbosity on each hind leg. Other species such as M. halophilus , M. trunovae and M. marlenae , should be also considered as belonging to the persimilis-polonicus complex and possibly also M. hyperboreus and M. anemone , even though in reality they are morphologically distinguishable from the species in the complex by the absence of eye spots and absence of teeth on the lunules of the hind legs.

Morphological data show that all new species here described are clearly distinguishable from M. persimilis and M. polonicus , including M. dolosus sp. nov. found in the type locality of M. polonicus . Unfortunately, data on cox1 are lacking for M. persimilis and M. polonicus from their respective type localities. However, Wełnicz et al. (2011) referenced data on 18S mDNA from a specimen collected in the type locality of M. polonicus . To further support the differences noted at the morphological level between the type material of M. polonicus and that subsequently collected by us in the same locality, it should be noted that the sequences of 18S rDNA of the specimens collected by us in that locality differ from the data in the literature by two substitutions, which leads us to confirm that two distinct species have been found in the same locality.

A difference ranging from 2 to 7 substitutions is also noted between that literature data and all the other species we examined from the molecular point of view. In comparison, regarding cox1, the differences between the examined species are always very high, ranging from 16.0 to 18.6%. Two populations found in Austria and Slovakia ( Vecchi & Stec, 2021), attributed to M. polonicus , have very similar cox1 sequences to those of M. dolosus sp. nov., and therefore can be ascribed to this species (0.3–1.8%, Table 3). A French specimen cited as M. cf. hufelandi in the literature ( Czechowski et al., 2012), with a sequence very similar to that of M. dolosus sp. nov. (0.3–1.5%, Table S3), must be attributed to this latter species too. We do not have morphological information on Macrobiotus aff. polonicus cited by Vecchi and Stec (2021), but in our molecular tree it is not included in the lineage of the persimilis-polonicus complex.

Unfortunately, no cox1 or 18S rDNA sequences attributable to M. persimilis are available, but there is extreme morphological similarity with the other species in the complex. Regarding M. polonicus , as said, we only have an 18S rDNA sequence of specimens from the type locality of the species, but no morphological information on the specimens from which the DNA was extracted ( Wełnicz et al., 2011). In any case that haplotype is included in the same lineage of the newly examined populations ( Fig. 10 ) and, as said above, it differs by two substitutions from the haplotype of M. dolosus sp. nov. that we found in the type locality of M. polonicus , and by 2–7 substitutions from the other species of the complex.

Specimens collected from a moss in Bremen ( Germany) by Baumann (1970) and reported as Macrobiotus hufelandii Schultze (at that time very few species of the hufelandi group were described) should also be included at least in the persimilis group. Baumann reported that males have a lateral gibbosity (“vorgewölbten lateralen Zipfel”) on each hind leg, which is absent in females, and that these gibbosities appeared after the second molting.

Figures

Fig.10 Macrobiotus hyperboreus, (type material, PhC). a Buccalpharyngeal apparatus; b egg with evident dots around the process bases