For food-caching animals inhabiting environments with strong seasonal variation, harsh winter conditions may limit access to naturally available food and favour the evolution of enhanced spatial ...memory. Spatial memory enables animals to remember the locations of food caches for overwinter survival, therefore animals in harsher conditions may benefit more from more accurate spatial memory than conspecifics living under relatively mild conditions. Despite numerous laboratory studies lending indirect support to the hypothesis that a harsh environment favours the evolution of spatial memory, there is no direct evidence showing fitness consequences of variation in spatial memory. As a step towards evaluating this hypothesis in natural populations, we established spatial arrays of programmable bird feeders equipped with radio frequency identification technology (RFID) to test for individual variation in spatial memory in food-caching mountain chickadees, Poecile gambeli, at two elevations differing in winter climate severity. Individuals could only access food at a single rewarding feeder within an array of eight, and each individual had to learn the location of their unique rewarding feeder. Birds at higher elevations visited the arrays significantly more frequently than birds at lower elevations, suggesting more intense food caching. They also performed better at locating their rewarding feeder than birds from lower elevations. Individuals showing better performance participated in more overall trials, suggesting a link between food-caching propensity and memory performance, but higher overall levels of activity within each array yielded less accurate memory performance. Finally, rotating the arrays showed that birds relied specifically on spatial memory in order to locate their rewarding feeder. To our knowledge, this is the first explicit test of spatial memory performance in food-caching birds under natural conditions. Our results corroborate earlier laboratory-based work showing large individual variation in spatial memory performance and lay the groundwork for future investigation into the fitness consequences of individual variation and the evolution of spatial memory.
•Harsh winters may favour the evolution of enhanced spatial memory in resident birds.•We tested spatial memory in chickadees from different elevations with radio frequency identification technology.•High-elevation birds outperformed low-elevation birds in a spatial memory task.•This is the first test of spatial memory variation in a food-caching bird in the wild.
Summary
Background
Personal exposure to fungal bioaerosols derived from contaminated building materials or agricultural commodities may induce or exacerbate a variety of adverse health effects. The ...genomic mechanisms that underlie pulmonary immune responses to fungal bioaerosols have remained unclear.
Objective
The impact of fungal viability on the pulmonary microRNA and messenger RNA profiles that regulate murine immune responses was evaluated following subchronic inhalation exposure to Aspergillus fumigatus conidia.
Methods
Three groups of naïve B6C3F1/N mice were exposed via nose‐only inhalation to A. fumigatus viable conidia, heat‐inactivated conidia (HIC), or HEPA‐filtered air twice a week for 13 weeks. Total RNA was isolated from whole lung 24 and 48 h postfinal exposure and was further processed for gene expression and microRNA array analysis. The molecular network pathways between viable and HIC groups were evaluated.
Results
Comparison of data sets revealed increased Il4, Il13 and Il33 expression in mice exposed to viable vs. HIC. Of 415 microRNAs detected, approximately 50% were altered in mice exposed to viable vs. HIC 48 h postexposure. Significantly down‐regulated (P ≤ 0.05) miR‐29a‐3p was predicted to regulate TGF‐β3 and Clec7a, genes involved in innate responses to viable A. fumigatus. Also significantly down‐regulated (P ≤ 0.05), miR‐23b‐3p regulates genes involved in pulmonary IL‐13 and IL‐33 responses and SMAD2, downstream of TGF‐β signalling. Using Ingenuity Pathway Analysis, a novel interaction was identified between viable conidia and SMAD2/3.
Conclusions and Clinical Relevance
Examination of the pulmonary genetic profiles revealed differentially expressed genes and microRNAs following subchronic inhalation exposure to A. fumigatus. MicroRNAs regulating genes involved in the pulmonary immune responses were those with the greatest fold change. Specifically, germinating A. fumigatus conidia were associated with Clec7a and were predicted to interact with Il13 and Il33. Furthermore, altered microRNAs may serve as potential biomarkers to evaluate fungal exposure.
Summary
Background
Personal exposure to fungal bioaerosols derived from contaminated building materials or agricultural commodities may induce or exacerbate a variety of adverse health effects. The ...genomic mechanisms that underlie pulmonary immune responses to fungal bioaerosols have remained unclear.
Objective
The impact of fungal viability on the pulmonary micro
RNA
and messenger
RNA
profiles that regulate murine immune responses was evaluated following subchronic inhalation exposure to
Aspergillus fumigatus
conidia.
