Effects of ultraviolet radiation on the transmission process of an intertidal trematode parasite

The transmission of parasites takes place under exposure to a range of fluctuating environmental factors, one being the changing levels of solar ultraviolet radiation (UVR). Here, we investigated the effects of ecologically relevant levels of UVR on the transmission of the intertidal trematode Maritrema novaezealandensis from its first intermediate snail host (Zeacumantus subcarinatus) to its second intermediate amphipod host (Paracalliope novizealandiae). We assessed the output of parasite transmission stages (cercariae) from infected snail hosts, the survival and infectivity of cercariae, the susceptibility of amphipod hosts to infection (laboratory experiments) and the survival of infected and uninfected amphipod hosts (outdoor experiment) when exposed to photo-synthetically active radiation only (PAR, 400-700 nm; no UV), PAR+UVA (320-700 nm) or PAR+UVA+UVB (280-700 nm). Survival of cercariae and susceptibility of amphipods to infection were the only two steps significantly affected by UVR. Survival of cercariae decreased strongly in a dose-dependent manner, while susceptibility of amphipods increased after exposure to UVR for a prolonged period. Exposure to UVR thus negatively affects both the parasite and its amphipod host, and should therefore be considered an influential component in parasite transmission and host-parasite interactions in intertidal ecosystems.     

Resistance of an invasive gastropod to an indigenous trematode parasite in Lake Malawi

Successful establishment and spread of biological invaders may be promoted by the absence of population-regulating enemies such as pathogens, parasites or predators. This may come about when introduced taxa are missing enemies from their native habitats, or through immunity to enemies within invaded habitats. Here we provide field evidence that trematode parasites are absent in a highly invasive morph of the gastropod Melanoides tuberculata in Lake Malawi, and that the invasive morph is resistant to indigenous trematodes that castrate and induce gigantism in native M. tuberculata. Since helminth infections can strongly influence host population abundances in other host-parasite systems, this enemy release may have provided an advantage to the invasive morph in terms of reproductive capacity and survivorship.     

Responses of estuarine intertidal microphytobenthic algal assemblages to enhanced ultraviolet B radiation

As a result of ozone depletion, ground doses of ultraviolet B (UVB) radiation in the mid latitudes of the Northern Hemisphere have increased since the 1980s, and current predictions indicate no possible alleviation until at least post 2020. Mudflats and sandflats are important coastal-zone habitats, and support extensive biofilms of benthic microalgae (microphytobenthos). In intertidal situations, these assemblages are exposed to high levels of UVB radiation during periods of tidal exposure. Exposure of intertidal biofilms dominated by epipelic (mud-inhabiting) diatoms to 0, 0.18 or 0.35 W m⁻² UVB radiation for between 4 and 10 days resulted in no significant decreases in the maximum PSII quantum efficiency (F_v/F_m) throughout diel exposure periods. Although the quantum efficiency of electron transport (F_q′/F_m′) showed significant reductions early in some experiments, the major response was an increase in F_q′/F_m′ in UVB exposed biofilms. This increase in F_q′/F_m′ was suggestive of a protective vertical migration down into the sediment. Single-cell and whole biofilm fluorescence imaging demonstrated, for the first time, that motile diatoms are able to detect UVB radiation independently of UVA or photosynthetically active radiation (PAR) and migrate rapidly down (within 15 min) into the sediments to avoid it. This behavioural acclimation mechanism appears to prevent significant accumulation of UVB induced damage to the algae. UVB exposure had no significant effect of biofilm photosynthesis (measured by ¹⁴C carbon fixation), but did alter organic carbon allocation patterns, with significantly less new carbon allocated to intracellular storage (glucan) and extracellular colloidal carbohydrate fractions. Significant reductions in the sediment standing stocks of chlorophyll a (Chl a), colloidal carbohydrates, extracellular polymeric substances (EPS) were seen after 7 days of UVB exposure. This study showed that marine intertidal benthic diatoms use a behavioural strategy to avoid exposure to UVB and that this response is effective as a short-term protection mechanism against UVB damage. However, altered carbon allocation patterns feed forward over time into changes in biofilm biomass and sediment carbohydrate dynamics. This suggests that continual long-term exposure to UVB may impact on sediment carbon cycling and trophic interactions and on the stabilization of sediments by microalgal biofilms through their production of extracellular carbohydrates.     

