Nematode Assemblages Research Articles

Do functional traits and biochemical biomarkers of the nematode Oncholaimus campylocercoides De Coninck and Schuurmans Stekhoven, 1933 affected by fluoranthene and polystyrene microplastics? Results from a microcosm bioassay and molecular modeling

The current experiment measured the multifaceted effects of polystyrene and fluoranthene, acting alone or in a mixture, on the meiobenthic nematode species Oncholaimus campylocercoides. This Oncholaimid was first experimentally selected from an entire nematode assemblage taken from the Jeddah coasts (Saudi Arabia). Several discernible changes were found in morphometry and functional traits after exposure to single and combined treatments. An increase in the activity of the biochemical biomarkers catalase and glutathione S-transferase was also observed following the exposure of males and gravid females of O. campylocercoides to 37.5 ng fluoranthene·g−1 dry weight (DW) and 62.5 mg polystyrene·kg−1 DW paralleled by a higher vulnerability of females. Moreover, the reproduction and feeding of this species were impaired, starting from 37.5 ng fluoranthene·g−1 and 62.5 mg polystyrene·kg−1, respectively. These results have been confirmed by good binding affinities and molecular interactions of fluoranthene and polystyrene with both GLD-3 and SDP receptors.

Unveiling the meiobenthic community structure of Prydz Bay, Antarctica during austral summer

Meiobenthos are bottom-dwelling aquatic invertebrates having a size range of 63–500 μm. They play a pivotal role in ecosystem functioning, biogeochemical and trophic nutrient cycling. Due to the presence of Antarctic Circumpolar Current and steep gradient in nutrients and temperature, many taxa of the Southern Ocean (SO) show diverse biodiversity patterns in comparison to other deep sea areas of the world. Over the years, several Indian SO Expeditions have been carried out in the Indian sector of SO (ISSO), but this is a pioneer attempt to unveil the meiobenthic community structure and their functional diversity pattern from Prydz Bay (Indian sector of Southern Ocean), Antarctica. Meiobenthic community structures were investigated in eight different sampling sites along with their vertical profiling from the Prydz Bay during the austral summer 2020. Total meiofaunal abundance ranged from 24 to 521 indv. 10 cm-2, with the highest abundance recorded at station 23 and the lowest at station 9. A total of 9 meiobenthic taxa were found from this eco-region, with the highest percentage being the free-living marine nematodes as metazoan taxa. A total of 86 free-living nematode species were identified, where Sabatieria was the most common genus and represented by eleven species. Several univariate and multivariate analyses deciphered a distinct spatial variation in the meiobenthic community structure. Sediment texture and depth were the most significant environmental variables in shaping nematode assemblages. Biological Trait Analysis was performed using a total of 24 traits in 5 categories to unravel the functional diversity of free-living marine nematodes. The most dominant morphotypes were slender body shape, conical tail shape, dotted cuticle pattern, and non-selective deposit feeders with colonizing abilities of 2 (c–p score 2, in a scale from 1 to 5). Maturity Index (MI) and Index of Trophic Diversity (ITD) were highest in stations 15 and 32, respectively. RLQ approach with fourth-corner analysis was used to decipher the relationship between traits and environmental parameters. The RLQ analysis revealed the positive association of non-selective deposit feeder and slender body-shaped nematodes with higher water depth. The characterization of meiobenthic (especially nematode) communities in the context of taxonomic and functional attributes could help to evaluate the ecological status of ISSO. Further long term monitoring is also needed to get a comprehensive idea about their role in benthic ecosystem functioning in the milieu of global climate change.

