Ultraviolet Radiation Tolerance Research Articles

Interspecific differences and ecological correlations of ultraviolet radiation tolerance in low- and high-altitude fishes

Ultraviolet radiation (UVR) is a ubiquitous environmental factor and with complex and diverse effects on organisms, and the UVR tolerance of species varies due to selection, adaptation and evolution. This study aimed to improve our understanding of the interspecific differences in UVR tolerance of fishes. First, we compared skin histology between high-altitude fishes and their low-altitude relatives. Second, we assessed the skin histological changes of 22 fish species after UVR exposure and quantified their damage levels. Finally, the factors affecting the difference in UVR tolerance among fishes were studied. Thin or absent scales was a common characteristic of high-altitude fishes in different taxonomic groups, but other skin structure parameters (the thickness of the dermis and epidermis, the size and number of mucous and club cells) did not show convergence. After UVR exposure, the size and number of mucous cells and club cells in the experimental fishes were generally reduced, but the changes in epidermal and dermal thickness varied among species. The change rata of melanin area was strong negatively correlated with the level of damage, indicating that increased melanin was helpful to reduce UVR damage. On the whole, the skin histological changes of high-altitude fishes after UVR exposure did not differ from those of low-altitude fishes. However, the epidermis and dermis of Gymnocypris eckloni and Oncorhynchus mykiss, which had the highest UVR tolerance, were nonpathologically thickened, indicating that they may contribute to UVR tolerance. There were significant interspecific differences in UVR tolerance among the experimental fishes, with high-altitude and cold water fishes showing stronger UVR tolerance. Interestingly, some low-altitude cold water fish (e.g., O. mykiss) also showed high UVR tolerance, suggesting that besides high-altitude adaptation, low-temperature adaptation also may play an important role in organismal adaptation to UVR.

Transcriptomic Effects of Acute Ultraviolet Radiation Exposure on Two Syntrichia Mosses.

Ultraviolet radiation (UVR) is a major environmental stressor for terrestrial plants. Here we investigated genetic responses to acute broadband UVR exposure in the highly desiccation-tolerant mosses Syntrichia caninervis and Syntrichia ruralis, using a comparative transcriptomics approach. We explored whether UVR protection is physiologically plastic and induced by UVR exposure, addressing the following questions: (1) What is the timeline of changes in the transcriptome with acute UVR exposure in these two species? (2) What genes are involved in the UVR response? and (3) How do the two species differ in their transcriptomic response to UVR? There were remarkable differences between the two species after 10 and 30 min of UVR exposure, including no overlap in significantly differentially abundant transcripts (DATs) after 10 min of UVR exposure and more than twice as many DATs for S. caninervis as there were for S. ruralis. Photosynthesis-related transcripts were involved in the response of S. ruralis to UVR, while membrane-related transcripts were indicated in the response of S. caninervis. In both species, transcripts involved in oxidative stress and those important for desiccation tolerance (such as late embryogenesis abundant genes and early light-inducible protein genes) were involved in response to UVR, suggesting possible roles in UVR tolerance and cross-talk with desiccation tolerance in these species. The results of this study suggest potential UVR-induced responses that may have roles outside of UVR tolerance, and that the response to URV is different in these two species, perhaps a reflection of adaptation to different environmental conditions.

Phenology of alpine zooplankton populations and the importance of lake ice-out

AbstractThe prolonged ice cover inherent to alpine lakes incurs unique challenges for aquatic life, which are compounded by recent shifts in the timing and duration of ice cover. To understand the responses of alpine zooplankton, we analyzed a decade (2009–2019) of open-water samples of Daphnia pulicaria and Hesperodiaptomus shoshone for growth, reproduction and ultraviolet radiation tolerance. Due to reproductive differences between taxa, we expected clonal cladocerans to exhibit a more rapid response to ice-cover changes relative to copepods dependent on sexual reproduction. For D. pulicaria, biomass and melanization were lowest after ice clearance and increased through summer, whereas fecundity was highest shortly after ice-off. For H. shoshone, biomass and fecundity peaked later but were generally less variable through time. Among years, ice clearance date varied by 49 days; years with earlier ice-out and a longer growing season supported higher D. pulicaria biomass and clutch sizes along with greater H. shoshone fecundity. While these large-bodied, stress tolerant zooplankton taxa were relatively resilient to phenological shifts during the observation period, continued losses of ice cover may create unfavorably warm conditions and facilitate invasion by montane species, emphasizing the value of long-term data in assessing future changes to these sensitive ecosystems.