Methods
Three groups of naïve B6C3F1/N mice were exposed via nose‐only inhalation to
A. fumigatus
viable conidia, heat‐inactivated conidia (HIC), or
HEPA
‐filtered air twice a week for 13 weeks. Total
RNA
was isolated from whole lung 24 and 48 h postfinal exposure and was further processed for gene expression and micro
RNA
array analysis. The molecular network pathways between viable and HIC groups were evaluated.
Results
Comparison of data sets revealed increased
Il4
,
Il13
and
Il33
expression in mice exposed to viable vs. HIC. Of 415 micro
RNA
s detected, approximately 50% were altered in mice exposed to viable vs. HIC 48 h postexposure. Significantly down‐regulated (
P
≤ 0.05) miR‐29a‐3p was predicted to regulate
TGF
‐
β
3
and
Clec7a
, genes involved in innate responses to viable
A. fumigatus
. Also significantly down‐regulated (
P
≤ 0.05), miR‐23b‐3p regulates genes involved in pulmonary
IL
‐13 and
IL
‐33 responses and
SMAD
2
, downstream of
TGF
‐β signalling. Using Ingenuity Pathway Analysis, a novel interaction was identified between viable conidia and
SMAD
2/3
.
Conclusions and Clinical Relevance
Examination of the pulmonary genetic profiles revealed differentially expressed genes and micro
RNA
s following subchronic inhalation exposure to
A. fumigatus
. Micro
RNA
s regulating genes involved in the pulmonary immune responses were those with the greatest fold change. Specifically, germinating
A. fumigatus
conidia were associated with
Clec7a
and were predicted to interact with
Il13
and
Il33
. Furthermore, altered micro
RNA
s may serve as potential biomarkers to evaluate fungal exposure.
Remnant radio-loud AGN in the Herschel-ATLAS field Mahatma, V H; Hardcastle, M J; Williams, W L ...
Monthly notices of the Royal Astronomical Society,
04/2018, Letnik:
475, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Abstract
Only a small fraction of observed active galactic nuclei (AGN) display large-scale radio emission associated with jets, yet these radio-loud AGN have become increasingly important in models ...of galaxy evolution. In determining the dynamics and energetics of the radio sources over cosmic time, a key question concerns what happens when their jets switch off. The resulting ‘remnant' radio-loud AGN have been surprisingly evasive in past radio surveys, and therefore statistical information on the population of radio-loud AGN in their dying phase is limited. In this paper, with the recent developments of Low-Frequency Array (LOFAR) and the Very Large Array, we are able to provide a systematically selected sample of remnant radio-loud AGN in the Herschel-ATLAS field. Using a simple core-detection method, we constrain the upper limit on the fraction of remnants in our radio-loud AGN sample to 9 per cent, implying that the extended lobe emission fades rapidly once the core/jets turn off. We also find that our remnant sample has a wide range of spectral indices ($-1.5\leqslant \alpha ^{1400}_{150}\leqslant -0.5$), confirming that the lobes of some remnants may possess flat spectra at low frequencies just as active sources do. We suggest that, even with the unprecedented sensitivity of LOFAR, our sample may still only contain the youngest of the remnant population.
Deep Chandra observations of Pictor A Hardcastle, M J; Lenc, E; Birkinshaw, M ...
Monthly notices of the Royal Astronomical Society,
02/2016, Letnik:
455, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We report on deep Chandra observations of the nearby broad-line radio galaxy Pictor A, which we combine with new Australia Telescope Compact Array (ATCA) observations. The new X-ray data have a ...factor of 4 more exposure than observations previously presented and span a 15 yr time baseline, allowing a detailed study of the spatial, temporal and spectral properties of the AGN, jet, hotspot and lobes. We present evidence for further time variation of the jet, though the flare that we reported in previous work remains the most significantly detected time-varying feature. We also confirm previous tentative evidence for a faint counterjet. Based on the radio through X-ray spectrum of the jet and its detailed spatial structure, and on the properties of the counterjet, we argue that inverse-Compton models can be conclusively rejected, and propose that the X-ray emission from the jet is synchrotron emission from particles accelerated in the boundary layer of a relativistic jet. For the first time, we find evidence that the bright western hotspot is also time-varying in X-rays, and we connect this to the small-scale structure in the hotspot seen in high-resolution radio observations. The new data allow us to confirm that the spectrum of the lobes is in good agreement with the predictions of an inverse-Compton model and we show that the data favour models in which the filaments seen in the radio images are predominantly the result of spatial variation of magnetic fields in the presence of a relatively uniform electron distribution.
LOFAR FACET CALIBRATION Weeren, R. J. van; Williams, W. L.; Hardcastle, M. J. ...