Fertilization restructures nematode assemblages by modifying soil pH in croplands of Northeast China

Fertilization restructures nematode assemblages by modifying soil pH in croplands of Northeast China

A review of the nematode assemblages of the genus Perameles (Peramelidae), Australian bandicoots, held in the South Australian Museum

ABSTRACT A total of 210 vials of nematodes collected from four species of Perameles (representing 15 individuals of P. bougainville, 83 of P. gunnii, 54 of P. nasuta and 19 of P. pallescens) held in the Australian Helminthological Collection of the South Australian Museum were examined. Nematodes were identified and parasite assemblages of the four hosts were compared. Using only the number of nematodes identified to species as an indicator of diversity, the nematode community of P. bougainville was the most depauperate (4 species) followed by P. gunnii (11 species), P. pallescens (12 species) and P. nasuta (20 species). None of the species were found in all four hosts. Excluding P. bougainville, Sorensen’s index of similarity showed that P. gunnii and P. pallescens had the least similar, 0.26, and P. pallescens and P. nasuta the most similar, 0.50, nematode communities. Linstowinema warringtoni Smales, 1997, Mackerrastrongylus peramelis (Johnston & Mawson, 1938) and Peramelistrongylus skedastos Mawson, 1960 were found in three hosts, P. gunnii, P. nasuta and P. pallescens. Each of the four hosts had a unique species profile: four species of Physaloptera being found in P. nasuta, three in P. pallescens, one in P. gunnii and none in P. bougainville. Of the trichostrongyloids, Mackerrastrongylus peramelis was the most prevalent in P. pallescens and Peramelistrongylus skedastos in P. gunnii and P. nasuta. The influence of nematode collection techniques, sample sizes and host geographic range and ecology may have had on the assemblages we observed is discussed.

Soil nematode assemblages respond to interacting environmental changes.

Multi-factor experiments suggest that interactions among environmental changes commonly influence biodiversity and community composition. However, most field experiments manipulate only single factors. Soil food webs are critical to ecosystem health and may be particularly sensitive to interactions among environmental changes that include soil warming, eutrophication, and altered precipitation. Here, we asked how environmental changes interacted to alter soil nematode communities in a northern Chihuahuan Desert grassland. Factorial manipulations of nitrogen, winter rainfall, and nighttime warming matched predictions for regional environmental change. Warming reduced nematode diversity by 25% and genus-level richness by 32%, but declines dissipated with additional winter rain, suggesting that warming effects occurred via drying. Interactions between precipitation and nitrogen also altered nematode community composition, but only weakly affected total nematode abundance, indicating that most change involved reordering of species abundances. Specifically, under ambient precipitation, nitrogen fertilizer reduced bacterivores by 68% and herbivores by 73%, but did not affect fungivores. In contrast, under winter rain addition, nitrogen fertilization increased bacterivores by 95%, did not affect herbivores, and doubled fungivore abundance. Rain can reduce soil nitrogen availability and increase turnover in the microbial loop, potentially promoting the recovery of nematode populations overwhelmed by nitrogen eutrophication. Nematode communities were not tightly coupled to plant community composition and may instead track microbes, including biocrusts or decomposers. Our results highlight the importance of interactions among environmental change stressors for shaping the composition and function of soil food webs in drylands.

Greenhouse gases concentrations influence on vertical distribution of nematode communities in the Ba Lai river, Vietnam

Vertical distribution of free–living nematodes from the tropical region are still poorly documented, especially in Vietnam. Field sampling was conducted at the Ba Lai river, a tributary of the Mekong river, to insight into the regularity of the vertical pattern of nematode assemblages. Furthermore, some sediment environmental characteristics such as greenhouse gases were also detected in order to understand how to influence nematode distribution. The study found that nematode composition differed significantly between the upper and deeper layers of sediment but not among the deeper layers. Nematode density showed spatial variability across layers, with higher values in the upper layer. Nematode diversity decreased with increasing depth. Non–selective deposit feeders (1B) were dominated in the surface layers, while the predator–omnivores feeders (2B) was numerous in the deeper layers. In the dry season, both methane and hydrogen sulfur were found negatively affecting nematode diversity in sediment profile, particularly, methane effects negatively also to species richness, densities, and evenness. However, only methane has a significant correlation to the diversity, species richness, densities, and evenness of the nematode communities.