UV-shielding and wavelength conversion by centric diatom nanopatterned frustules

Diatoms can represent the major component of phytoplankton and contribute massively to global primary production in the oceans. Over tens of millions of years they developed an intricate porous silica shell, the frustule, which ensures mechanical protection, sorting of nutrients from harmful agents, and optimization of light harvesting. Several groups of microalgae evolved different strategies of protection towards ultraviolet radiation (UVR), which is harmful for all living organisms mainly through the formation of dimeric photoproducts between adjacent pyrimidines in DNA. Even in presence of low concentrations of UV-absorbing compounds, several diatoms exhibit significant UVR tolerance. We here investigated the mechanisms involved in UVR screening by diatom silica investments focusing on single frustules of a planktonic centric diatom, Coscinodiscus wailesii, analyzing absorption by the silica matrix, diffraction by frustule ultrastructure and also UV conversion into photosynthetically active radiation exerted by nanostructured silica photoluminescence. We identified the defects and organic residuals incorporated in frustule silica matrix which mainly contribute to absorption; simulated and measured the spatial distribution of UVR transmitted by a single valve, finding that it is confined far away from the diatom valve itself; furthermore, we showed how UV-to-blue radiation conversion (which is particularly significant for photosynthetic productivity) is more efficient than other emission transitions in the visible spectral range.

Divergence in DNA photorepair efficiency among genotypes from contrasting UV radiation environments in nature.

Populations of organisms routinely face abiotic selection pressures, and a central goal of evolutionary biology is to understand the mechanistic underpinnings of adaptive phenotypes. Ultraviolet radiation (UVR) is one of earth's most pervasive environmental stressors, potentially damaging DNA in any organism exposed to solar radiation. We explored mechanisms underlying differential survival following UVR exposure in genotypes of the water flea Daphnia melanica derived from natural ponds of differing UVR intensity. The UVR tolerance of a D.melanica genotype from a high-UVR habitat depended on the presence of visible and UV-A light wavelengths necessary for photoenzymatic repair of DNA damage, a repair pathway widely shared across the tree of life. We then measured the acquisition and repair of cyclobutane pyrimidine dimers, the primary form of UVR-caused DNA damage, in D.melanica DNA following experimental UVR exposure. We demonstrate that genotypes from high-UVR habitats repair DNA damage faster than genotypes from low-UVR habitats in the presence of visible and UV-A radiation necessary for photoenzymatic repair, but not in dark treatments. Because differences in repair rate only occurred in the presence of visible and UV-A radiation, we conclude that differing rates of DNA repair, and therefore differential UVR tolerance, are a consequence of variation in photoenzymatic repair efficiency. We then rule out a simple gene expression hypothesis for the molecular basis of differing repair efficiency, as expression of the CPD photolyase gene photorepair did not differ among D.melanica lineages, in both the presence and absence of UVR.

Effects of UV radiation on optimum quantum yield and sunscreen contents in members of the genera Interfilum, Klebsormidium, Hormidiella and Entransia (Klebsormidiophyceae, Streptophyta)

