2,138 research outputs found
Repeatability of evolution on epistatic landscapes
Evolution is a dynamic process. The two classical forces of evolution are
mutation and selection. Assuming small mutation rates, evolution can be
predicted based solely on the fitness differences between phenotypes.
Predicting an evolutionary process under varying mutation rates as well as
varying fitness is still an open question. Experimental procedures, however, do
include these complexities along with fluctuating population sizes and
stochastic events such as extinctions. We investigate the mutational path
probabilities of systems having epistatic effects on both fitness and mutation
rates using a theoretical and computational framework. In contrast to previous
models, we do not limit ourselves to the typical strong selection, weak
mutation (SSWM)-regime or to fixed population sizes. Rather we allow epistatic
interactions to also affect mutation rates. This can lead to qualitatively
non-trivial dynamics. Pathways, that are negligible in the SSWM-regime, can
overcome fitness valleys and become accessible. This finding has the potential
to extend the traditional predictions based on the SSWM foundation and bring us
closer to what is observed in experimental systems
Eco-evolutionary dynamics of social dilemmas
Social dilemmas are an integral part of social interactions. Cooperative
actions, ranging from secreting extra-cellular products in microbial
populations to donating blood in humans, are costly to the actor and hence
create an incentive to shirk and avoid the costs. Nevertheless, cooperation is
ubiquitous in nature. Both costs and benefits often depend non-linearly on the
number and types of individuals involved -- as captured by idioms such as `too
many cooks spoil the broth' where additional contributions are discounted, or
`two heads are better than one' where cooperators synergistically enhance the
group benefit. Interaction group sizes may depend on the size of the population
and hence on ecological processes. This results in feedback mechanisms between
ecological and evolutionary processes, which jointly affect and determine the
evolutionary trajectory. Only recently combined eco-evolutionary processes
became experimentally tractable in microbial social dilemmas. Here we analyse
the evolutionary dynamics of non-linear social dilemmas in settings where the
population fluctuates in size and the environment changes over time. In
particular, cooperation is often supported and maintained at high densities
through ecological fluctuations. Moreover, we find that the combination of the
two processes routinely reveals highly complex dynamics, which suggests common
occurrence in nature.Comment: 26 pages, 11 figure
Evolutionary Multiplayer Games
Evolutionary game theory has become one of the most diverse and far reaching
theories in biology. Applications of this theory range from cell dynamics to
social evolution. However, many applications make it clear that inherent
non-linearities of natural systems need to be taken into account. One way of
introducing such non-linearities into evolutionary games is by the inclusion of
multiple players. An example is of social dilemmas, where group benefits could
e.g.\ increase less than linear with the number of cooperators. Such
multiplayer games can be introduced in all the fields where evolutionary game
theory is already well established. However, the inclusion of non-linearities
can help to advance the analysis of systems which are known to be complex, e.g.
