Thermal acclimation of locomotor performance in tadpoles of the frog Limnodynastes peronii

Previous analyses of thermal acclimation of locomotor performance in amphibians have only examined the adult life history stage and indicate that the locomotor system is unable to undergo acclimatory changes to temperature. In this study, we examined the ability of tadpoles of the striped marsh frog (Limnodynastes peronii) to acclimate their locomotor system by exposing them to either 10 °C or 24 °C for 6 weeks and testing their burst swimming performance at 10, 24, and 34 °C. At the test temperature of 10 °C, maximum velocity (U_max) of the 10 °C-acclimated tadpoles was 47% greater and maximum acceleration (A_max) 53% greater than the 24 °C-acclimated animals. At 24 °C, U_max was 16% greater in the 10 °C-acclimation group, while there was no significant difference in A_max or the time taken to reach U_max (T-U_max). At 34 °C, there was no difference between the acclimation groups in either U_max or A_max, however T-U_max was 36% faster in the 24 °C-acclimation group. This is the first study to report an amphibian (larva or adult) possessing the capacity to compensate for cool temperatures by thermal acclimation of locomotor performance. To determine whether acclimation period affected the magnitude of the acclimatory response, we also acclimated tadpoles of L. peronii to 10 °C for 8 months and compared their swimming performance with tadpoles acclimated to 10 °C for 6 weeks. At the test temperatures of 24 °C and 34 °C, U_max and A_max were significantly slower in the tadpoles acclimated to 10 °C for 8 months. At 10 °C, T-U_max was 40% faster in the 8-month group, while there were no differences in either U_max or A_max. Although locomotor performance was enhanced at 10 °C by a longer acclimation period, this was at the expense of performance at higher temperatures. Accepted: 25 June 1999     

Biochemical acclimation of metabolic enzymes in response to lowered temperature in tadpoles of Limnodynastes peronii

We measured the rate at which the metabolic enzymes lactate dehydrogenase (LDH), citrate synthase (CS), and cytochrome c oxidase (CCO) acclimate in the response to lowered temperature in the axial muscle of tadpoles of Limnodynastes peronii (Anura: Myobatrachidae) over 6 weeks. In addition, we measured growth rates of the tadpoles kept at both temperatures and examined the activities of these enzymes in the liver tissue of the control group and cold-acclimated group at the end of the experiment. We found that LDH acclimates in axial muscle; the differences between the control and cold-acclimated group became apparent after 21 days. After 42 days, the activity of LDH in axial muscle in the cold-acclimated group was 30% greater than the control group. Growth rates were maintained at 0.7 mm/week within both treatments despite the 10 degrees C difference in temperature between experimental groups. Both LDH and CS were increased in activity in the liver (5 and 1.3 times greater, respectively, in the cold-acclimated group). The thermal sensitivity (Q(10)) of LDH was between 20 and 30 degrees C in the cold-acclimated group (1.2+/-0.01) when compared to the control group (1.6+/-0.15). The rate at which acclimation in this species occurs is appropriate for seasonal changes in temperature, and these animals may not be able to respond to a rapid drop in temperature.     

Ecological modulation of environmental stress: interactions between ultraviolet radiation, epibiotic snail embryos, plants and herbivores

1. The distribution of egg masses of the freshwater snails Lymnaea stagnalis and Planorbarius corneus on the undersides of water lily leaves (e.g. Nuphar lutea) is related to the prevalence of the leaf-mining beetle Galerucella nymphaeae. 2. When given the choice, Planorbarius significantly avoids leaves that were infested by the mining beetle. Conversely, Lymnaea did not discriminate against mined leaves. 3. Intact Nuphar leaves block over 95% of incident ultraviolet radiation. Yet, ultraviolet transmission reaches almost 100% under beetle mining scars. These are several times wider than snail embryos. 4. When exposed to natural sunlight, Lymnaea embryos proved to be resistant to ambient ultraviolet, while Planorbarius embryos were rapidly killed. Thus, one selective advantage of Planorbarius discrimination against mined leaves when depositing its eggs could be the avoidance of ultraviolet radiation passing through mining scars. 5. Other mining-related modifications of the leaves, reduced area, decreased longevity, altered aufwuchs (i.e. biofilm and epibionts) are discussed but seem less relevant for the oviposition preference of Planorbarius. 6. The discriminatory behaviour of this snail species was triggered by water-borne cues emitted by the damaged leaf, not by the eggs or larvae of the beetle. 7. This study illustrates how environmental stress on a given species, ultraviolet radiation in this case, can be ecologically buffered (shading by Nuphar) or enhanced (reduction of Nuphar shading through beetle mining) by associated species. It highlights how the impact of a given stress depends on the identity of the target species as well as on the identity and role of other species in the community.     

