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.     

Fish community responses to ecosystem stressors in coastal estuarine wetlands: a functional basis for wetlands management and restoration

Functional responses of estuarine fish species to environmental perturbations such as wetland impoundment, changes in water quality, and sediment accretion are investigated. The study focuses on the feeding, growth and habitat use by California killifish (Fundulus parvipinnis), topsmelt (Antherinops affinis), and juvenile California halibut (Paralichthys californicus) in impacted coastal wetlands to provide an ecological basis for guidance on the management and restoration of these ecosystems. The ecology of California killifish, Fundulus parvipinnis, is closely tied with the marsh surface, which they access at high tide to feed and grow. Field estimates of food consumption show that killifish can increase their food intake by two-fold to five-fold by adding marsh surface foods to their diet. Bioenergetics modeling predicts that killifish can grow over an order of magnitude faster if they add intertidal marsh surfaces to their subtidal feeding areas. Tidal inlet closures and increased marsh surface elevations due to sediment accretion can restrict killifish access to the marsh surface, affecting its growth and fitness. An open tidal inlet and tidal creek networks that allow killifish to access the marsh at high tide must be incorporated into the restoration design. Topsmelt and California halibut are also adversely affected by tidal inlet closures. Food consumption rates of topsmelt are 50% lower when the tidal inlet is closed, compared to when the estuary is tidally-flushed. Tidal inlet closures inadvertently induce variations in water temperature and salinity and negatively affect growth of juvenile California halibut. Tidal creek networks which consist of channels and creeks of various orders are also important to halibut. Large halibut (>200 mm TL) inhabit deeper, high order channels for thermal refuge, while small halibut (<120 mm TL) are abundant in lower order channels where they can feed on small-sized prey which are typically less abundant in high order channels. Maintaining an open tidal inlet, implementing sediment management programs and designing coastal wetlands with tidal creek networks adjacent to intertidal salt marsh habitat (for fish access) are key elements that need to be considered during the planning and implementation of coastal wetland restoration projects.     

Exploring Core Response Mechanisms to Multiple Environmental Stressors Via A Genome‐Wide Study in the Brown Alga Saccharina japonica (Laminariales,Phaeophyceae)

Saccharina japonica is an important large brown alga and a major component of productive beds on the northwest coast of the Pacific Ocean. Abiotic stress response mechanisms are receiving considerable attention because global climate change is increasing their abiotic stress levels. However, our knowledge of how S. japonica broadly responds to stress is limited. In this study, we investigated the S. japonica responsive genes underlying acclimation to diverse stressors of acidification, high light, high temperature, hypersalinity, and hyposalinity and identified 408 core genes constantly and differentially expressed in response to all stressors. Our results confirm that stressors had strong effects on genes participating in photosynthesis, amino acid metabolism, carbohydrate metabolism, halogen metabolism, and reactive oxygen species defense. These findings will improve our understanding of brown algal response mechanisms linked to environmental stress and provide a list of candidate genes for improving algal stress tolerance in light of environmental stress in future studies.     

Experimental strategies to assess the biological ramifications of multiple drivers of global ocean change—A review

Marine life is controlled by multiple physical and chemical drivers and by diverse ecological processes. Many of these oceanic properties are being altered by climate change and other anthropogenic pressures. Hence, identifying the influences of multifaceted ocean change, from local to global scales, is a complex task. To guide policy‐making and make projections of the future of the marine biosphere, it is essential to understand biological responses at physiological, evolutionary and ecological levels. Here, we contrast and compare different approaches to multiple driver experiments that aim to elucidate biological responses to a complex matrix of ocean global change. We present the benefits and the challenges of each approach with a focus on marine research, and guidelines to navigate through these different categories to help identify strategies that might best address research questions in fundamental physiology, experimental evolutionary biology and community ecology. Our review reveals that the field of multiple driver research is being pulled in complementary directions: the need for reductionist approaches to obtain process‐oriented, mechanistic understanding and a requirement to quantify responses to projected future scenarios of ocean change. We conclude the review with recommendations on how best to align different experimental approaches to contribute fundamental information needed for science‐based policy formulation.     

Social stressors and coping mechanisms in wild female baboons (Papio hamadryas ursinus)

We examined the social correlates of fecal glucocorticoid (GC) levels in wild female baboons during a period of social and demographic stability. Females' GC levels were not affected by individual attributes such as number of kin or dominance rank, nor could we detect any significant seasonal effects. Instead, GC levels were influenced by behavioral attributes that varied between individuals and within individuals across time. Pregnant and cycling females who received high rates of aggression had higher GC levels than others. In contrast, pregnant and cycling females who received grunts - vocal signals of benign intent - at high frequencies from dominant females had lower GC levels than females who received grunts at lower frequencies. Lactating females showed the opposite trend, apparently as a consequence of the high rate of grunting and intense, unsolicited attention that their infants received from others. All females experienced lower GC levels in months when they concentrated their grooming among a small number of partners than when their grooming was more evenly distributed among many partners. Although GC levels in female baboons are most strongly influenced by events that directly affect their reproductive success, subtle social factors associated with the loss of predictability and control also seem to exert an effect. Loss of control may be mitigated if a female is able to predict others' intentions - for example, if others grunt to her to signal their intentions - and if she is able to express some preference over the timing and identities of her grooming partners.     

Cladocera assemblages from the surface sediments of south-central Ontario (Canada) lakes and their relationships to measured environmental variables

Fossil cladoceran remains preserved in surface sediment samples from 44 oligotrophic lakes in south-central Ontario were examined to evaluate the relationships between species assemblages and measured environmental variables. Differences in cladoceran assemblages were related to physical and chemical variables using multivariate techniques. Redundancy Analysis (RDA) identified five environmental variables as significantly influencing assemblage composition: sulphate (SO₄²⁻), calcium (Ca²⁺), pH, maximum lake depth (Z _max) and dissolved organic carbon (DOC). There was a distinct separation of lakes and taxa along the ion gradient based on SO₄, Ca and pH. Additionally, cladoceran communities in coloured, shallow lakes had relatively higher abundances of littoral chydorid species and the pelagic taxa Holopedium spp., and the Daphnia pulex complex. Deep, clear lakes had relatively higher abundances of other pelagic taxa. Predation by fish (measured as presence–absence) and Chaoborus (measured as density) were less significant than some of the physico-chemical variables in influencing cladoceran assemblage structure. However, this could be due to the limited resolution of the predation data that was available at the time of this study. The distribution of cladocerans in the surface sediment, and their relation to these important environmental variables, suggests that there is considerable potential for the use of sedimentary cladoceran remains as environmental indicators in south-central Ontario lakes. Handling editor: J. Saros     

Signaling mechanism mediating the anti-senescence effect of low-concentration chemical stressors sprayed onto bean seedlings

The anti-senescence effect of low-concentrations of some stress-inducing compounds of different toxicity and chemical nature such as Cd and Pb salts or 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) was investigated in the primary leaves of bean seedlings. In these leaves treated by spraying, chlorophyll content and photosynthetic activity increased, the active cytokinin content of roots and leaves was also significantly higher as compared to the control. These symptoms of stimulation could be eliminated by the inhibitors Li and PD [2-(2′-amino-3′-methoxyphenyl)-oxanaphthalen-4-one] added to each agent, indicating the involvement of PIP₂-IP₃/DAG and MAPK signaling pathways, respectively, in the response.     

Combined impacts of warming and salinisation on trophic interactions and mortality of a specialist ephemeral wetland predator

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