scholarly journals A continuum of biological adaptations to environmental fluctuation

2019 ◽  
Vol 286 (1912) ◽  
pp. 20191623 ◽  
Author(s):  
Ming Liu ◽  
Dustin R. Rubenstein ◽  
Wei-Chung Liu ◽  
Sheng-Feng Shen
Keyword(s):  
Overlapping Generations ◽  
Bet Hedging ◽  
Environmental Fluctuation ◽  
Infinite Population ◽  
Biological Adaptation ◽  
Hedging Strategies ◽  
Wide Range ◽  
Population Sizes ◽  
Environmental Unpredictability ◽  
Per Capita

Bet-hedging—a strategy that reduces fitness variance at the expense of lower mean fitness among different generations—is thought to evolve as a biological adaptation to environmental unpredictability. Despite widespread use of the bet-hedging concept, most theoretical treatments have largely made unrealistic demographic assumptions, such as non-overlapping generations and fixed or infinite population sizes. Here, we extend the concept to consider overlapping generations by defining bet-hedging as a strategy with lower variance and mean per capita growth rate across different environments. We also define an opposing strategy—the rising-tide—that has higher mean but also higher variance in per capita growth. These alternative strategies lie along a continuum of biological adaptions to environmental fluctuation. Using stochastic Lotka–Volterra models to explore the evolution of the rising-tide versus bet-hedging strategies, we show that both the mean environmental conditions and the temporal scales of their fluctuations, as well as whether population dynamics are discrete or continuous, are crucial in shaping the type of strategy that evolves in fluctuating environments. Our model demonstrates that there are likely to be a wide range of ways that organisms with overlapping generations respond to environmental unpredictability beyond the classic bet-hedging concept.

scholarly journals Biological adaptation under fluctuating selection

2018 ◽  
Author(s):  
Ming Liu ◽  
Dustin R. Rubenstein ◽  
Wei-Chung Liu ◽  
Sheng-Feng Shen
Keyword(s):  
Evolutionary Strategy ◽  
Bet Hedging ◽  
Negative Effects ◽  
Fluctuating Selection ◽  
Hedging Strategy ◽  
Biological Adaptation ◽  
Wide Range ◽  
Population Sizes ◽  
Mean And Variance ◽  
Environmental Unpredictability

AbstractBet-hedging—an evolutionary strategy that reduces fitness variance at the expense of lower mean fitness—is the primary explanation for most forms of biological adaptation to environmental unpredictability. However, most applications of bet-hedging theory to biological problems have largely made unrealistic demographic assumptions, such as non-overlapping generations and fixed population sizes. Consequently, the generality and applicability of bet-hedging theory to real world phenomena remains unclear. Here we use continuous-time, stochastic Lotka-Volterra models to relax overly restrictive demographic assumptions and explore a suite of biological adaptations to fluctuating environments. We discover a novel “rising-tide strategy” that—unlike the bet-hedging strategy—generates both a higher mean and variance in fitness. The positive fitness effects of the rising-tide strategy’s specialization to good years can overcome any negative effects of higher fitness variance in unpredictable environments. Moreover, we show not only that the rising-tide strategy will be selected for over a much broader range of environmental conditions than the bet-hedging strategy, but also under more realistic demographic circumstances. Ultimately, our model demonstrates that there are likely to be a wide range of ways that organisms respond to environmental unpredictability.

scholarly journals Stochasticity-induced stabilization in ecology and evolution

2019 ◽  
Author(s):  
Antony Dean ◽  
Nadav M. Shnerb
Keyword(s):  
Population Genetics ◽  
Species Richness ◽  
Diffusion Approximation ◽  
Generation Time ◽  
Overlapping Generations ◽  
Storage Effect ◽  
Asymmetric Competition ◽  
Bet Hedging ◽  
Qualitative And Quantitative ◽  
Hedging Strategies

AbstractThe ability of random environmental variation to stabilize competitor coexistence was pointed out long ago and, in recent years, has received considerable attention. Here we suggest a novel and generic synthesis of stochasticity-induced stabilization (SIS) phenomena. The storage effect in the lottery model, together with other well-known examples drawn from population genetics, microbiology and ecology, are placed together, reviewed, and explained within a clear, coherent and transparent theoretical framework. Implementing the diffusion approximation we show that in all these systems (including discrete and continuous dynamics, with overlapping and non-overlapping generations) the ratio between the expected growth and its variance governs both qualitative and quantitative features of persistence and invasibility. We further clarify the relationships between bet-hedging strategies, generation time and SIS, study the dynamics of extinction when SIS fails and the explain effects of species richness and asymmetric competition on the stabilizing mechanism.