in the case of non-Mendelian inheritance. We review the diachronic theory and
applications of multiplayer evolutionary games and present the current state of
the field. Our aim is a summary of the theoretical results from well-mixed
populations in infinite as well as finite populations. We also discuss examples
from three fields where the theory has been successfully applied, ecology,
social sciences and population genetics. In closing, we probe certain future
directions which can be explored using the complexity of multiplayer games
while preserving the promise of simplicity of evolutionary games.Comment: 14 pages, 2 figures, review pape
Mutualism and evolutionary multiplayer games: revisiting the Red King
Coevolution of two species is typically thought to favour the evolution of
faster evolutionary rates helping a species keep ahead in the Red Queen race,
where `it takes all the running you can do to stay where you are'. In contrast,
if species are in a mutualistic relationship, it was proposed that the Red King
effect may act, where it can be beneficial to evolve slower than the
mutualistic species. The Red King hypothesis proposes that the species which
evolves slower can gain a larger share of the benefits. However, the
interactions between the two species may involve multiple individuals. To
analyse such a situation, we resort to evolutionary multiplayer games. Even in
situations where evolving slower is beneficial in a two-player setting, faster
evolution may be favoured in a multiplayer setting. The underlying features of
multiplayer games can be crucial for the distribution of benefits. They also
suggest a link between the evolution of the rate of evolution and group size
Chaotic provinces in the kingdom of the Red Queen
The interplay between parasites and their hosts is found in all kinds of
species and plays an important role in understanding the principles of
evolution and coevolution. Usually, the different genotypes of hosts and
parasites oscillate in their abundances. The well-established theory of
oscillatory Red Queen dynamics proposes an ongoing change in frequencies of the
different types within each species. So far, it is unclear in which way Red
Queen dynamics persists with more than two types of hosts and parasites. In our
analysis, an arbitrary number of types within two species are examined in a
deterministic framework with constant or changing population size. This general
framework allows for analytical solutions for internal fixed points and their
stability. For more than two species, apparently chaotic dynamics has been
reported. Here we show that even for two species, once more than two types are
considered per species, irregular dynamics in their frequencies can be observed
in the long run. The nature of the dynamics depends strongly on the initial
configuration of the system; the usual regular Red Queen oscillations are only
observed in some parts of the parameter region
The pace of evolution across fitness valleys
How fast does a population evolve from one fitness peak to another? We study
the dynamics of evolving, asexually reproducing populations in which a certain
number of mutations jointly confer a fitness advantage. We consider the time
until a population has evolved from one fitness peak to another one with a
higher fitness. The order of mutations can either be fixed or random. If the
order of mutations is fixed, then the population follows a metaphorical ridge,
a single path. If the order of mutations is arbitrary, then there are many ways
to evolve to the higher fitness state. We address the time required for
fixation in such scenarios and study how it is affected by the order of
mutations, the population size, the fitness values and the mutation rate
Implementing the Flipped Classroom in an Undergraduate Corporate Finance Course
This study analyzes flipped mode of instruction in Corporate Finance. In the current environment, with many students in quarantine and greater emphasis on self-study, it is even more relevant to understand how students understand and retain concepts derived from online environment. In this study, performance of students in flipped mode is compared with the performance in traditional lecture-style. In flipped class, students watched a brief video-lecture, took an online assessment quiz prior to attending an interactive discussion-based class session, unlike the traditional lecture style. The results of this study suggest that with flipped mode, most students take greater responsibility of their learning, prefer hands-on learning, achieve more and feel more satisfied with their performance. However, there is no statistical difference in the test scores of students in the flipped classroom as compared to the traditional classroom
Implementing the Flipped Classroom in an Undergraduate Corporate Finance Course
This study analyzes flipped mode of instruction in Corporate Finance. In the current environment, with many students in quarantine and greater emphasis on self-study, it is even more relevant to understand how students understand and retain concepts derived from online environment. In this study, performance of students in flipped mode is compared with the performance in traditional lecture-style. In flipped class, students watched a brief video-lecture, took an online assessment quiz prior to attending an interactive discussion-based class session, unlike the traditional lecture style. The results of this study suggest that with flipped mode, most students take greater responsibility of their learning, prefer hands-on learning, achieve more and feel more satisfied with their performance. However, there is no statistical difference in the test scores of students in the flipped classroom as compared to the traditional classroom
Numerical Modelling of Scramjet Combustor
Numerical modelling of turbulent-reacting flow field of supersonic combustion ramjet(scramjet) combustors are presented. The developed numerical procedure is based on the implicittreatment of chemical source terms by preconditioning and solved along with unstedy turbulentNavier-Stokes equations explicitly. Reaction is modelled using an eight-step hydrogen-airchemistry. Code is validated against a standard wall jet experimental data and is successfullyused to model the turbulent-reacting flow field resulting due to the combustion of hydrogeninjected from diamond-shaped strut and also in the wake region of wedge-shaped strut placedin the heated supersonic airstream. The analysis could demonstrate the effect of interaction ofoblique shock wave with a supersonic stream of hydrogen in its (fuel-air) mixing and reactionfor strut-based scramjet combustors
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