2,704 research outputs found
Geographic body size variation in ectotherms: effects of seasonality on an anuran from the southern temperate forest
Indexación: Web of Science; Scopus.Background: Body size variation has played a central role in biogeographical research, however, most studies have aimed to describe trends rather than search for underlying mechanisms. In order to provide a more comprehensive understanding of the causes of intra-specific body size variation in ectotherms, we evaluated eight hypotheses proposed in the literature to account for geographical body size variation using the Darwin's frog (Rhinoderma darwinii), an anuran species widely distributed in the temperate forests of South America. Each of the evaluated hypotheses predicted a specific relationship between body size and environmental variables. The level of support for each of these hypotheses was assessed using an information-theoretic approach and based on data from 1015 adult frogs obtained from 14 sites across the entire distributional range of the species.
Results: There was strong evidence favouring a single model comprising temperature seasonality as the predictor variable. Larger body sizes were found in areas of greater seasonality, giving support to the "starvation resistance" hypothesis. Considering the known role of temperature on ectothermic metabolism, however, we formulated a new, non-exclusive hypothesis, termed "hibernation hypothesis": greater seasonality is expected to drive larger body size, since metabolic rate is reduced further and longer during colder, longer winters, leading to decreased energy depletion during hibernation, improved survival and increased longevity (and hence growth). Supporting this, a higher post-hibernation body condition in animals from areas of greater seasonality was found.
Conclusions: Despite largely recognized effects of temperature on metabolic rate in ectotherms, its importance in determining body size in a gradient of seasonality has been largely overlooked so far. Based on our results, we present and discuss an alternative mechanism, the "hibernation hypothesis", underlying geographical body size variation, which can be helpful to improve our understanding of biogeographical patterns in ectotherms.https://frontiersinzoology.biomedcentral.com/articles/10.1186/s12983-015-0132-
Feynman parametrization and Mellin summation at finite temperature
We show that the Mellin summation technique (MST) is a well defined and
useful tool to compute loop integrals at finite temperature in the
imaginary-time formulation of thermal field theory, especially when interested
in the infrared limit of such integrals. The method makes use of the Feynman
parametrization which has been claimed to have problems when the analytical
continuation from discrete to arbitrary complex values of the Matsubara
frequency is performed. We show that without the use of the MST, such problems
are not intrinsic to the Feynman parametrization but instead, they arise as a
result of (a) not implementing the periodicity brought about by the possible
values taken by the discrete Matsubara frequencies before the analytical
continuation is made and (b) to the changing of the original domain of the
Feynman parameter integration, which seemingly simplifies the expression but in
practice introduces a spurious endpoint singularity. Using the MST, there are
no problems related to the implementation of the periodicity but instead, care
has to be taken when the sum of denominators of the original amplitude
vanishes. We apply the method to the computation of loop integrals appearing
when the effects of external weak magnetic fields on the propagation of scalar
particles is considered.Comment: 16 pages, 1 figure. Discussion expanded. References added. Published
versio
Black Holes: Scatterers, Absorbers and Emitters of Particles
Accurate and powerful analytic and computational methods developped by the
author allow to obtain the highly non trivial total absorption spectrum of the
Black Hole, as well as phase shifts and cross sections (elastic and inelastic),
the angular distribution of absorbed and scattered waves, and the Hawking
emission rates. The exact total absorption spectrum of waves by the Black Hole
presents as a function of frequency a remarkable oscillatory behaviour
characteristic of a diffraction pattern. It oscillates around its optical
geometric limit (27/4) pi (r_s)^2 with decreasing amplitude and almost constant
period. This is an unique distinctive feature of the black hole absorption, and
due to its r=0 singularity. Ordinary absorptive bodies and optical models do
not present these features. The Hamiltonian describing the wave-black hole
interaction is non hermitian (despite being real) due to its singularity at the
origin (r=0). The unitarity optical theorem of scattering theory is generalized
to the black hole case explicitely showing that absorption takes place only at
the origin (r = 0). All these results allow to understand and reproduce the
Black Hole absorption spectrum in terms of Fresnel-Kirchoff diffraction theory.
These fundamental features will be present for generic higher dimensional Black
Hole backgrounds, and whatever the low energy effective theory they arise from.