Heavy Logging Machinery Impacts Soil Physical Properties More than Nematode Communities

Mechanized logging equipment causes considerable soil disturbance, but little information is available regarding thresholds for impacts on soil nematodes—critical members of soil foodwebs which perform important ecological functions. We examined responses of nematode communities and soil physical characteristics to the increasing number of passes (one, three, or nine) by a tracked feller buncher during thinning of a xeric mixed conifer forest in New Mexico, USA. Within and between the harvester tracks, we measured soil surface penetration resistance and shear strength, quantified bulk density at four depth increments up to a maximum depth of 27 cm, and characterized nematode assemblages in the upper 10 cm. Eight months after treatment, nematode communities were less impacted than soil physical properties by harvester passes. Total nematode abundance was unaffected by any level of feller buncher disturbance, and sensitive K-selected nematode groups were reduced only at nine passes. Conversely, soil compaction occurred with a single pass and extended deep into the soil profile to at least 23–27 cm. The first pass also decreased surface penetration resistance and shear strength, indicating disruption of soil surface structural integrity. Additional passes did not further increase bulk density or decrease surface structural integrity. Our results indicate that low levels of logging machinery traffic may have negligible effects on nematode communities, but nevertheless emphasize the importance of minimizing areas subjected to disturbance because of impacts on soil physical properties.

Free-living nematode assemblages along a water-depth gradient in the Perdido belt, northwestern Gulf of Mexico

This study investigated nematode assemblages in the Perdido belt, northwestern Gulf of Mexico (GoM) in terms of species composition, distribution, density, and diversity. We examined 27 sediment samples collected at depths of 44-3466 m. The nematodes were identified at the lowest level possible and classified into four trophic groups based on their buccal cavity. Additionally, their sex and stage of life were determined. The sediment composition was determined, as well as the percentage of organic carbon (OC). The density per site fluctuated between 0.02 and 13.30 ind/10 cm2. A total of 1768 nematodes were identified, belonging to 9 orders, 35 families, 96 genera, and 153 species, of which 9 genera and 15 species are new records for the GoM. The families Xyalidae and Comesomatidae were the most diverse genera (9 and 8, respectively). Sabatieria sp. 1 was the most abundant and widely distributed species. The number of species varied at different depths (range 1-60 species) and Pielou evenness (0.7-1). Most of the organisms collected were adult females. The non-selective deposit feeders were the most abundant (49%), followed by epigrowth feeders (20%). Most of the sites consisted of sand (range 10.1-70.2%). The percentage of OC varied at different depths (0.1-1.4%). No significant correlation was found between species richness and depth. The species composition changes with depth, density and most of the trophic groups tend to decrease with increasing depth. The dominant species are more related to the percentage of sands and silts than to clays and OC.

Whale falls as chemosynthetic refugia: a perspective from free-living deep-sea nematodes

Whale carcasses create habitats in the deep sea which are colonized by organisms related to other chemosynthetic environments suggesting that whale falls may act as intermediate refugia for the dispersal and evolution of deep-sea organisms. Such evidence comes mainly from macrofaunal organisms whereas for the smaller meiofauna, data on whalebone assemblages is lacking. In this study, we investigated nematode colonization of whalebones experimentally deployed at 1500 and 3300 m depth and bones from a natural whale carcass found at 4204 m, in the Southwest Atlantic Ocean, off Brazil. By comparing whalebone assemblages to other deep-sea environments, we tested the hypothesis that whale fall nematode assemblages are more similar to those from other cognate chemosynthetic-based habitats, rather than those from sediments surrounding the carcass or other deep-sea habitats. Our results showed that whalebone nematode assemblages resemble those of hydrothermal vents and cold seeps and suggest that organic falls may act as intermediate refugia for meiofauna from chemosynthetic environments. It also showed that oceanographic conditions and the age of the carcasses on the ocean floor could influence nematode assemblage composition and richness. Such findings highlight the importance of organic falls for understanding the connectivity and phylogeny of benthic organisms, including representatives of the meiofauna.

