Ontogenetic shifts in a prey’s chemical defences influence feeding responses of a snake predator

Foraging theory suggests that predator responses to potential prey should be influenced by prey chemical defences, but the effects of ontogenetic variation in such defences on prey vulnerability to predators remain unclear. Cane toads (Rhinella marina) are toxic to anurophagous snakes, including the keelback (Tropidonophis mairii, a natricine colubrid that occurs within the toads' invasive range in Australia). Toxin levels and diversity change through toad ontogeny, decreasing from the egg stage to metamorphosis, then increasing in postmetamorphic toads. If the toxin content of a prey item influences predator responses, we predict that keelbacks should exhibit selective predation on toads close to metamorphosis. The results of our laboratory trials on adult (field-collected, and thus toad-experienced) and hatchling (laboratory-incubated, and thus toad-naive) keelbacks supported this prediction. The snakes selectively consumed later-stage rather than earlier-stage tadpoles, and earlier-stage rather than later-stage metamorphs. Our data are thus consistent with the hypothesis that ontogenetic changes in toxin content can affect individuals' vulnerability to predation.     

Dissociable Processes for Orientation Discrimination Learning and Contextual Illusion Magnitude

Previous research suggests an inverse relationship between human orientation discrimination sensitivity and tilt illusion magnitude. To test whether these perceptual functions are inherently linked, we measured both orientation discrimination sensitivity and the magnitude of the tilt illusion before and after participants had been trained for three days on an orientation discrimination task. Discrimination sensitivity improved with training and this improvement remained one month after the initial learning. However, tilt illusion magnitude remained unchanged before and after orientation training, at either trained or untrained orientations. Our results suggest that orientation discrimination sensitivity and illusion magnitude are not inherently linked. They also provide further evidence that, at least for the training periods we employed, perceptual learning of orientation discrimination may involve high-level processes.     

Mixed population genomics support for the central marginal hypothesis across the invasive range of the cane toad (Rhinella marina) in Australia

Understanding factors that cause species' geographic range limits is a major focus in ecology and evolution. The central marginal hypothesis (CMH) predicts that species cannot adapt to conditions beyond current geographic range edges because genetic diversity decreases from core to edge due to smaller, more isolated edge populations. We employed a population genomics framework using 24 235–33 112 SNP loci to test major predictions of the CMH in the ongoing invasion of the cane toad (Rhinella marina) in Australia. Cane toad tissue samples were collected along broad‐scale, core‐to‐edge transects across their invasive range. Geographic and ecological core areas were identified using GIS and habitat suitability indices from ecological niche modelling. Bayesian clustering analyses revealed three genetic clusters, in the northwest invasion‐front region, northeast precipitation‐limited region and southeast cold temperature‐limited region. Core‐to‐edge patterns of genetic diversity and differentiation were consistent with the CMH in the southeast, but were not supported in the northeast and showed mixed support in the northwest. Results suggest cold temperatures are a likely contributor to southeastern range limits, consistent with CMH predictions. In the northeast and northwest, ecological processes consisting of a steep physiological barrier and ongoing invasion dynamics, respectively, are more likely explanations for population genomic patterns than the CMH.     

Why do lizards avoid weeds?

Invasion of native habitats by exotic plants often causes reductions in faunal diversity. However, there is little direct evidence of native fauna actively avoiding invaded habitat and few quantitative studies on the mechanisms underlying such avoidance. We quantified alterations made to the composition and physical structure of an Australian tropical savanna by grader grass (Themeda quadrivalvis); an understudied invasive grass that is associated with reduced faunal abundance and diversity. We found that grader grass profoundly changed the physical structure and floral composition of tropical savanna, forming dense lawn-like monocultures unlike the native savanna. Second, we investigated the habitat preferences of small ectotherms in partially invaded habitat, using a rainbow skink (Carlia schmeltzii) as a model system and discovered that they actively avoided grader grass. Finally, we experimentally tested predictions regarding mechanisms that may have driven the avoidance of grader grass. Predation rates and food availability were not likely the cause of grader grass avoidance, because experiments using models deployed in the field showed that predation rates were higher in native grass, and collection of invertebrates in both habitats indicated that prey availability was similar. However, mesocosm experiments on habitat selection in relation to vegetation structure, along with field measures of available operative environmental temperatures, suggested that small ectotherms probably avoid grader-grass-invaded savanna due to a suboptimal thermal environment and lack of appropriate habitat structural heterogeneity.     