Risk of predation enhances the lethal effects of UV‐B in amphibians

Amphibian declines are a prominent part of the global biodiversity crisis and have received special consideration because they have occurred relatively recently, on a global scale, and in seemingly pristine habitats where no obvious anthropogenic cause is apparent. Although several causes for declines have been implicated, the isolation of a singular cause has proven elusive. Consequently, it has been hypothesized that complex interactions between multiple environmental stressors, particularly those associated with global change, may be responsible. Increasing ultraviolet‐B radiation (UV‐B) associated with stratospheric ozone depletion is one such stressor that has received considerable attention. UV‐B causes enhanced lethal effects when combined with other factors such as aquatic pH, contaminants, temperature and pathogens, but little is known of how UV‐B interacts with pervasive biological stressors, such as risk of predation. We exposed Limnodynastes peronii tadpoles to UV‐B and predatory chemical cues in a controlled laboratory experiment to determine their independent and interactive effects on survival and morphology. We show that UV‐B and risk of predation interact synergistically to enhance mortality above the additive effects of the independent stressors, and that exposure to UV‐B affects the ability of tadpoles to morphologically respond to predatory chemical cues (i.e. predator‐induced phenotypic plasticity), which has implications for their survival in an environment with predators. This highlights the importance of considering both anthropogenic and naturally occurring stressors when examining the underlying causes of amphibian declines.     

Survivorship, development, and DNA damage in echinoderm embryos and larvae exposed to ultraviolet radiation (290-400 nm)

Laboratory experiments utilizing ecologically relevant irradiances of ultraviolet radiation (UVR) known to occur in shallow Gulf of Maine waters were conducted on the planktonic embryos and larvae of two common benthic echinoids; the green sea urchin Strongylocentrotus droebachiensis and the sand dollar Echinarachnius parma. Significant decreases in survivorship were observed in freshly fertilized embryos of both species with greater mortality in E. parma that was associated with the absence of UVR-absorbing compounds, the mycosporine-like amino acids. Experiments on blastula, gastrula, and prism larval stages of S. droebachiensis also showed significant decreases in survivorship, delays in development, and abnormal embryos and larvae associated with exposure to UVR. Additionally, all developmental stages of S. droebachiensis experimentally exposed to UVR resulted in significant increases in DNA damage, measured as cyclobutane pyrimidine dimer photoproducts. The observed delays in early cleavage and subsequent developmental stages for S. droebachiensis are correlated with DNA damage. It is postulated that cell cycle arrest at critical checkpoints after DNA damage, mediated by a suite of cell cycle genes, is a component of the observed UVR induced developmental delays.     

紫外辐射增加对植物生长及某些生理代谢的影响

本文就紫外线辐射增加对植物生长发育、生理特性和作物产量等方面的影响进行了论述。     

A test of the effect of supplemental UV-B radiation on the common frog, Rana temporaria L., during embryonic development

The release of certain man-made chemicals has led to recurrent, seasonal destruction of ozone in the upper atmosphere, allowing more solar radiation in the UV-B waveband to reach the Earth. Consequently, many amphibians may suffer increased exposure to UV-B at various stages in their lives. Embryonic stages of species which spawn in the spring, in shallow, open water, are at high risk of increased exposure. We exposed newly fertilized eggs of one such species, Rana temporaria L., to sunlight with and without supplemental UV-B. We used outdoor arrays of lamps to simulate the increase in UV-B which might result from previously documented ozone depletion. From immediately after fertilization to when hatchlings began feeding, ambient solar UV-B, weighted for DNA-damaging potential, was supplemented by ≈ 81% in 1995 and 113% in 1996. These levels of supplementation approximated the increase in solar UV-B expected to result from losses of 21% and 25%, respectively, of the total amount of ozone in the atmospheric column, relative to pre-ozone-depletion values. We found no evidence that these additions of UV-B radiation increased the incidence of mortality or overt developmental abnormality among embryos. We stress the need for appropriate dosimetry in studies of effects of UV-B on organisms.     

Survival of human metallothionein-2 transplastomic Chlamydomonas reinhardtii to ultraviolet B exposure

Solar ultraviolet (UV) radiation has a great influence on green organisms,especially planktonlike Chlamydomonas.A human metallothionein-2 gene,which is generally considered to have an anti-radiationfunction by its coding product,was transferred into the chloroplast genome of Chlamydomonas reinhardtii.To dynamically measure the UV effects on Chlamydomonas cells grown in liquid tris-acetate-phosphatemedium,a new method was developed based on the relationship between the chlorophyll content of an algalculture and its absorbance at 570 nm after the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromideassay.In this experiment,both the wild-type and the transplastomic C.reinhardtii ceils were cultivated in 96-well microplates containing liquid tris-acetate-phosphate medium in the absence or presence of zinc,copper,cadmium and cysteine.The transgenic C.reinhardtii showed a higher resistance than wild-type to UV-Bexposure under all the examined conditions.Metals in the medium had positive impacts on both types of cells,but had significant influence only on the transplastomic cells.However,the high cell viability of the trans-genie alga at the end of the 8 h UV-B treatment disappeared after a 20-h recovery culture.Cysteine did notprotect cells from UV-B damage,but clearly enhanced the growth of both wild-type and transgenic C.reinhardtii.     

