9,783 research outputs found
The consequences of gene flow for local adaptation and differentiation: A two-locus two-deme model
We consider a population subdivided into two demes connected by migration in
which selection acts in opposite direction. We explore the effects of
recombination and migration on the maintenance of multilocus polymorphism, on
local adaptation, and on differentiation by employing a deterministic model
with genic selection on two linked diallelic loci (i.e., no dominance or
epistasis). For the following cases, we characterize explicitly the possible
equilibrium configurations: weak, strong, highly asymmetric, and
super-symmetric migration, no or weak recombination, and independent or
strongly recombining loci. For independent loci (linkage equilibrium) and for
completely linked loci, we derive the possible bifurcation patterns as
functions of the total migration rate, assuming all other parameters are fixed
but arbitrary. For these and other cases, we determine analytically the maximum
migration rate below which a stable fully polymorphic equilibrium exists. In
this case, differentiation and local adaptation are maintained. Their degree is
quantified by a new multilocus version of \Fst and by the migration load,
respectively. In addition, we investigate the invasion conditions of locally
beneficial mutants and show that linkage to a locus that is already in
migration-selection balance facilitates invasion. Hence, loci of much smaller
effect can invade than predicted by one-locus theory if linkage is sufficiently
tight. We study how this minimum amount of linkage admitting invasion depends
on the migration pattern. This suggests the emergence of clusters of locally
beneficial mutations, which may form `genomic islands of divergence'. Finally,
the influence of linkage and two-way migration on the effective migration rate
at a linked neutral locus is explored. Numerical work complements our
analytical results
Diversity and Genetic structure of the Spanish collection of durum wheat (Triticum turgidum L) landraces
The objectives of this study were to assess diversity and genetic structure of a collection of Spanish durum wheat (Triticum turgidum L) landraces, using SSRs, DArTs and gliadin-markers, and to correlate the distribution of diversity with geographic and climatic features, as well as agro-morphological traits. A high level of diversity was detected in the genotypes analyzed, which were separated into nine populations with a moderate to great genetic divergence among them. The three subspecies taxa, dicoccon, turgidum and durum, present in the collection, largely determined the clustering of the populations. Genotype variation was lower in dicoccon (one major population) and turgidum (two major populations) than in durum (five major populations). Genetic differentiation by the agro-ecological zone of origin was greater in dicoccon and turgidum than in durum. DArT markers revealed two geographic substructures, east-west for dicoccon and northeast-southwest for turgidum. The ssp. durum had a more complex structure, consisting of seven populations with high intra-population variation. DArT markers allowed the detection of subgroups within some populations, with agro-morphological and gliadin differences, and distinct agro-ecological zones of origin. Two different phylogenetic groups were detected; revealing that some durum populations were more related to ssp. turgidum from northern Spain, while others seem to be more related to durum wheats from North Afric
MAX: a mechatronic model building environment
Abstract: A description is given of the state of the art and the functionality of MAX, an expert system for supporting conceptual design of mechatronic systems. Three model building principles are combined in MAX: – embedding equations in networks: a tight coupling between the graphical model formulation and the underlying equations assists the user in model building and evaluation. – multiple model formulations: one system can be manipulated and inspected simultaneously in multiple formulations (languages). – polymorphic modelling: a submodel definition is divided into a type that defines essential properties, and a specification that defines incidental properties. One type generally has multiple specifications, and types are organised hierarchically inside the library. By means of a simple case study, the utility of these principles is demonstrated. It is shown that MAX is a powerful model building environment that is well adapted to usage by designers.
Differential Privacy versus Quantitative Information Flow
Differential privacy is a notion of privacy that has become very popular in
the database community. Roughly, the idea is that a randomized query mechanism
provides sufficient privacy protection if the ratio between the probabilities
of two different entries to originate a certain answer is bound by e^\epsilon.
In the fields of anonymity and information flow there is a similar concern for
controlling information leakage, i.e. limiting the possibility of inferring the
secret information from the observables. In recent years, researchers have
proposed to quantify the leakage in terms of the information-theoretic notion
of mutual information. There are two main approaches that fall in this
category: One based on Shannon entropy, and one based on R\'enyi's min entropy.
The latter has connection with the so-called Bayes risk, which expresses the
probability of guessing the secret. In this paper, we show how to model the
query system in terms of an information-theoretic channel, and we compare the
notion of differential privacy with that of mutual information. We show that
the notion of differential privacy is strictly stronger, in the sense that it
implies a bound on the mutual information, but not viceversa
Phenotypic evolution and hidden speciation in Candidula unifasciata ssp. (Helicellinae, Gastropoda) inferred by 16S variation and quantitative shell traits
In an effort to link quantitative morphometric information with molecular data on the population level, we have analysed 19 populations of the conchologically variable land snail Candidula unifasciata from across the species range for variation in quantitative shell traits and at the mitochondrial 16S ribosomal (r)DNA locus. In genetic analysis, including 21 additional populations, we observed two fundamental haplotype clades with an average pairwise sequence divergence of 0.209 ± 0.009 between clades compared to 0.017 ± 0.012 within clades, suggesting the presence of two different evolutionary lineages. Integrating additional shell material from the Senckenberg Malacological Collection, a highly significant discriminant analysis on the morphological shell traits with fundamental haplotype clades as grouping variable suggested that the less frequent haplotype corresponds to the described subspecies C. u. rugosiuscula, which we propose to regard as a distinct species. Both taxa were highly subdivided genetically (FST = 0.648 and 0.777 P < 0.001). This was contrasted by the partition of morphological variance, where only 29.6% and 21.9% of the variance were distributed among populations, respectively. In C. unifasciata, no significant association between population pairwise FST estimates and corresponding morphological fixation indices could be detected, indicating independent evolution of the two character sets. Partial least square analysis of environmental factors against shell trait variables in C. u. unifasciata revealed significant correlations between environmental factors and certain quantitative shell traits, whose potential adaptational values are discussed
Earthquakes: from chemical alteration to mechanical rupture
In the standard rebound theory of earthquakes, elastic deformation energy is
progressively stored in the crust until a threshold is reached at which it is
suddenly released in an earthquake. We review three important paradoxes, the
strain paradox, the stress paradox and the heat flow paradox, that are
difficult to account for in this picture, either individually or when taken
together. Resolutions of these paradoxes usually call for additional
assumptions on the nature of the rupture process (such as novel modes of
deformations and ruptures) prior to and/or during an earthquake, on the nature
of the fault and on the effect of trapped fluids within the crust at
seismogenic depths. We review the evidence for the essential importance of
water and its interaction with the modes of deformations. Water is usually seen
to have mainly the mechanical effect of decreasing the normal lithostatic
stress in the fault core on one hand and to weaken rock materials via
hydrolytic weakening and stress corrosion on the other hand. We also review the
evidences that water plays a major role in the alteration of minerals subjected
to finite strains into other structures in out-of-equilibrium conditions. This
suggests novel exciting routes to understand what is an earthquake, that
requires to develop a truly multidisciplinary approach involving mineral
chemistry, geology, rupture mechanics and statistical physics.Comment: 44 pages, 1 figures, submitted to Physics Report
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