Redescription and phylogenetic analysis of the type species of the genus Panagrellus Thorne, 1938 (Rhabditida, Panagrolaimidae), P. pycnus Thorne, 1938, including the first SEM study

Abstract The identity of Panagrellus pycnus, the type species of the genus Panagrellus, is discussed after studying specimens from a cultured population collected in Italy that fits the original material of the species. A new characterization is consequently provided as follows: body 0.93–1.32 mm long, lip region continuous with the adjoining body, stoma with gymnostom very reduced, pharynx with not swollen metacorpus, neck 161–203 µm long, excretory pore at level of the metacorpus, post-vulval uterine sac 99–162 µm long or 2.6–3.8 times as long as the body diameter divided in a short tubular proximal part and a long swollen distal part, vulva post-equatorial (V = 63–69), female tail conica…

Additional file 1 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 1: SM.01. Saturation plots for COI and ITS markers.

Phylogenetic position of two Macrobiotus species with a revisional note on Macrobiotus sottilei Pilato, Kiosya, Lisi & Sabella, 2012 (Tardigrada: Eutardigrada: Macrobiotidae)

In a moss and lichen sample collected on the Polish coast, a new population of Macrobiotus sottilei was found. Given that the original description of M. sottilei was based solely on the morphology observed under light microscopy and measurements of a few individuals, we provide, by means of integrative taxonomy, a revisional note on this species. We present a comprehensive set of morphometric and morphological data from light and scanning electron microscopy analysis together with nucleotide sequences of three nuclear (18S rRNA, 28S rRNA, ITS-2) and one mitochondrial (COI) DNA fragments. We also provide the same set of DNA sequences for Macrobiotus glebkai from a population recently found i…

Tardigrades of Finland: new records and an annotated checklist

Species checklists are powerful and important tools of communication between taxonomists and applied environmental biologists, which in turn lead to well-planned and successful conservation strategies and ecological studies. Despite this, only recently the interest on compiling systematic checklists is growing among taxonomists who study tardigrades—micrometazoans that inhabit almost every habitat worldwide. As the Finnish records of tardigrades (a.k.a. water bears) species are incomplete, outdated and no checklist has ever been compiled for this country, an easy-to-consult checklist is here reported. This checklist covers all Finnish tardigrade taxa identified in the past and in the 13 sam…

A New Species of the Genus Crenubiotus (Tardigrada: Eutardigrada: Adorybiotidae) from Salt Spring Island, Strait of Georgia, British Columbia (Canada)

Currently, the recently erected genus Crenubiotus (Adorybiotidae, Macrobiotoidea) includes only three species, all of which are characterised by dentate lunulae and cuticular tubercules organised in the band in the dorso-caudal part of the body. By means of integrative taxonomy, we describe a fourth species of the genus: Crenubiotus salishani sp. nov., from Salt Spring Island in British Columbia, Canada. The new species has been found in the moss growing on rock and differs from the other species in the genus due to the presence of a median anterior mucrone in the third band of the oral cavity armature (OCA) and by the presence of evident thickenings on the eggshell connecting the neighbour…

Integrative descriptions of two new Macrobiotus species (Tardigrada, Eutardigrada, Macrobiotidae) from Mississippi (USA) and Crete (Greece)

In this paper, we describe two new Macrobiotus species from Mississippi (USA) and Crete (Greece) by means of integrative taxonomy. Detailed morphological data from light and scanning electron microscopy, as well as molecular data (sequences of four genetic markers: 18S rRNA, 28S rRNA, ITS-2 and COI), are provided in support of the descriptions of the new species. Macrobiotus annewintersaesp. nov. from Mississippi belongs to the Macrobiotus persimilis complex (Macrobiotus clade B) and exhibits a unique egg processes morphology, similar only to Macrobiotus anemone Meyer, Domingue & Hinton, 2014, but mainly differs from that species by the presence of eyes, granulation on all legs, den…

First insights into female sperm storage duration in tardigrades.

Female sperm storage is ubiquitous in the animal kingdom and it has been shown to be linked to several evolutionary processes, from postcopulatory sexual selection to dispersal. Here we report, for the first time, long-term sperm storage in females of the tardigrade Macrobiotus polonicus. Females, isolated after a short contact with a male, were able to use the stored sperm for up to 5 weeks (mean of 2 weeks), which translates to a considerable proportion of female post-mating longevity under controlled laboratory conditions (60% on average). Our study provides the first insights into the duration of sperm storage, an underexplored feature of the reproductive biology of tardigrades. Additio…

Desiccation risk favours prevalence and diversity of tardigrade communities and influences their trophic structure in alpine ephemeral rock pools

AbstractRock pools are ephemeral freshwater habitats characterized by their small size, well-defined boundaries, and periodic desiccation, making them ideal model systems to answer numerous ecological questions. Although there are numerous studies on rock pool fauna around the world, tardigrades have only rarely been recorded. We conducted the first tardigrade-focused study on rock pools by quantitatively extracting and classifying them from rock pools in the Italian Apennines. Rock pools were divided into three types, based on maximum duration of their inundation period. Following the patterns usually observed with rock pool invertebrates, we tested the hypothesis that desiccation has a ne…