Many members of the Klebsormidiophyceae typically occur in terrestrial habitats where they are exposed to ultraviolet radiation (UVR). To evaluate the extent of tolerance to this waveband, 32 strains of the genera Entransia, Hormidiella, Interfilum and Klebsormidium were exposed to identical artificial UVR. The respective response patterns were determined in terms of optimum quantum yield of PSII as well as the capability to synthesize and accumulate mycosporine-like amino acids (MAAs) as sunscreens. After exposure to UVR most of the investigated isolates of Hormidiella, Interfilum and Klebsormidium exhibited only a moderate or no decrease in optimum quantum yield. In contrast, both isolates of Entransia showed strong photoinhibition. These photosynthetic activity data are well reflected in the biochemical capability to synthesize MAAs. With the exception of both Entransia strains, where not even traces of MAAs could be detected, all other isolates of Hormidiella, Interfilum and Klebsormidium accumulated UV-absorbing compounds after UVR exposure. While Interfilum and Klebsormidium contained the same putative MAA with an absorption maximum at 324 nm, Hormidiella attenuata showed another putative MAA with an absorption maximum at 325 nm. In addition, both compounds exhibited different retention times during HPLC analysis, suggesting their chemical structure must be different. All data indicated a generally high UVR tolerance in Hormidiella, Interfilum and Klebsormidium which explains well their aeroterrestrial lifestyle.

Bioprocess of Kosa bioaerosols: Effect of ultraviolet radiation on airborne bacteria within Kosa (Asian dust)

Kosa (Asian dust) is a well-known weather phenomenon in which aerosols are carried by the westerly winds from inland China to East Asia. Recently, the frequency of this phenomenon and the extent of damage caused have been increasing. The airborne bacteria within Kosa are called Kosa bioaerosols. Kosa bioaerosols have affected ecosystems, human health and agricultural productivity in downwind areas. In order to develop a new and useful bacterial source and to identify the source region of Kosa bioaerosols, sampling, isolation, identification, measurement of ultraviolet (UV) radiation tolerance and experimental simulation of UV radiation conditions were performed during Kosa bioaerosol transportation. We sampled these bioaerosols using a Cessna 404 airplane and a bioaerosol sampler at an altitude of approximately 2900m over the Noto Peninsula on March 27, 2010. The bioaerosol particles were isolated and identified as Bacillus sp. BASZHR 1001. The results of the UV irradiation experiment showed that the UV radiation tolerance of Kosa bioaerosol bacteria was very high compared with that of a soil bacterium. Moreover, the UV radiation tolerance of Kosa bioaerosol spores was higher than that of soil bacterial spores. This suggested that Kosa bioaerosols are transported across the atmosphere as living spores. Similarly, by the experimental simulation of UV radiation conditions, the limited source region of this Kosa bioaerosol was found to be southern Russia and there was a possibility of transport from the Kosa source area.

Mechanisms of ultraviolet radiation tolerance in the freshwater snail Physa acuta

Identifying mechanisms of ultraviolet radiation (UVR) tolerance is an important step in understanding the direct and indirect effects of UVR exposure on aquatic organisms. We used laboratory exposure experiments and a solar exposure experiment to evaluate mechanisms of UVR tolerance in the freshwater snail, Physa acuta. Survival following short-wavelength UVB exposure was higher in the presence of simultaneous exposure to longer-wavelength UVA and visible light than with UVB alone, indicating that P. acuta possessed photoenzymatic repair. Survival also increased as a function of body size and shell thickness, suggesting that the shell provides photoprotection. Last, snails actively selected locations further below the water surface in the presence than in the absence of solar UVR, suggesting behavioral avoidance as another mechanism of UVR tolerance. These defense mechanisms can be influenced by environmental conditions, so effects of UVR exposure may vary widely among populations and will be strongest in systems with a combination of low temperature, high transparency, and low Ca concentrations.

The Uve1 Endonuclease Is Regulated by the White Collar Complex to Protect Cryptococcus neoformans from UV Damage

The pathogenic fungus Cryptococcus neoformans uses the Bwc1-Bwc2 photoreceptor complex to regulate mating in response to light, virulence and ultraviolet radiation tolerance. How the complex controls these functions is unclear. Here, we identify and characterize a gene in Cryptococcus, UVE1, whose mutation leads to a UV hypersensitive phenotype. The homologous gene in fission yeast Schizosaccharomyces pombe encodes an apurinic/apyrimidinic endonuclease acting in the UVDE-dependent excision repair (UVER) pathway. C. neoformans UVE1 complements a S. pombe uvde knockout strain. UVE1 is photoregulated in a Bwc1-dependent manner in Cryptococcus, and in Neurospora crassa and Phycomyces blakesleeanus that are species that represent two other major lineages in the fungi. Overexpression of UVE1 in bwc1 mutants rescues their UV sensitivity phenotype and gel mobility shift experiments show binding of Bwc2 to the UVE1 promoter, indicating that UVE1 is a direct downstream target for the Bwc1-Bwc2 complex. Uve1-GFP fusions localize to the mitochondria. Repair of UV-induced damage to the mitochondria is delayed in the uve1 mutant strain. Thus, in C. neoformans UVE1 is a key gene regulated in response to light that is responsible for tolerance to UV stress for protection of the mitochondrial genome.

