4,024 research outputs found
Evolved polygenic herbicide resistance in Lolium rigidum by low-dose herbicide selection within standing genetic variation
The interaction between environment and genetic traits under selection is the basis of evolution. In this study, we have investigated the genetic basis of herbicide resistance in a highly characterized initially herbicide-susceptible Lolium rigidum population recurrently selected with low (below recommended label) doses of the herbicide diclofop-methyl. We report the variability in herbicide resistance levels observed in F1 families and the segregation of resistance observed in F2 and back-cross (BC) families. The selected herbicide resistance phenotypic trait(s) appear to be under complex polygenic control. The estimation of the effective minimum number of genes (NE), depending on the herbicide dose used, reveals at least three resistance genes had been enriched. A joint scaling test indicates that an additive-dominance model best explains gene interactions in parental, F1, F2 and BC families. The Mendelian study of six F2 and two BC segregating families confirmed involvement of more than one resistance gene. Cross-pollinated L. rigidum under selection at low herbicide dose can rapidly evolve polygenic broad-spectrum herbicide resistance by quantitative accumulation of additive genes of small effect. This can be minimized by using herbicides at the recommended dose which causes high mortality acting outside the normal range of phenotypic variation for herbicide susceptibility
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Benchmarking 2D hydraulic models for urban flood simulations
This paper describes benchmark testing of six two-dimensional (2D) hydraulic models (DIVAST, DIVASTTVD, TUFLOW, JFLOW, TRENT and LISFLOOD-FP) in terms of their ability to simulate surface flows in a densely urbanised area. The models are applied to a 1·0 km × 0·4 km urban catchment within the city of Glasgow, Scotland, UK, and are used to simulate a flood event that occurred at this site on 30 July 2002. An identical numerical grid describing the underlying topography is constructed for each model, using a combination of airborne laser altimetry (LiDAR) fused with digital map data, and used to run a benchmark simulation. Two numerical experiments were then conducted to test the response of each model to topographic error and uncertainty over friction parameterisation. While all the models tested produce plausible results, subtle differences between particular groups of codes give considerable insight into both the practice and science of urban hydraulic modelling. In particular, the results show that the terrain data available from modern LiDAR systems are sufficiently accurate and resolved for simulating urban flows, but such data need to be fused with digital map data of building topology and land use to gain maximum benefit from the information contained therein. When such terrain data are available, uncertainty in friction parameters becomes a more dominant factor than topographic error for typical problems. The simulations also show that flows in urban environments are characterised by numerous transitions to supercritical flow and numerical shocks. However, the effects of these are localised and they do not appear to affect overall wave propagation. In contrast, inertia terms are shown to be important in this particular case, but the specific characteristics of the test site may mean that this does not hold more generally
Random Sequential Renormalization of Networks I: Application to Critical Trees
We introduce the concept of Random Sequential Renormalization (RSR) for
arbitrary networks. RSR is a graph renormalization procedure that locally
aggregates nodes to produce a coarse grained network. It is analogous to the
(quasi-)parallel renormalization schemes introduced by C. Song {\it et al.}
(Nature {\bf 433}, 392 (2005)) and studied more recently by F. Radicchi {\it et
al.} (Phys. Rev. Lett. {\bf 101}, 148701 (2008)), but much simpler and easier
to implement. In this first paper we apply RSR to critical trees and derive
analytical results consistent with numerical simulations. Critical trees
exhibit three regimes in their evolution under RSR: (i) An initial regime
, where is the number of nodes at some step in the
renormalization and is the initial size. RSR in this regime is described
by a mean field theory and fluctuations from one realization to another are
small. The exponent is derived using random walk arguments. The
degree distribution becomes broader under successive renormalization --
reaching a power law, with and a variance
that diverges as at the end of this regime. Both of these results
are derived based on a scaling theory. (ii) An intermediate regime for
, in which hubs develop, and
fluctuations between different realizations of the RSR are large. Crossover
functions exhibiting finite size scaling, in the critical region , connect the behaviors in the first two regimes. (iii)
The last regime, for , is characterized by the
appearance of star configurations with a central hub surrounded by many leaves.
