Terrestrial nematodes from the Maritime Antarctic.

Background: Soil nematodes are one of the most important terrestrial faunal groups in Antarctica, as they are a major component of soil micro-food webs. Despite their crucial role in soil processes, knowledge of their species diversity and distribution is still incomplete. Taxonomic studies of Antarctic nematodes are fragmented, which prevents assessment of the degree of endemicity and distribution of the species, as well as other aspects of biogeography. New information: The present study is focused on the nematode fauna of one of the three Antarctic sub-regions, the Maritime Antarctic and summarises all findings published up to April 2023. A species list that includes 44 species, belonging to 21 genera, 16 families and eight orders is provided. A review of the literature on terrestrial nematodes inhabiting the Maritime Antarctic showed that the sites are unevenly studied. Three islands (Signy, King George and Livingston Islands) revealed highest species richness, probably due to the highest rates of research effort. Most species and four genera (Antarctenchus, Pararhyssocolpus, Amblydorylaimus and Enchodeloides) are endemic, proving that nematode fauna of the Maritime Antarctic is autochthonous and unique. Several groups of islands/sites have been revealed, based on their nematode fauna. The study showed that species with a limited distribution prevailed, while only two species (Plectusantarcticus and Coomansusgerlachei) have been found in more than 50% of the sites. Based on the literature data, details on species localities, microhabitat distribution, plant associations and availability of DNA sequences are provided.

Composition and diversity of bacterial communities associated with honey bee foragers from two contrasting environments.

The honey bee is associated with a diverse community of microbes (viruses, bacteria, fungi, and protists), commonly known as the microbiome. Here, we present data on honey bee microbiota from two localities having different surrounding landscapes - mountain (the Rhodope Mountains) and lowland (the Danube plain). The bacterial communities of abdomen of adult bees were studied using amplicon sequencing of the 16S rRNA gene. The composition and dominance structure and their variability within and between localities, alpha and beta diversity, and core and differential taxa were compared at different hierarchical levels (operational taxonomic units to phylum). Seven genera (Lactobacillus, Gilliamella, Bifidobacterium, Commensalibacter, Bartonella, Snodgrassella, and Frischella), known to include core gut-associated phylotypes or species clusters, dominated (92-100%) the bacterial assemblages. Significant variations were found in taxa distribution across both geographical regions and within each apiary. Lactobacillus (Firmicutes) prevailed significantly in the mountain locality followed by Gilliamella and Bartonella (Proteobacteria). Bacteria of four genera, core (Bartonella and Lactobacillus) and non-core (Pseudomonas and Morganella), dominated the bee-associated assemblages of the Danube plain locality. Several ubiquitous bacterial genera (e.g., Klebsiella, Serratia, and Providencia), some species known also as potential and opportunistic bee pathogens, had been found in the lowland locality. Beta diversity analyses confirmed the observed differences in the bacterial communities from both localities. The occurrence of non-core taxa contributes substantially to higher microbial richness and diversity in bees from the Danube plain locality. We assume that the observed differences in the microbiota of honey bees from both apiaries are due to a combination of factors specific for each region. The surrounding landscape features of both localities and related vegetation, anthropogenic impact and land use intensity, the beekeeping management practices, and bee health status might all contribute to observed differences in bee microbiota traits.

Molecular and morphological characterisation of Longidoruspolyae sp. n. and L.pisi Edward, Misra & Singh, 1964 (Dorylaimida, Longidoridae) from Bulgaria.

Longidoruspolyae sp. n., a bisexual nematode species found in the rhizosphere of pear tree (Pyruscommunis L.), is described and characterised using an integrative approach. The new species has a female body length of 6.8-9.1 mm; a comparatively long odontostyle (114.0-127.5 µm); a narrow lip region (14.0-15.5 µm), anteriorly flattened and almost continuous with the body profile; pocket-like amphidial pouches long, deeply bilobed, and slightly asymmetrical, a guide ring at 37-42 µm from the anterior end; normal arrangement of pharyngeal glands; and a short bluntly rounded to hemispherical tail. Four juvenile stages identified: the first stage with a digitate tail, and the second and subsequent stages with a bluntly rounded tail. Males have one adcloacal pair and a row of 10 or 11 single ventromedian supplements; spicules 71.0-74.5 µm long. Based on morphometric data, the new species belongs to a group of species spread over Europe (L.arthensis, L.silvae, L.uroshis,), Iran (L.kheirii), and Syria (L.pauli), which share common characters such as amphidial fovea, lip region and tail shapes, similar odontostyle and body length, and similar first-stage juvenile tail shape. Codes for identifying the new species are A5, B2, C34, D3, E3, F45, G12, H1, I2, J1, K7. The phylogenetic analysis based on D2-D3 expansion domains of the rRNA gene revealed that the new species has the closest relationships with L.athesinus from Italy and three unidentified Longidorus spp. from USA (Longidorus sp. 1, Longidorus sp. 2, and Longidorus sp. 6). New morphometric and molecular data (18S rRNA gene, ITS1-5.8S-ITS2 regions and D2-D3 28S rRNA gene sequences) for three populations of L.pisi from Bulgaria were obtained and variations between populations are discussed.