长波紫外线辐射对脊椎动物的影响

臭氧层空洞的加剧使紫外辐射不断加强,造成的环境污染已经成为广为关注的问题,但大多数都集中在中波紫外线(UVB)的生物学作用及其与两栖动物衰减关系的研究,有关长波紫外线(UVA)对生物体损伤作用的研究却甚少。本文综述了近年来UVA对脊椎动物损伤的研究概况,从细胞结构、酶活性、遗传物质、膜结构以及免疫系统等方面阐述了UVA的损伤机理,并对低剂量辐射诱导兴奋效应对紫外损伤的保护作用进行了简要概述。最后分析和总结了关于UVA损伤研究所存在的问题及两栖动物作为实验用动物模型在研究紫外线损伤中的作用。     

Effects of ultraviolet radiation on human cutaneous nerve fibres

Due to an increasing number of skin diseases as a result of exposure to ultraviolet (UV) radiation, it is necessary to evaluate the effectiveness of new skin care formulations with broad-spectrum sunscreens.
Objectives:  This study aims to assess the status of nerve fibres in healthy human skin, to quantify effects of UV radiation on nerve endings, and to evaluate neuroprotective effects of new skin care formulations against UV exposure damage.
Methods:  Samples were obtained from 34 female patients enrolled for plastic surgery and were immediately treated (10 min) with three emulsions: Cream 1, Cream 2 (placebo) and a sunscreen with sun protection factor 15 (SPF15). Control samples and those treated with the cream emulsions were exposed to UVA and UVB for 60 min. Nerve fibres were identified by immunofluorescence using a monoclonal antibody (anti-human CD56/NCAM). Cell damage was assessed by image analysis.
Results:  Several cellular nervous structures were identified in the skin samples, including free nerve endings. UVA and UVB significantly decreased (40–60%) density of nerve endings in the control samples and those treated with placebo (Cream 2) or SPF15 (all P  < 0.001). Cream 1 completely blocked effects of UV radiation on nerve endings ( P  > 0.05 vs. control).
Conclusions:  Quantification of cell damage induced by UV radiation provides useful information for identification of new skin care compounds with neuroprotective properties.     

Effects of ultraviolet radiation on the membranes ofChara corallina

Summary The effects of 253.7 nm ultraviolet (UV) radiation on the membrane properties ofChara corallina have been studied. UV irradiation caused depolarization of the membrane potential (p.d.) and a decrease in membrane resistance. These effects were largely reversible with steady values being obtained within 40 minutes after the UV was turned off. The effects on ionic fluxes of Na⁺, K⁺ and Cl^– have also been studied using radioactive tracer techniques. The influxes were unchanged by irradiation. The chloride efflux was increased sevenfold during the irradiation period but recovered to the pre-irradiation value within 30 minutes after the irradiation period. The potassium efflux was also increased and reached a maximum 10 minutes after irradiation. The resting potential and the average depolarized p.d. reached during irradiation were in good agreement with those calculated from permeability coefficients indicated by the observed passive fluxes, using the Goldman equation for p.d. However, the plasmalemma resistance and its change due to irradiation did not match the values calculated from the same permeability coefficients used to estimate p.d. This disagreement, and an apparent imbalance in the charge transferred across the resting or irradiated plasmalemma, suggest the participation of another ion species as well as K⁺, Na⁺ and Cl^–.     

