Diversity Of Nematode Assemblages Research Articles

Do the morphological and functional traits of free-living marine nematodes mirror taxonomical diversity?

The taxonomical structure and diversity of nematode assemblages are the main attributes analyzed in ecology, but nematode adaptations to their habitats are still understudied. Accordingly, a survey on some known and other newly proposed morpho-functional traits was carried out in order to: determine if the morpho-functional diversity of nematodes mirrors their taxonomical diversity; and assess potential nematode adaptations to sediment type and hydrodynamic stress. Morpho-functional traits were investigated both singularly and together and showed significant differences related to these environmental factors. The greatest taxonomical and morpho-functional diversity was found in medium-coarse sand (M-CS) and at an intermedium energy level (IEL). The M-CS and IEL were probably richer in micro-habitats and subject to a low selective pressure, hosting nematodes with a wide range of adaptations. The mirroring of morpho-functional diversity with taxonomical diversity is crucial for the future growth of the use of nematodes in biomonitoring. This is because the study of their morpho-functional traits could reduce the level of work involved and the costs of any analyses.

Benthic freshwater nematode community dynamics under conditions of Tilapia aquaculture in Egypt

Studies of the influence of fish aquaculture on benthic freshwater nematode assemblages are scarce, but could provide a way of gauging environmental effects. The abundance and diversity of nematode assemblages in response to Oreochromis niloticus aquaculture were investigated in Kafr El-Sheikh Governorate, Egypt, from July to November 2014 under conditions of irrigation (reference), fish farm pond with high Tilapia density, and fish farm pond effluent canal without fish. The nematode genera Adoncholaimus, Punctodora, Labronema, Oncholaimus and Odontolaimus were present at all sites. Environmental factors were not related to nematode distribution patterns. Tilapia predation and/or disturbance may explain reduced nematode abundance, especially of the largest genera, Adoncholaimus, Punctodora and Labronema at the fish farm site. The absence of fish from the drainage site allowed intergeneric nematode competitive exclusion, benefitting the largest nematodes and reducing diversity indices.

Regional patterns among soil nematode assemblages in Australasian pastures and effects of management practices

Abundance, composition and diversity of nematode assemblages at 58 sites from five Australasian regions (New Zealand, South Australia, coastal southern Australia, New South Wales and Queensland) are analysed with particular reference to rainfall, pasture type and proportions of plant-, bacterial- and fungal-feeders. Nematode abundance was generally related to plant production or surrogates such as soil carbon concentration. Diversity was lowest in Queensland, where absolute abundance was lower than expected, given the carbon concentrations in the soil. The composition of the nematode community indicated that bacterial-mediated decomposition was more important in coastal southern Australia (winter-spring rainfall) than in northern New South Wales (summer-dominant rainfall). Within the southern region, the contribution of bacteria relative to fungi increased with sward legume content. Cephalobidae were the most abundant bacterial-feeders in every region. Across 11 non-irrigated New Zealand sites and the 40 Australian sites, Rhabditidae showed strong correlations with rainfall. Conversely, under drier conditions, fungal-feeding nematodes were more important, as expected where plant residues are less readily decomposed. While the low contribution of plant-feeding nematodes in coastal southern Australia may be related to sampling time, suppressive factors in the soil may have contributed. Simple cluster analysis placed 40 of the 58 sites into discrete regional clusters, but local climate and soil conditions, on both the ancient Australian and young New Zealand landscapes, explain other groupings. Impacts of elevated carbon dioxide and intensification of land management on nematode abundance and functional groups are also described.

Pressure plate studies to determine how moisture affects access of bacterial‐feeding nematodes to food in soil

SummaryNematode activity in the soil depends on the presence of free water. We conducted pressure plate experiments to understand better how soil matric potential and structural degradation affect the population growth of three bacterial‐feeding nematodes (Cephalobus, Pristionchus, Rhabditis). We took undisturbed cores from six soils (sand, silt loam and silty clay loam with four management regimes), and removed all fauna from them. Ten or 30 nematodes were added, and pressures corresponding to soil matric potentials of −10, −33, −50, −100 or −1500 kPa were applied for 35 days. The nematodes were then counted. Significant reproduction of all bacterial‐feeding nematodes occurred when the diameters of water‐filled pores were approximately 1 μm. This confirms observations using repacked soils and field manipulations. Only for Pristionchus did declining populations match the reduction in total soil porosity related to intensification of land use on the silty clay loam. We had not expected Cephalobus to have the fastest increase in population of the three nematodes in intact soil cores, and our evidence questions the relative importance given to the three nematode families in soil processes. The differing rates of population increase of the three nematodes in the various soils reflect both habitable pore space and trophic interactions. This suggests that the very diversity of nematode assemblages is crucial in the resilience of biological soil processes. That water‐filled pores as small as 1 μm provide suitable spaces for sizeable populations of bacterial‐feeding nematodes accords with the observed migration of infective juveniles of trichostrongylid nematodes and mermithids in water films on herbage. Our results imply that assessment of the role of nematodes in soil processes may be a key to the understanding of biological interactions in water films, and the selection pressures on nematode morphology.

Diversity of nematode assemblages along a Mediterranean deep-sea transect

Diversity of nematode assemblages along a Mediterranean deep-sea transect