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.

     

Disentangling population strategies of two cladocerans adapted to different ultraviolet regimes

Zooplankton have evolved several mechanisms to deal with environmental threats, such as ultraviolet radiation (UVR), and in order to identify strategies inherent to organisms exposed to different UVR environments, we here examine life‐history traits of two lineages of Daphnia pulex. The lineages differed in the UVR dose they had received at their place of origin from extremely high UVR stress at high‐altitude Bolivian lakes to low UVR stress near the sea level in temperate Sweden. Nine life‐history variables of each lineage were analyzed in laboratory experiments in the presence and the absence of sub‐lethal doses of UVR (UV‐A band), and we identified trade‐offs among variables through structural equation modeling (SEM). The UVR treatment was detrimental to almost all life‐history variables of both lineages; however, the Daphnia historically exposed to higher doses of UVR (HighUV) showed a higher overall fecundity than those historically exposed to lower doses of UVR (LowUV). The total offspring and ephippia production, as well as the number of clutches and number of offspring at first reproduction, was directly affected by UVR in both lineages. Main differences between lineages involved indirect effects that affected offspring production as the age at first reproduction. We here show that organisms within the same species have developed different strategies as responses to UVR, although no increased physiological tolerance or plasticity was shown by the HighUV lineage. In addition to known tolerance strategies to UVR, including avoidance, prevention, or repairing of damages, we here propose a population strategy that includes early reproduction and high fertility, which we show compensated for the fitness loss imposed by UVR stress.     

A comparative study of ultraviolet radiation tolerance in different populations of Diaptomus minutus

A series of experiments was conducted to test the hypothesis that populations of Diaptomus minutus routinely experiencing high levels of ultraviolet radiation (UVR) are more tolerant of UVR than are those that routinely experience low levels of UVR. The relative degree of UVR tolerance was determined by monitoring mortality induced by either lamp or solar UVR. Diaptomus minutus from the low-dissolved organic carbon (DOC), high-UVR Lake Giles were consistently more tolerant of lamp and solar UVR than were those from the moderate-DOC, low-UVR Lake Lacawac. This difference in UVR tolerance was apparent throughout the year in freshly collected animals, but it did not persist in cultured animals. The lamp UVR tolerances of cultured D.minutus were similar, except for those initiated from September collections. The September culture of Lake Giles animals was significantly more tolerant than the Lake Giles cultures initiated in December, May and June. The September culture of Lake Lacawac animals was significantly more tolerant than the June culture. The lamp UVR tolerance of freshly collected Lake Giles animals was greatest from late June through October, but the Lake Lacawac population was least tolerant in July and August. No differences in lamp UVR tolerances were detected between animals collected from the surface and those collected from deeper water of either lake. It is concluded that the Lake Giles population was more tolerant than the Lake Lacawac population and that the period of greatest tolerance occurred several months after the time period with the highest ambient levels of solar UVR. Collectively, the experiments with both field and laboratory-cultured animals suggest that acclimation time plays a large role in UVR tolerance.      

Prey selection and baculovirus dissemination by carabid predators of Lepidoptera

Abstract.

• 1 The interaction between coleopteran predators and baculovirus-infected larvae was studied in the laboratory and the field in order to assess the potential role of predators in the dissemination of a nucleopolyhedrovirus (NPV).
• 2 Preference tests using three carabid species, Harpalus rufipes De Geer, Pterostichus melanarius Illiger and Agonum dorsale Pont, showed no evidence of discrimination between healthy and diseased larvae of the cabbage moth Mamestra brassicae L. (Lepidoptera: Noctuidae) as prey items.
• 3 Virus infectivity was maintained after passage through the predator's gut. NPV mortality ranged from 97% to 20% when test larvae were exposed to faeces collected immediately after and 15 days post-infected meal respectively.
• 4 The potential for transfer of inoculum in the environment was estimated in the laboratory by soil bioassay. Carabids continuously passed infective virus to the soil for at least 15 days after feeding on infected larvae.
• 5 Field experiments showed that carabids which had previously fed on diseased larvae transferred sufficient virus to the soil to cause low levels of mortality in larval populations of the cabbage moth at different instars.

     

Effects of grapevine bunch exposure to sunlight on berry surface temperature and Lobesia botrana (Lepidoptera: Tortricidae) egg laying,hatching and larval settlement

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Effects of herbivory and genotype on growth and survivorship of sand-dune willow (Salix cordata)

Abstract.

