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D. Lawrence Venable - One of the best experts on this subject based on the ideXlab platform.

  • Offspring polymorphism and bet hedging: a large-scale, phylogenetic analysis.
    Ecology letters, 2020
    Co-Authors: Joshua P. Scholl, Leonardo Calle, Nicholas Miller, D. Lawrence Venable
    Abstract:

    Offspring polymorphism is a reproductive strategy where individual organisms simultaneously produce offspring that differ in morphology and ecology. It occurs across the Tree of Life but is particularly common among plants, where it is termed seed (diaspore) heteromorphism. The prevalence of this strategy in unpredictably varying environments has resulted in the assumption that it serves as a Bet-Hedging mechanism. We found 101 examples of this strategy in southwestern North America. We provide phylogenetically informed evidence for the hypothesis that the occurrence of seed heteromorphism increases with increasing environmental variability, though this pattern was only significant for aridity, one of our two rainfall variability metrics. We provide a strong test of bet hedging for a large, taxonomically diverse set of seed heteromorphic species, lending support to the hypothesis that bet hedging is an important mechanistic driver for the evolution of seed heteromorphism.

  • Within-and among-year germination in Sonoran Desert winter annuals: bet hedging and predictive germination in a variable environment.
    Ecology letters, 2016
    Co-Authors: Jennifer R. Gremer, Sarah Kimball, D. Lawrence Venable
    Abstract:

    In variable environments, organisms must have strategies to ensure fitness as conditions change. For plants, germination can time emergence with favourable conditions for later growth and reproduction (predictive germination), spread the risk of unfavourable conditions (bet hedging) or both (integrated strategies). Here we explored the adaptive value of within- and among-year germination timing for 12 species of Sonoran Desert winter annual plants. We parameterised models with long-term demographic data to predict optimal germination fractions and compared them to observed germination. At both temporal scales we found that bet hedging is beneficial and that predicted optimal strategies corresponded well with observed germination. We also found substantial fitness benefits to varying germination timing, suggesting some degree of predictive germination in nature. However, predictive germination was imperfect, calling for some degree of bet hedging. Together, our results suggest that desert winter annuals have integrated strategies combining both predictive plasticity and bet hedging.

  • Bet hedging in desert winter annual plants: optimal germination strategies in a variable environment.
    Ecology letters, 2014
    Co-Authors: Jennifer R. Gremer, D. Lawrence Venable
    Abstract:

    In bet hedging, organisms sacrifice short-term success to reduce the long-term variance in success. Delayed germination is the classic example of bet hedging, in which a fraction of seeds remain dormant as a hedge against the risk of complete reproductive failure. Here, we investigate the adaptive nature of delayed germination as a bet hedging strategy using long-term demographic data on Sonoran Desert winter annual plants. Using stochastic population models, we estimate fitness as a function of delayed germination and identify evolutionarily stable strategies for 12 abundant species in the community. Results indicate that delayed germination meets the criteria as a bet hedging strategy for all species. Density-dependent models, but not density-independent ones, predicted optimal germination strategies that correspond remarkably well with observed patterns. By incorporating naturally occurring variation in seed and seedling dynamics, our results present a rigorous test of bet hedging theory within the relevant environmental context.

  • Bet hedging via seed banking in desert evening primroses (Oenothera, Onagraceae): demographic evidence from natural populations.
    The American Naturalist, 2007
    Co-Authors: Margaret E. K. Evans, Régis Ferrière, Michael J. Kane, D. Lawrence Venable
    Abstract:

    Abstract: Bet hedging is one solution to the problem of an unpredictably variable environment: fitness in the average environment is sacrificed in favor of lower variation in fitness if this leads to higher long‐run stochastic mean fitness. While bet hedging is an important concept in evolutionary ecology, empirical evidence that it occurs is scant. Here we evaluate whether bet hedging occurs via seed banking in natural populations of two species of desert evening primroses (Oenothera, Onagraceae), one annual and one perennial. Four years of data on plants and 3 years of data on seeds yielded two transitions for the entire life cycle. One year was exceptionally dry, leading to reproductive failure in the sample areas, and the other was above average in precipitation, leading to reproductive success in four of five populations. Stochastic simulations of population growth revealed patterns indicative of bet hedging via seed banking, particularly in the annual populations: variance in fitness and fitness in ...