Differences in Immune Defense Evasion of Selected Inbred Lines of Heterorhabditis Bacteriophora in Two White Grub Species.

We determined virulence of seven Heterorhabditis bacteriophora strain GPS11 inbred lines possessing superior infective juvenile longevity, and heat and ultra violet radiation tolerance against white grubs Popillia japonica and Cyclocephala borealis. At 1 and 2 weeks after treatment, inbred line A2 was significantly more virulent towards P. japonica compared to the parent strain GPS11 and inbred lines A7, A8, A12 and A21; and line A2 caused significantly higher C. borealis mortality than lines A6 and A12. Penetration, encapsulation and survival of two inbred lines, A2 and A12, that showed the highest and lowest virulence against both grub species were then assessed. There were no differences between the two lines for the total number of nematodes penetrated in either P. japonica or C. borealis within the first 24 h, but a significantly higher percentage of penetrated nematodes were alive in line A2 compared to the line A12 in both grub species. P. japonica immune response over time to hemocoel-injected nematodes of A2, A12 and the parent strain was further investigated. While all injected nematodes were encapsulated at 6 h post injection, non-encapsulated living nematodes were detected at 12 and 24 h post injection, showing the breakage out of encapsulation. A higher percentage of non-encapsulated living nematodes and a lower percentage of dead nematodes were found in line A2 as compared to the line A12 after 12 h post injection. These data suggest that virulence differences in the studied H. bacteriophora inbred lines are not due to differences in nematode penetration or recognition by the grub immune system, but are related to the ability of the infective juveniles to break out of encapsulation.

Ultraviolet radiation tolerance in hydrated and desiccated eutardigrades

So far, most studies on tardigrade resistance to extreme stresses have focused on their responses to several chemical and physical extremes, but there is still a paucity of data regarding the tardigrade responses to ultraviolet radiation. Considering also the future perspectives offered by space flights, we compared the biological responses of two eutardigrade species (Paramacrobiotus richtersi and Ramazzottius oberhaeuseri) to UV irradiation, alone or in combination with multiple stressors (temperature and air relative humidity) in two different physiological conditions (desiccated and hydrated states). Tardigrades were exposed to seven different UV doses (from 10.32 up to 87.72 kJ m−2) in a controlled climatic chamber. The results showed that active and anhydrobiotic tardigrades were able to withstand high doses of ultraviolet radiations. The survival rate of hydrated or desiccated specimens of both species was inversely related to the UV doses, with P. richtersi that better tolerated the increase of UV dose than R. oberhaeuseri. Surprisingly, the tolerance to physical and chemical extreme stresses is not an exclusive property of desiccated tardigrades; in certain environmental conditions (high air humidity level or low temperature), desiccated tardigrades have a lower or similar ability to withstand UV irradiation than hydrated ones. This represents a further demonstration of the uniqueness of this animal group in tolerating extreme stresses. In addition, we demonstrated that high temperatures have a strong impact on tardigrade survival during UV exposition both in hydrated and desiccated animals. La maggior parte degli studi sulla resistenza dei tardigradi agli stress estremi hanno portato ad analizzare la loro tolleranza a diversi stress chimici e fisici, ma molto poco è stato fatto sulla tolleranza dei tardigradi alle radiazioni ultraviolette. Considerando anche le future prospettive offerte dai voli spaziali, in questo lavoro abbiamo confrontato le risposte di esemplari essiccati (in anidrobiosi) o idratati (attivi) di due specie di eutardigradi (Paramacrobiotus richtersi e Ramazzottius oberhaeuseri) alle sole radiazioni ultraviolette (UV), o alla combinazione delle radiazioni UV con altri fattori di stress (temperatura e umidità relativa dell’aria, RH). I tardigradi sono stati esposti a sette diverse dosi di radiazioni UV (da 10.32 a 87.72 kJ m−2) in una camera climatica controllata. I risultati evidenziano che sia itardigradi idratati che quelli essiccati sono in grado di resistere ad elevate dosi di radiazioni ultraviolette. La percentuale di sopravvivenza degli esemplari attivi o essiccati di entrambe le specie è inversamente proporzionale alle dosi di radiazione UV somministrate, anche se P. richtersiè risultato più resistente di R. oberhaeuseri. Sorprendentemente, è emerso che la tolleranza a stress chimico-fisici estremi non è una proprietà esclusiva dei tardigradi essiccati, tanto che in alcune condizioni ambientali (alti livelli di RH o basse temperature) i tardigradi essiccati resistono meno, o in ugual misura, alle radiazioni UV rispetto a quelli attivi. Ciò rappresenta un’ulteriore dimostrazione dell’unicità di questo gruppo animale nella tolleranza agli stress estremi. Inoltre, abbiamo dimostrato che le alte temperature hanno un forte impatto sulla sopravvivenza dei tardigradi attivi ed essiccati durante l’esposizione alle radiazioni ultraviolette.