• 1 The response of different clones of sand-dune willow, Salix cordata, to herbivory by a specialist herbivore, Altica subplicata, was studied in three glasshouse experiments. Plants were caged and exposed to three herbivory treatments: no beetles, low number of beetles, and high number of beetles.
• 2 Plants consistently had significantly higher growth rates in the absence of herbivory than under conditions of low or high herbivory (1.5–6 times higher).
• 3 Herbivore treatment influenced mortality from drought stress; more plants from the low and high herbivory treatments (40% and 80%) died from drought stress than did control plants (0%).
• 4 Clone genotype significantly influenced growth rates and the susceptibility of plants to drought stress. However, clones showed similar growth responses to herbivory, suggesting a lack of genetic variation in tolerance or resistance to herbivory.

     

The effect of sunlight on leaf litter quality reduces growth of the shredder Klapopteryx kuscheli

• 1 The direct effect of sunlight on the conditioning, breakdown and incorporation of leaf litter in stream food webs has not yet been considered. The aim here was to evaluate the effects of light intensity on the colonization of leaf litter by microorganisms and its resulting quality as food for the stonefly shredder Klapopteryx kuscheli.
• 2 Leaf litter was conditioned for 2 months in an open reach of a second‐order stream in litter bags either exposed to or shaded from direct sunlight. Subsequently, we performed laboratory experiments to test larval consumption, growth, growth efficiency and feeding preference fed on both leaf litter treatments.
• 3 Leaf litter in the unshaded treatment had three times more chlorophyll‐a (Chl‐a) than that in the shaded treatment, 50% lower fungal biomass and similar bacterial abundance. Although larvae did not prefer either food and fed at the same rate on both leaf litter treatments, they grew twice as fast on the shade‐conditioned leaves and attained a two‐fold higher growth efficiency.
• 4 Sunlight can have significant effects on detritus‐based food webs. Riparian modification induced by human activities in forested catchments increases the potential for sunlight to influence detritus dynamics.

     

Behavioural responses to co-occurring threats of predation and ultraviolet radiation in Daphnia

1. Organisms in the wild are faced with multiple threats and a common response is a change in behaviour. To disentangle responses to several threats, we exposed two differently sized species of the freshwater invertebrate Daphnia to solar ultraviolet radiation (UVR) and predation from either moving pelagic or benthic ambush predators.
2. Using an advanced nanotechnology-based method, we tracked the three-dimensional movements of those mm-sized animals at the individual level. Each behavioural trial was performed both under conditions resembling night (no UVR) and day (UVR) and we examined patterns of the depth distribution and swimming speed by Daphnia across three treatments: no predator (control); bottom-dwelling damselfly (Calopteryx sp.); and fish (stickleback, Pungitius pungitius) predators. We also quantified the actual predation rate by the two predators on the two Daphnia species, Daphnia manga and Daphnia pulex.
3. We show that individual Daphnia are able to identify predators with different feeding habitats, rank multiple and simultaneously occurring risks and respond in accordance with the actual threat; complex responses that are generally associated with larger animals.
4. In a broader context, our results highlight and quantify how a cocktail of everyday threats is perceived and handled by invertebrates, which advances our understanding of species distribution in space and time, and thereby of population dynamics and ecosystem function in natural ecosystems.

     

Predation yields greater population performance: what are the contributions of density‐ and trait‐mediated effects?

1. Population responses to extrinsic mortality can yield no change in the number of survivors (compensation) or an increase in the number of survivors (overcompensation) when the population is regulated by negative density‐dependence. This intriguing response has been the subject of theoretical studies, but few experiments have explored how the source of extrinsic mortality affects the response.
2. This study tests abilities of three functionally diverse predators, alone and combined, to induce (over)compensation of a prey population. Larval Aedes aegypti (Diptera: Culicidae) were exposed to predation by Mesocyclops longisetus (Crustacea: Copepoda), Anopheles barberi (Diptera: Culicidae), Corethrella appendiculata (Diptera: Corethrellidae), all three in a substitutive design, or no predation.
3. Predator treatment had no significant effect on the total number of adult survivors, nor on numbers of surviving males or females. The female development rate and a composite index of performance (r′) were greater with predation relative to no‐predator control. No differences were detected between diverse and single‐species predator treatments.
4. Sensitivity analyses indicated predation effects on the number of female adults produced, despite not being affected significantly, was the largest contributing factor to significant treatment effects on the demographic index r′. While predation did not significantly increase the production of adults, it did release survivors from density‐dependent effects sufficiently to increase population performance. This study provides an empirical test of mechanisms by which predation may yield positive mortality effects on victim populations, a phenomenon predicted to occur across many taxa and food webs.

