49 research outputs found
Limited role of spatial selfstructuring in emergent trade-offs during pathogen evolution
Pathogen transmission and virulence are main evolutionary variables broadly assumed to be linked
through trade-offs. In well-mixed populations, these trade-offs are often ascribed to physiological
restrictions, while populations with spatial self-structuring might evolve emergent trade-offs. Here,
we reexamine a spatially-explicit, SIR model of the latter kind proposed by Ballegooijen and Boerlijst
with the aim of characterising the mechanisms causing the emergence of the trade-off and its structural
robustness. Using invadability criteria, we establish the conditions under which an evolutionary
feedback between transmission and virulence mediated by pattern formation can poise the system to
a critical boundary separating a disordered state (without emergent trade-off) from a self-structured
phase (where the trade-off emerges), and analytically calculate the functional shape of the boundary
in a certain approximation. Beyond evolutionary parameters, the success of an invasion depends
on the size and spatial structure of the invading and invaded populations. Spatial self-structuring is
often destroyed when hosts are mobile, changing the evolutionary dynamics to those of a well-mixed
population. In a metapopulation scenario, the systematic extinction of the pathogen in the disordered
phase may counteract the disruptive effect of host mobility, favour pattern formation and therefore
recover the emergent trade-off.This work has been supported by the Spanish Ministerio de Economía, Industria y Competitividad and FEDER
funds of the EU through grants ViralESS (FIS2014-57686-P and FIS2017-84256-P). The internship of VB was
financed by the Severo Ochoa Centers of Excellence Program (SEV-2013-0347)
Evolutionary instability of Zero Determinant strategies demonstrates that winning isn't everything
Zero Determinant (ZD) strategies are a new class of probabilistic and
conditional strategies that are able to unilaterally set the expected payoff of
an opponent in iterated plays of the Prisoner's Dilemma irrespective of the
opponent's strategy, or else to set the ratio between a ZD player's and their
opponent's expected payoff. Here we show that while ZD strategies are weakly
dominant, they are not evolutionarily stable and will instead evolve into less
coercive strategies. We show that ZD strategies with an informational advantage
over other players that allows them to recognize other ZD strategies can be
evolutionarily stable (and able to exploit other players). However, such an
advantage is bound to be short-lived as opposing strategies evolve to
counteract the recognition.Comment: 14 pages, 4 figures. Change in title (again!) to comply with Nature
Communications requirements. To appear in Nature Communication
Spatial Pattern Switching Enables Cyclic Evolution in Spatial Epidemics
Infectious diseases often spread as spatial epidemic outbreak waves. A number of model studies have shown that such spatial pattern formation can have important consequences for the evolution of pathogens. Here, we show that such spatial patterns can cause cyclic evolutionary dynamics in selection for the length of the infectious period. The necessary reversal in the direction of selection is enabled by a qualitative change in the spatial pattern from epidemic waves to irregular local outbreaks. The spatial patterns are an emergent property of the epidemic system, and they are robust against changes in specific model assumptions. Our results indicate that emergent spatial patterns can act as a rich source for complexity in pathogen evolution
Multilevel Selection in Models of Prebiotic Evolution II: A Direct Comparison of Compartmentalization and Spatial Self-Organization
Multilevel selection has been indicated as an essential factor for the evolution of complexity in interacting RNA-like replicator systems. There are two types of multilevel selection mechanisms: implicit and explicit. For implicit multilevel selection, spatial self-organization of replicator populations has been suggested, which leads to higher level selection among emergent mesoscopic spatial patterns (traveling waves). For explicit multilevel selection, compartmentalization of replicators by vesicles has been suggested, which leads to higher level evolutionary dynamics among explicitly imposed mesoscopic entities (protocells). Historically, these mechanisms have been given separate consideration for the interests on its own. Here, we make a direct comparison between spatial self-organization and compartmentalization in simulated RNA-like replicator systems. Firstly, we show that both mechanisms achieve the macroscopic stability of a replicator system through the evolutionary dynamics on mesoscopic entities that counteract that of microscopic entities. Secondly, we show that a striking difference exists between the two mechanisms regarding their possible influence on the long-term evolutionary dynamics, which happens under an emergent trade-off situation arising from the multilevel selection. The difference is explained in terms of the difference in the stability between self-organized mesoscopic entities and externally imposed mesoscopic entities. Thirdly, we show that a sharp transition happens in the long-term evolutionary dynamics of the compartmentalized system as a function of replicator mutation rate. Fourthly, the results imply that spatial self-organization can allow the evolution of stable folding in parasitic replicators without any specific functionality in the folding itself. Finally, the results are discussed in relation to the experimental synthesis of chemical Darwinian systems and to the multilevel selection theory of evolutionary biology in general. To conclude, novel evolutionary directions can emerge through interactions between the evolutionary dynamics on multiple levels of organization. Different multilevel selection mechanisms can produce a difference in the long-term evolutionary trend of identical microscopic entities