Growth Parameter Components of Adaptive Specificity during Experimental Evolution of the UVR-Inducible Mutator Pseudomonas cichorii 302959

BackgroundMutagenic DNA repair (MDR) transiently increases mutation rate through the activation of low-fidelity repair polymerases in response to specific, DNA-damaging environmental stress conditions such as ultraviolet radiation (UVR) exposure. These repair polymerases also confer UVR tolerance, intimately linking mutability and survival in bacteria that colone habitats subject to regular UVR exposure.Methodology/Principal FindingsHere, we investigate adaptive specificity in experimental lineages of the highly UVR-mutable epiphytic plant pathogen Pseudomonas cichorii 302959. Relative fitness measurements of isolates and population samples from replicate lineages indicated that adaptive improvements emerged early in all lineages of our evolution experiment and specific increases in relative fitness correlated with distinct improvements in doubling and lag times. Adaptive improvements gained under UVR and non-UVR conditions were acquired preferentially, and differentially contributed to relative fitness under varied growth conditions.ConclusionsThese results support our earlier observations that MDR activation may contribute to gains in relative fitness without impeding normal patterns of adaptive specificity in P. cichorii 302959.

Effects of sunscreen on human skin’s ultraviolet radiation tolerance

To observe the alteration ultraviolet radiation (UVR) of skin's tolerance after its exposure to the small dose of UVR under the protection of sunscreen. Eleven subjects who applied sunscreen were exposed to 0.75 dose minimal persistent pigment darkening (MPPD) and minimal erythema dose (MED) by the Phototherapy Unit for 4 weeks. Each week their MPPDs and MEDs were measured by solar simulator. Meanwhile, SPECTCOLOMETER® and VISIOSCAN VC98® were used to detect the test areas and control areas. The values of MPPD and MED increased significantly after the exposure to UVR. But there were no visible changes on the surface of skin's texture. With the protection of sunscreen, the UVR tolerance of skin was greatly increased after the skin's exposure to the small dose UV.

Photosensitivity Disorders Are No Picnic

Photosensitivity disorders that involve low tolerance to ultraviolet radiation are usually chronic. Moderate and severe conditions require adjustments

Adaptation to local ultraviolet radiation conditions among neighbouringDaphniapopulations