Climate and edaphic factors drive soil nematode diversity and community composition in urban ecosystems

Rapid urbanization profoundly affects global biodiversity. How urbanization modifies soil biodiversity and perturbs nematodes remains limited. Here, we investigated soil nematodes in four land-use types: Parks, residential areas, natural forests, and maize fields across 12 cities in China. Urban parks and surrounding forests had similar nematode richness exceeding that in urban residential areas and surrounding farmlands. Nematode communities in parks and residential areas were, however, more homogenous than in forests and farmlands. Variations in nematode assemblages in both core urban and urban surroundings were mainly due to taxa replacement, indicating that nematodes were spatially isolated in cities. Urban residential areas were colonized by the lowest number of specialists (i.e., with narrow niche width) and smaller body sizes. Urban parks, conversely, served as hotspots for soil nematodes in cities. Together, our results indicate that urbanization processes reduce nematode diversity, with e.g., 30% loss in residential areas compared to forests, and homogenize soil nematode communities.

Deterministic versus stochastic control in β-diversity, abundance and co-occurrence patterns of a soil nematode assemblage living in a Mediterranean soil

In this paper we studied the determinism-stochasticity trade-off affecting the structure of a soil nematode assemblage. Specifically, in a field experiment that lasted six months, the soil temperature and moisture conditions were manipulated in 14 plots. The generic composition of the soil nematode assemblage was explored by estimations of β-diversity, its turnover and nestedness components and by fitting rank abundance models. Further the associative aspects between the assemblage members and between them and habitat attributes were accounted for by analyzing the niche overlap based on Pearson correlation coefficients. Using variation partitioning and null models, we found that the generic diversity of the assemblage was more strongly determined by non-registered lateral experimental factors (stochastic control). By contrast, the deterministic control—less strong than the stochastic counterpart—was exerted both in synchronization with the changes in habitat characteristics and/or with a time delay. The network analysis showed that, under favorable habitat conditions in July, September and October, reduced network modularity and enhanced connectivity were favored, which probably led to a niche-based deterministic selection that outperformed stochasticity. Conversely, under changing experimental conditions in August and lower temperature in November and December, stochasticity would be superior to niche identity, leading to enhanced modularity and relatively loose networks.

An exploration of nematode assemblages in the hydroponic media beds of a commercial aquaponics system

Summary Nematodes perform important ecosystem services in soils and are well studied in traditional farming, but their role in newer soil-less food production systems is unstudied. We determined the nematode assemblages from substrates within the hydroponic media beds of a commercial aquaponics system. Three substrates were studied: coir, compost and lightweight expanded clay aggregate (LECA), with the nematode assemblages ascertained via traditional morphological analysis. All substrates were suitable for nematodes but abundance was lower compared with traditional compost. Compost from within the hydroponic media beds had nematode assemblages with similar maturity indices (MI) to compost external to the system, and both composts housed nematodes with a high proportion of bacterivores, a high degree of enrichment and no structure. LECA that were regularly disturbed and had little organic build up resembled compost – highly enriched and lacking structure. LECA that had been left undisturbed for longer and allowed to accumulate more organic matter had highly structured assemblages and showed less enrichment than the other substrates. Nematode assemblages within the coir showed very little enrichment but had higher MI and were more structured than compost. Problematic plant-parasitic nematodes were not found in any of the samples. We present the first glimpse into the role of nematodes in aquaponics systems and encourage future studies to explore how nematodes in these systems affect yield and plant health.

A functional perspective of nematode assemblages as proxy of quality in tropical estuarine tidal flats

Functional aspects of biological communities influence ecosystem processes and it is urgent to understand how human disturbances affect functional diversity and ecosystem functions and services. Our purpose was to address the use of different functional metrics of nematode assemblages to evaluate the ecological status of tropical estuaries subjected to different human activities, aiming to advance and improve the knowledge about the usefulness of functional attributes as indicators of environmental quality. Three approaches were compared: functional diversity indexes, single trait, and multi traits using the Biological Traits Analysis. The RLQ + fourth-corner combined method was used to identify relationships among functional traits, inorganic nutrients, and metals concentrations. Lower values of FDiv, FSpe, and FOri indicate a convergence of functions, characterizing impacted conditions. A dominant set of traits was related to disturbance, mainly inorganic nutrient enrichment. All the approaches allowed for the detection of disturbed conditions, however, multi traits was the most sensitive one.