Macrobiotus naginae sp. nov., a New Xerophilous Tardigrade Species from Rokua Sand Dunes (Finland)

Animals that colonize soil show specific adaptations to soil. Compared to closely related species living on the surface, the limbs of soil-dwelling animals are often shortened, reduced, or absent to allow a less restricted passage through cavities between soil particles. This pattern of limb reduction has also been observed in tardigrades, where multiple lineages that colonized the below-ground habitat show independent reduction and/or loss of legs and claws. In the tardigrade superfamily Macrobiotoidea, leg and claw reductions are a common trait found in the Macrobiotus pseudohufelandi complex. This rarely found species complex currently contains four nominal taxa. Here we describe, with t…

Further insights in the Tardigrada microbiome: phylogenetic position and prevalence of infection of four new Alphaproteobacteria putative endosymbionts

Abstract Data from a previous study showed that microbiomes of six tardigrade species are species-specific and distinct from associated environmental microbes. We here performed a more in-depth analyses of those data, to identify and characterize new potential symbionts. The most abundant bacterial operational taxonomic units (OTUs) found in tardigrades are classified, and their prevalence in other environments is assessed using public databases. A subset of OTUs was selected for molecular phylogenetic analyses based on their affiliation with host-associated bacterial families in tardigrades. Almost 22.6% of the most abundant OTUs found do not match any sequence at 99% identity in the IMNGS…

Negative impact of freeze–thaw cycles on the survival of tardigrades

Global warming effects in temperate and polar regions include higher average temperatures and a decrease in snow cover, which together lead to an increase in the number of freeze–thaw cycles (FTC). These changes could affect the fitness of both terrestrial and aquatic species. In this study, we tested how tardigrades, ubiquitous microscopic invertebrates, face FTC. Tardigrades are amongst the most resistant animals to unfavorable conditions, including long and deep freezing periods, and are an emerging model group for invertebrate ecology and evolution. We used 12 populations of tardigrades, representing different families within order Parachela, inhabiting different ecosystems (glaciers, s…

Sisubiotus hakaiensis sp. nov. (Tardigrada, Macrobiotidae), a new tardigrade species from Calvert Island (British Columbia, Canada)

Tardigrades reports from British Columbia (Canada) trace back to 1908 and numerous species have been recorded from this region, despite the relatively few published sampling studies. We describe by integrative taxonomy (light microscopy morphology, morphometrics, and DNA sequencing) a new tardigrade species, Sisubiotus hakaiensis sp. nov. from the British Columbia central coast. The new species has been found in moss collected from a vertical rock outcrop near the Hakai Institute Calvert Island Field Station. Sisubiotus hakaiensis sp. nov. differs from all the other known species in the genus by the presence of a labyrinthine layer inside the egg process walls, whereas no consistent differe…

Expanding Acutuncus : Phylogenetics and morphological analyses reveal a considerably wider distribution for this tardigrade genus

The tardigrade genus Acutuncus has been long thought to be an Antarctic endemism, well adapted to this harsh environment. The Antarctic endemicity of Acutuncus was recently dispelled with the description of Acutuncus mariae Zawierucha, 2020 found in the Svalbard archipelago. The integrated analyses on two newly found Acutuncus populations from UK and Italy, and a population of Acutuncus antarcticus found close to its type locality allowed us to expand the climatic and geographic range of the genus Acutuncus. These findings also allowed us to re-evaluate the morphological diagnoses of Acutuncus and accommodate it in the newly proposed monotypic family Acutuncidae fam. nov. Two new Acutuncus …

A lift in snail's gut provides an efficient colonization route for tardigrades.

New multilocus phylogeny reorganises the family Macrobiotidae (Eutardigrada) and unveils complex morphological evolution of the Macrobiotus hufelandi group

The family Macrobiotidae is one of the most speciose and diverse groups among tardigrades. Although there have been attempts to reconstruct the phylogeny of this family, the evolutionary relationships within Macrobiotidae are only superficially determined as available genetic data cover only a small fraction of this vast group. Here, we present the first extensive molecular phylogeny of the family based on four molecular markers (18S rRNA, 28Sr RNA, ITS-2 and COI) associated with detailed morphological data for the majority of taxa. The phylogenetic analysis includes nearly two hundred sequences representing more than sixty species, including sixteen taxa that have never been sequenced and/…

The toughest animals of the Earth versus global warming: Effects of long-term experimental warming on tardigrade community structure of a temperate deciduous forest

Abstract Understanding how different taxa respond to global warming is essential for predicting future changes and elaborating strategies to buffer them. Tardigrades are well known for their ability to survive environmental stressors, such as drying and freezing, by undergoing cryptobiosis and rapidly recovering their metabolic function after stressors cease. Determining the extent to which animals that undergo cryptobiosis are affected by environmental warming will help to understand the real magnitude climate change will have on these organisms. Here, we report on the responses of tardigrades within a five‐year‐long, field‐based artificial warming experiment, which consisted of 12 open‐to…

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

AbstractThe 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, …

Resolving the systematics of Richtersiidae by multilocus phylogeny and an integrative redescription of the nominal species for the genus Crenubiotus (Tardigrada)