In recent and increasing litterature on absorption cross sections (`grey body
factors') of black holes (whatever ordinary, stringy, D-braned), the
fundamental remarkable features of the Black Hole Absorption spectrum are
overlooked.Comment: LaTex, 19 pages, Lectures delivered at the Chalonge School, Nato ASI:
Phase Transitions in the Early Universe: Theory and Observations. To appear
in the Proceedings, Editors H. J. de Vega, I. Khalatnikov, N. Sanchez.
(Kluwer Pub
Droplet impact onto moving liquids
From rain drops landing on the ocean to inkjet printing, the impact of droplets onto moving liquid surfaces is a ubiquitous process in nature and in industry. A rich range of phenomena can arise. The behaviour depends on the inertia, the properties of the drops and the relative speeds in the impact zone. While the result ranges from tranquil coalescence to violent splashing, intermediate regimes also occur, including partial and complete bouncing and even 'surfing' of the droplet. These regimes are determined by the ratio of the drop and surface velocities and the liquid properties. A regime diagram can be constructed in which distinct dynamical regimes are clearly identified.This project was supported by the EPSRC (grant EP/H018913/1), the John Fell Oxford University Press Research Fund, and the Royal Society (through a University Research Fellowship and a Research Grant)
Nonadiabatic forces in ion-solid interactions: the initial stages of radiation damage
The Born-Oppenheimer approximation is the keystone for molecular dynamics simulations of radiation damage processes; however, actual materials response involves nonadiabatic energy exchange between nuclei and electrons. In this work, time dependent density functional theory is used to calculate the electronic excitations produced by energetic protons in Al. We study the influence of these electronic excitations on the interatomic forces and find that they differ substantially from the adiabatic case, revealing a nontrivial connection between electronic and nuclear stopping that is absent in the adiabatic case. These results unveil new effects in the early stages of radiation damage cascades
Cryptic disease-induced mortality may cause host extinction in an apparently stable host- parasite system
The decline of wildlife populations due to emerging infectious disease often shows a common pattern: the parasite invades a naive host population, producing epidemic disease and a population decline, sometimes with extirpation. Some susceptible host populations can survive the epidemic phase and persist with endemic parasitic infection. Understanding host–parasite dynamics leading to persistence of the system is imperative to adequately inform conservation practice. Here we combine field data, statistical and mathematical modelling to explore the dynamics of the apparently stable Rhinoderma darwinii–Batrachochytrium dendrobatidis (Bd) system. Our results indicate that Bd-induced population extirpation may occur even in the absence of epidemics and where parasite prevalence is relatively low. These empirical findings are consistent with previous theoretical predictions showing that highly pathogenic parasites are able to regulate host populations even at extremely low prevalence, highlighting that disease threats should be investigated as a cause of population declines even in the absence of an overt increase in mortality
String Driven Cosmology and its Predictions
We present a minimal model for the Universe evolution fully extracted from
effective String Theory. This model is by its construction close to the
standard cosmological evolution, and it is driven selfconsistently by the
evolution of the string equation of state itself. The inflationary String
Driven stage is able to reach enough inflation, describing a Big Bang like
evolution for the metric. By linking this model to a minimal but well
established observational information, (the transition times of the different
cosmological epochs), we prove that it gives realistic predictions on early and
current energy density and its results are compatible with General Relativity.
Interestingly enough, the predicted current energy density is found Omega = 1
and a lower limit Omega \geq 4/9 is also found. The energy density at the exit
of the inflationary stage also gives | Omega |_{inf}=1. This result shows an
agreement with General Relativity (spatially flat metric gives critical energy
density) within an inequivalent Non-Einstenian context (string low energy
effective equations). The order of magnitude of the energy density-dilaton
coupled term at the beginning of the radiation dominated stage agrees with the
GUT scale. The predicted graviton spectrum is computed and analyzed without any
free parameters. Peaks and asymptotic behaviours of the spectrum are a direct
consequence of the dilaton involved and not only of the scale factor evolution.
Drastic changes are found at high frequencies: the dilaton produces an
increasing spectrum (in no string cosmologies the spectrum is decreasing).
Without solving the known problems about higher order corrections and graceful
exit of inflation, we find this model closer to the observational Universe than
the current available string cosmology scenarii.Comment: LaTex, 22 pages, Lectures delivered at the Chalonge School, Nato ASI:
Phase Transitions in the Early Universe: Theory and Observations. To appear
in the Proceedings, Editors H. J. de Vega, I. Khalatnikov, N. Sanchez.