A review of the nematode assemblage of the Australian bandicoot, Isoodon macrourus (Peramelidae), from material held in the South Australian Museum with the description of Sprattellus cassonei n. sp. (Mackerrastrongylidae).

A total of 235 vials of nematodes held in the Australian Helminthological Collection of the South Australian Museum from 125 individuals of Isoodon macrourus were examined. The nematode assemblage of I. macrourus, comprising 12 families, including 16 genera and 23 identified species, was compared with the sympatric bandicoot species Perameles nasuta, 20 identified species (Sorensen's index of similarity 0.56) and P. pallescens, 12 identified species (Sorensen's index 0.51). Sprattellus cassonei n. sp. is distinguished from its congeners by having a synlophe with 7-8 ridges with the anterior ventral ridges interrupted, the morphology of the dorsal ray and the branching of the spicule tips. A single male specimen identified as Linstowinema sp. 1. is characterised by seven circles of body hooks, the oesophagus terminating at the level of the seventh circle and robust scale-like spines on the posterior ventral body. A complete description of the species will require additional material, including females. Difficulties in identifying individuals of the genus Mackerrastrongylus to species level are discussed. Overall similarities in the nematode assemblages of the three bandicoot hosts are likely due to shared relationships and similar behaviours.

Marine Meiobenthic Nematode Assemblages as Potential Bioindicators and Carbon Sequesters in Coastal Sediments

Marine Meiobenthic Nematode Assemblages as Potential Bioindicators and Carbon Sequesters in Coastal Sediments

Assessment of the ecological state of the Danube delta coastal area (northwestern part of the Black Sea) based on meiobenthos and nematode assemblages

Assessment of the ecological state of the Danube delta coastal area (northwestern part of the Black Sea) based on meiobenthos and nematode assemblages

The response of meiobenthinc sediment-dwelling nematodes to pyrene: Results from open microcosms, toxicokinetics and in silico molecular interactions.

An experiment conducted with 'open microcosm' made by connected sedimentary compartments with different qualities was for 30days to evaluate the migratory behaviour of nematodes as induced by exposure to pyrene. The nematofauna was collected along with sediment from a reference site in Bizerte lagoon. Following one week acclimatization period, the populated sediments were topped with azoic sediments, with a pyrene concentration of 150μgkg-1. The concentration of pyrene from sediments was measured on a weekly basis. A stable status of nematode assemblages was reached between the upper and lower compartments in each microcosm, whatever the treatment type. An upward exploratory phase was observed during the first two weeks within the assemblages, possibly induced by the repellent chemodetection of pyrene. This observation was confirmed by the toxicokinetic properties and molecular interactions of pyrene with the germ-line development Protein 3 and sex-determining protein of Caenorhabditis elegans as nematode model.

Depth-related patterns and regional diversity of free-living nematodes in the deep-sea Southwestern Gulf of Mexico