scholarly journals Bet-hedging strategies in expanding populations

2018 ◽  
Author(s):  
Martín Paula Villa ◽  
Miguel A. Muñoz ◽  
Simone Pigolotti
Keyword(s):  
Phenotypic Diversity ◽  
Phenotypic Switching ◽  
Bet Hedging ◽  
Uncertain Environments ◽  
Adverse Conditions ◽  
Hedging Strategies ◽  
Spatial Fluctuations ◽  
Fluctuating Environments ◽  
Population Sizes ◽  
Mixed Populations

AbstractIn ecology, species can mitigate their extinction risks in uncertain environments by diversifying individual phenotypes. This observation is quantified by the theory of bet-hedging, which provides a reason for the degree of phenotypic diversity observed even in clonal populations. The theory of bet-hedging in well-mixed populations is rather well developed. However, many species underwent range expansions during their evolutionary history, and the importance of phenotypic diversity in such scenarios still needs to be understood. In this paper, we develop a theory of bet-hedging for populations colonizing new, unknown environments that fluctuate either in space or time. In this case, we find that bet-hedging is a more favorable strategy than in well-mixed populations. For slow rates of variation, temporal and spatial fluctuations lead to different outcomes. In spatially fluctuating environments, bet-hedging is favored compared to temporally fluctuating environments. In the limit of frequent environmental variation, no opportunity for bet-hedging exists, regardless of the nature of the environmental fluctuations. For the same model, bet-hedging is never an advantageous strategy in the well-mixed case, supporting the view that range expansions strongly promote diversification. These conclusions are robust against stochasticity induced by finite population sizes. Our findings shed light on the importance of phenotypic heterogeneity in range expansions, paving the way to novel approaches to understand how biodiversity emerges and is maintained.Author summaryEcological populations are often exposed to unpredictable and variable environmental conditions. A number of strategies have evolved to cope with such uncertainty. One of them is stochastic phenotypic switching, by which some individuals in the community are enabled to tackle adverse conditions, even at the price of reducing overall growth in the short term. In this paper, we study the effectiveness of these “bet-hedging” strategies for a population in the process of colonizing new territory. We show that bet-hedging is more advantageous when the environment varies spatially rather than temporally, and infrequently rather than frequently.

scholarly journals 2000 Fleming Lecture. The origin and evolution of hepatitis viruses in humans

2001 ◽  
Vol 82 (4) ◽  
pp. 693-712 ◽  
Author(s):  
Peter Simmonds
Keyword(s):  
Large Population ◽  
Human Populations ◽  
Hepatitis Viruses ◽  
Hepatitis G Virus ◽  
Origin And Evolution ◽  
Wide Range ◽  
Population Sizes ◽  
History Of ◽  
Virus C ◽  
Time Of Divergence

The spread and origins of hepatitis C virus (HCV) in human populations have been the subject of extensive investigations, not least because of the importance this information would provide in predicting clinical outcomes and controlling spread of HCV in the future. However, in the absence of historical and archaeological records of infection, the evolution of HCV and other human hepatitis viruses can only be inferred indirectly from their epidemiology and by genetic analysis of contemporary virus populations. Some information on the history of the latter may be obtained by dating the time of divergence of various genotypes of HCV, hepatitis B virus (HBV) and the non-pathogenic hepatitis G virus (HGV)/GB virus-C (GBV-C). However, the relatively recent times predicted for the origin of these viruses fit poorly with their epidemiological distributions and the recent evidence for species-associated variants of HBV and HGV/GBV-C in a wide range of non-human primates. The apparent conservatism of viruses over long periods implied by these latter observations may be the result of constraints on sequence change peculiar to viruses with single-stranded genomes, or with overlapping reading frames. Large population sizes and intense selection pressures that optimize fitness may be the factors that set virus evolution apart from that of their hosts.