Apology and forgiveness evolve to resolve failures in cooperative agreements
Making agreements on how to behave has been shown to be an evolutionarily viable strategy in one-shot social dilemmas. However, in many situations agreements aim to establish long-term mutually beneficial interactions. Our analytical and numerical results reveal for the first time under which conditions revenge, apology and forgiveness can evolve and deal with mistakes within ongoing agreements in the context of the Iterated Prisoners Dilemma. We show that, when the agreement fails, participants prefer to take revenge by defecting in the subsisting encounters. Incorporating costly apology and forgiveness reveals that, even when mistakes are frequent, there exists a sincerity threshold for which mistakes will not lead to the destruction of the agreement, inducing even higher levels of cooperation. In short, even when to err is human, revenge, apology and forgiveness are evolutionarily viable strategies which play an important role in inducing cooperation in repeated dilemmas.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Critical mutation rate has an exponential dependence on population size for eukaryotic-length genomes with crossover
The critical mutation rate (CMR) determines the shift between survival-of-the-fittest and survival of individuals with greater mutational robustness (“flattest”). We identify an inverse relationship between CMR and sequence length in an in silico system with a two-peak fitness landscape; CMR decreases to no more than five orders of magnitude above estimates of eukaryotic per base mutation rate. We confirm the CMR reduces exponentially at low population sizes, irrespective of peak radius and distance, and increases with the number of genetic crossovers. We also identify an inverse relationship between CMR and the number of genes, confirming that, for a similar number of genes to that for the plant Arabidopsis thaliana (25,000), the CMR is close to its known wild-type mutation rate; mutation rates for additional organisms were also found to be within one order of magnitude of the CMR. This is the first time such a simulation model has been assigned input and produced output within range for a given biological organism. The decrease in CMR with population size previously observed is maintained; there is potential for the model to influence understanding of populations undergoing bottleneck, stress, and conservation strategy for populations near extinction
Adaptation of HIV-1 Depends on the Host-Cell Environment
Many viruses have the ability to rapidly develop resistance against antiviral drugs and escape from the host immune system. To which extent the host environment affects this adaptive potential of viruses is largely unknown. Here we show that for HIV-1, the host-cell environment is key to the adaptive potential of the virus. We performed a large-scale selection experiment with two HIV-1 strains in two different T-cell lines (MT4 and C8166). Over 110 days of culture, both virus strains adapted rapidly to the MT4 T-cell line. In contrast, when cultured on the C8166 T-cell line, the same strains did not show any increase in fitness. By sequence analyses and infections with viruses expressing either yellow or cyan fluorescent protein, we were able to show that the absence of adaptation was linked to a lower recombination rate in the C8166 T-cell line. Our findings suggest that if we can manipulate the host-cellular factors that mediate viral evolution, we may be able to significantly retard viral adaptability
Taking Multiple Infections of Cells and Recombination into Account Leads to Small Within-Host Effective-Population-Size Estimates of HIV-1
Whether HIV-1 evolution in infected individuals is dominated by deterministic or stochastic effects remains unclear because current estimates of the effective population size of HIV-1 in vivo, Ne, are widely varying. Models assuming HIV-1 evolution to be neutral estimate Ne∼102–104, smaller than the inverse mutation rate of HIV-1 (∼105), implying the predominance of stochastic forces. In contrast, a model that includes selection estimates Ne>105, suggesting that deterministic forces would hold sway. The consequent uncertainty in the nature of HIV-1 evolution compromises our ability to describe disease progression and outcomes of therapy. We perform detailed bit-string simulations of viral evolution that consider large genome lengths and incorporate the key evolutionary processes underlying the genomic diversification of HIV-1 in infected individuals, namely, mutation, multiple infections of cells, recombination, selection, and epistatic interactions between multiple loci. Our simulations describe quantitatively the evolution of HIV-1 diversity and divergence in patients. From comparisons of our simulations with patient data, we estimate Ne∼103–104, implying predominantly stochastic evolution. Interestingly, we find that Ne and the viral generation time are correlated with the disease progression time, presenting a route to a priori prediction of disease progression in patients. Further, we show that the previous estimate of Ne>105 reduces as the frequencies of multiple infections of cells and recombination assumed increase. Our simulations with Ne∼103–104 may be employed to estimate markers of disease progression and outcomes of therapy that depend on the evolution of viral diversity and divergence
Assessing ecological resilience to human induced environmental change in shallow lakes
Sudden unpredictable changes in ecosystems are an increasing source of concern because of
their inherent unpredictability and the difficulties involved in restoration. Our understanding
of the changes that occur across different trophic levels and the form of this change is lacking.