Description of Longidorus cheni sp. n. (Nematoda, Longidoridae) from China.

Longidorus chenisp. n., an amphimictic species recovered from the rhizosphere of Larix principis-rupprechtii and Pyracantha fortuneana in Shanxi and Beijing, China, is described and illustrated. The taxonomic position of L. chenisp. n. among other species within the genus was elucidated using morphometric and molecular data, and phylogenetic relationships were inferred using D2-D3 expansion domains of 28S and 18S rRNA genes by Bayesian Inference (BI) method. The new species is characterised by females with a medium body size (L = 4.9-6.6 mm), a lip region slightly expanded, broadly rounded frontally and laterally, the amphidial fovea broad and symmetrically bilobed at base, odontostyle long and slender (143-168 µm), odonthophore slightly swollen at the base, tail short bluntly conoid to rounded. Guide ring located far posterior from the oral aperture (70-93 µm). Males with two ad-cloacal pairs of supplements preceded by a row of 10-14 ventromedian supplements, with robust spicules measuring 111-126 µm along the median line. Three juvenile stages were present, tail shape of J1 elongate conoid while in J2 and J3 the tail gradually becomes bluntly rounded. Codes for identifying the new species are: A6-B3-C5-D2-E2-F3-G1-H1-I2-J2-K2. Longidorus chenisp. n. belongs to a group of species with a guide ring at the mid-odontostyle position that have a predominantly Asiatic origin. It differs from all of them by a combination of morphological characters and unique sequences of partial 18S and D2-D3 region of 28S rRNA genes. The percentage dissimilarities in partial 18S and D2-D3 28S rRNA genes of L. cheni to the closest species (L. litchii, L. fangi, L. jonesi and L. juglans) were 1.5 %-1.8 % and 16.8-18.3 %, respectively.

Biogeography and phylogenetic position of Enchodeloides signyensis (Loof, 1975), gen. n., comb. n. from Maritime Antarctic (Nematoda, Nordiidae).

The taxonomic position of the endemic Antarctic species Enchodeloides signyensis (Loof, 1975), gen. n., comb. n. (= Enchodelus signyensis Loof, 1975) is discussed on the basis of morphological study, including SEM, morphometric data, postembryonic observations, and sequence data of 18S rDNA and the D2-D3 expansion fragments of the large subunit rDNA. A number of characters such as the cuticle and stoma structures, including the presence of moderately developed cuticularised ring around the oral aperture, peculiarities of pharynx expansion, size and position of the posterior pair of pharyngeal nuclei, a less complex uterus, and the position of a posterior ventromedian supplement show that this species differs substantially from the other members of the genus Enchodelus. Furthermore, both the 18S and 28S rDNA-based phylogenetic trees of the Enchodelus sequences available in the GenBank formed two distinct clusters with E. signyensis being a part of a well-supported group with species of the genus Pungentus; therefore, it is proposed that its taxonomic position should be reconsidered.

The morphological and molecular identity of Longidorus piceicola Lisková, Robbins & Brown, 1997 from Romania (Nematoda, Dorylaimida).

