Evidence and perceptions of rainfall change in Malawi: Do maize cultivar choices enhance climate change adaptation in sub-Saharan Africa?

Getting farmers to adopt new cultivars with greater tolerance for coping with climatic extremes and variability is considered as one way of adapting agricultural production to climate change. However, for successful adaptation to occur, an accurate recognition and understanding of the climate signal by key stakeholders (farmers, seed suppliers and agricultural extension services) is an essential precursor. This paper presents evidence based on fieldwork with smallholder maize producers and national seed network stakeholders in Malawi from 2010 to 2011, assessing understandings of rainfall changes and decision-making about maize cultivar choices. Our findings show that preferences for short-season maize cultivars are increasing based on perceptions that season lengths are growing shorter due to climate change and the assumption that growing shorter-season crops represents a good strategy for adapting to drought. However, meteorological records for the two study areas present no evidence for shortening seasons (or any significant change to rainfall characteristics), suggesting that short-season cultivars may not be the most suitable adaptation option for these areas. This demonstrates the dangers of oversimplified climate information in guiding changes in farmer decision-making about cultivar choice

Coquillettidia (Culicidae, Diptera) mosquitoes are natural vectors of avian malaria in Africa

<p>Abstract</p> <p>Background</p> <p>The mosquito vectors of <it>Plasmodium </it>spp. have largely been overlooked in studies of ecology and evolution of avian malaria and other vertebrates in wildlife.</p> <p>Methods</p> <p><it>Plasmodium </it>DNA from wild-caught <it>Coquillettidia </it>spp. collected from lowland forests in Cameroon was isolated and sequenced using nested PCR. Female <it>Coquillettidia aurites </it>were also dissected and salivary glands were isolated and microscopically examined for the presence of sporozoites.</p> <p>Results</p> <p>In total, 33% (85/256) of mosquito pools tested positive for avian <it>Plasmodium </it>spp., harbouring at least eight distinct parasite lineages. Sporozoites of <it>Plasmodium </it>spp. were recorded in salivary glands of <it>C. aurites </it>supporting the PCR data that the parasites complete development in these mosquitoes. Results suggest <it>C. aurites</it>, <it>Coquillettidia pseudoconopas </it>and <it>Coquillettidia metallica </it>as new and important vectors of avian malaria in Africa. All parasite lineages recovered clustered with parasites formerly identified from several bird species and suggest the vectors capability of infecting birds from different families.</p> <p>Conclusion</p> <p>Identifying the major vectors of avian <it>Plasmodium </it>spp. will assist in understanding the epizootiology of avian malaria, including differences in this disease distribution between pristine and disturbed landscapes.</p

Determining the Initiation of Shear Zone Deformation Using Titanite Petrochronology

We present an integrative petrochronological approach to dating the initiation of shear zone deformation in granitic rocks, using the mineral titanite (CaTiSiO5). This method is suited to granitoid-hosted shear zones in continental arc settings, where the interplay between tectonics, magmatism, and deformation is actively debated. Microstructural observations including crystallographic misorientations, fabric context, and backscattered electron images were used to identify relict magmatic, partially to fully recrystallized, and neoblastic titanite crystals. Principal component analysis of trace element compositional variance in titanite was used to further distinguish and quantify the crystal chemical response to deformation. High-precision isotope dilution U-Pb geochronological measurements on relict magmatic, partially to fully recrystallized, and neoblastic titanite crystals was used to constrain the timing of shear zone initiation. For a sample of a porphyritic orthogneiss from the western Idaho shear zone of the northern U.S. Cordillera, U-Pb zircon geochronology dates emplacement of this unit to between ca. 105 and 103 Ma, whereas the age of partially recrystallized and neoblastic titanite grains indicate that the western Idaho shear zone initiated between ca. 98 and 96 Ma. The \u3e5 Ma lag between pluton emplacement and the onset of deformation indicates that mid-Cretaceous deformation in the western Idaho shear zone is temporally distinct from Late Jurassic–Early Cretaceous accretionary tectonics. Our integrated petrochronological investigation documents that: 1) deformation induces textural, chemical, and isotopic changes in titanite; 2) the geochemical properties of primary magmatic titanite collapse into a discernible trend of subsolidus syn-deformational titanite compositions; and 3) the onset of deformation and progression of strain accumulation are preserved in the U-Pb ages of these titanite crystals