Effects of macroalgal mats on intertidal sandflats: an experimental study

The growth of green macroalgal mats is becoming increasingly common in many marine intertidal habitats. While the ecological effects of such growth has previously been experimentally investigated on mudflats, such experiments have rarely been performed on intertidal sandflats. This study investigated the ecological effects of macroalgal cover on a moderately exposed intertidal sandflat, Drum Sands, Firth of Forth, Scotland. Artificially implanted Enteromorpha prolifera (Müller) caused marked changes in the macrobenthos, together with significant changes in all the measured sediment variables. After 6 weeks, the weed significantly increased the macrofaunal diversity. The numbers of Pygospio elegans (Claparède) were significantly reduced under weed mats, while those of Capitella capitata (Fabricius), oligochaetes and gammarids increased. Percent water, organics and silt/clay contents, medium phi and sorting coefficient significantly increased in the sediments under weed mats which also became significantly more reduced between 1 and 8 cm depth. After 20 weeks, a macrofaunal community numerically dominated by C. capitata, with a significantly reduced diversity, was present under weed mats, while sediment variables were no longer significantly different from controls. The negative effect of E. prolifera on P. elegans was mainly due to larval filtering, suggesting that weed is likely to have detrimental effects on population maintenance of most species which rely on planktonic larval recruitment. These results are broadly similar to those obtained from algal manipulation experiments performed in much more sheltered, muddier environments. We suggest that a predictable deterioration in environmental quality results from the growth of macroalgal mats in soft-bottom habitats. However, the longer term effects of such algal growth are less predictable and depend upon the spatial distributions of the most abundant infaunal species and the spatial heterogeneity of weed mat establishment.     

Effects of ultraviolet radiation on corals and other coral reef organisms

The discovery of the importance of solar ultraviolet radiation (UVR) as a factor affecting the biology of coral reefs dates only to about 1980. Interest has heightened during the past five years owing to the demonstration of loss of stratospheric ozone through human activities. We have only begun to document gross, qualitative effects of UVR on coral reef organisms, usually in experiments comparing the biological response to the presence or absence of UVR through the use of UV-cutoff filters, or to varying levels of UVR in transplantation studies. Most such studies have not distinguished between the effects of UVA (320–400 nm) and those of UVB (290–320 nm), although in the context of global change involving stratospheric ozone loss, it is the latter wavelengths that are relevant. To date we have been addressing physiological and ecological questions, not yet attempting to evaluate quantitatively the impact of forecast increases in solar UVB penetration. Interacting and synergistic effects of UVR with increased temperature, pollutants, sedimentation, visible light, etc. have scarcely been studied but will be essential to understanding and predicting the fate of coral reefs under conditions of global change. Here we comprehensively review the effects of UVR on corals and other reef macroorganisms, mindful that although much is known of proximal effects, little of this knowledge is directly useful in making long-term predictions regarding the health of coral reefs. We conclude that even small anthropogenic increases in UVB levels will have sublethal physiological manifestations in corals and other reef organisms, but that this will have relatively small impact on the distribution of reef corals and coral reefs, perhaps affecting their minimum depths of occurrence.     

Measurements of microbial protection from ultraviolet radiation in polar terrestrial microhabitats

Biological dosimeters made from a monolayer of Bacillus subtilis spores were used to investigate the penetration of ultraviolet radiation into some widespread terrestrial microbial microhabitats at polar latitudes: at Mars Oasis (72°S) and Rothera Station (67°S) (UK) in the Antarctic (November 2000) and on Devon Island, Canadian High Arctic (75°N) (July 2000 and 2001). Layers of soil or dust of 𔘬 µm thickness, particularly in ice-free regions of the Arctic, could reduce UV exposure such that no inactivation of spores could be measured after 3 days. Control spores were killed in 24 h. Spores in artificial cryptoendolithic habitats with ~1 mm rock covering obtained a reduction of UV radiation-induced inactivation of at least 2 orders of magnitude. Hypolithic spores were protected against any inactivation for at least 4 days. Snow covers of between 5 and 15 cm thickness, depending on age and heterogeneity, attenuated UV radiation by an order of magnitude, although snow cover is seasonal and subject to climatic factors. These dosimetric data demonstrate that, except for microbes on the surface of soil grains, many terrestrial microbial communities are well protected from incident UV radiation by a variety of physical and biological coverings. This is in contrast to data reported for many polar aquatic microbial taxa, and might imply a greater robustness of terrestrial microbial communities against the effects of ozone depletion.     