The Astrophysical journal. Supplement series,
03/2016, Letnik:
223, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT LOFAR, the Low-Frequency Array, is a powerful new radio telescope operating between 10 and 240 MHz. LOFAR allows detailed sensitive high-resolution studies of the low-frequency radio sky. At ...the same time LOFAR also provides excellent short baseline coverage to map diffuse extended emission. However, producing high-quality deep images is challenging due to the presence of direction-dependent calibration errors, caused by imperfect knowledge of the station beam shapes and the ionosphere. Furthermore, the large data volume and presence of station clock errors present additional difficulties. In this paper we present a new calibration scheme, which we name facet calibration, to obtain deep high-resolution LOFAR High Band Antenna images using the Dutch part of the array. This scheme solves and corrects the direction-dependent errors in a number of facets that cover the observed field of view. Facet calibration provides close to thermal noise limited images for a typical 8 hr observing run at ∼ 5 ″ resolution, meeting the specifications of the LOFAR Tier-1 northern survey.
ABSTRACT We present deep LOFAR observations between 120 and 181 MHz of the "Toothbrush" (RX J0603.3+4214), a cluster that contains one of the brightest radio relic sources known. Our LOFAR ...observations exploit a new and novel calibration scheme to probe 10 times deeper than any previous study in this relatively unexplored part of the spectrum. The LOFAR observations, when combined with VLA, GMRT, and Chandra X-ray data, provide new information about the nature of cluster merger shocks and their role in re-accelerating relativistic particles. We derive a spectral index of at the northern edge of the main radio relic, steepening toward the south to . The spectral index of the radio halo is remarkably uniform ( , with an intrinsic scatter of ). The observed radio relic spectral index gives a Mach number of , assuming diffusive shock acceleration. However, the gas density jump at the northern edge of the large radio relic implies a much weaker shock ( , with an upper limit of ). The discrepancy between the Mach numbers calculated from the radio and X-rays can be explained if either (i) the relic traces a complex shock surface along the line of sight, or (ii) if the radio relic emission is produced by a re-accelerated population of fossil particles from a radio galaxy. Our results highlight the need for additional theoretical work and numerical simulations of particle acceleration and re-acceleration at cluster merger shocks.
NGC 326: X-shaped no more Hardcastle, M J; Croston, J H; Shimwell, T W ...
Monthly notices of the Royal Astronomical Society,
09/2019, Letnik:
488, Številka:
3
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
We present new 144-MHz Low-Frequency Array (LOFAR) observations of the prototypical ‘X-shaped’ radio galaxy NGC 326, which show that the formerly known wings of the radio lobes extend ...smoothly into a large-scale, complex radio structure. We argue that this structure is most likely the result of hydrodynamical effects in an ongoing group or cluster merger, for which pre-existing X-ray and optical data provide independent evidence. The large-scale radio structure is hard to explain purely in terms of jet reorientation due to the merger of binary black holes, a previously proposed explanation for the inner structure of NGC 326. For this reason, we suggest that the simplest model is one in which the merger-related hydrodynamical processes account for all the source structure, though we do not rule out the possibility that a black hole merger has occurred. Inference of the black hole–black hole merger rate from observations of X-shaped sources should be carried out with caution in the absence of deep, sensitive low-frequency observations. Some X-shaped sources may be signposts of cluster merger activity, and it would be useful to investigate the environments of these objects more generally.
We report L-band VLA observations of 1RXS J0603.3+4214, a cluster that hosts a bright radio relic, known as the Toothbrush, and an elongated giant radio halo. These new observations allow us to study ...the surface brightness distribution down to 1 arcsec resolution with very high sensitivity. Our images provide an unprecedented detailed view of the Toothbrush, revealing enigmatic filamentary structures. To study the spectral index distribution, we complement our analysis with published LOFAR and GMRT observations. The bright "brush" of the Toothbrush shows a prominent narrow ridge to its north with a sharp outer edge. The spectral index at the ridge is in the range −0.70 ≤ ≤ −0.80. We suggest that the ridge is caused by projection along the line of sight. With a simple toy model for the smallest region of the ridge, we conclude that the magnetic field is below 5 G and varies significantly across the shock front. Our model indicates that the actual Mach number is higher than that obtained from the injection index and agrees well with the one derived from the overall spectrum, namely . The radio halo shows an average spectral index of = −1.16 0.05 and a slight gradient from north to south. The southernmost part of the halo is steeper and possibly related to a shock front. Excluding the southernmost part, the halo morphology agrees very well with the X-ray morphology. A power-law correlation is found between the radio and X-ray surface brightness.
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