Understanding the historical processes that generated current patterns of phenotypic diversity in nature is particularly challenging in subdivided populations. Populations often exhibit heritable genetic differences that correlate with environmental variables, but the non-independence among neighbouring populations complicates statistical inference of adaptation. To understand the relative influence of adaptive and non-adaptive processes in generating phenotypes requires joint evaluation of genetic and phenotypic divergence in an integrated and statistically appropriate analysis. We investigated phenotypic divergence, population-genetic structure and potential fitness trade-offs in populations of Daphnia melanica inhabiting neighbouring subalpine ponds of widely differing transparency to ultraviolet radiation (UVR). Using a combination of experimental, population-genetic and statistical techniques, we separated the effects of shared population ancestry and environmental variables in predicting phenotypic divergence among populations. We found that native water transparency significantly predicted divergence in phenotypes among populations even after accounting for significant population structure. This result demonstrates that environmental factors such as UVR can at least partially account for phenotypic divergence. However, a lack of evidence for a hypothesized trade-off between UVR tolerance and growth rates in the absence of UVR prevents us from ruling out the possibility that non-adaptive processes are partially responsible for phenotypic differentiation in this system.

Long-Term Effects of Inducible Mutagenic DNA Repair on Relative Fitness and Phenotypic Diversification in Pseudomonas cichorii 302959

Mutagenic DNA repair (MDR) employs low-fidelity DNA polymerases capable of replicating past DNA lesions resulting from exposure to high-energy ultraviolet radiation (UVR). MDR confers UVR tolerance and activation initiates a transient mutator phenotype that may provide opportunities for adaptation. To investigate the potential role of MDR in adaptation, we have propagated parallel lineages of the highly mutable epiphytic plant pathogen Pseudomonas cichorii 302959 with daily UVR activation (UVR lineages) for approximately 500 generations. Here we examine those lineages through the measurement of relative fitness and observation of distinct colony morphotypes that emerged. Isolates and population samples from UVR lineages displayed gains in fitness relative to the ancestor despite increased rates of inducible mutation to rifampicin resistance. Regular activation of MDR resulted in the maintenance of genetic diversity within UVR lineages, including the reproducible diversification and coexistence of "round" and "fuzzy" colony morphotypes. These results suggest that inducible mutability may present a reasonable strategy for adaptive evolution in stressful environments by contributing to gains in relative fitness and diversification.

Increased tolerance to ultraviolet radiation (UVR) and cotolerance to cadmium in UVR‐acclimatized freshwater periphyton

We studied the long‐term acclimatization of freshwater periphyton communities exposed to low and high ultraviolet radiation (UVR) intensities that simulate UVR doses received by lowland and high‐mountain streams of central Europe. To assess changes induced by UVR, we compared the community structure (species and biomass), function (photosynthetic yield), and tolerance to UVR and cadmium of periphyton growing in microcosms (artificial channels). On the basis of the rationale behind the pollution‐induced community tolerance concept, we expected that an increase in UVR tolerance would be through the replacement of more sensitive taxa by more tolerant taxa. After 38 d of exposure, periphyton in the high‐UVR treatment was dominated by Cyanobacteria, whereas diatoms dominated periphyton in the low‐UVR treatment. Concomitantly, the high‐UVR community increased its tolerance to UVR and showed cotolerance to cadmium (Cd). Structural changes contributing to this increased tolerance included an increase in UVR‐absorbing compounds, and the formation of cell aggregates that increased self shading. Induction of antioxidant enzymes after UVR and Cd exposure might be involved as defense mechanisms against oxidative stress. These changes reduced the exposure and effects of UVR, resulting in the protection of photosynthesis (high‐UVR photosynthetic yield was unaffected). A fivefold reduction in chlorophyll a in the high‐UVR treatment suggested that acclimatization had high metabolic costs. Additional experiments showed that even though biomass accrual offered some protection against UVR and Cd, the community changes experienced by the high‐UVR community contributed the most to UVR tolerance. Periphyton exposed to high UVR may experience simultaneous positive (tolerance to UVR and cotolerance to Cd) and negative effects (biomass reduction can increase accessibility by toxicants).