AbstractThe family Richtersiidae, although established recently with the use of phylogenetic methods, was considered potentially paraphyletic at the time of its erection. Until now, the family comprised four genera, Richtersius, Diaforobiotus, Adorybiotus and a newly erected genus Crenubiotus. However, the genetic characterisation for the latter two genera was very limited or absent. To address concerns about the phylogenetic affinity of these two genera, we present a multilocus phylogeny of the families Richtersiidae and Murrayidae based on four molecular markers (18S rRNA, 28S rRNA, ITS-2 and COI). Our results show a distinct evolutionary lineage composed of Adorybiotus and Crenubiotus, w…

Additional file 11 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 11: SM.10. Results of PCA randomization tests.

Additional file 9 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 9: SM.08. Raw morphometric data for Macrobiotus ripperi sp. nov. from Finland (FI.066, additional population).

Additional file 4 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 4: SM.04a. R data for morphometric analysis.

Additional file 7 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 7: SM.06. Raw morphometric data for Macrobiotus pseudopallarii sp. nov. from Montenegro (ME.007, type population).

Additional file 8 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 8: SM.07. Raw morphometric data for Macrobiotus ripperi sp. nov. from Poland (PL.015, type population).

Additional file 9 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 9: SM.08. Raw morphometric data for Macrobiotus ripperi sp. nov. from Finland (FI.066, additional population).

Supplementary material 2 from: Vecchi M, Stec D (2021) Integrative descriptions of two new Macrobiotus species (Tardigrada, Eutardigrada, Macrobiotidae) from Mississippi (USA) and Crete (Greece). Zoosystematics and Evolution 97(1): 281-306. https://doi.org/10.3897/zse.97.65280

Raw morphometric data for Macrobiotus rybaki sp. nov. from Greece (GR.011, type population)

Supplementary material 6 from: Vecchi M, Stec D (2021) Integrative descriptions of two new Macrobiotus species (Tardigrada, Eutardigrada, Macrobiotidae) from Mississippi (USA) and Crete (Greece). Zoosystematics and Evolution 97(1): 281-306. https://doi.org/10.3897/zse.97.65280

MrBayes output consensus tree

Additional file 6 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 6: SM.05. Raw morphometric data for Macrobiotus pallarii Maucci, 1954 from the topotypic population (IT.337).

Additional file 7 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 7: SM.06. Raw morphometric data for Macrobiotus pseudopallarii sp. nov. from Montenegro (ME.007, type population).

Additional file 5 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 5: SM.04b. R script for morphometric analysis.

Additional file 6 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 6: SM.05. Raw morphometric data for Macrobiotus pallarii Maucci, 1954 from the topotypic population (IT.337).

Additional file 8 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 8: SM.07. Raw morphometric data for Macrobiotus ripperi sp. nov. from Poland (PL.015, type population).

Supplementary material 1 from: Vecchi M, Stec D (2021) Integrative descriptions of two new Macrobiotus species (Tardigrada, Eutardigrada, Macrobiotidae) from Mississippi (USA) and Crete (Greece). Zoosystematics and Evolution 97(1): 281-306. https://doi.org/10.3897/zse.97.65280

Raw morphometric data for Macrobiotus annewintersae sp. nov. from U.S.A (S207 – US.084, type population)

Additional file 10 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 10: SM.09. Raw morphometric data for Macrobiotus margoae sp. nov. from USA (US.057, type population).

Additional file 3 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 3: SM.03. The p-distances between species of the Macrobiotus pallarii complex.

Additional file 2 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 2: SM.02. MrBayes analysis input file with the alignment.

Supplementary material 4 from: Vecchi M, Stec D (2021) Integrative descriptions of two new Macrobiotus species (Tardigrada, Eutardigrada, Macrobiotidae) from Mississippi (USA) and Crete (Greece). Zoosystematics and Evolution 97(1): 281-306. https://doi.org/10.3897/zse.97.65280

Partitions and models selection results

Supplementary material 3 from: Vecchi M, Stec D (2021) Integrative descriptions of two new Macrobiotus species (Tardigrada, Eutardigrada, Macrobiotidae) from Mississippi (USA) and Crete (Greece). Zoosystematics and Evolution 97(1): 281-306. https://doi.org/10.3897/zse.97.65280

Thorpe normalization calculations and results

Additional file 3 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 3: SM.03. The p-distances between species of the Macrobiotus pallarii complex.

Supplementary material 5 from: Vecchi M, Stec D (2021) Integrative descriptions of two new Macrobiotus species (Tardigrada, Eutardigrada, Macrobiotidae) from Mississippi (USA) and Crete (Greece). Zoosystematics and Evolution 97(1): 281-306. https://doi.org/10.3897/zse.97.65280

MrBayes analysis input file with the alignment

Additional file 4 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 4: SM.04a. R data for morphometric analysis.

Additional file 5 of Integrative taxonomy resolves species identities within the Macrobiotus pallarii complex (Eutardigrada: Macrobiotidae)

Additional file 5: SM.04b. R script for morphometric analysis.