Searching for young Jupiter analogs around AP Col: L-band high-contrast imaging of the closest pre-main sequence star

The nearby M-dwarf AP Col was recently identified by Riedel et al. 2011 as a pre-main sequence star (age 12 - 50 Myr) situated only 8.4 pc from the Sun. The combination of its youth, distance, and intrinsically low luminosity make it an ideal target to search for extrasolar planets using direct imaging. We report deep adaptive optics observations of AP Col taken with VLT/NACO and Keck/NIRC2 in the L-band. Using aggressive speckle suppression and background subtraction techniques, we are able to rule out companions with mass m >= 0.5 - 1M_Jup for projected separations a>4.5 AU, and m >= 2 M_Jup for projected separations as small as 3 AU, assuming an age of 40 Myr using the COND theoretical evolutionary models. Using a different set of models the mass limits increase by a factor of ~2. The observations presented here are the deepest mass-sensitivity limits yet achieved within 20 AU on a star with direct imaging. While Doppler radial velocity surveys have shown that Jovian bodies with close-in orbits are rare around M-dwarfs, gravitational microlensing studies predict that ~17% of these stars host massive planets with orbital separations of 1-10 AU. Sensitive high-contrast imaging observations, like those presented here, will help to validate results from complementary detection techniques by determining the frequency of gas giant planets on wide orbits around M-dwarfs.Comment: Accepted for publication in ApJ, 6 pages text ApJ style (incl. references), 4 figures, 1 tabl

Biophysical mechanisms that maintain biodiversity through trade-offs

Published onlineJournal ArticleTrade-offs are thought to arise from inevitable, biophysical limitations that prevent organisms from optimizing multiple traits simultaneously. A leading explanation for biodiversity maintenance is a theory that if the shape, or geometry, of a trade-off is right, then multiple species can coexist. Testing this theory, however, is difficult as trait data is usually too noisy to discern shape, or trade-offs necessary for the theory are not observed in vivo. To address this, we infer geometry directly from the biophysical mechanisms that cause trade-offs, deriving the geometry of two by studying nutrient uptake and metabolic properties common to all living cells. To test for their presence in vivo we isolated Escherichia coli mutants that vary in a nutrient transporter, LamB, and found evidence for both trade-offs. Consistent with data, population genetics models incorporating the trade-offs successfully predict the co-maintenance of three distinct genetic lineages, demonstrating that trade-off geometry can be deduced from fundamental principles of living cells and used to predict stable genetic polymorphisms

Stable Isotope Analysis of an Invasive Crab Species, Charybdis hellerii, in the Indian River Lagoon

The world has never been more connected than it is today. While this is true for people, it is also true for Earth\u27s flora and fauna. Unfortunately, this connectedness has contributed to unprecedented invasive species introductions around the world. Most introductions result in an introduced species dying out in the newly invaded territory and never becoming established. Other introduced species establish and persist for years, but never have a noticeable effect on local ecosystems. However, occasionally, an invasive species gets introduced to a new area and has negative impacts on native plant and animal life. The Indo-Pacific swimming crab, Charybdis hellerii, was introduced to the southern Indian River Lagoon (IRL) in the 1990s. Recently, it has been reported to be expanding its non-native range northward up the IRL and into more northerly east coast states. To better understand the ecological role C. hellerii fills in the lagoon and the threat it poses to the economically important and native Callinectes sapidus, this study utilized stable isotope analysis to assess dietary overlap and competition between these species. The results of this study indicate significant overlap in dietary resource usage suggesting C. hellerii is likely feeding on some of the same prey items and competing with native C. sapidus. Based on the increasing numbers of C. hellerii and their reported range expansion, they appear to be establishing populations in the U.S. and will continue to compete with C. sapidus. This could negatively impact C. sapidus populations in the IRL, which is bad for the crab, bad for the fishery, and bad for the lagoon. Further, competition in the IRL is concerning for the rest of the southeastern U.S. states that appear to be in the early stages of a C. hellerii invasion. The findings of this study illuminate the need for further research into the ecological niche C. hellerii is filling in the IRL and the interactions it is having with, as well as the effects it is having on, native species in the lagoon. This study and future research will allow fisheries managers to devise more effective strategies to limit the spread of C. hellerii and minimize the harm it can do in non-native environments

Heating of the solar wind with electron and proton effects

We examine the effects of including effects of both protons and electrons on the heating of the fast solar wind through two different approaches. In the first approach, we incorporate the electron temperature in an MHD turbulence transport model for the solar wind. In the second approach, we adopt more empirically based methods by analyzing the measured proton and electron temperatures to calculate the heat deposition rates. Overall, we conclude that incorporating separate proton and electron temperatures and heat conduction effects provides an improved and more complete model of the heating of the solar wind

