23,609 research outputs found
Evolutionary games between epithelial cells: the impact of population structure and tissue dynamics on the success of cooperation
Cooperation is usually understood as a social phenomenon. However, it also occurs on the cellular level. A number of key mutations associated with malignancy can be considered cooperative, as they rely on the production of diffusible growth factors to confer a fitness benefit. Evolutionary game theory provides a framework for modelling the evolutionary dynamics of these cooperative mutations. This thesis uses evolutionary game theory to examine the evolutionary dynamics of cooperation within epithelial cells, which are the origin point of most cancers. In particular, we consider how the structure and dynamics of an epithelium affect cooperative success. We use the Voronoi tessellation model to represent an epithelium. This allows us much greater flexibility, compared to evolutionary graph theory models, to explore realistic dynamics for population updating. Initially, we consider a model where death and division are spatially decoupled. We analyse pairwise social dilemma games, focussing on the additive prisonerâs dilemma, and multiplayer public goods games. We calculate fixation probabilities, and conditions for cooperative success, by simulation, as well as deriving quasi-analytic results. Comparing with results for graph structured populations with spatially coupled birth and death, or well-mixed populations, we find that in general cooperation is promoted by local game play, but global competition for offspring. We then introduce a more realistic model of population updating, whereby death and division are spatially coupled as a consequence of contact inhibition. The strength of this coupling is positively correlated with the strength of contact inhibition. However, the extent to which strong spatial coupling inhibits cooperation depends on mechanical properties of the tissue
Spatial Invasion of Cooperative Parasites
In this paper we study invasion probabilities and invasion times of
cooperative parasites spreading in spatially structured host populations. The
spatial structure of the host population is given by a random geometric graph
on , , with a Poisson()-distributed number of
vertices and in which vertices are connected over an edge when they have a
distance of at most for some
and . At a host infection many parasites are
generated and parasites move along edges to neighbouring hosts. We assume that
parasites have to cooperate to infect hosts, in the sense that at least two
parasites need to attack a host simultaneously. We find lower and upper bounds
on the invasion probability of the parasites in terms of survival probabilities
of branching processes with cooperation. Furthermore, we characterize the
asymptotic invasion time.
An important ingredient of the proofs is a comparison with infection dynamics
of cooperative parasites in host populations structured according to a complete
graph, i.e. in well-mixed host populations. For these infection processes we
can show that invasion probabilities are asymptotically equal to survival
probabilities of branching processes with cooperation.
Furthermore, we build in the proofs on techniques developed in [BP22], where
an analogous invasion process has been studied for host populations structured
according to a configuration model.
We substantiate our results with simulations
Heterogeneity for IGF-II production maintained by public goods dynamics in neuroendocrine pancreatic cancer
The extensive intratumor heterogeneity revealed by sequencing cancer genomes is an essential determinant of tumor progression, diagnosis, and treatment. What maintains heterogeneity remains an open question because competition within a tumor leads to a strong selection for the fittest subclone. Cancer cells also cooperate by sharing molecules with paracrine effects, such as growth factors, and heterogeneity can be maintained if subclones depend on each other for survival. Without strict interdependence between subclones, however, nonproducer cells can free-ride on the growth factors produced by neighboring producer cells, a collective action problem known in game theory as the âtragedy of the commons,â which has been observed in microbial cell populations. Here, we report that similar dynamics occur in cancer cell populations. Neuroendocrine pancreatic cancer (insulinoma) cells that do not produce insulin-like growth factor II (IGF-II) grow slowly in pure cultures but have a proliferation advantage in mixed cultures, where they can use the IGF-II provided by producer cells. We show that, as predicted by evolutionary game theory, producer cells do not go extinct because IGF-II acts as a nonlinear public good, creating negative frequency-dependent selection that leads to a stable coexistence of the two cell types. Intratumor cell heterogeneity can therefore be maintained even without strict interdependence between cell subclones. Reducing the amount of growth factors available within a tumor may lead to a reduction in growth followed by a new equilibrium, which may explain relapse in therapies that target growth factors
A dynamical trichotomy for structured populations experiencing positive density-dependence in stochastic environments
Positive density-dependence occurs when individuals experience increased
survivorship, growth, or reproduction with increased population densities.
Mechanisms leading to these positive relationships include mate limitation,
saturating predation risk, and cooperative breeding and foraging. Individuals
within these populations may differ in age, size, or geographic location and
thereby structure these populations. Here, I study structured population models
accounting for positive density-dependence and environmental stochasticity i.e.
random fluctuations in the demographic rates of the population. Under an
accessibility assumption (roughly, stochastic fluctuations can lead to
populations getting small and large), these models are shown to exhibit a
dynamical trichotomy: (i) for all initial conditions, the population goes
asymptotically extinct with probability one, (ii) for all positive initial
conditions, the population persists and asymptotically exhibits unbounded
growth, and (iii) for all positive initial conditions, there is a positive
probability of asymptotic extinction and a complementary positive probability
of unbounded growth. The main results are illustrated with applications to
spatially structured populations with an Allee effect and age-structured
populations experiencing mate limitation
Resistance to learning and the evolution of cooperation
In many evolutionary algorithms, crossover is the main operator used in generating new
individuals from old ones. However, the usual mechanism for generating offsprings in spatially
structured evolutionary games has to date been clonation. Here we study the effect of
incorporating crossover on these models. Our framework is the spatial Continuous Prisoner's
Dilemma. For this evolutionary game, it has been reported that occasional errors (mutations) in
the clonal process can explain the emergence of cooperation from a non-cooperative initial
state. First, we show that this only occurs for particular regimes of low costs of cooperation.
Then, we display how crossover gets greater the range of scenarios where cooperative mutants
can invade selfish populations. In a social context, where crossover involves a general rule of
gradual learning, our results show that the less that is learnt in a single step, the larger the
degree of global cooperation finally attained. In general, the effect of step-by-step learning can
be more efficient for the evolution of cooperation than a full blast one
Robust permanence for interacting structured populations
The dynamics of interacting structured populations can be modeled by
where , , and
are matrices with non-negative off-diagonal entries. These models are
permanent if there exists a positive global attractor and are robustly
permanent if they remain permanent following perturbations of .
Necessary and sufficient conditions for robust permanence are derived using
dominant Lyapunov exponents of the with respect to
invariant measures . The necessary condition requires for all ergodic measures with support in the boundary of the
non-negative cone. The sufficient condition requires that the boundary admits a
Morse decomposition such that for all invariant
measures supported by a component of the Morse decomposition. When the
Morse components are Axiom A, uniquely ergodic, or support all but one
population, the necessary and sufficient conditions are equivalent.
Applications to spatial ecology, epidemiology, and gene networks are given
Long-lasting, kin-directed female interactions in a spatially structured wild boar social network
We thank W. JÄdrzejewski for his support and logistical help in trapping wild boar. We are grateful to R. Kozak, A. Waszkiewicz and many students and volunteers for their help with fieldwork as well as to A. N. Bunevich, T. Borowik and local hunters for providing genetic samples. Genetic analyses were performed in the laboratory of the Department of Science for Nature and Environmental Resources, University of Sassari, Italy, with the help of L. Iacolina and D. Biosa. We are grateful to K. OâMahony who revised English and to A. Widdig, K. Langergraber and one anonymous reviewer for valuable comments on the earlier version of the manuscript.Peer reviewedPublisher PD
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