Longidorus piceicola, a new geographical and host record from Romania, was described and illustrated on the basis of two populations originating from a coniferous and a deciduous forest. The main morphological characters of specimens from Romania correspond very well with the type material collected from the soil around Picea abies L. (Slovakia) except for the shorter body and tail. The D2-D3 fragment of 28S rDNA from both populations was amplified and sequenced, and the sequences were identical to L. piceicola sequence from Slovakia. The partial 18S-ITS1-5.8S-ITS2 rDNA regions from one of the populations were sequenced for the first time. The evolutionary relationships between L. piceicola and the closest species L. intermedius based on D2-D3 sequence divergence and single-nucleotide polymorphisms are discussed. Although having very low sequence dissimilarity (0.3-0.9 %) both species have distinct morphology and biology. Longidorus piceicola differs from L. intermedius in having a much longer odontostyle, body, distance anterior end - guide ring, a wider lip region, more ventromedian supplements (11 vs 5-7) in the male, and develops through four rather than three juvenile stages. Furthermore, L. piceicola occurs more frequently in association with conifers, while L. intermedius is found mainly in oak forests.

Morphological and molecular characterisation, and phylogenetic position of X. browni sp. n., X. penevi sp. n. and two known species of Xiphinema americanum-group (Nematoda, Longidoridae).

Using ribosomal (18S, ITS1, ITS2, D2-D3 expansion segments of 28S rDNA) and mitochondrial (partial cox1 and nad4) DNA markers in a study of several populations of Xiphinema americanum-group from Europe and Morocco, two cryptic species Xiphinema browni sp. n. (formerly reported as Xiphinema pachtaicum) and Xiphinema penevi sp. n. were revealed. The species are described, illustrated and their phylogenetic relationships discussed. The first species is most similar to Xiphinema parasimile and is a member of Xiphinema simile species complex. The phylogenetic reconstructions inferred from three molecular markers (18S, D2-D3 28S rDNA and cox1) showed that Xiphinema penevi sp. n. is part of Xiphinema pachtaicum-subgroup and is closely related to Xiphinema incertum, Xiphinema pachtaicum, Xiphinema parapachydermum, Xiphinema plesiopachtaicum, Xiphinema astaregiense and Xiphinema pachydermum. Also, a separate "Xiphinema simile-subgroup", outside the Xiphinema pachtaicum-subgroup and so far consisting only of the parthenogenetic species Xiphinema simile, Xiphinema parasimile, Xiphinema browni sp. n. and probably Xiphinema vallense was formed. New primers for amplification and sequencing of part of the nad4 mitochondrial gene were designed and used.

New data on two remarkable Antarctic species Amblydorylaimusisokaryon (Loof, 1975) Andrássy, 1998 and Pararhyssocolpusparadoxus (Loof, 1975), gen. n., comb. n. (Nematoda, Dorylaimida).

The taxonomic position of two antarctic dorylaimid species Amblydorylaimusisokaryon (Loof, 1975) Andrássy, 1998 and Pararhyssocolpusparadoxus (Loof, 1975), gen. n., comb. n. are discussed on the basis of morphological, including SEM study, morphometric, postembryonic and sequence data of 18S rDNA and the D2-D3 expansion fragments of large subunit rDNA. The evolutionary trees inferred from 18S sequences show insufficient resolution to determine the assignment of the two species to particular families, moreover Pararhyssocolpusparadoxus gen. n., comb. n. (=Rhyssocolpusparadoxus) previously regarded as a member of Nordiidae or Qudsianematidae, showed distant relationship both to Rhyssocolpusvinciguerrae and Eudorylaimus spp. The phylogram inferred from 28S sequences revealed that Amblydorylaimusisokaryon is a member of a well-supported group comprised of several Aporcelaimellus spp., while, no close relationships could be revealed for the Pararhyssocolpusparadoxus gen. n., comb. n. to any nematode genus. On the basis of molecular data and morphological characteristics, some taxonomic changes are proposed. Amblydorylaimusisokaryon is transferred from family Qudsianematidae to family Aporcelaimidae, and a new monotypic genus Pararhyssocolpus gen. n. is proposed, attributed to Pararhyssocolpidaefam. n. The diagnosis of the new family is provided together with emended diagnosis of the genera Amblydorylaimus and Pararhyssocolpus gen. n. Data concerning distribution of these endemic genera in the Antarctic region are also given.

Calcaridorylaimus castaneae sp. n. (Nematoda, Dorylaimidae) from Bulgaria with an identification key to the species of the genus.