Dynamics of short-term acclimation to UV radiation in marine diatoms

In order to investigate the dynamics of the acclimation of marine diatoms to ultraviolet radiation (UVR), Amphora coffeaeformis, Odontella aurita and Skeletonema costatum were exposed for 5 h per day to a combination of UVA and UVB (UVBR/UVAR ratio 4.5%) with a total UVR daily dose of 110 kJ m −2, which is equivalent to that observed in the natural environment. This treatment was applied in the middle of the photoperiod and was repeated on five successive days. During the UVR treatment, chlorophyll fluorescence parameters were monitored, damage and repair constants were calculated from effective quantum yield values ( ϕ PSII), and rapid light curves (electron transport rate versus irradiance curves using short light steps of different intensity) were plotted to determine the maximum relative electron transport rate (rETR max) and maximum light use efficiency ( α). In all species the growth rate was lower than control from day 1–3, but increased thereafter, except for S. costatum. The cellular chlorophyll a content increased significantly with repeated daily exposure to UVR for A. coffeaeformis only. In all species, the fluorescence parameters ( F m, the maximum fluorescence level measured in the dark, ϕ PSII, rETR max and α) decreased during UVR exposure, in contrast to F 0 (the minimum fluorescence level measured in the dark). The response to UVR stress was species-specific. S. costatum was very sensitive, and failed to survive for more than three days, whereas A. coffeaeformis and O. aurita were able to acclimate to UVR stress. These two species used different strategies. In A. coffeaeformis, the repair constant was lower than the damage constant, but ϕ PSII values returned to baseline values at the beginning of each experimental day, indicating that an effective active recovery process occurred after stress. In O. aurita, the repair processes took place during the stress, and could account for the UVR tolerance of this species.

Storage temperature influences desiccation and ultra violet radiation tolerance of entomopathogenic nematodes

1. The effect of cold (5 °C) and warm (35 °C) storage on desiccation tolerance of cold-adapted Steinernema feltiae, intermediate S. carpocapsae and warm-adapted S. riobrave was evaluated at 5 and 35 °C. 2. Desiccation survival of all three species at 5 °C was enhanced by both the cold and warm storage. At 35 °C, desiccation survival of S. feltiae and S. riobrave was enhanced by only warm storage and of S. carpocapsae by only cold storage. 3. When desiccated at 5 °C, both warm and cold stored S. carpocapsae and S. feltiae, and the cold stored S. riobrave maintained significantly higher original virulence against Galleria mellonella larvae than cohorts stored at culture temperature. When desiccated at 35 °C, both warm and cold stored S. riobrave, and warm stored S. carpocapsae and S. feltiae maintained significantly higher original virulence than cohorts stored at culture temperature. 4. After 3 h exposure to ultra violet (UV) radiation stress at 340 nm, the warm and cold stored S. carpocapsae and S. riobrave maintained significantly higher original virulence than cohorts stored at culture temperature. The virulence of UV stressed S. feltiae was unaffected by storage temperature. 5. Trehalose content of both warm and cold stored S. feltiae, cold stored S. carpocapsae and warm stored S. riobrave was positively correlated with their desiccation survival at 5 and 35 °C. Trehalose content was also positively correlated with the virulence of both warm and cold stored S. carpocapsae, and warm stored S. riobrave following exposure to UV stress.

Developmental differences and a test for reciprocity in the tolerance of Chaoborus punctipennis larvae to ultraviolet radiation

We estimated the ultraviolet radiation (UVR) tolerance of Chaoborus punctipennis in five 2- to 4-day in situ experiments conducted with third and fourth instar larvae at 0.25, 1.25, 3.0, and 5.0 m in Ruth Roy Lake, a lake with low dissolved organic carbon levels (0.2 mg·L–1). UVR tolerance increased with larval age. Third and late fourth instar LD50 (median lethal dose) ranged from 52.3 to 62.2 J·cm–2 and from 82.4 to 119.6 J·cm–2, respectively, among the four depths. Reciprocity held for UVR exposure down to 5.0 m, i.e., toxicity was independent of dose rate. At any given depth, the LT50 (median lethal time) increased with larval stage, but even at 5.0 m, third and late fourth instars died in less than 10 and 20 h, respectively, under sunny skies. These results suggest that Chaoborus abundance and distribution might be affected by UVR, especially in clear lakes. If UVR levels continue to increase in some lakes because of stratospheric ozone loss and climate change, we predict that UVR damage to Chaoborus will increase in the future, thereby affecting trophic interactions in temperate freshwater food webs.