Evaluating agricultural bet-hedging strategies in the Kona Field System: New high-precision230Th/U and14C dates and plant microfossil data from Kealakekua, Hawai‘i Island

2016 ◽  
Vol 52 (1) ◽  
pp. 70-80 ◽  
Author(s):  
MARK D. McCOY ◽  
MARA A. MULROONEY ◽  
MARK HORROCKS ◽  
HAI CHENG ◽  
THEGN N. LADEFOGED
Keyword(s):  
Bet Hedging ◽  
Field System ◽  
Hedging Strategies ◽  
Plant Microfossil

scholarly journals Seasonality and competition select for variable germination behavior in perennials

2022 ◽  
Author(s):  
Hanna ten Brink ◽  
Thomas Ray Haaland ◽  
Oystein Hjorthol Opedal
Keyword(s):  
Simulation Models ◽  
Population Variation ◽  
Priority Effects ◽  
Bet Hedging ◽  
Environmental Predictability ◽  
Hedging Strategies ◽  
Unpredictable Environments ◽  
Evolutionary Simulation ◽  
Negative Frequency Dependent Selection ◽  
Germination Timing

The common occurrence of within-population variation in germination behavior and associated traits such as seed size has long fascinated evolutionary ecologists. In annuals, unpredictable environments are known to select for bet-hedging strategies causing variation in dormancy duration and germination strategies. Variation in germination timing and associated traits is also commonly observed in perennials, and often tracks gradients of environmental predictability. Although bet-hedging is thought to occur less frequently in long-lived organisms, these observations suggest a role of bet-hedging strategies in perennials occupying unpredictable environments. We use complementary numerical and evolutionary simulation models of within- and among-individual variation in germination behavior in seasonal environments to show how bet-hedging interacts with density dependence, life-history traits, and priority effects due to competitive differences among germination strategies. We reveal substantial scope for bet-hedging to produce variation in germination behavior in long-lived plants, when "false starts" to the growing season results in either competitive advantages or increased mortality risk for alternative germination strategies. Additionally, we find that two distinct germination strategies can evolve and coexist through negative frequency-dependent selection. These models extend insights from bet-hedging theory to perennials and explore how competitive communities may be affected by ongoing changes in climate and seasonality patterns.

scholarly journals Incorporating genetic selection into individual-based models (IBMs) of malaria and other infectious diseases

2019 ◽  
Author(s):  
Ian M. Hastings ◽  
Raman Sharma
Keyword(s):  
Control Strategies ◽  
Genetic Parameter ◽  
Genetic Selection ◽  
Wait Time ◽  
Antimicrobial Drug Resistance ◽  
Infinite Population ◽  
Individual Based Models ◽  
Population Sizes ◽  
Human Infections ◽  
The Impact

AbstractOptimal control strategies for human infections are often investigated by computational approaches using individual-based models (IBMs). These typically track humans and evaluate the impact of control interventions in terms of human deaths, clinical cases averted, interruption of transmission etc. Genetic selection can be incorporated into these IBMs and used to track the spread of mutations whose origin and spread are often driven by the intervention, and which subsequently undermine the control strategy; for example, mutations which encode antimicrobial drug resistance or diagnosis- or vaccine-escape phenotypes. Basic population genetic descriptions of selection are based on infinite population sizes (so that chance fluctuations in allele frequency are absent) but IBMs track finite population sizes. We describe how the finite sizes of IBMs affect simulating the dynamics of genetic selection and how best to incorporate genetic selection into these models. We use the OpenMalaria IBM of malaria as an example, but the same principles apply to IBMs of other diseases. We identify four strategies to incorporate selection into IBMs and make the following four recommendations. Firstly, calculate and report the selection coefficients, s, of the advantageous allele as the key genetic parameter. Secondly, use these values of ‘s’ to calculate the wait-time until a mutation successful establishes itself in the population. The wait time for the mutation can be added to speed of selection, s, to calculate when the mutation will reach significant, operationally important levels. Thirdly, quantify the ability of the IBM to robustly estimate small selection coefficients. Fourthly, optimise computational efficacy: when ‘s’ is small it is plausible that fewer replicates of larger IBMs will be more efficient than a larger number of replicates of smaller size.