Biological weighting functions for DNA damage in sea urchin embryos exposed to ultraviolet radiation

Laboratory experiments examining the effects of ultraviolet radiation (UVR, 290-400 nm) on DNA damage were carried out using the embryos of three species of sea urchins from different habitats; Strongylocentrotus droebachiensis from the Gulf of Maine, Sterechinus neumayeri from the Antarctic, and Evechinus chloroticus from New Zealand. All three species exhibited significant amounts of accumulated DNA damage, measured as cyclobutane pyrimidine dimers (CPD) photoproducts, when exposed to UVR in the laboratory. Biological weighting functions (BWFs) revealed that S. neumayeri has significantly higher sensitivity to UVR-induced DNA damage across most of the UVR spectrum compared to the other two species, and all species were observed to have weightings in the ultraviolet-A (UVA, 320-400 nm) portion of the spectrum. The increased sensitivity to ultraviolet-B (290-320 nm) and UVA in S. neumayeri is correlated with the lowest concentration of UVR absorbing compounds observed in the embryos of the three species of urchin used in this study. Sea urchin embryos and larvae in the respective habitats of the species tested are known to occur within 5 m of the surface of the ocean where both UVB and UVA wavelengths occur. Solar irradiances of UVR at a depth of 5 m, weighted using the urchin DNA damage BWFs, show that E. chloroticus receives the greatest amount of biologically effective UVR despite having the lowest wavelength dependent weightings for DNA damage when compared to the other two species.     

Effects of ultraviolet radiation on the eggs of landlocked Galaxias maculatus (Galaxiidae, Pisces) in northwestern Patagonia

• 1 Ultraviolet radiation (UVR) damages early life stages of several fish species. Galaxias maculatus is a small catadromous fish, with landlocked forms occurring in many lakes within the Nahuel Huapi National Park (Patagonia, Argentina). In this work, the vulnerability of G. maculatus eggs exposed to both natural and artificial UVR was investigated in relation to water transparency.
• 2 Field experiments were performed in two lakes differing in UVR attenuation. Galaxias maculatus eggs were exposed to in situ levels of UVR in quartz tubes incubated at various depths. For laboratory experiments, the eggs were exposed to five levels of artificial UVB radiation.
• 3 Exposure to natural UVR causes various degrees of egg mortality depending on water transparency and incubation depth. In the less transparent lake (K_d320 = 3.08 m^‐1), almost complete mortality was observed near the surface. At a depth of 43 cm the observed mortality was only 22%, but was still significantly different from the dark control. In the most transparent lake (K_d320 = 0.438 m^‐1), almost total mortality was observed in tubes incubated at 2.56 m or shallower. A gradual decline in mortality was recorded from that depth to 3.78 m where the values approached those in the dark control treatments.
• 4 A monotonic relationship between mortality and UV exposure could be observed both in field and laboratory experiments. Using the results from field incubations, a LD₅₀ of 2.5 J cm^‐2 nm^‐1 was estimated. In a few mountain lakes, this value would be exceeded even if the eggs were laid at the maximum depth of the lake. Thus UVR seems a sufficient cause to explain the absence of G. maculatus populations in some mountain lakes. For most lakes, however, UVR is probably one of several important environmental factors, which together determine the habitat suitability.

     

Effects of solar ultraviolet radiation on the periphyton community in lotic systems: comparison of attached algae and bacteria during their development

The effects of solar ultraviolet radiation (UVR) on the development of a periphyton community were studied in an outdoor artificial stream apparatus. Algal biomass, species composition, and bacterial cell density were measured under full sunlight and non-UVR (photosynthetically active radiation [PAR]-only) conditions. Attachment of algae was detected on days 6–9. Although the chlorophyll-a concentration under non-UVR conditions was 2–4 times that under full sunlight (PAR + UVR) throughout the experiment, neither net algal growth rate nor species composition differed significantly between the two light conditions. The relative carotenoid pigment contents of attached algae in the PAR + UVR condition were 1.1–1.3 times those in the non-UVR condition. Rates of increase of bacterial cell densities under the PAR + UVR condition were depressed by solar UVR for the first few days, although there were no apparent differences in the rates of increase between the light conditions later in the experiment. The small effect of UVR on the development of this periphyton community may be attributable to low UV flux at this study site and to the experimental conditions under which the algae were kept: a high physiological state with high nutrient conditions. Attached bacteria and algae that colonize substrata first are likely to be sensitive to solar UVR, and the negative effects of UVR are mitigated by the development of a periphyton community.     

