Patterns of sexual dimorphism in the armoured tardigrades

Sexual dimorphism is widespread among animals, with diverse patterns and proposed explanations observed across the Tree of Life. Here we present the first formal analysis of the patterns of sexual dimorphism in body size and cephalic sensory appendages across 40 species (from 10 genera) of armoured tardigrades (Echiniscidae). Phylogenetic signal was found for body size traits and the cephalic papilla relative size, indicating that the association between these traits between the sexes has high evolutionary persistence. The Echiniscidae body size dimorphism is generally female-biased, which would be in accordance with the fecundity hypothesis. No strong evidence of allometric patterns of body size sexual dimorphism was found. In contrast, some of the cephalic appendages show male-biased sexual dimorphism, particularly those that, by being more innervated, are thought to function as chemodetection organs used by males during mate search. The latter is consistent with the sexual selection hypothesis. As the first systematic quantification and analysis of the patterns of sexual dimorphism in the phylum Tardigrada, this study provides important insights into their ecology and evolution, such as corroborating the suggestion that cephalic appendages evolved for mate searching.

Atlas of the Echiniscidae (Heterotardigrada) of the Worldpart I: West Palaearctic Echiniscus species

Traditionally Eurocentric tardigrade taxonomy has started to dissect endemics from very few truly cosmopolitan or widely distributed species, originally described mostly from the West Palaearctic, in the last decade. Obviously, the most problematic for taxonomic identification are species in large genera containing over 100 species in the case of Tardigrada. In limno-terrestrial heterotardigrades, only Echiniscus C.A.S. Schultze, 1840 fulfils this criterion, being a perfect example of taxonomic inflation. In Echiniscidae, this phenomenon results predominantly from the historical fallacy of attaching more importance to chaetotaxy than to the analysis of dorsal plate sculpturing. In this paper, the first of a series on echiniscids of the World, we review the current state of knowledge on the West Palaearctic Echiniscus species. Echiniscus granulatus (Doyre, 1840) and E. spinulosus (Doyre, 1840) are re-described based on multiple population data. Echiniscus lapponicus Thulin, 1911 and E. militaris Murray, 1911 are provided with the first SEM and molecular data, respectively. Following synonymies are made based on analyses of ample comparative material, type series, and redescriptions: E. blumi schizofilus Barto, 1941 syn. nov. and E. trojanus Maucci, 1973 syn. nov. of E. blumi blumi Richters, 1903; E. inocelatus Miheli, 1938 syn. nov., E. heterospinosus Maucci, 1954 syn. nov. and E. egnatiae Durante Pasa & Maucci, 1979 syn. nov. of E. granulatus; Echiniscus merokensis suecicus Thulin, 1911 syn. nov., E. columinis Murray, 1911 syn. nov., E. batramiae Iharos, 1936 syn. nov., E. jagodici Miheli, 1951 syn. nov. and E. laterospinosus Rudescu, 1964 syn. nov. of E. merokensis merokensis Richters, 1904; E. hexacanthus Maucci, 1973 syn. nov. of E. militaris Murray, 1911; E. carusoi Pilato, 1972 syn. nov. of E. spinulosus; E. osellai Maucci, 1974 syn. nov. of E. trisetosus Cunot, 1932. Two new nomina dubia are proposed: E. apuanus M. Bertolani, 1946 sp. dub. (and a probable synonymy with E. merokensis suggested) and E. pajstunensis Barto, 1941 sp. dub. Two new nomina inquirenda are established: E. marleyi Li, 2007 sp. inq. (another chaetotaxy-based morphotype of the Echiniscus blumi-canadensis complex) and E. punctus McInnes, 1995 sp. inq. (the lack of reliable morphological criteria separating it from E. granulatus). We summarise the morphological, phylogenetic and biogeographic information for the West Palaearctic Echiniscus species, and conclude with a total of 21 valid and identifiable taxa. We predict this number will decrease further with solving the species delimitation issues within the Echiniscus blumi-canadensis complex. Among these 21 taxa, 13 species (62%) are to be found solely in the Western Palaearctic and/or entire Holarctic regions. This augments the many recent findings that tardigrades are typically biogeographically structured and form clearly defined faunae.

