Genetic diversity is a fundamental requirement for evolution and adaptation. Nonetheless, the forces that maintain patterns of genetic variation in wild populations are not completely understood. ...Neutral theory posits that genetic diversity will increase with a larger effective population size and the decreasing effects of drift. However, the lack of compelling evidence for a relationship between genetic diversity and population size in comparative studies has generated some skepticism over the degree that neutral sequence evolution drives overall patterns of diversity. The goal of this study was to measure genetic diversity among sympatric populations of related lizard species that differ in population size and other ecological factors. By sampling related species from a single geographic location, we aimed to reduce nuisance variance in genetic diversity owing to species differences, for example, in mutation rates or historical biogeography. We compared populations of zebra-tailed lizards and western banded geckos, which are abundant and short-lived, to chuckwallas and desert iguanas, which are less common and long-lived. We assessed population genetic diversity at three protein-coding loci for each species. Our results were consistent with the predictions of neutral theory, as the abundant species almost always had higher levels of haplotype diversity than the less common species. Higher population genetic diversity in the abundant species is likely due to a combination of demographic factors, including larger local population sizes (and presumably effective population sizes), faster generation times and high rates of gene flow with other populations.
The E12-14-012 experiment, performed in Jefferson Lab Hall A, has measured the $(e, e'p)$ cross section in parallel kinematics using a natural argon target. Here, we report the full results of the ...analysis of the data set corresponding to beam energy 2.222 GeV, and spanning the missing momentum and missing energy range $15 \lesssim p_m \lesssim 300$ MeV/c and $12 \lesssim E_m \lesssim 80$ MeV. The reduced cross section, determined as a function of $p_m$ and $E_m$ with $\approx$4\% accuracy, has been fitted using the results of Monte Carlo simulations involving a model spectral function and including the effects of final state interactions. The overall agreement between data and simulations turns out to be quite satisfactory ($\chi^2$/n.d.o.f.=1.9). Furthermore, the resulting spectral function will provide valuable new information, needed for the interpretation of neutrino interactions in liquid argon detectors.
The E12-14-012 experiment, performed in Jefferson Lab Hall A, has measured the (e, e'p) cross section in parallel kinematics using a natural titanium target. In this paper, we report the analysis of ...the dataset obtained in different kinematics for our solid natural titanium target. Data were obtained in a range of missing momentum and missing energy between 15 ≲ pm ≲ 250 MeV / c and 12 ≲ Em ≲ 80 MeV, respectively, and using an electron beam energy of 2.2 GeV. We measured the reduced cross section with ~7% accuracy as a function of both missing momentum and missing energy. Furthermore, our Monte Carlo simulation, including both a model spectral function and the effects of final-state interactions, satisfactorily reproduces the data.
Abstract Many insects and other animals carry microbial endosymbionts that influence their reproduction and fitness. These relationships only persist if endosymbionts are reliably transmitted from ...one host generation to the next. Wolbachia are maternally transmitted endosymbionts found in most insect species, but transmission rates can vary across environments. Maternal transmission of w Mel Wolbachia depends on temperature in natural Drosophila melanogaster hosts and in transinfected Aedes aegypti , where w Mel is used to block pathogens that cause human disease. In D. melanogaster , w Mel transmission declines in the cold as Wolbachia become less abundant in host ovaries and at the posterior pole plasm (the site of germline formation) in mature oocytes. Here, we assess how temperature affects maternal transmission and underlying patterns of Wolbachia localization across 10 Wolbachia strains diverged up to 50 million years—including strains closely related to w Mel—and their natural Drosophila hosts. Many Wolbachia maintain high transmission rates across temperatures, despite highly variable (and sometimes low) levels of Wolbachia in the ovaries and at the developing germline in late-stage oocytes. Identifying strains like closely related w Mel-like Wolbachia with stable transmission across variable environmental conditions may improve the efficacy of Wolbachia -based biocontrol efforts as they expand into globally diverse environments.
An approach is described for automatic assessment of crop and weed area in images of widely spaced (0.25 m) cereal crops, captured from a tractor mounted camera. A form of vegetative index, which is ...invariant over the range of natural daylight illumination, was computed from the red, green and blue channels of a conventional CCD camera. The transformed image can be segmented into soil and vegetative components using a single fixed threshold. A previously reported algorithm was applied to robustly locate the crop rows. Assessment zones were automatically positioned; for crop growth directly over the crop rows, and for weed growth between the rows. The proportion of crop and weed pixels counted was compared with a manual assessment of area density on the basis of high resolution plan view photographs of the same area; this was performed for views with a range of crop and weed levels. The correlation of the manual and automatic measures was examined, and used to obtain a calibration for the automatic approach. The results of mapping of a small field, at two times, are presented. The results of the automated mapping appear to be consistent with manual assessment.
