67 research outputs found
Trade-offs drive resource specialization and the gradual establishment of ecotypes
Speciation is driven by many different factors. Among those are trade-offs
between different ways an organism utilizes resources, and these trade-offs can
constrain the manner in which selection can optimize traits. Limited migration
among allopatric populations and species interactions can also drive
speciation, but here we ask if trade-offs alone are sufficient to drive
speciation in the absence of other factors. We present a model to study the
effects of trade-offs on specialization and adaptive radiation in asexual
organisms based solely on competition for limiting resources, where trade-offs
are stronger the greater an organism's ability to utilize resources. In this
model resources are perfectly substitutable, and fitness is derived from the
consumption of these resources. The model contains no spatial parameters, and
is therefore strictly sympatric. We quantify the degree of specialization by
the number of ecotypes formed and the niche breadth of the population, and
observe that these are sensitive to resource influx and trade-offs. Resource
influx has a strong effect on the degree of specialization, with a clear
transition between minimal diversification at high influx and multiple species
evolving at low resource influx. At low resource influx the degree of
specialization further depends on the strength of the trade-offs, with more
ecotypes evolving the stronger trade-offs are. The specialized organisms
persist through negative frequency-dependent selection. In addition, by
analyzing one of the evolutionary radiations in greater detail we demonstrate
that a single mutation alone is not enough to establish a new ecotype, even
though phylogenetic reconstruction identifies that mutation as the branching
point. Instead, it takes a series of additional mutations to ensure the stable
coexistence of the new ecotype in the background of the existing ones,
reminiscent of a recent observaComment: 19 pages, 3 figure
Critical properties of complex fitness landscapes
Evolutionary adaptation is the process that increases the fit of a population
to the fitness landscape it inhabits. As a consequence, evolutionary dynamics
is shaped, constrained, and channeled, by that fitness landscape. Much work has
been expended to understand the evolutionary dynamics of adapting populations,
but much less is known about the structure of the landscapes. Here, we study
the global and local structure of complex fitness landscapes of interacting
loci that describe protein folds or sets of interacting genes forming pathways
or modules. We find that in these landscapes, high peaks are more likely to be
found near other high peaks, corroborating Kauffman's "Massif Central"
hypothesis. We study the clusters of peaks as a function of the ruggedness of
the landscape and find that this clustering allows peaks to form interconnected
networks. These networks undergo a percolation phase transition as a function
of minimum peak height, which indicates that evolutionary trajectories that
take no more than two mutations to shift from peak to peak can span the entire
genetic space. These networks have implications for evolution in rugged
landscapes, allowing adaptation to proceed after a local fitness peak has been
ascended.Comment: 7 pages, 6 figures, requires alifex11.sty. To appear in Proceedings
of 12th International Conference on Artificial Lif
The Effect of Marker-less Augmented Reality on Task and Learning Performance
Augmented Reality (AR) technologies have evolved rapidly over the last years, particularly with regard to user interfaces, input devices, and cameras used in mobile devices for object and gesture recognition. While early AR systems relied on pre-defined trigger images or QR code markers, modern AR applications leverage machine learning techniques to identify objects in their physical environments. So far, only few empirical studies have investigated AR\u27s potential for supporting learning and task assistance using such marker-less AR. In order to address this research gap, we implemented an AR application (app)with the aim to analyze the effectiveness of marker-less AR applied in a mundane setting which can be used for on-the-job training and more formal educational settings. The results of our laboratory experiment show that while participants working with AR needed significantly more time to fulfill the given task, the participants who were supported by AR learned significantly more
Genotype Network Intersections Promote Evolutionary Innovation