(Kluwer Pub
Salmonella heterogeneously expresses flagellin during colonization of plants
Minimally processed or fresh fruits and vegetables are unfortunately linked to an increasing number of food-borne diseases, such as salmonellosis. One of the relevant virulence factors during the initial phases of the infection process is the bacterial flagellum. Although its function is well studied in animal systems, contradictory results have been published regarding its role during plant colonization. In this study, we tested the hypothesis that Salmonella’s flagellin plays a versatile function during the colonization of tomato plants. We have assessed the persistence in plant tissues of a Salmonella enterica wild type strain, and of a strain lacking the two flagellins, FljB and FliC.The work carried out in the C.R.B. and J.R. laboratory has been granted by Ministerio de Ciencia, Innovación y Universidades (MCIU, Spain, RTI2018-095069-B-100) awarded to C.R.B. and J.R., and Proyectos de Excelencia (Junta de AndalucÃa; PY18-2398) awarded to C.B. This work was co-funded by Fondos Europeos de Desarrollo Regional (FEDER). N.L. received funding for a short training mission (STSM) in the A.S. laboratory from CA 16110 HUPLANT from the EU Cost Action Program. We would like to thank DAAD for scholarship funding of A.A.Z.Peer reviewe
Chytridiomycosis outbreak in a Chilean giant frog (Calyptocephalella gayi) captive breeding program: genomic characterization and pathological findings
Emerging infectious diseases in wildlife are increasingly associated with animal mortality and species declines, but their source and genetic characterization often remains elusive. Amphibian chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), has been associated with catastrophic and well-documented amphibian population declines and extinctions at the global scale. We used histology and whole-genome sequencing to describe the lesions caused by, and the genetic variability of, two Bd isolates obtained from a mass mortality event in a captive population of the threatened Chilean giant frog (Calyptocephalella gayi). This was the first time an association between Bd and high mortality had been detected in this charismatic and declining frog species. Pathological examinations revealed that 30 dead metamorphosed frogs presented agnathia or brachygnathia, a condition that is reported for the first time in association with chytridiomycosis. Phylogenomic analyses revealed that Bd isolates (PA1 and PA2) from captive C. gayi group with other Bd isolates (AVS2, AVS4, and AVS7) forming a single highly supported Chilean Bd clade within the global panzootic lineage of Bd (BdGPL). These findings are important to inform the strengthening of biosecurity measures to prevent the impacts of chytridiomycosis in captive breeding programs elsewhere
Synthesis of Batrachochytrium dendrobatidis infection in South America: amphibian species under risk and areas to focus research and disease mitigation
Amphibian chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd), has been recognized as the infectious disease causing the most catastrophic loss of biodiversity known to science, with South America being the most impacted region. We tested whether Bd prevalence is distributed among host taxonomy, ecoregion, conservation status and habitat preference in South America. Here we provide a synthesis on the extent of Bd infection across South America based on 21 648 molecular diagnostic assays, roles of certain species in the epidemiology of Bd and explore its association with the reported amphibian catastrophic declines in the region. We show that Bd is widespread, with a continental prevalence of 23.2%. Its occurrence in the region shows a phylogenetic signal and the probability of infection is determined by ecoregion, preferred habitat and extinction risk hosts' traits. The taxa exhibiting highest Bd occurrence were mostly aquatic amphibians, including Ranidae, Telmatobiidae, Hylodidae, Calyptocephalellidae and Pipidae. Surprisingly, families exhibiting unusually low Bd prevalence included species in which lethal chytridiomycosis and population declines have been described (genera Atelopus, Rhinoderma and Eleutherodactylus). Higher than expected prevalence of Bd occurred mainly in amphibians living in association with mountain environments in the Andes and Atlantic forests, reflecting highly favourable Bd habitats in these areas. Invasive amphibian species (e.g. Lithobates catesbeianus and Xenopus laevis) exhibited high Bd prevalence; thus we suggest using these as sentinels to understand their potential role as reservoirs, vectors or spreaders of Bd that can be subjected to management. Our results guide on the prioritization of conservation actions to prevent further biodiversity loss due to chytridiomycosis in the world's most amphibian diverse region
- …