An unknown species belonging to the genusCalcaridorylaimus Andrássy, 1986 was collected from the litter of broadleaf forests dominated by Castanea sativa Mill. and mixed with Quercus daleshampii Ten. and Fagus sylvatica L. on Belasitsa Mountain, south-western Bulgaria. Calcaridorylaimus castaneae sp. n. is characterised by its long body (1.4-2.1 mm), lip region practically not offset, vulva transverse, short odontostyle (14.5-16 µm) and tail (75.5-110.5 µm, c=14.7-23.6; c'=2.9-4.4) in females and 38-46 µm long spicules with small spur before their distant end in males. It is most similar to C. andrassyi Ahmad & Shaheen, 2004, but differs in having transverse vs pore-like vulva and shorter spicules (38-46 µm vs 52-57 µm). An identification key to the species of the genus Calcaridorylaimus is proposed. Phylogenetic analyses were performed on 18S and D2-D3 expansion domains of 28S rRNA genes by Neighbor-Joining, Maximum Likelihood and Bayesian Inference methods. The phylograms inferred from 18S sequences showed closest relationships of the new species with some species belonging to the genus Mesodorylaimus. However, insufficient molecular data for members of both genera do not allow the phylogenetic relationships of Calcaridorylaimus and the new species described herein to be elucidated.

Description of Longidorus cholevae sp. n. (Nematoda, Dorylaimida) from a riparian habitat in the Rila Mountains, Bulgaria.

A description is provided of Longidorus cholevae sp. n., a bisexual species associated with wild cherry (Prunus avium L.) from the Rila Mountains, Bulgaria. The position of L. cholevae sp. n. among other species of the genus was elucidated by using morphological and molecular data. Phylogenetic analyses were performed of D2-D3 expansion domains of the 28S rRNA and the partial ITS1 containing regions by Neighbor-Joining, Maximum Likelihood and Bayesian Inference methods. The species is characterised by a female body length of 6.1-8.1 mm; long odontostyle (106-129 µm); lip region wide (21.5-24 µm) rounded and continuous with the body profile; amphidial pouches short and wide, funnel-shaped; a posteriorly situated guide ring (30-37 µm); normal arrangement of pharyngeal glands, and short bluntly rounded to hemispherical tail. Four juvenile stages indentified, first stage with elongate conoid tail. Males with 2-4 adanal pairs and a row of 11-13 single ventromedian supplements, spicules 96-120 µm long. Based both on morphological and molecular data the new species appearred to be the most similar witha group of species distributed in Europe sharing common charcters such as amphidial fovea, lip region and tail shapes, and having similar odontostyle and body length: L. poessneckensis, L. caespiticola, L. macrososma, L. helveticus, L. carniolensis and L. pius. An updated list of Longidorus species and a partial polytomous keys to the Longidorus species with long odontostyle (code A45) and short tail (code H1) are provided.

Morphological and molecular characterisation of Xiphinema macroacanthum Lamberti, Roca & Agostinelli, 1989 (Nematoda: Longidoridae) from olive orchards in southern Italy.

A population of Xiphinema macroacanthum Lamberti, Roca & Agostinelli, 1989 originating from olive orchards in Brindisi, Italy and containing both adults and all juvenile stages, is described and illustrated. The first juvenile stage is reported for the first time. Molecular characterisation of this species, using the D2-D3 expansion domains of the 28S rDNA and ITS region, was carried out. PCR-RFLP analyses of the ribosomal gene regions determined species-specific patterns that clearly differentiate X. macroacanthum. Sequences of the D2-D3 domains and the partial 18S-ITS1 rRNA genes were analysed using several methods for inferring phylogeny to reconstruct the relationships between X. macroacanthum and other Xiphinema species.

Studies of the genus Enchodelus Thorne, 1939 (Nematoda, Nordiidae) from Arctic polar deserts. 1. Species with long odontostyle: E. makarovae sp. n. and E. groenlandicus (Ditlevsen, 1927) Thorne, 1939, with an identification key to the species of the E. macrodorus group.

Two nematode species of the genus Enchodelus Thorne, 1939, one new and one known from Arctic polar deserts were studied. Enchodelus makarovaesp. n. is an amphimictic species, characterised by females with body length of 1.57-2.00 mm, lip region 15-17.5 µm wide, amphid duplex, odontostyle 38-43 µm long or 2.3-2.8 times lip region diam. Odontophore with flanges, 1.2-1.4 times as long as odontostyle; pharynx length 320-377 µm, pharyngeal expansion 113-130 µm long or 32-37% of total pharynx length; female genital system amphidelphic, uterus tripartite, pars refringens vaginae with two trapezoid sclerotisations, vulva a transverse slit (V=45-51%); tail bluntly conoid (25-35 µm, c=45.8-70.3, c'=0.6-0.9 in females, and 29-33 µm, c=46.4-58.9, c'=0.7-0.8 in males). Males with 65-74 µm long spicules and 10-12 spaced ventromedian supplements. Additional information for Enchodelus groenlandicus is provided, this being a new geographic record for the Putorana Plateau, Russian Arctic.