Progranulin derivative Atsttrin protects against early osteoarthritis in mouse and rat models

Background

Atsttrin, an engineered protein composed of three tumor necrosis factor receptor (TNFR)-binding fragments of progranulin (PGRN), shows therapeutic effect in multiple murine models of inflammatory arthritis . Additionally, intra-articular delivery of PGRN protects against osteoarthritis (OA) progression. The purpose of this study is to determine whether Atsttrin also has therapeutic effects in OA and the molecular mechanisms involved.

Methods

Surgically induced and noninvasive rupture OA models were established in mouse and rat, respectively. Cartilage degradation and OA were evaluated using Safranin O staining, immunohistochemistry, and ELISA. Additionally, expressions of pain-related markers, degenerative factors, and anabolic and catabolic markers known to be involved in OA were analyzed. Furthermore, the anabolic and anti-catabolic effects and underlying mechanisms of Atsttrin were determined using in-vitro assays with primary chondrocytes.

Results

Herein, we found Atsttrin effectively prevented the accelerated OA phenotype associated with PGRN deficiency. Additionally, Atsttrin exhibited a preventative effect in OA by protecting articular cartilage and reducing OA-associated pain in both nonsurgically induced rat and surgically induced murine OA models. Mechanistic studies revealed that Atsttrin stimulated TNFR2-Akt-Erk1/2-dependent chondrocyte anabolism, while inhibiting TNFα/TNFR1-mediated inflammatory catabolism.

Conclusions

These findings not only provide new insights into the role of PGRN and its derived engineered protein Atsttrin in cartilage homeostasis as well as OA in vivo, but may also lead to new therapeutic alternatives for OA as well as other relative degenerative joint diseases.

     

Experience shapes the utility of natural statistics for perceptual contour integration

Segmenting meaningful targets from cluttered scenes is a fundamental function of the visual system. Evolution and development have been suggested to optimize the brain's solution to this computationally challenging task by tuning the visual system to features that co-occur frequently in natural scenes (e.g., collinear edges) [1, 2, 3]. However, the role of shorter-term experience in shaping the utility of scene statistics remains largely unknown. Here, we ask whether collinearity is a specialized case, or whether the brain can learn to recruit any image regularity for the purpose of target identification. Consistent with long-term optimization for typical scene statistics, observers were better at detecting collinear contours than configurations of elements oriented at orthogonal or acute angles to the contour path. However, training resulted in improved detection of orthogonal contours that lasted for several months, suggesting retuning rather than transient changes of visual sensitivity. Improvement was also observed for acute contours but only after longer training. These results demonstrate that the brain flexibly exploits image regularities and learns to use discontinuities typically associated with surface boundaries (orthogonal, acute alignments) for contour linking and target identification. Thus, short-term experience in adulthood shapes the interpretation of scenes by assigning new statistical utility to image regularities.     

DOES TOTAL REPRODUCTIVE EFFORT EVOLVE INDEPENDENTLY OF OFFSPRING SIZE?

In all species, patterns of reproductive allocation have important fitness consequences and therefore important implications for life-history evolution. Nearly universally, theory in this field has modeled as independent the evolution of total allocation to offspring and the subsequent division of this allocation into many small versus few large offspring. Yet, some theory and a very small amount of experimental evidence suggest that these life-history traits may be evolutionarily linked. Using comparative analyses of copepod life histories, we illustrate that rather than being evolutionarily independent these traits can be linked, in this case, across a very large clade of invertebrates. Our results indicate that a more complete understanding of the evolution of these traits will require greater consideration of simultaneous allocation decisions, rather than sequential ones, and other genetic and selective mechanisms.     

Estimates of radiological risk from a terrorist attack using plutonium

The possible use of radioactivity dispersal devices by terrorist groups has been recently reported in the news. In this paper, we discuss the threat of terrorist attacks by plutonium, with particular attention to the dispersal of plutonium by explosion or fire. Doses resulting from inhalation of radioactive aerosol induced by a plutonium explosion or fire are simulated using a Gaussian plume model (the HOTSPOT code) for different meteorological conditions. Ground contamination and resuspension of dust are also considered in the simulations. Our simulations suggest that acute effects from a plutonium dispersal attack are very unlikely. For late stochastic effects, the explosion poses a greater hazard than fire. However, even in the worst-case scenario, the dispersed plutonium would cause relatively few excess cancers (around 80 in a city of 2 million inhabitants) after many years from the explosion, and these excess cancers would remain undetected against the background of cancer fatalities.