The arms race between tetrodotoxin-bearing Pacific newts (Taricha) and their garter snake predators (Thamnophis) in western North America has become a classic example of coevolution, shedding light ...on predator-prey dynamics, the molecular basis of adaptation, and patterns of convergent evolution. Newts are defended by tetrodotoxin (TTX), a neurotoxin that binds to voltage-gated sodium channels (Na
proteins), arresting electrical activity in nerves and muscles and paralyzing would-be predators. However, populations of the common garter snake (T. sirtalis) have overcome this defense, largely through polymorphism at the locus SCN4A, which renders the encoded protein (Na
1.4) less vulnerable to TTX. Previous work suggests that SCN4A commonly shows extreme deviations from Hardy-Weinberg equilibrium (HWE) in these populations, which has been interpreted as the result of intense selection imposed by newts. Here we show that much of this apparent deviation can be attributed to sex linkage of SCN4A. Using genomic data and quantitative PCR, we show that SCN4A is on the Z chromosome in Thamnophis and other advanced snakes. Taking Z-linkage into account, we find that most apparent deviations from HWE can be explained by female hemizygosity rather than low heterozygosity. Sex linkage can affect mutation rates, selection, and drift, and our results suggest that Z-linkage of SCN4A may make significant contributions to the overall dynamics of the coevolutionary arms race between newts and snakes.
Convergent phenotypes often result from similar underlying genetics, but recent work suggests convergence may also occur in the historical order of substitutions en route to an adaptive outcome. We ...characterized convergence in the mutational steps to two independent outcomes of tetrodotoxin (TTX) resistance in separate geographic lineages of the common garter snake (Thamnophis sirtalis) that coevolved with toxic newts. Resistance is largely conferred by amino acid changes in the skeletal muscle sodium channel (Nav1.4) that interfere with TTX-binding. We sampled variation in Nav1.4 throughout western North America and found clear evidence that TTX-resistant changes in both lineages began with the same isoleucine-valine mutation (I1561V) within the outer pore of Nav1.4. Other point mutations in the pore, shown to confer much greater resistance, accumulate later in the evolutionary progression and always occur together with the initial I1561V change. A gene tree of Nav1.4 suggests the I1561V mutations in each lineage are not identical-by-decent, but rather they arose independently. Convergence in the evolution of channel resistance is likely the result of shared biases in the two lineages of T. sirtalis—only a few mutational routes can confer TTX resistance while maintaining the conserved function of voltage-gated sodium channels.
Spaceflight induces lasting enlargement of the brain's ventricles as well as intracranial fluid shifts. These intracranial fluid shifts have been attributed to prolonged microgravity exposure, ...however, the potential effects of hypergravity exposure during launch and landing have yet to be elucidated. Here we describe a case report of a Crewmember who experienced an Aborted Launch ("CAL"). CAL's launch and landing experience was dissociated from prolonged microgravity exposure. Using MRI, we show that hypergravity exposure during the aborted launch did not induce lasting ventricular enlargement or intracranial fluid shifts resembling those previously reported with spaceflight. This case study therefore rules out hypergravity during launch and landing as a contributing factor to previously reported long-lasting intracranial fluid changes following spaceflight.
Environmental and commercial pressures are pushing vegetable and salad growers away from a reliance on herbicides. Whilst inter-row cultivation provides a relatively efficient method of removing ...weeds between crop rows, hand labour is often required to remove weeds within rows. A machine vision guidance has been used to address the problem of mechanically removing weeds within rows of transplanted vegetables and salads.
The experimental machine was based on a commercially available steerage hoe equipped with conventional inter-row cultivation blades. It was also fitted with two novel shallow cultivation modules acting within crop rows. Each module featured a hydraulically driven disc rotating about a substantially vertical axis. Each disc had an interior section cut away to allow crop plants to pass undamaged. A vision system detected the phase of approaching plants and that information was combined with measured disc rotation to calculate a phase error between the next plant and disc cut-out. This phase error was corrected by advancing or retarding the hydraulic drive enabling synchronisation of the mechanism even in the presence of crop spacing variability.
Field trials in transplanted cabbage indicated that under normal commercial growing conditions crop damage levels were low with weed reductions in the range 62–87% measured within a 240
mm radius zone around crop plants.
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