A mixed methods study of the challenges for geoscience majors in identifying potential careers and the benefits of a career awareness and planning course

Undergraduates majoring in geoscience are often unaware of their career options beyond traditional resource industries; they need explicit supports to consider their post-graduation options. This mixed methods study sought to fill gaps in the literature related to the overabundance of solely quantitative studies related to career awareness and the dearth of studies on career awareness courses that are guided by theory. The study investigates the challenges geoscience undergraduate students face when considering a career, what resources students use to find career information, and the benefits of a geoscience career awareness and planning course (career course) rooted in cognitive information processing (CIP) theory. Data were collected via our Career Resource Survey (from both career course participants and a comparison group), course assignments, and focus groups. Findings indicate that many students do not know what careers they can pursue in the geosciences, nor what the specific titles of careers mean (e.g., hydrology technician vs. hydrologist). Undergraduate students report using a variety of resources to learn more about careers and to find jobs, but no particular resource stands out as being primarily used. The career course supported students in terms of guidance, tools, and connecting with geoscience careers. Specifically, the course supported students in exploring myriad geoscience-related careers, identifying the specific steps needed to pursue these careers, meeting and connecting with a variety of people in geoscience careers, and seeing the value of their geoscience degrees. Other geoscience programs may consider creating a similar course, or implementing components of the course as connected to CIP theory. Professional geoscientists and organizations may consider being more proactive in connecting with undergraduate students to support their knowledge of, and transition into, geoscience careers. Being deliberate in exposing undergraduates to geoscience career opportunities may help to attract and keep students engaged in the field, and to graduate geoscientists who are more highly-qualified for the workforce.</p

Recalibrating the Devonian Time Scale: A New Method for Integrating Radioisotopic and Astrochronologic Ages in a Bayesian Framework

The numerous biotic, climatic, and tectonic events of the Devonian cannot be correlated and investigated without a well-calibrated time scale. Here, we updated the calibration of the Devonian time scale using a Bayesian age-depth model that incorporates radioisotopic ages and astrochronology durations. We used existing radioisotopic ages collected and harmonized in the last two geologic time scale compilations, as well as new U-Pb zircon ages from Emsian {Hercules I K-bentonite, Wetteldorf, Germany: 394.290 ± 0.097(0.21)[0.47] Ma} and Eifelian K-bentonites {Tioga B and Tioga F K-bentonites, Fayette, New York, USA: 390.82 ± 0.18(0.26)[0.48] Ma and 390.14 ± 0.14(0.23)[0.47] Ma, respectively}. We anchored floating astrochronology stage durations on radioisotopic ages and chained astrochronologic constraints and uncertainty together to extrapolate conditioning age likelihoods up or down the geologic time scale, which is a new method for integrating astrochronology into age-depth modeling. The modeling results in similar ages and durations for Devonian stages regardless of starting biostratigraphic scaling assumptions. We produced a set of rescaled biostratigraphic zonations, and a new numerical calibration of Devonian stage boundary ages with robust uncertainty estimates, which allow us to evaluate future targets for Devonian time scale research. These methods are broadly applicable for time scale work and provide a template for an integrated stratigraphic approach to time scale modeling

The Interpretability of Stable Hydrogen Isotopes in Modern Herbivore Tooth Enamel

