Early-life exposure to a herbicide has enduring effects on pathogen-induced mortality

Exposure to stressors at formative stages in the development of wildlife and humans can have enduring effects on health. Understanding which, when and how stressors cause enduring health effects is crucial because these stressors might then be avoided or mitigated during formative stages to prevent lasting increases in disease susceptibility. Nevertheless, the impact of early-life exposure to stressors on the ability of hosts to resist and tolerate infections has yet to be thoroughly investigated. Here, we show that early-life, 6-day exposure to the herbicide atrazine (mean ± s.e.: 65.9±3.48 µg l⁻¹) increased frog mortality 46 days after atrazine exposure (post-metamorphosis), but only when frogs were challenged with a chytrid fungus implicated in global amphibian declines. Previous atrazine exposure did not affect resistance of infection (fungal load). Rather, early-life exposure to atrazine altered growth and development, which resulted in exposure to chytrid at more susceptible developmental stages and sizes, and reduced tolerance of infection, elevating mortality risk at an equivalent fungal burden to frogs unexposed to atrazine. Moreover, there was no evidence of recovery from atrazine exposure. Hence, reducing early-life exposure of amphibians to atrazine could reduce lasting increases in the risk of mortality from a disease associated with worldwide amphibian declines. More generally, these findings highlight that a better understanding of how stressors cause enduring effects on disease susceptibility could facilitate disease prevention in wildlife and humans, an approach that is often more cost-effective and efficient than reactive medicine.     

Impacts of thermal mismatches on chytrid fungus Batrachochytrium dendrobatidis prevalence are moderated by life stage,body size,elevation and latitude

Global climate change is increasing the frequency of unpredictable weather conditions; however, it remains unclear how species‐level and geographic factors, including body size and latitude, moderate impacts of unusually warm or cool temperatures on disease. Because larger and lower‐latitude hosts generally have slower acclimation times than smaller and higher‐latitude hosts, we hypothesised that their disease susceptibility increases under ‘thermal mismatches’ or differences between baseline climate and the temperature during surveying for disease. Here, we examined how thermal mismatches interact with body size, life stage, habitat, latitude, elevation, phylogeny and International Union for Conservation of Nature (IUCN) conservation status to predict infection prevalence of the chytrid fungus Batrachochytrium dendrobatidis (Bd) in a global analysis of 32 291 amphibian hosts. As hypothesised, we found that the susceptibility of larger hosts and hosts from lower latitudes to Bd was influenced by thermal mismatches. Furthermore, hosts of conservation concern were more susceptible than others following thermal mismatches, suggesting that thermal mismatches might have contributed to recent amphibian declines.     

Water T2 relaxation in sugar solutions

1H spin-spin relaxation times of water were measured with the CPMG sequence in dilute aqueous solutions of glucitol, mannitol, glycerol, glycol, the methyl D-pyranosides of alpha-glucose, beta-glucose, alpha-galactose, beta-galactose, alpha-xylose, beta-xylose, beta-arabinose and sucrose, alpha,alpha-trehalose, beta-maltose, maltotriose and maltoheptaose. The relaxation-time dispersion was measured by varying the CPMG pulse spacing, tau. These data were interpreted by means of the Carver-Richards model in which exchange between water protons and labile solute hydroxyl protons provides a significant contribution to the relaxation. From the dependences on temperature and tau, parameters characteristic of the pool of hydroxyls belonging to a given solute were extracted by nonlinear regression, including: the fraction of exchangeable protons, P, the chemical-shift difference between water protons and hydroxyl protons, deltaomega, the intrinsic spin-spin relaxation time, T2, and the chemical exchange rate, k. These solute-specific parameters are related, respectively, to the concentration, identity, mobility and exchange life-time of the hydroxyl site. At 298 K, values of deltaomega, T2 and k were found to be of the order of 1 ppm, 100 ms and 1000 s(-1), respectively. Effects of molecular size, conformation and solute concentration were investigated. The exchange mechanism was characterised by Eyring activation enthalpies and entropies with values in the ranges 50-70 kJ mol(-1) and -10 to 60 J K(-1)mol(-1), respectively.     

Controlling Dengue with Vaccines in Thailand

Background

Dengue is a mosquito-borne infectious disease that constitutes a growing global threat with the habitat expansion of its vectors Aedes aegyti and A. albopictus and increasing urbanization. With no effective treatment and limited success of vector control, dengue vaccines constitute the best control measure for the foreseeable future. With four interacting dengue serotypes, the development of an effective vaccine has been a challenge. Several dengue vaccine candidates are currently being tested in clinical trials. Before the widespread introduction of a new dengue vaccine, one needs to consider how best to use limited supplies of vaccine given the complex dengue transmission dynamics and the immunological interaction among the four dengue serotypes.