The distribution of sizes where stars first form is found numerically to be a
power law up to a cutoff that scales as with
Curvature-direction measures of self-similar sets
We obtain fractal Lipschitz-Killing curvature-direction measures for a large
class of self-similar sets F in R^d. Such measures jointly describe the
distribution of normal vectors and localize curvature by analogues of the
higher order mean curvatures of differentiable submanifolds. They decouple as
independent products of the unit Hausdorff measure on F and a self-similar
fibre measure on the sphere, which can be computed by an integral formula. The
corresponding local density approach uses an ergodic dynamical system formed by
extending the code space shift by a subgroup of the orthogonal group. We then
give a remarkably simple proof for the resulting measure version under minimal
assumptions.Comment: 17 pages, 2 figures. Update for author's name chang
Life history traits and phenotypic selection among sunflower crop–wild hybrids and their wild counterpart: implications for crop allele introgression
Hybridization produces strong evolutionary forces. In hybrid zones, selection can differentially occur on traits and selection intensities may differ among hybrid generations. Understanding these dynamics in crop–wild hybrid zones can clarify crop-like traits likely to introgress into wild populations and the particular hybrid generations through which introgression proceeds. In a field experiment with four crop–wild hybrid Helianthus annuus (sunflower) cross types, we measured growth and life history traits and performed phenotypic selection analysis on early season traits to ascertain the likelihood, and routes, of crop allele introgression into wild sunflower populations. All cross types overwintered, emerged in the spring, and survived until flowering, indicating no early life history barriers to crop allele introgression. While selection indirectly favored earlier seedling emergence and taller early season seedlings, direct selection only favored greater early season leaf length. Further, there was cross type variation in the intensity of selection operating on leaf length. Thus, introgression of multiple early season crop-like traits, due to direct selection for greater early season leaf length, should not be impeded by any cross type and may proceed at different rates among generations. In sum, alleles underlying early season sunflower crop-like traits are likely to introgress into wild sunflower populations
Death feigning as an adaptive anti‐predator behaviour: Further evidence for its evolution from artificial selection and natural populations
Death feigning is considered to be an adaptive antipredator behaviour. Previous studies on Tribolium castaneum have shown that prey which death feign have a fitness advantage over those that do not when using a jumping spider as the predator. Whether these effects are repeatable across species or whether they can be seen in nature is, however, unknown. Therefore, the present study involved two experiments: (a) divergent artificial selection for the duration of death feigning using a related species T. freemani as prey and a predatory bug as predator, demonstrating that previous results are repeatable across both prey and predator species, and (b) comparison of the death‐feigning duration of T. castaneum populations collected from field sites with and without predatory bugs. In the first experiment, T. freemani adults from established selection regimes with longer durations of death feigning had higher survival rates and longer latency to being preyed on when they were placed with predatory bugs than the adults from regimes selected for shorter durations of death feigning. As a result, the adaptive significance of death‐feigning behaviour was demonstrated in another prey–predator system. In the second experiment, wild T. castaneum beetles from populations with predators feigned death longer than wild beetles from predator‐free populations. Combining the results from these two experiments with those from previous studies provided strong evidence that predators drive the evolution of longer death feigning
Golden gaskets: variations on the Sierpi\'nski sieve
We consider the iterated function systems (IFSs) that consist of three
general similitudes in the plane with centres at three non-collinear points,
and with a common contraction factor \la\in(0,1).
As is well known, for \la=1/2 the invariant set, \S_\la, is a fractal
called the Sierpi\'nski sieve, and for \la<1/2 it is also a fractal. Our goal
is to study \S_\la for this IFS for 1/2<\la<2/3, i.e., when there are
"overlaps" in \S_\la as well as "holes". In this introductory paper we show
that despite the overlaps (i.e., the Open Set Condition breaking down
completely), the attractor can still be a totally self-similar fractal,
although this happens only for a very special family of algebraic \la's
(so-called "multinacci numbers"). We evaluate \dim_H(\S_\la) for these
special values by showing that \S_\la is essentially the attractor for an
infinite IFS which does satisfy the Open Set Condition. We also show that the
set of points in the attractor with a unique ``address'' is self-similar, and
compute its dimension.
For ``non-multinacci'' values of \la we show that if \la is close to 2/3,
then \S_\la has a nonempty interior and that if \la<1/\sqrt{3} then \S_\la$
has zero Lebesgue measure. Finally we discuss higher-dimensional analogues of
the model in question.Comment: 27 pages, 10 figure
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