     

Response of oxidative stress parameters and sunscreening compounds in Arctic amphipods during experimental exposure to maximal natural UVB radiation

The paper investigates tolerance to UV radiation (UVR) in 3 amphipod species from the Arctic Kongsfjord, Spitsbergen: the herbivore Gammarellus homari (0- to 5-m water depth), the strictly carnivore scavenger Anonyx nugax (2- to 5-m water depth) and the detritivore/carnivore Onisimus edwardsi (2- to 5-m water depth). In previous radiation exposure experiments, both carnivore species displayed elevated mortality rates already at moderate UVR levels. Therefore, the concentrations of sunscreening compounds (mycosporine-like amino acids, MAAs, and carotenoids) and two antioxidant enzymes (superoxide dismutase, catalase) were studied in the animals under control conditions and following moderate as well as high UVR exposure.In both carnivore amphipods elevated sensitivity to experimental UVR exposure went along with a degradation of the tissue carotenoid and MAAs and a decrease of the enzymatic antioxidant defence, which resulted in increased lipid peroxidation in exposed animals. In contrast, the herbivore G. homari seems well protected by high concentrations of MAAs absorbed from its algal diet, and no oxidative stress occurred under experimental UVR. The species-specific degree of UV tolerance correlates well with the animals' typical vertical distribution in the water column.     

ADAPTATION OF A PSYCHROPHILIC FRESHWATER DINOFLAGELLATE TO ULTRAVIOLET RADIATION1

Little is known about the UV photobiology of psychrophilic dinoflagellates, particularly in freshwater systems. We addressed the life strategies of Borghiella dodgei Moestrup, Gert. Hansen et Daugbjerg to cope with ambient levels of ultraviolet radiation (UVR) under cold conditions. Several physiological parameters related to growth, metabolism, and UVR protection were determined for 4 d in UVR‐exposed and control cells by applying stable isotope analysis, spectrophotometry, and liquid chromatography–mass spectrometry (LC/MS). In UVR‐exposed cells, assimilation of ¹⁵N and ¹³C and content of chl a and carotenoids, specifically diatoxanthin with respect to dinoxanthin and diadinoxanthin, were increased; furthermore, catalase activity showed a cyclic pattern with a strong increase after UVR exposure but a rapid return to preexposure levels. Both in UVR‐exposed and control cells, no lipid peroxidation of galactolipids was observed. However, in UVR‐exposed cells, content of galactolipids was higher and linked to an increase in monogalactosyldiacylglycerols (MGDGs). We concluded that Borghiella's adaptation to UVR depended on a general metabolic enhancement and efficient scavenging of oxygen radicals to mitigate and counteract damage. While Borghiella seemed to be well adapted to ambient UVR, the interactive effects of higher temperature and UVR on psychrophilic species in front of climate change merit further investigation.     

Parasite infection alters host stable‐isotope composition under controlled feeding

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Natural UVR Does Not Affect Decomposition by Aquatic Hyphomycetes

We performed field and laboratory experiments to evaluate the effect of solar radiation (UVR and PAR) on leaf litter decomposition, fungal biomass and sporulation rates, in the Andean Patagonia, where high UVR levels are common. Leaves of Alnus glutinosa exposed to three treatments, normal radiation (PAR + UVR), protected from UVR and protected from total radiation (SHADE) by plastic films lost 31–37% of their mass. Leaves of Nothofagus pumilio lost 61–64% of their mass under the same conditions. For both leaf species, differences in mass losses among treatments were not statistically significant. Sporulation rates were significantly lower in the SHADE treatment. Fungal biomass accounted for 6.2 to 7.1% of leaf mass, without significant differences among treatments. In the laboratory, leaf discs of A. glutinosa colonized by single species of aquatic hyphomycetes (Articulospora tetracladia, Flagellospora curta or Lunulospora curvula) and exposed to or protected from UVR did not differ in mass loss and sporulation rates. Pure cultures of two fungal species grew at the same rates when exposed to light (PAR and PAR + UVR) or to the SHADE. In summary, we found no evidences that current high levels of UV radiation affect litter decomposition mediated by aquatic hyphomycetes. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mechanisms of competition between tadpoles of Australian frogs (Litoria spp.) and invasive cane toads (Rhinella marina)

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Multi‐wavelength Pulse Amplitude Modulated fluorometry (Phyto‐PAM) reveals differential effects of ultraviolet radiation on the photosynthetic physiology of phytoplankton pigment groups

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Non-target impacts of poison baiting for predator control in Australia