Methodology/Principal Findings

We developed an individual-level (including both humans and mosquitoes), stochastic simulation model for dengue transmission and control in a semi-rural area in Thailand. We calibrated the model to dengue serotype-specific infection, illness and hospitalization data from Thailand. Our simulations show that a realistic roll-out plan, starting with young children then covering progressively older individuals in following seasons, could reduce local transmission of dengue to low levels. Simulations indicate that this strategy could avert about 7,700 uncomplicated dengue fever cases and 220 dengue hospitalizations per 100,000 people at risk over a ten-year period.

Conclusions/Significance

Vaccination will have an important role in controlling dengue. According to our modeling results, children should be prioritized to receive vaccine, but adults will also need to be vaccinated if one wants to reduce community-wide dengue transmission to low levels.     

Fungicide-induced declines of freshwater biodiversity modify ecosystem functions and services

Although studies on biodiversity and ecosystem function are often framed within the context of anthropogenic change, a central question that remains is how important are direct vs. indirect (via changes in biodiversity) effects of anthropogenic stressors on ecosystem functions in multitrophic-level communities. Here, we quantify the effects of the fungicide chlorothalonil on 34 species-, 2 community- and 11 ecosystem-level responses in a multitrophic-level system. At ecologically relevant concentrations, chlorothalonil increased mortality of amphibians, gastropods, zooplankton, algae and a macrophyte (reducing taxonomic richness), reduced decomposition and water clarity and elevated dissolved oxygen and net primary productivity. These ecosystem effects were indirect and predictable based on changes in taxonomic richness. A path analysis suggests that chlorothalonil-induced reductions in biodiversity and top-down and bottom-up effects facilitated algal blooms that shifted ecosystem functions. This work emphasises the need to re-evaluate the safety of chlorothalonil and to further link anthropogenic-induced changes in biodiversity to altered ecosystem functions.     

Ecology and behavior of tilefishes, Hoplolatilus starcki, H. fronticinctus and related species (Malacanthidae): non-mound and mound builders

Observations on habitat and behavior are reported for 10 of the 12 known species of the genus Hoplolatilus. These small (6 to 20 cm total length) fishes are widespread in the tropical Indo-Pacific and Red Sea. Adults live as stable monogamous pairs and each pair shares a burrow. They feed on plankton during the day and retreat into a burrow to escape disturbances and to retire for the night. Usually the burrow location is inconspicuous, but 3 of the deeper water species build elaborate rubble mounds, to over 3 m in diameter, around their burrows. We studied the shallowest (13 to 61 m depth) species, H. starcki, that does not build mounds, and compared it with the shallowest (51 to 73+ m) mound builder H. fronticinctus. Over 60 pairs of H. starcki were studied. Ten-min observations (N=237) on 14 pairs were analyzed by time of day for feeding rates, courtship behavior, and distances of pairs in relation to each other and their burrows. Over 20 pairs of H. fronticinctus were studied by divers and on video from a remotely operated vehicle. These data showed a high rate of moving rubble (96.0 h^-1), an activity almost absent in non-mound builders (0.1 h^-1). Observations are also reported for non-mound builders H. chlupatyi, H. cuniculus, H. luteus, H. marcosi, H. oreni, H. purpureus, H. sp. (an undescribed species), and the mound builder H. pohle. The results of a survey of 159 dive sites with suitable habitats to over 25 m depth (including 49 dive sites over 50 m) indicate an abundance of Hoplolatilus species in the southwest Pacific. In comparison, 41 survey dive sites (including 20 over 50 m) in the Red Sea resulted in an unexplained absence of Hoplolatilus species except in deep water (>60 m). Mound builder, H. geo, is known in the north Red Sea (depths 80-116 m). H. fronticinctus, newly reported here, was found in the south Red Sea (depths 70-73 m). We also report, for the first time, live sightings of the rare H. oreni and H. sp. living unpaired and without mounds below 60 m in the south Red Sea. The wide distribution of H. fronticinctus, like the related Malacanthus brevirostris, suggests a possible advantage to building mounds even though mounds reveal the location of burrows. Recent techniques to extend scuba depths should increase our knowledge of the distribution of Hoplolatilus species.