Excision repair of ultraviolet radiation damage in toluene treated Escherichia coli

ATP independent excision repair of UV damage has been studied in $\text{E. coli}$ made permeable to nucleotides by treatment with toluene. In using this system, separation of the first step from the subsequent steps in the repair process is achieved. It was found that completion of repair is observed only in strains that have normal levels of DNA polymerase I.     

Effects of ultraviolet radiation on carotenoid-containing and albino strains of Neurospora crassa

To determine the influence of carotenoids on UV sensitivity of Neurospora crassa conidia, the dose-response curves of 3 albino strains were compared to that of the wild type. In a control experiment the genetic background effects were eliminated by irradiating the wild type in which carotenoid synthesis had been inhibited by β-ionone, and comparing the dose-response curve to that of untreated wild type. All strains used had similar γ-ray survival curves and nuclei per conidium which precluded differences in UV sensitivity due to morphological differences.The albinos and β-ionone-treated strains showed a greater sensitivity (mean LD50 4.35·10³ erg/mm²) to UV irradiation than the wild type (LD50 7.30·10³ erg/mm²).     

阳光紫外辐射对褐藻羊栖菜生长和光合作用的影响

为探讨经济褐藻羊栖菜对阳光紫外辐射变化的响应,我们在全波段阳光辐射(280－700 nm),去除UV-B辐射(320－700 nm)以及光合有效辐射PAR (400－700 nm)三种辐射条件下对其进行培养,测定了其光合作用与生长的变化。羊栖菜的生长是通过每两天测量一次藻体的湿重来测定的,光合放氧是用Clark型氧电极测定的,为了测定藻体叶绿素a和紫外吸收物质的含量,从250 nm到750 nm对羊栖菜的甲醇提取液进行扫描,叶绿素a的浓度用Porra的公式计算,紫外吸收物质的计算是根据Dunlap的方法先计算紫外吸收物质和叶绿素a的比率,然后乘以每单位藻体叶绿素a的含量。结果表明,当藻体接收较多的日辐射量时有较高的相对生长速率,当滤除UVR后,较高的太阳辐射也导致了较高的光合放氧。然而太阳紫外辐射能够抑制藻体的光合放氧和生长速率,降低叶绿素a的浓度,并且这种抑制作用随着辐射水平的升高而增强。此外,阳光紫外辐射也诱导产生了一定量的紫外吸收物质,但并不足以抵抗紫外辐射对藻体的伤害作用。     

Photobiology of natural populations of zooxanthellae from the sea anemone Aiptasia pallida: assessment of the host's role in protection against ultraviolet radiation

Natural populations of the sea anemone Aiptasia pallida containing endosymbiotic dinoflagellates were acclimated to different irradiance regimes, with and without ultraviolet radiation (UV). They showed a compensatory response in the amount of chlorophyll and the activities of enzymes responsible for detoxifying active species of oxygen that are produced by the interaction between visible or ultraviolet radiation and photosynthetically produced oxygen. Protection from active species of oxygen is essential to prevent the photooxidation of chlorophyll and the concomitant loss of productivity. Bulk analyses of chlorophyll showed differences between the populations exposed to varying irradiance regimes, but revealed no significant independent effect of UV. However, analysis by flow cytometry of the individual cells from treated populations did detect statistically significant differences in cell size and the amount of chlorophyll fluorescence per cell, which could be attributed to treatment with ultraviolet radiation. With flow cytometry we are able to detect the population variability that is undetectable by bulk measurements which is important in assessing the effects of environmental parameters in both symbiotic and free-living microalgae. Research using simultaneous measurements by flow cytometry could add considerable insight into the population dynamics of both zooxanthellae and host cells.