Surface and Groundwater Quality and Health, with a Focus on the United Kingdom

2003 ◽  
Author(s):  
Colin Neal
Keyword(s):  
Drinking Water ◽  
United Kingdom ◽  
Water Resources ◽  
Groundwater Quality ◽  
Global Climate ◽  
The United Kingdom ◽  
Wide Range ◽  
Basic Sanitation ◽  
Per Capita ◽  
Surface And Groundwater

Freshwater environments are of major importance to health issues in both direct (e.g., drinking water and sanitation) and indirect (e.g., industry, agriculture, and amenity/recreation) ways. However, water resources are finite, and, though renewable, demands have multiplied over the last 100 years due to escalating human populations and the growing requirements of industry and agriculture. Hence, there are increasing global concerns over the extent of present and future good quality water resources. As Gleick (1998) emphasizes: . . . ·Per-capita water demands are increasing, but percapita water availability is decreasing due to population growth and economic development. . . . . . . ·Half the world’s population lacks basic sanitation and more than a billion people lack potable drinking water; these numbers are rising. Incidences of some water-related diseases are rising. . . . . . . ·The per-capita amount of irrigated land is falling and competition for agricultural water is growing. . . . . . . ·Political and military tensions/conflicts over shared water resources are growing. . . . . . . ·A groundwater overdraft exists, the size of which is accelerating; groundwater supplies occur on every continent except Antarctica. . . . . . . ·Global climate change is evident, and the hydrological cycle will be seriously affected in ways that are only beginning to be understood. . . . The chemical composition of surface and groundwaters is influenced by a wide range of processes, some of which are outside the influence of humans while others are a direct consequence of anthropogenic pollution or changing of the environment. Starting with the range and nature of the processes involved, the changing nature of surface and groundwater quality is illustrated here, based on the evolution of the United Kingdom from a rural to an industrial and to a post- industrial society. The issue of what constitutes a health risk is outlined in relation to the pragmatic approaches required for environmental management. Surface and groundwater exhibit a wide range of chemical compositions, and, in ecosystems uninfluenced by humans, the range of compositions can vary considerably.

Forward and backward processes in bisexual models with fixed population sizes

1994 ◽  
Vol 31 (02) ◽  
pp. 309-332 ◽  
Author(s):  
M. Möhle
Keyword(s):  
Overlapping Generations ◽  
Weak Limit ◽  
Fixed Number ◽  
Uhlenbeck Process ◽  
Fisher Model ◽  
Extinction Probabilities ◽  
Ornstein Uhlenbeck Process ◽  
Population Sizes ◽  
Watson Process ◽  
Fixed Population

This paper introduces exchangeable bisexual models with fixed population sizes and non-overlapping generations. In each generation there are N pairs of individuals consisting of a female and a male. The N pairs of a generation produce N daughters and N sons altogether, and these 2N children form the N pairs of the next generation at random. First the extinction of the lines of descendants of a fixed number of pairs is studied, when the population size becomes large. Under suitable conditions this structure can be approximately treated in the framework of a Galton-Watson process. In particular it is shown for the Wright-Fisher model that the discrepancy between the extinction probabilities in the model and in the approximating Galton-Watson process is of order N. Next, the process of the number of ancestor-pairs of all pairs of a generation is analysed. Under suitable conditions this process, properly normed, has a weak limit as N becomes large. For the Wright-Fisher model this limit is an Ornstein–Uhlenbeck process (restricted to a discrete time-set). The corresponding stationary distributions of the backward processes converge to the normal distribution, as expected.

scholarly journals Regional Integration: Do Intra-African Trade and Migration Improve Income in Africa?

2019 ◽  
Vol 43 (6) ◽  
pp. 587-631 ◽  
Author(s):  
Blaise Gnimassoun
Keyword(s):  
Regional Integration ◽  
Capita Income ◽  
Per Capita Income ◽  
Cross Sectional ◽  
Wide Range ◽  
Per Capita ◽  
Migration Flows ◽  
And Migration ◽  
The Impact

Regional integration in Africa is a subject of great interest, but its impact on income has not been studied sufficiently. Using cross-sectional and panel estimations, this article examines the impact of African integration on real per capita income in Africa. Accordingly, we consider intra-African trade and migration flows as quantitative measures reflecting the intensity of regional integration. To address the endogeneity concerns, we use a gravity-based, two-stage least-squares strategy. Our results show that, from a long-term perspective, African integration has not been strong enough to generate a positive, significant, and robust impact on real per capita income in Africa. However, it does appear to be significantly income-enhancing in the short and medium terms but only through intercountry migration. These results are robust to a wide range of specifications.

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