Diversity of free-living marine nematode assemblages in the Southwestern Gulf of Mexico (SW GoM) is scarcely studied. Here, we aimed (1) to analyze the influence of a water depth gradient on the species richness, feeding type and taxonomic composition of assemblages; and (2) to document the regional diversity of free-living nematodes in the SW GoM. We sampled 63 sites along a water depth gradient from 186 to 3774 m during four oceanographic cruises. We found clear variations along the depth gradient of bottom water (temperature, salinity, and dissolved oxygen) and sediment variables (grain size and organic content). We identified 1881 nematodes belonging to 108 genera, 33 families, ten orders, and two classes. The abundance and species richness decreased with water depth. However, the expected number of species for a same level of abundance did not change along the depth gradient likely because the scarcity of food was compensated by reduced environmental stress (e.g., higher oxygen content and physical stability). Microbial sucker was the most abundant feeding type indicating the important role of sediment bacteria in the nematode’s diet. Species composition varied along the depth gradient with dominance in the upper slope sites of species of Comesomatidae tolerant to reduced sediments (e.g., Dorylaimopsis sp., Sabatieria spp., and Setosabatieria hilarula). Many congeneric species typical of deep sea were restricted to the deepest sites such as Acantholaimus spp., Ledovitia spp., Desmoscolex spp., and Halalaimus spp. The nematode regional diversity of SW GoM was 154 species, but the Chao 1 estimator indicated a richness of about 194 species and a highest limit of 246 species. The accumulation curves of richness were non-asymptotic suggesting a substantial fraction of undiscovered richness. Our study increased the free-living nematode fauna of GoM in 144 species (76%) respect to Hope’s list (2009). The large diversity of nematodes stands out the necessity of further studies to unravel the environmental drivers of α- and β-diversities and highlights the potential of this taxon for monitoring the deep sea of the Gulf of Mexico.

Size spectra, biomass, and trophic groups of free‐living marine nematodes along a water‐depth gradient in the northwestern Gulf of Mexico

AbstractWater depth can affect the size spectra (SS) and biomass of free‐living nematodes, but these relationships are largely unknown for the Gulf of Mexico (GoM). Here, we examined the SS and biomass of meiofaunal nematode assemblages at 27 sites along a water‐depth gradient from 44 to 3466 m in the Perdido belt, northwestern GoM. Nematodes were identified to species level, measured (length and width), and assigned to shape morphotypes and trophic groups. Nematode SS were defined by a median length of 951 μm (range: 223–4289 μm) and a median width of 33 μm (range: 12–109 μm). SS revealed a dominant long/slender morphotype (e.g., Paramicrolaimus sp., Filoncholaimus sp., and Ledovitia sp.), better adapted to the very fine sediments of the deep sea, whereas stout/short nematodes (mostly Desmoscolex sp., Greeffiella sp., and Quadricoma sp.) were less abundant. Water‐depth gradient significantly influenced mean individual (IB) and total biomasses likely because reduced availability of organic carbon with depth. The two deepest sites had particularly high mean IB suggesting local sources of organic carbon in the abyssal region related to the Perdido belt oil field. The most abundant trophic group was microbial feeder sucker (56%), followed by microbial feeder scraper (23%), and predator ingester (20%). The mean IB of predator nematodes was significantly larger than that of nematode preys. However, the logarithm of ratio IBpredator/IBprey was rather low (0.34) and in agreement with the empiric consumer‐resource body‐size relationship calculated for marine invertebrates. Our study provides novel insights about the structure of benthic nematode assemblages in the western Gulf of Mexico across a wide depth gradient.

The habitat preferences of nematode assemblages in relation to the sediment granulometry in the Ba Lai estuary, Vietnam

This study investigated the habitat preference of nematode communities in relation to sediment composition in the Ba Lai dammed estuary, which is a branch of Mekong estuarine system in the southern Vietnam. Sediment samples were collected for granulometry and nematode analyses in dry season from 6 subtidal stations along the estuary starting from its mouth, of which three were in the downstream of the dam and the other three located in the upstream. The present research showed the heterogeneity in sediment granulometry, which is mostly represented by silt component, except sandy sediment in the estuarine mouth and sand–silt sediment in the middle part. The nematode assemblage was low in abundance but high in diversity including genera richness and Shannon–Wiener diversity index. The communities showed differences in the habitat preference associated with sediment. The higher silt component presented in the riverbed was found to be limiting factor for abundance and diversity and genus Pseudochromadora. Pseudochromadora was dominant in the mouth station, which is characterized as sandy sediment, Rhabdolaimus was abundant in sand–silt bottom, while two genera Parodontophora and Theristus thrived in the silty environment.