Longidorus carniolensis sp. n. (Nematoda, Longidoridae) from vineyard soil in Slovenia.

A new needle nematode, Longidorus carniolensissp. n., recovered from the soil around the roots of grapevine Vitis vinifera L. from Slovenia, is described and illustrated. Longidorus carniolensisis an amphimictic species, characterised by females with a moderately long (L=5.6-8.2 mm) and plump (a=51-72.4, ave. 66.3) body, assuming a spiral to C-shape when heat relaxed. Head region continuous, anteriorly almost flat, lip region 23-25 µm wide; guiding ring situated posteriorly (42-47 µm, 43-50 µm in males), odontostyle long (ave. 146.6 (136-157) µm); pharyngeal glands with normal location, their nuclei of approximately equal size; tail bluntly conoidal to almost hemispherical. Males abundant, spicules slender and long (122-145 µm), ventromedian supplements 13-17, irregularly spaced, preceded by an adanal pair. Four juvenile stages present, the first stage juvenile with bluntly conoidal tail. Codes for identifying the new species when using the key by Chen et al. (1997) are: A 56, B 4, C 4, D 1, E 4, F 35, G 1, H 1, I 2. The new species is morphologically the most similar to Longidorus poessneckensis Altherr, 1974, Longidorus macrosoma Hooper, 1961, Longidorus caespiticola Hooper, 1961, Longidorus helveticus Lamberti et al., 2001, Longidorus macroteromucronatus Altherr, 1974, Longidorus pius Barsi & Lamberti, 2001, Longidorus raskii Lamberti & Agostinelli, 1993, Longidorus kheirii Pedram et al. 2008, Longidorus silvae Roca, 1993, Longidorus iuglandis Roca et al., 1985, Longidorus vinearum Bravo & Roca, 1995 and Longidorus major Roca & d'Erico, 1987, but differs from these species either by the body and odontostyle length, position of guide ring, head region and tail shape or the shape of the first stage juvenile tail. Sequence data from the D2-D3 region of the 28S rDNA distinguishes this new species from other speciesof the genus Longidorus with known sequences. Relationships of Longidorus carniolensissp. n. with other Longidorus species based on analysis of this DNA fragment and morphology are discussed.

Xiphinema pirinense n. sp. (Nematoda: Dorylaimida: Longidoridae), a new species from Bulgaria with a digitate tail.

A description of Xipinema pirinense n. sp. is provided. This is a parthenogenetic nematode found associated with Fragaria sp. and Alchemilla sp. (Rosaceae) close to pine trees in the Pirin Mountains, Bulgaria. The species is characterised by its medium body length (3.2-3.9 mm), rounded head region slightly demarcated by a shallow depression, long odontostyle (116-134.5 microm), tripartite uterus with a Z-differentiation consisting of 4-7 irregular moderately refractive bodies with a clear central part, and a digitate tail with a ventral peg. The new species is most similar to X. index Thorne & Allen, 1950 and X. diversicaudatum (Micoletzky, 1927) Thorne, 1939.

Ribosomal and Mitochondrial DNA Analyses of Xiphinema americanum-Group Populations.

The 18S ribosomal DNA (rDNA) and cytochrome oxidase I region of mitochondrial DNA (mtDNA) were sequenced for 24 Xiphinema americanum-group populations sourced from a number of geographically disparate locations. Sequences were subjected to phylogenetic analysis and compared. 18S rDNA strongly suggested that only X. pachtaicum, X. simile (two populations) and a X. americanum s.l. population from Portugal were different from the other 20 populations studied, whereas mtDNA indicated some heterogeneity between populations. Phylogenetically, based on mtDNA, an apparent dichotomy existed amongst X. americanum-group populations from North America and those from Asia, South America and Oceania. Analyses of 18S rDNA and mtDNA sequences underpin the classical taxonomic issues of the X. americanum-group and cast doubt on the degree of speciation within the X. americanum-group.