Effect of solar ultraviolet radiation on survival of krill larvae and copepods in Antarctic Ocean

The effect of solar ultraviolet radiation on the survival rate of Antarctic zooplankton was examined in February–March in 2002. We investigated survival rate of calyptopis larvae of Euphausia superba and late copepodite stages (IV and V) of large dominant calanoid species, Calanoides acutus and Calanus propinquus reared in quartz jars with three different radiation regimes (total radiation, exclusion of UVB, exclusion of UVA and UVB) and a dark control. The survival rates of the krill larvae decreased after 3 days from start of the experiment, being below 50% at 4 days in the treatments with total radiation and exclusion of UVB, although most individuals could survive until the end of the experiments in the treatments with exclusion of both UVA and UVB and dark control. The calanoid juveniles showed almost same pattern of survival curves as the krill larvae did, but survived slightly longer. Although >10% of surface UVA radiation at 340 and 380 nm penetrated down to 30 m, both C. acutus and C. propinquus were mostly distributed above 20 m. Surface swarm of the krill larvae can be often recognized in the previous studies. These results suggest that not only solar UVB but also UVA radiation potentially lower the survival rate of Antarctic zooplankton at depth less than 20 m.     

Transition temperatures in the sensitivity of escherichia coli B/r to lysozyme

Lysozyme attacked Escherichia coli B/r in the absence of EDTA or imposed osmotic shocks when the cells were rapidly cooled below specific temperatures. Cells subjected to lysozyme while being cooled to below 20°C began to lose ability to subsequently form colonies. This sensitivity increased with decreasing temperatures and almost all cells cooled to 0°C were affected. Slightly hypertonic solutions did not improve survival. Cells cooled first to as low as 5°C and then subjected to lysozyme while cool did not lose their ability to form colonies subsequent to rewarming. However, 70% of the cells cooled first to 0°C and subjected to lysozyme lost their colony-forming ability. Cell lysis also began when treated near 5°C, but even when treated at 0°C about 50% of the cells maintained their rod shape in the presence of lysozyme. These results are discussed in terms of a possible phase transition in a portion of the cell envelope and/or a transient osmotic swelling as a results of metabolic pumps failing at the low temperatures.     

Spectral dependence of flavonol and betacyanin accumulation in Mesembryanthemum crystallinum under enhanced ultraviolet radiation

Mesembryanthemum crystallinum L. (Aizoaceae) is a drought‐ and salt‐tolerant halophyte that is able to endure harsh environmental conditions. Upon irradiation with high light irradiance (1200–1500 µmol m^?2 s^?1) it displays a rapid cell‐specific accumulation of plant secondary metabolites in the upper leaf epidermis; a phenomenon that is not detectable with salt or drought treatment. The accumulation of these compounds, the betacyanins and acylated flavonol glycosides, increases if the plants are exposed to polychromatic radiation with a progressively decreasing short‐wave cut‐off in the ultraviolet range. The response is localized in the epidermal bladder cells on the tips of young leaves and epidermal layers of fully expanded leaves. It is demonstrated that the accumulation of flavonols and betacyanins can be described by a weakly sigmoid dose function in combination with an exponential decrease of the response function of the plant with increasing wavelength.     

Growth characteristics of the diatoms Pseudonitzschia pungens and P. fraudulenta exposed to ultraviolet radiation

Interest in the biology of planktonic, chain-forming Pseudonitzschia species has grown recently after the discovery of toxin production in Pseudonitzschia pungens and related taxa, following the outbreak of shellfish toxicity in Canada in 1987. As part of a broader study on the effects of enhanced ultraviolet light on the growth of bloom-forming phytoplankton, we have examined the growth rates and production of the toxin domoic acid and two additional chemicals [bacillariolides I and II] by Pseudonitzschia pungens varieties and Pseudonitzschia fraudulenta from Narragansett Bay, Rhode Island. Growth of P. fraudulenta is significantly inhibited by enhanced UV, P. pungens var. pungens shows slight inhibition, and P. pungens var. multiseries is unaffected. Production of bacillariolides I and II by P. pungens var. multiseries is similar in enhanced and deleted UV light. Tolerance of UV light by P. pungens var. multiseries appears to be acquired, and persistent. If ambient UV light continues to increase as a result of global ozone depletion, one may expect UV-resistant taxa such as P. pungens var. multiseries to become more prominent in coastal phytoplankton communities.