Evolutionary innovations are qualitatively novel traits that emerge through evolution and increase biodiversity. The genetic mechanisms of innovation remain poorly understood. A systems view of innovation requires the analysis of genotype networks—the vast networks of genetic variants that produce the same phenotype. Innovations can occur at the intersection of two different genotype networks. However, the experimental characterization of genotype networks has been hindered by the vast number of genetic variants that need to be functionally analyzed. Here, we use high-throughput sequencing to study the fitness landscape at the intersection of the genotype networks of two catalytic RNA molecules (ribozymes). We determined the ability of numerous neighboring RNA sequences to catalyze two different chemical reactions, and we use these data as a proxy for a genotype to fitness map where two functions come in close proximity. We find extensive functional overlap, and numerous genotypes can catalyze both functions. We demonstrate through evolutionary simulations that these numerous points of intersection facilitate the discovery of a new function. However, the rate of adaptation of the new function depends upon the local ruggedness around the starting location in the genotype network. As a consequence, one direction of adaptation is more rapid than the other. We find that periods of neutral evolution increase rates of adaptation to the new function by allowing populations to spread out in their genotype network. Our study reveals the properties of a fitness landscape where genotype networks intersect and the consequences for evolutionary innovations. Our results suggest that historic innovations in natural systems may have been facilitated by overlapping genotype networks
Intramedullary nail versus sliding hip screw for stable and unstable trochanteric and subtrochanteric fractures: 17,341 patients from the Norwegian Hip Fracture Register
Aims
The aim of this study was to investigate if there are differences in outcome between sliding hip screws (SHSs) and intramedullary nails (IMNs) with regard to fracture stability.
Methods
We assessed data from 17,341 patients with trochanteric or subtrochanteric fractures treated with SHS or IMN in the Norwegian Hip Fracture Register from 2013 to 2019. Primary outcome measures were reoperations for stable fractures (AO Foundation/Orthopaedic Trauma Association (AO/OTA) type A1) and unstable fractures (AO/OTA type A2, A3, and subtrochanteric fractures). Secondary outcome measures were reoperations for A2, A3, and subtrochanteric fractures individually, one-year mortality, quality of life (EuroQol five-dimension three-level index score), pain (visual analogue scale (VAS)), and satisfaction (VAS) for stable and unstable fractures. Hazard rate ratios (HRRs) for reoperation were calculated using Cox regression analysis with adjustments for age, sex, and American Society of Anesthesiologists score.
Results
Reoperation rate was lower after surgery with IMN for unstable fractures one year (HRR 0.82, 95% confidence interval (CI) 0.70 to 0.97; p = 0.022) and three years postoperatively (HRR 0.86, 95% CI 0.74 to 0.99; p = 0.036), compared with SHS. For individual fracture types, no clinically significant differences were found. Lower one-year mortality was found for IMN compared with SHS for stable fractures (HRR 0.87; 95% CI 0.78 to 0.96; p = 0.007), and unstable fractures (HRR 0.91, 95% CI 0.84 to 0.98; p = 0.014).
Conclusion
This national register-based study indicates a lower reoperation rate for IMN than SHS for unstable trochanteric and subtrochanteric fractures, but not for stable fractures or individual fracture types. The choice of implant may not be decisive to the outcome of treatment for stable trochanteric fractures in terms of reoperation rate. One-year mortality rate for unstable and stable fractures was lower in patients treated with IMN.acceptedVersio
Subsequent ipsi- and contralateral femoral fractures after intramedullary nailing of a trochanteric or subtrochanteric fracture: a cohort study on 2012 patients
Background: The literature is inconclusive as to whether an intramedullary nail changes the distribution of a subsequent ipsi- or contralateral fracture of the femur. We have compared the incidence, localisation, and fracture pattern of subsequent femoral fractures after intramedullary nailing of trochanteric or subtrochanteric fractures in patients without previous implants in either femur at the time of surgery.
Methods: Retrospective analysis was performed of a two-centre cohort of 2012 patients treated with a short or long intramedullary nail for the management of trochanteric or subtrochanteric fracture between January 2005 and December 2018. Subsequent presentations with ipsi- and contralateral femoral fractures were documented. Only patients with no previous femoral surgery performed, other than the index nailing were followed. Odds ratios (ORs) for subsequent femoral fracture were calculated using robust variance estimates in logistic regression.
