Change in dominance determines herbivore effects on plant biodiversity

Herbivores alter plant biodiversity (species richness) in many of the world’s ecosystems, but the magnitude and the direction of herbivore effects on biodiversity vary widely within and among ecosystems. One current theory predicts that herbivores enhance plant biodiversity at high productivity but have the opposite effect at low productivity. Yet, empirical support for the importance of site productivity as a mediator of these herbivore impacts is equivocal. Here, we synthesize data from 252 large-herbivore exclusion studies, spanning a 20-fold range in site productivity, to test an alternative hypothesis—that herbivore-induced changes in the competitive environment determine the response of plant biodiversity to herbivory irrespective of productivity. Under this hypothesis, when herbivores reduce the abundance (biomass, cover) of dominant species (for example, because the dominant plant is palatable), additional resources become available to support new species, thereby increasing biodiversity. By contrast, if herbivores promote high dominance by increasing the abundance of herbivory-resistant, unpalatable species, then resource availability for other species decreases reducing biodiversity. We show that herbivore-induced change in dominance, independent of site productivity or precipitation (a proxy for productivity), is the best predictor of herbivore effects on biodiversity in grassland and savannah sites. Given that most herbaceous ecosystems are dominated by one or a few species, altering the competitive environment via herbivores or by other means may be an effective strategy for conserving biodiversity in grasslands and savannahs globally

Novel etiopathophysiological aspects of thyrotoxic periodic paralysis

Thyrotoxicosis can lead to thyrotoxic periodic paralysis (TPP), an endocrine channelopathy, and is the most common cause of acquired periodic paralysis. Typically, paralytic attacks cease when hyperthyroidism is abolished, and recur if hyperthyroidism returns. TPP is often underdiagnosed, as it has diverse periodicity, duration and intensity. the age at which patients develop TPP closely follows the age at which thyrotoxicosis occurs. All ethnicities can be affected, but TPP is most prevalent in people of Asian and, secondly, Latin American descent. TPP is characterized by hypokalemia, suppressed TSH levels and increased levels of thyroid hormones. Nonselective beta adrenergic blockers, such as propranolol, are an efficient adjuvant to antithyroid drugs to prevent paralysis; however, an early and definitive treatment should always be pursued. Evidence indicates that TPP results from the combination of genetic susceptibility, thyrotoxicosis and environmental factors (such as a high-carbohydrate diet). We believe that excess T-3 modifies the insulin sensitivity of skeletal muscle and pancreatic beta cells and thus alters potassium homeostasis, but only leads to a depolarization-induced acute loss of muscle excitability in patients with inherited ion channel mutations. An integrated etiopathophysiological model is proposed based on molecular findings and knowledge gained from long-term follow-up of patients with TPP.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fleury GroupUniversidade Federal de São Paulo, Escola Paulista Med, Dept Biochem, BR-04039032 São Paulo, BrazilUniversidade Federal de São Paulo, Escola Paulista Med, Dept Med, Lab Mol & Translat Endocrinol, BR-04039032 São Paulo, BrazilUniversidade Federal de São Paulo, Escola Paulista Med, Dept Biochem, BR-04039032 São Paulo, BrazilUniversidade Federal de São Paulo, Escola Paulista Med, Dept Med, Lab Mol & Translat Endocrinol, BR-04039032 São Paulo, BrazilWeb of Scienc

Identification of carbon dioxide in an exoplanet atmosphere

Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (i.e., elements heavier than helium, also called "metallicity"), and thus formation processes of the primary atmospheres of hot gas giants. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets. Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2 but have not yielded definitive detections due to the lack of unambiguous spectroscopic identification. Here we present the detection of CO2 in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science Program (ERS). The data used in this study span 3.0 to 5.5 {\mu}m in wavelength and show a prominent CO2 absorption feature at 4.3 {\mu}m (26{\sigma} significance). The overall spectrum is well matched by one-dimensional, 10x solar metallicity models that assume radiative-convective-thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide, and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0 {\mu}m that is not reproduced by these models