Stable hydrogen isotopes (δD values) in animal organic tissues such as collagen and keratin typically correlate with local meteoric water, but little is known about δD in tooth enamel apatite. In this study, we analyzed comminuted tooth enamel for oxygen isotopes (δ18O) of the CO3 component and for δD of bulk enamel. We find positive correlations between enamel δD and δ18O (R2 = 0.70) and between enamel δD and local precipitation δD (R2 = 0.53). However, the slopes of these relationships are much shallower (less variation in tooth enamel δD) than expected from studies of other tissues. Based on mass spectrometric peak areas, H2 contents for enamel are 2–5 times higher than expected from chemical compositions, and we interpret as much as 50–90% of measured hydrogen from tooth enamel may be adsorbed water derived from laboratory water vapor. We tested this hypothesis by equilibrating tooth enamel with very high and very low δD values of water vapor, then exposing to laboratory air for different periods of time ranging from minutes to 8 hours. These experiments show that the apparent δD value of enamel converges to a nearly constant δD value in 1 to 2 hours. The large amount of adsorbed water and rapid approach to equilibrium will make it difficult to infer provenance from δD measurements alone, or to reproduce measured tooth enamel δD values among laboratories with different water vapor compositions. Heating at 70 °C for 48 hours in air does not remove adsorbed hydrogen, but does reduce δD values by c. 10‰ compared to unheated samples. Differences in δD values for heated vs. unheated enamel may reflect either a different, temperature-dependent partition coefficient between adsorbed water (on apatite) and water vapor, exchange of structural H at elevated temperatures, or subtle changes to crystal structure, such as loss of structural H

Timescales of Impact Melt Sheet Crystallization and the Precise Age of the Morokweng Impact Structure, South Africa

Impact cratering was a fundamental geological process in the early Solar System and, thus, constraining the timescales over which large impact structures cool is critical to understanding the thermal evolution and habitability of early planetary crusts. Additionally, impacts can induce mass extinctions and establishing the precise timing of the largest impacts on Earth can shed light on their role in such events. Here we report a high-precision zircon U–Pb geochronology study of the Morokweng impact structure, South Africa, which appears to have a maximum present-day diameter of ∼80 km. Our work provides (i) constraints on the cooling of large impact melt sheets, and (ii) a high-precision age for one of Earth\u27s largest impact events, previously proposed to have overlapped the ca. 145 Ma Jurassic–Cretaceous (J–K) boundary. High-precision U–Pb geochronology was performed on unshocked, melt-grown zircon from five samples from a borehole through approximately 800 m of preserved impact melt rock. Weighted mean 206Pb/238U dates for the upper four samples are indistinguishable, with relative uncertainties (internal errors) of better than 20 ka, whereas the lowermost sample is distinguishably younger than the others. Thermal modeling suggests that the four indistinguishable dates are consistent with in situ conductive cooling of melt at this location within 30 kyr of the impact. The younger date from the lowest sample cannot be explained by in situ conductive cooling in line with the overlying samples, but the date is within the ∼65 kyr timeframe for melt-present conditions in footwall rocks below the impact melt sheet that is indicated by our thermal model. The Morokweng impact event is here constrained to 146.06 ± 0.16 Ma (2σ; full external uncertainty), which precedes current estimates of the age of the J–K boundary by several million years

The major genetic determinants of HIV-1 control affect HLA class I peptide presentation.

Infectious and inflammatory diseases have repeatedly shown strong genetic associations within the major histocompatibility complex (MHC); however, the basis for these associations remains elusive. To define host genetic effects on the outcome of a chronic viral infection, we performed genome-wide association analysis in a multiethnic cohort of HIV-1 controllers and progressors, and we analyzed the effects of individual amino acids within the classical human leukocyte antigen (HLA) proteins. We identified &gt;300 genome-wide significant single-nucleotide polymorphisms (SNPs) within the MHC and none elsewhere. Specific amino acids in the HLA-B peptide binding groove, as well as an independent HLA-C effect, explain the SNP associations and reconcile both protective and risk HLA alleles. These results implicate the nature of the HLA-viral peptide interaction as the major factor modulating durable control of HIV infection

A Theory of Natural Addiction

Economic theories of rational addiction aim to describe consumer behavior in the presence of habit-forming goods. We provide a biological foundation for this body of work by formally specifying conditions under which it is optimal to form a habit. We demonstrate the empirical validity of our thesis with an in-depth review and synthesis of the biomedical literature concerning the action of opiates in the mammalian brain and their effects on behavior. Our results lend credence to many of the unconventional behavioral assumptions employed by theories of rational addiction, including adjacent complementarity and the importance of cues, attention, and self-control in determining the behavior of addicts. Our approach suggests, however, that addiction is “harmful” only when the addict fails to implement the optimal solution. We offer evidence for the special case of the opiates that harmful addiction is the manifestation of a mismatch between behavioral algorithms encoded in the human genome and the expanded menu of choices--generated for example, by advances in drug delivery technology--faced by consumers in the modern world