Results: The mean age of the cohort was 82.4 years and 72.1% were female. The total number of patients presenting with subsequent femoral fractures was 299 (14.9%). The number of patients presenting with subsequent ipsilateral and contralateral femoral fractures was 51 (2.5%) and 248 (12.3%) respectively (OR 5.0; CI 3.7–6.9). Twenty-six (8.7%) of all subsequent femoral fractures occured in the ipsilateral shaft, 14 (4.7%) in the ipsilateral metaphyseal area, one (0.33%) in the contralateral shaft, and three (1.0%) in the contralateral metaphysis (OR 10; CI 3.6–29).
Conclusion: An intramedullary nail significantly changes the fracture pattern in the event of a second low-energy trauma, reducing the risk of subsequent proximal ipsilateral femoral fractures and increasing the risk of subsequent ipsilateral femoral fractures in the shaft and distal metaphyseal area compared with the native contralateral femur.publishedVersio
Effects of Epistasis and Pleiotropy on Fitness Landscapes
The factors that influence genetic architecture shape the structure of the
fitness landscape, and therefore play a large role in the evolutionary
dynamics. Here the NK model is used to investigate how epistasis and pleiotropy
-- key components of genetic architecture -- affect the structure of the
fitness landscape, and how they affect the ability of evolving populations to
adapt despite the difficulty of crossing valleys present in rugged landscapes.
Populations are seen to make use of epistatic interactions and pleiotropy to
attain higher fitness, and are not inhibited by the fact that valleys have to
be crossed to reach peaks of higher fitness.Comment: 10 pages, 6 figures. To appear in "Origin of Life and Evolutionary
Mechanisms" (P. Pontarotti, ed.). Evolutionary Biology: 16th Meeting 2012,
Springer-Verla
The accretion disc in the quasar SDSS J0924+0219
We present single-epoch multi-wavelength optical-NIR observations of the
"anomalous" lensed quasar SDSS J0924+0219, made using the Magellan 6.5-metre
Baade telescope at Las Campanas Observatory, Chile. The data clearly resolve
the anomalous bright image pair in the lensed system, and exhibit a strong
decrease in the anomalous flux ratio with decreasing wavelength. This is
interpreted as a result of microlensing of a source of decreasing size in the
core of the lensed quasar. We model the radius of the continuum emission
region, sigma, as a power-law in wavelength, sigma lambda^zeta. We place an
upper limit on the Gaussian radius of the u'-band emission region of 3.04E16
h70^{-1/2} (/M_sun)^{1/2} cm, and constrain the size-wavelength power-law
index to zeta<1.34 at 95% confidence. These observations rule out an alpha-disc
prescription for the accretion disc in SDSS J0924+0219 with 94% confidence.Comment: 8 pages, 5 figures. Accepted for publication in MNRA
Predicting evolution and visualizing high-dimensional fitness landscapes
The tempo and mode of an adaptive process is strongly determined by the
structure of the fitness landscape that underlies it. In order to be able to
predict evolutionary outcomes (even on the short term), we must know more about
the nature of realistic fitness landscapes than we do today. For example, in
order to know whether evolution is predominantly taking paths that move upwards
in fitness and along neutral ridges, or else entails a significant number of
valley crossings, we need to be able to visualize these landscapes: we must
determine whether there are peaks in the landscape, where these peaks are
located with respect to one another, and whether evolutionary paths can connect
them. This is a difficult task because genetic fitness landscapes (as opposed
to those based on traits) are high-dimensional, and tools for visualizing such
landscapes are lacking. In this contribution, we focus on the predictability of
evolution on rugged genetic fitness landscapes, and determine that peaks in
such landscapes are highly clustered: high peaks are predominantly close to
other high peaks. As a consequence, the valleys separating such peaks are
shallow and narrow, such that evolutionary trajectories towards the highest
peak in the landscape can be achieved via a series of valley crossingsComment: 12 pages, 7 figures. To appear in "Recent Advances in the Theory and
Application of Fitness Landscapes" (A. Engelbrecht and H. Richter, eds.).
Springer Series in Emergence, Complexity, and Computation, 201
- …