Coevolution Drives the Emergence of Complex Traits and Promotes Evolvability

The evolution of complex organismal traits is obvious as a historical fact, but the underlying causes—including the role of natural selection—are contested. Gould argued that a random walk from a necessarily simple beginning would produce the appearance of increasing complexity over time. Others contend that selection, including coevolutionary arms races, can systematically push organisms toward more complex traits. Methodological challenges have largely precluded experimental tests of these hypotheses. Using the Avida platform for digital evolution, we show that coevolution of hosts and parasites greatly increases organismal complexity relative to that otherwise achieved. As parasites evolve to counter the rise of resistant hosts, parasite populations retain a genetic record of past coevolutionary states. As a consequence, hosts differentially escape by performing progressively more complex functions. We show that coevolution's unique feedback between host and parasite frequencies is a key process in the evolution of complexity. Strikingly, the hosts evolve genomes that are also more phenotypically evolvable, similar to the phenomenon of contingency loci observed in bacterial pathogens. Because coevolution is ubiquitous in nature, our results support a general model whereby antagonistic interactions and natural selection together favor both increased complexity and evolvability

Gain-of-Function Experiments With Bacteriophage Lambda Uncover Residues Under Diversifying Selection in Nature

Viral gain-of-function mutations frequently evolve during laboratory experiments. Whether the specific mutations that evolve in the lab also evolve in nature and whether they have the same impact on evolution in the real world is unknown. We studied a model virus, bacteriophage λ, that repeatedly evolves to exploit a new host receptor under typical laboratory conditions. Here, we demonstrate that two residues of λ’s J protein are required for the new function. In natural λ variants, these amino acid sites are highly diverse and evolve at high rates. Insertions and deletions at these locations are associated with phylogenetic patterns indicative of ecological diversification. Our results show that viral evolution in the laboratory mirrors that in nature and that laboratory experiments can be coupled with protein sequence analyses to identify the causes of viral evolution in the real world. Furthermore, our results provide evidence for widespread host-shift evolution in lambdoid viruses

Does the Choice of Extraction Site During Minimally Invasive Colorectal Surgery Change the Incidence of Incisional Hernia? Protocol for a Systematic Review and Network Meta-Analysis.

BACKGROUND: Various sites are used for specimen extraction in oncological minimally invasive colorectal surgery. The objective is to determine if the choice of extraction site modulates the incidence of incisional hernia (IH). METHODS/DESIGN: A systematic review will be performed in accordance to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. MEDLINE, Embase and CENTRAL will be searched to look for original studies reporting the incidence of IH after minimally invasive colorectal surgery. Studies will be excluded from the analysis if: 1) they do not report original data, 2) the outcome of interest (incidence of incisional hernia) is not clearly reported and does not allow to extrapolate and/or calculate the required data for network meta-analysis, 3) they include pediatric patients, 4) they include a patients' population with a conversion rate to laparotomy >10%, 5) they do not compare at least two different extraction sites for the operative specimen, 6) they report patients who underwent pure (and not hybrid) natural orifice transluminal endoscopic surgery (NOTES). Network meta-analysis will be performed to determine the incidence of IH per extraction site. DISCUSSION: By determining which specimen extraction site leads to reduced rate of IH, this systematic review and network meta-analysis will help colorectal surgeons to choose their extraction site and reduce the morbidity and costs associated with IH. REGISTRATION: The systematic review and meta-analysis protocol is registered in the International Prospective Register of Ongoing Systematic Reviews (PROSPERO) with number CRD42021272226. HIGHLIGHTS: Various sites are used for specimen extraction in oncological minimally invasive colorectal surgery, and the choice of the site may probably modulate the incidence of incisional hernia.The present protocol aims to design a systematic review which will identify original studies comparing two extraction sites during minimally invasive colorectal surgery in terms of incidence of incisional hernia.Network meta-analysis will be performed to determine the incidence of IH per extraction site

Gain-of-Function Experiments With Bacteriophage Lambda Uncover Residues Under Diversifying Selection in Nature

Viral gain-of-function mutations frequently evolve during laboratory experiments. Whether the specific mutations that evolve in the lab also evolve in nature and whether they have the same impact on evolution in the real world is unknown. We studied a model virus, bacteriophage λ, that repeatedly evolves to exploit a new host receptor under typical laboratory conditions. Here, we demonstrate that two residues of λ’s J protein are required for the new function. In natural λ variants, these amino acid sites are highly diverse and evolve at high rates. Insertions and deletions at these locations are associated with phylogenetic patterns indicative of ecological diversification. Our results show that viral evolution in the laboratory mirrors that in nature and that laboratory experiments can be coupled with protein sequence analyses to identify the causes of viral evolution in the real world. Furthermore, our results provide evidence for widespread host-shift evolution in lambdoid viruses

Shear sum rules at finite chemical potential

We derive sum rules which constrain the spectral density corresponding to the retarded propagator of the T_{xy} component of the stress tensor for three gravitational duals. The shear sum rule is obtained for the gravitational dual of the N=4 Yang-Mills, theory of the M2-branes and M5-branes all at finite chemical potential. We show that at finite chemical potential there are additional terms in the sum rule which involve the chemical potential. These modifications are shown to be due to the presence of scalars in the operator product expansion of the stress tensor which have non-trivial vacuum expectation values at finite chemical potential.Comment: The proof for the absence of branch cuts is corrected.Results unchange