• 1 Mammalian predators are controlled by poison baiting in many parts of the world, often to alleviate their impacts on agriculture or the environment. Although predator control can have substantial benefits, the poisons used may also be potentially harmful to other wildlife.
• 2 Impacts on non‐target species must be minimized, but can be difficult to predict or quantify. Species and individuals vary in their sensitivity to toxins and their propensity to consume poison baits, while populations vary in their resilience. Wildlife populations can accrue benefits from predator control, which outweigh the occasional deaths of non‐target animals. We review recent advances in Australia, providing a framework for assessing non‐target effects of poisoning operations and for developing techniques to minimize such effects. We also emphasize that weak or circumstantial evidence of non‐target effects can be misleading.
• 3 Weak evidence that poison baiting presents a potential risk to non‐target species comes from measuring the sensitivity of species to the toxin in the laboratory. More convincing evidence may be obtained by quantifying susceptibility in the field. This requires detailed information on the propensity of animals to locate and consume poison baits, as well as the likelihood of mortality if baits are consumed. Still stronger evidence may be obtained if predator baiting causes non‐target mortality in the field (with toxin detected by post‐mortem examination). Conclusive proof of a negative impact on populations of non‐target species can be obtained only if any observed non‐target mortality is followed by sustained reductions in population density.
• 4 Such proof is difficult to obtain and the possibility of a population‐level impact cannot be reliably confirmed or dismissed without rigorous trials. In the absence of conclusive evidence, wildlife managers should adopt a precautionary approach which seeks to minimize potential risk to non‐target individuals, while clarifying population‐level effects through continued research.

     

A specialised pollination system using nectar‐seeking thynnine wasps in Caladenia nobilis (Orchidaceae)

• Caladenia is a diverse Australian genus that is exceptional among orchids in having both species pollinated by food‐seeking and sexually deceived insects. Here, we investigated the pollination of Caladenia nobilis, a species predicted to be food‐deceptive due to its large, cream‐coloured and apparently nectarless flowers.
• Pollinator observations were made using experimental clumps of flowers. Measurements of floral colour were undertaken with a spectrometer, nectar was tested using GC‐MS, and reproductive success was quantified for 2 years.
• While C. nobilis attracted nine species of insect, only males of the thynnine wasp Rhagigaster discrepans exhibited the correct size and behaviour to remove and deposit pollen. Male R. discrepans attempted to feed from the surface of the labellum, often crawling to multiple flowers, but showed no evidence of sexual attraction. Most flowers produced little or no nectar, although some may provide enough sucrose to act as a meagre reward to pollinators. Floral colouration was similar to a related Caladenia species pollinated by sexual deception, although the sexually deceptive species had a dull‐red labellum. Reproductive success was generally low and highly variable between sites and years.
• In addition to most visitors being of inappropriate size for pollinia removal, the lack of response to the orchid by several co‐occurring species of thynnine wasp suggests filtering of potential pollinators at the attraction phase. Our discovery of a pollination strategy that may be intermediate between food deception and food reward raises the question, how many putatively rewardless orchids actually produce meagre amounts of nectar?

     

Steller sea lions Eumetopias jubatus and nutritional stress: evidence from captive studies

• 1 Numbers of Steller sea lions Eumetopias jubatus in the North Pacific have declined. According to the nutritional stress hypothesis, this decline is due to reduced food availability. Data from studies conducted on pinnipeds in the laboratory are used here to test if the nutritional stress hypothesis can explain the decline of Steller sea lions.
• 2 Overall, there is strong evidence for biologically meaningful differences in the nutritional quality of major prey species. Steller sea lions can partly compensate for low‐quality prey by increasing their food consumption.
• 3 There appear to be no detrimental effects of low‐lipid prey on sea lion growth or body composition when sea lions can consume sufficient quantities of prey. However, the ability to increase consumption is physiologically limited, particularly in young animals. Overall, it is more difficult to maintain energy intake on a diet of low‐quality prey than on a normal diet.
• 4 Under conditions of inadequate food intake (either due to decreased prey availability or quality, or increased energy requirements) the overall impacts of nutritional stress are complex, and are dependent upon season, prey quality, age and the duration and intensity of the nutritional stress event.
• 5 Studies on pinnipeds in the laboratory have been instrumental in identifying the conditions under which changes in sea lion prey can result in nutritional stress and the nature of the physiological impacts of nutritional stress events.

     

The roles of top and intermediate predators in herbivore suppression: contrasting results from the field and laboratory

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Biogenic methane contributes to the food web of a large,shallow lake

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