Neotropical jewels in the moss: biodiversity, distribution and evolution of the genus Barbaria (Heterotardigrada: Echiniscidae)

The genus Barbaria, recently established to accommodate the former Echiniscus bigranulatus group, is a tardigrade group emblematic for the South American tardigrade fauna. This unappendaged echiniscid lineage is widely recognized for the so-called ‘double’ sculpturing composed of endocuticular pillars and pseudopores or pores in the dorsal cuticle. The phylogenetic relationships in the genus have so far been completely unknown, but the discovery of two new species (B. paucigranulata sp. nov. and B. weglarskae sp. nov.), together with new genetic data for further six species (B. bigranulata, B. charrua comb. nov., B. danieli, B. jenningsi, B. madonnae and B. ollantaytamboensis), create an opportunity not only to uncover phyletic relationships, but also to reconstruct morphological evolution in the genus. To achieve this, we sequenced five genetic markers (18S rRNA, 28S rRNA, ITS1, ITS2, COI) for multiple populations of eight species of Barbaria (two-thirds of all known species) collected in Alabama (USA), Argentina and the Antarctic, and we analysed them in tandem with detailed morphological data. Our phylogentic analysis and the reconstruction of evolution of morphological traits suggests that the ancestor of the genus inhabited the Neotropics, and it was morphologically most similar to B. bigranulata. We also analyse literature records of Barbaria and conclude that the genus is most likely limited to the Neotropics, Antarctica and southern parts of the Nearctic. The findings are discussed in the context of the phylogeny of the Echiniscus evolutionary line.

Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

The taxonomy of many groups of meiofauna is challenging due to their low number of diagnostic morphological characters and their small body size. Therefore, with the advent of molecular techniques that provide a new source of traits, many cryptic species have started to be discovered. Tardigrades are not an exception, and many once thought to be cosmopolitan taxa are being found to be complexes of phenotypically similar species. Macrobiotus pallarii Maucci, 1954 was originally described in South Italy and has been subsequently recorded in Europe, America, and Asia. This allegedly wide geographic range suggests that multiple species may be hidden under this name. Moreover, recently, genetic evidence to support this was put forward, and the Macrobiotus pallarii complex has been proposed to accommodate putative species related to M. pallarii. Here, we describe three new pseudocryptic species based on populations that would have been all classified as Macrobiotus pallarii if molecular methods were not employed. Using an integrative taxonomy approach, we analyzed animals and eggs from the topotypic population of Macrobiotus pallarii, together with four other populations of the complex. We recovered four distinct phylogenetic lineages that, despite the overlap of morphometric traits, can be separated phenotypically by subtle but discrete morphological characters. One lineage corresponds to Macrobiotus pallarii, whereas the other three are newly described as Macrobiotus margoae Stec, Vecchi & Bartels, sp. nov. from the USA, Macrobiotus ripperi Stec, Vecchi & Michalczyk, sp. nov. from Poland and Finland, and Macrobiotus pseudopallarii Stec, Vecchi & Michalczyk, sp. nov. from Montenegro. To facilitate species identification, we provide a dichotomous key for species of the M. pallarii complex. Delimitation of these pseudocryptic taxa highlights the need for an integrative approach to uncover the phylum's diversity in full.

New Indomalayan Nebularmis species (Heterotardigrada: Echiniscidae) provoke a discussion on its intrageneric diversity

Recent years have brought undeniable progress in tardigrade taxonomy, and speciose complexes were detected in a number of phylogenetic lineages. The family Echiniscidae is one such lineage; it is one of the most diverse groups of limno-terrestrial tardigrades and can be characterized as having achieved great evolutionary success. In this contribution, using populations representing several species that originated from the Indomalayan region, we reconstructed phylogenetic affinities within Nebularmis, a recently erected genus within the Echiniscus lineage. Nebularmis auratus sp. nov. and Nebularmis burmensis sp. nov. are described from the Eastern Yoma Mountains and the Shan Hills (Myanmar), Nebularmis bhutanensis sp. nov. is described from the Eastern Himalayas (Bhutan), and Nebularmis indicus sp. nov. is described from the foothills of the Western Ghats (Goa, India). Moreover, males are reported in populations of the last two species. All known members of the genus can be phenotypically differentiated based on minute details of their dorsal sculpture and claws. Moreover, a very wide tropical distribution is demonstrated for Nebularmis cirinoi, recorded for the first time from islands of the Malay Archipelago. Furthemore, novel morphological, genetic, and geographic data allowed for the clarification of the generic diagnosis. Currently available data favor a scenario under which Nebularmis evolved in Southeast Asia and later dispersed to other regions of the globe.