724 research outputs found
Clonal selection prevents tragedy of the commons when neighbors compete in a rock-paper-scissors game
The rock-paper-scissors game is a model example of the on-going cyclic
turnover typical of many ecosystems, ranging from the terrestrial and aquatic
to the microbial. Here we explore the evolution of a rock-paper-scissors system
where three species compete for space. The species are allowed to mutate and
change the speed by which they invade one another. In the case when all species
have similar mutation rates, we observe a perpetual arms race where no single
species prevails. When only two species mutate, their aggressions increase
indefinitely until the ecosystem collapses and only the non-mutating species
survives. Finally we show that when only one species mutates, group selection
removes individual predators with the fastest growth rates, causing the growth
rate of the species to stabilize. We explain this group selection
quantitatively.Comment: 4 pages, 4 figure
The tragedy of the commons, the public goods dilemma, and the meaning of rivalry and excludability in evolutionary biology
Problem: In the study of conflicts, both economists and evolutionary biologists use the
concepts ‘tragedy of the commons’ and ‘public goods dilemma’. What is the relationship
between the economist and evolutionist views of these concepts?
Model features: The economics literature defines the tragedy of the commons and the public
goods dilemma in terms of rivalry and excludability of the good. In contrast, evolutionists
define these conflicts based on fitness functions with two components: individual and group
components of fitness.
Mathematical method: Evolutionary game theory and the calculation of evolutionarily stable
strategy trait values by standard optimization techniques and by replacing slopes of group
phenotype on individual genotype by coefficients of relatedness.
Conclusion: There is a direct relationship between rivalry and the individual component of
fitness and between excludability and the group component of fitness. Moreover, although the
prisoner’s dilemma constitutes a suitable metaphor to analyse both the public goods dilemma
and the tragedy of the commons, it gives the false idea that the two conflicts are symmetric since
they refer to situations in which individuals consume a common resource – tragedy of the
commons – or contribute to a collective action or common good – public goods dilemma.
However, the two situations are clearly not symmetric: from the economical point of view they
differ by rivalry, and from the evolutionary biology point of view the two conflicts differ by the
significance of the within-group competition in the fitness function
Nonequilibrium model for estimating parameters of deleterious mutations
Deleterious mutations are of extreme evolutionary importance because, even though they are eliminated by natural selection, their continuous pressure creates a pool of variability in natural populations. They are of potential relevance for the existence of several features in evolution, such as sexual reproduction, and pose a risk to small asexual populations. Despite their extreme importance, the deleterious mutation rate and the effects of each mutation on fitness are poorly known quantities. Here we analyze a simple model that can be applied to simple experiments, in microorganisms, aiming at the quantification of these values
Evaluación de la biosorción de cobre con cáscara de almendra
En este trabajo se analiza el potencial de la cáscara de almendra para su utilización como biosorbente de cobre presente en disoluciones acuosas. En primer lugar, se realizó una caracterización fÃsico-quÃmica del biosorbente. AsÃ, se ha determinado que los poros que posee la cáscara de almendra son mesoporos, con un ancho deporo medio de 54,5 Ã… y que la cantidad total de grupos activos es de 0,592 mmol/g, siendo el grupo carboxÃlico el mayoritario. A continuación, se analizó la influencia de las principales variables que intervienen en el proceso de biosorción. Se ha encontrado que el pH es uno de los parámetros más importantes que controlan la eliminación de cobre con cáscara de almendra, obteniéndose la máxima eficiencia del proceso a pH=5. El estudio cinético reveló que, en general, el proceso es rápido, aunque puede dividirse en dos etapas, una primera más rápida (primeros 20 minutos) y otra segunda etapa donde el proceso transcurre de forma más lenta. Se ha encontrado que el modelo de pseudo-segundo orden reproduce de forma adecuada el proceso. Por otra parte, el estudio del equilibrio mostró que a medida que aumenta la concentración inicial de cobre, se eleva la capacidad de biosorción del sólido hasta alcanzar un valor prácticamente constante para concentraciones superiores a 100 mg/L. El modelo de Langmuires el que mejor reproduce los resultados experimentales, obteniéndose una capacidad máxima de biosorción decobre de 9,44 mg/g
Plasmids Increase the Competitive Ability of Plasmid-Bearing Cells Even When Transconjugants Are Poor Donors, as Shown by Computer Simulations
Bacterial cells often suffer a fitness cost after conjugative plasmids’ entry because these cells replicate slower than plasmid-free cells. Compensatory mutations may appear after tens of or a few hundred generations, reducing or eliminating this cost. A previous work based on a mathematical model and computer simulations has shown that plasmid-bearing cells already adapted to the plasmid may gain a fitness advantage when plasmids transfer into neighboring plasmid-free cells because these cells are still unadapted to the plasmid. These slow-growing transconjugants use fewer resources, which can benefit donor cells. However, opportunities for compensatory mutations in transconjugants increase if these cells become numerous (through replication or conjugation). Moreover, transconjugants also gain an advantage when transferring the plasmid, but the original donors may be too distant from conjugation events to gain an advantage. To understand which consequence prevails, we performed further computer simulations allowing versus banning transfer from transconjugants. The advantage to donors is higher if transconjugants do not transfer plasmids, mainly when donors are rare and when the plasmid transfer rate (from donors) is high. These results show that conjugative plasmids are efficient biological weapons even if the transconjugant cells are poor plasmid donors. After some time, conjugative plasmids gain other host-benefit genes, such as virulence and drug-resistance.info:eu-repo/semantics/publishedVersio
Con seria intenzione di studiare gli uomini e le cose: Elio Modigliani e le sue raccolte etnografiche
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