This is especially true of large shallow lakes, where characteristics such as fetch and depth
are close to theoretical boundary values for hysteretic behaviour. The development of
reliable indicators capable of predicting these changes has been the focus of much research
in recent years. The success of these early warning indicators (EWIs) has so far been mixed.
There remain many unknowns about how they perform under a wide variety of conditions
and parameters. Future climate change is predicted to have a wide range of impacts through
the interaction of combined pressures, making the understanding of EWIs and the in-lake
processes that occur during regime shifts imperative. Loch Leven, Scotland, UK, is a large
shallow lake with a history of eutrophication, research and management and as such is an
ideal study site to better understand resilience and regime shifts under a range of interacting
stressors.
The objectives of this research are to: (1) analyse long term data to identify the occurrence
of common tipping points within the chemical (water column nutrient concentrations) and
biological (macrophytes, phytoplankton, zooplankton) components of the loch, then test
these tipping points using five statistical early warning indicators (EWIs) across multiple
rolling window sizes; and (2) quantify the changes in lake ecology using a before/after
analysis and testing for non-linearity, combined with modelling using the aquatic ecosystem
process model PCLake to determine the level of resilience following a regime shift during
recovery from eutrophication; (3) using PCLake, examine the sensitivity of Loch Leven to
regime shifts in the face of predicted environmental change (e.g. climate change, nutrient
pollution).
Statistical analysis identified tipping points across all trophic levels included, from physical
and chemical variables through to apex predators. The success of EWIs in predicting the
tipping points was highly dependent on the number of EWIs used, with window size having
a smaller impact. The 45% window size had the highest overall accuracy across all EWIs but
only detected 16.5% more tipping points than the window size with the lowest overall
accuracy. Differences between individual EWI performance and usage of them as a group
was substantial with a 29.7% increase between the two. In both individual and group use of
EWIs, false positives (early warning without a tipping point) were more common than true
positives (tipping point preceded by EWI), creating significant doubts about their reliability
as management tools.
Significant change was seen across multiple variables and trophic levels in the before/after
analysis following sudden recovery from eutrophication, with most variables also showing
evidence of non-linear change. Modelling of responses to nutrient loading for chlorophyll,
zooplankton and macrophytes, under states from before and after the shift, indicate
hysteresis and thus the presence of feedback mechanisms. The modelling of responses to
nutrient loading and predicted climate change in temperature and precipitation
demonstrated that increases in temperature and decreases in summer precipitation
individually had large impacts on chlorophyll and zooplankton at medium to high phosphorus
(P) loads. However, modelling of the combined effects of these changes resulted in the
highest lake chlorophyll concentrations of all tested scenarios. At low P loads higher
temperatures and increased winter precipitation had the greatest impact on system
resilience with a lower Critical Nutrient Load (CNL). The difference between chlorophyll and
zooplankton as opposed to macrophytes was in the presence of a lower CNL for the increased
winter precipitation-only scenarios which was not seen in the macrophytes. This highlights
the potential role of high winter inputs potentially loaded with particulate matter in reducing
resilience at lower P loads.
This research has highlighted the vulnerability and low resilience of Loch Leven to
environmental change. The presence of multiple tipping points and high levels of EWI activity
show a high level of flexibility in the system. Coupled with the occurrence of widespread
trophic change during a sudden recovery and a small level of hysteresis and high levels of
sensitivity to climate change, the low levels of resilience become clear. The impact of lake-specific
characteristics such as moderate depth, large fetch and a heterogeneous bed
morphology is particularly evident in the limitations on macrophyte cover and the reliance
on zooplankton to determine the hysteresis offset (amount of phosphorus (P) loading
between the two CNL). The presence of these characteristics can be used to identify other
lakes vulnerable to change. Improving the predictive capabilities of resilience indicators such
as EWIs, and better understanding of the ecological changes that occur during non-linear
change in response to recovery and climate change, can help target relevant ecosystem
components for preventative management. These actions may become necessary under
even the most conservative estimates of environmental change
Selection at the level of the community: the importance of spatial structure
To ask whether natural selection occurs at the level of the community is to
consider whether communities represent a major transition in evolution - can
particular community configurations evolve and maintain their integrity in the
face of disruption arising from the self-interest of component individuals? This
requires heritable variation among subcommunities in a landscape, and that
alternative subcommunities maintain a degree of individuality in both time
and space. Recently developed models show that spatial self-structuring in
multispecies systems can meet both criteria and provide a rich substrate for
community-level selection and a major transition in evolution