The Anhydrobiotic Potential of the Terrestrial NematodesPlectus parietinusandPlectus velox

Evolution of Life Cycles of Nematodes Parasitizing Woody Plants As a Result of Ecological and Phylogenetic Co-Adaptations with Hosts and Vectors

Fundamental aspects in the evolution of nematodes parasitizing woody plants are reviewed. (1) Nematode faunal lists of natural refugia are useful to predict the risks of opportunistic pathogens becoming true pathogens in the forest and park communities. (2) Nematode composition in natural refugia gives a chance to identify nematode antagonists of insect vectors of dangerous fungal and nematode infections, which can be potentially used as the biological agents for woody plants' protection. (3) Dauers in the ancestors of wood-inhabiting nematodes played a role as a survival stage in the detritus decomposition succession, and they later acquired the functions of dispersal and adaptations for transmission using insect vectors. (4) When inspecting wilted trees, it is necessary to use dauers for diagnostics, as sexually mature nematodes may be absent in tree tissues. (5) Plant parasitic nematodes originated from members of the detritus food web and retained a detritivorous phase in the life cycle as a part of the propagative generation. (6) Vectors in the life cycles of plant parasitic nematodes are inherited from the ancestral detritivorous nematode associations, rather than inserted in the dixenic life cycle of the 'nematode-fungus-plant' association. (7) Despite the significant difference in the duration of the nematode-tree and nematode-vector phases of the life cycle, the actual parasitic nematode specificity is dual: firstly to the vector and secondly to the natural host plant (as demonstrated in phytotests excluding a vector).

A novel nematode species from the Siberian permafrost shares adaptive mechanisms for cryptobiotic survival with C. elegans dauer larva

Some organisms in nature have developed the ability to enter a state of suspended metabolism called cryptobiosis when environmental conditions are unfavorable. This state-transition requires execution of a combination of genetic and biochemical pathways that enable the organism to survive for prolonged periods. Recently, nematode individuals have been reanimated from Siberian permafrost after remaining in cryptobiosis. Preliminary analysis indicates that these nematodes belong to the genera Panagrolaimus and Plectus. Here, we present precise radiocarbon dating indicating that the Panagrolaimus individuals have remained in cryptobiosis since the late Pleistocene (~46,000 years). Phylogenetic inference based on our genome assembly and a detailed morphological analysis demonstrate that they belong to an undescribed species, which we named Panagrolaimus kolymaensis. Comparative genome analysis revealed that the molecular toolkit for cryptobiosis in P. kolymaensis and in C. elegans is partly orthologous. We show that biochemical mechanisms employed by these two species to survive desiccation and freezing under laboratory conditions are similar. Our experimental evidence also reveals that C. elegans dauer larvae can remain viable for longer periods in suspended animation than previously reported. Altogether, our findings demonstrate that nematodes evolved mechanisms potentially allowing them to suspend life over geological time scales.

High-throughput mass spectrometry analysis revealed a role for glucosamine in potentiating recovery following desiccation stress in Chironomus

Desiccation tolerance is an essential survival trait, especially in tropical aquatic organisms that are vulnerable to severe challenges posed by hydroperiodicity patterns in their habitats, characterized by dehydration-rehydration cycles. Here, we report a novel role for glucosamine as a desiccation stress-responsive metabolite in the underexplored tropical aquatic midge, Chironomus ramosus. Using high- throughput liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) analysis, biochemical assays and gene expression studies, we confirmed that glucosamine was essential during the recovery phase in C. ramosus larvae. Additionally, we demonstrated that trehalose, a known stress-protectant was crucial during desiccation but did not offer any advantage to the larvae during recovery. Based on our findings, we emphasise on the collaborative interplay of glucosamine and trehalose in conferring overall resilience to desiccation stress and propose the involvement of the trehalose-chitin metabolic interface in insects as one of the stress-management strategies to potentiate recovery post desiccation through recruitment of glucosamine.

Life history traits of the free-living nematode, Plectus acuminatus Bastian, 1865, and responses to cadmium exposure

Free-living nematodes are ubiquitous and play an essential role in ecosystems. However, little is known about their standard life history traits (LHTs), which limits their inclusion in estimations of energy flows and carrying capacities of ecosystems, as well as in modelling population-level responses to toxicants. Thus, we used the hanging-drop method to measure LHTs of Plectus acuminatus with and without exposure to cadmium (2 mg l−1). In controls, the mean lifespan was 68 days and the maximum 114 days. Individuals laid eggs on average 19 days after hatching, while production of offspring peaked at 37 days. Plectus acuminatus individuals were very fertile, producing on average 848 juveniles. Population growth rate of 0.19 was estimated for the control cohort leading to an average population doubling time of 3.65 days. Exposure to cadmium reduced mean lifespan by 62% and affected reproduction as only 22% of individuals produced offspring, leading to a total fertility rate 85% lower than in controls.