Trichoderma infection of limno-terrestrial tardigrades.

Interactions between fungi and tardigrades have scarcely been described. The few studies that address such relationships suggest a primarily parasitic nature for various fungal taxa, including the infectious chytridiomycetes. The aim of this study was to determine the identity of a fungus growing on a tardigrade of the genus Diaforobiotus and if it could infect other tardigrade genera. Using morphological analysis and ITS barcoding, we identified a mold isolate belonging to the Trichoderma harzianum species complex and found that it infected Diaforobiotus tardigrades, as well as animals in the eutardigrade genus Milnesium, and heterotardigrade genus Viridiscus.

An evaluation of thermal tolerance in six tardigrade species in an active and dry state.

Tardigrades are known for their ability to survive extreme conditions. Reports indicate that tardigrade thermal tolerance is enhanced in the desiccated state; however, these reports have almost always used a single tardigrade species and drying/heating methods vary between studies. Using six different species of tardigrades we confirm that desiccation enhances thermal tolerance in tardigrades. Furthermore, we show that differences in thermal tolerance exist between tardigrade species both when hydrated and desiccated. While Viridiscus viridianus survives the highest temperatures in the hydrated state of any species tested here, under hydrated conditions, the thermal tolerance of V. viridianus is restricted to an acute transient stress. Furthermore, unlike other stresses, such as desiccation, where mild initial exposure preconditions some species to survive subsequent harsher treatment, for V. viridianus exposure to mild thermal stress in the hydrated state does not confer protection to harsher heating. Our results suggest that while tardigrades have the capacity to tolerate mild thermal stress while hydrated, survival of high temperatures in a desiccated state is a by-product of tardigrades' ability to survive desiccation.

Green armoured tardigrades (Echiniscidae: Viridiscus), including a new species from the Southern Nearctic, exemplify problems with tardigrade variability research.

Ranges of tardigrade intraspecific and interspecific variability are not precisely defined, both in terms of morphology and genetics, rendering descriptions of new taxa a cumbersome task. This contribution enhances the morphological and molecular dataset available for the heterotardigrade genus Viridiscus by supplying new information on Southern Nearctic populations of V. perviridis, V. viridianus, and a new species from Tennessee. We demonstrate that, putting aside already well-documented cases of significant variability in chaetotaxy, the dorsal plate sculpturing and other useful diagnostic characters, such as morphology of clavae and pedal platelets, may also be more phenotypically plastic characters at the species level than previously assumed. As a result of our integrative analyses, V. viridianus is redescribed, V. celatus sp. nov. described, and V. clavispinosus designated as nomen inquirendum, and its junior synonymy with regard to V. viridianus suggested. Morphs of three Viridiscus species (V. perviridis, V. viridianus, and V. viridissimus) are depicted, and the implications for general echiniscid taxonomy are drawn. We emphasise that taxonomic conclusions reached solely through morphological or molecular analyses lead to a distorted view on tardigrade α-diversity.