  • BET HEDGING IN A GUILD OF DESERT ANNUALS
    Ecology, 2007
    Co-Authors: D. Lawrence Venable
    Abstract:

    Evolutionary bet hedging encapsulates the counterintuitive idea that organisms evolve traits that reduce short-term reproductive success in favor of longer-term risk reduction. It has been widely investigated theoretically, and many putative examples have been cited including practical ones such as the dormancy involved in microbe and weed persistence. However, long-term data on demographic variation from the actual evolutionarily relevant environments have been unavailable to test for its mechanistic relationship to alleged bet hedging traits. I report an association between delayed germination (a bet hedging trait) and risk using a 22-year data set on demographic variation for 10 species of desert annual plants. Species with greater variation in reproductive success (per capita survival from germination to reproduction x per capita fecundity of survivors) were found to have lower average germination fractions. This provides a definitive test using realistic data on demographic variance that confirms the life history prediction for bet hedging. I also showed that the species with greater long-term demographic variation tended to be the ones with greater sensitivity of reproductive success to variation among years in growing-season precipitation.

Andrew M. Simons - One of the best experts on this subject based on the ideXlab platform.

  • experimental evolution of bet hedging under manipulated environmental uncertainty in neurospora crassa
    Proceedings of The Royal Society B: Biological Sciences, 2014
    Co-Authors: Jeffrey K Graham, Myron L Smith, Andrew M. Simons
    Abstract:

    All organisms are faced with environmental uncertainty. Bet-Hedging theory expects unpredictable selection to result in the evolution of traits that maximize the geometric-mean fitness even though such traits appear to be detrimental over the shorter term. Despite the centrality of fitness measures to evolutionary analysis, no direct test of the geometric-mean fitness principle exists. Here, we directly distinguish between predictions of competing fitness maximization principles by testing Cohen9s 1966 classic Bet-Hedging model using the fungus Neurospora crassa . The simple prediction is that propagule dormancy will evolve in proportion to the frequency of ‘bad’ years, whereas the prediction of the alternative arithmetic-mean principle is the evolution of zero dormancy as long as the expectation of a bad year is less than 0.5. Ascospore dormancy fraction in N. crassa was allowed to evolve under five experimental selection regimes that differed in the frequency of unpredictable ‘bad years’. Results were consistent with Bet-Hedging theory: final dormancy fraction in 12 genetic lineages across 88 independently evolving samples was proportional to the frequency of bad years, and evolved both upwards and downwards as predicted from a range of starting dormancy fractions. These findings suggest that selection results in adaptation to variable rather than to expected environments.

  • Playing smart vs. playing safe: the joint expression of phenotypic plasticity and potential bet hedging across and within thermal environments
    Journal of evolutionary biology, 2014
    Co-Authors: Andrew M. Simons
    Abstract:

    Adaptive phenotypic plasticity evolves when cues reliably predict fitness consequences of life-history decisions, whereas bet hedging evolves when environments are unpredictable. These modes of response should be jointly expressed, because environmental variance is composed of both predictable and unpredictable components. However, little attention has been paid to the joint expression of plasticity and bet hedging. Here, I examine the simultaneous expression of plasticity in germination rate and two potential Bet-Hedging traits - germination fraction and within-season diversification in timing of germination - in seeds from multiple seed families of five geographically distant populations of Lobelia inflata (L.) subjected to a thermal gradient. Populations differ in germination plasticity to temperature, in total germination fraction and in the expression of potential diversification in the timing of germination. The observation of a negative partial correlation between the expression of plasticity and germination variance (potential diversification), and a positive correlation between plasticity and germination fraction is suggestive of a trade-off between modes of response to environmental variance. If the observed correlations are indicative of those between adaptive plasticity and bet hedging, we expect an optimal balance to exist and differ among populations. I discuss the challenges involved in testing whether the balance between plasticity and bet hedging depends on the relative predictability of environmental variance.

  • Modes of response to environmental change and the elusive empirical evidence for bet hedging
    Proceedings. Biological sciences, 2011
    Co-Authors: Andrew M. Simons
    Abstract:

    Uncertainty is a problem not only in human decision-making, but is a prevalent quality of natural environments and thus requires evolutionary response. Unpredictable natural selection is expected to result in the evolution of Bet-Hedging strategies, which are adaptations to long-term fluctuating selection. Despite a recent surge of interest in bet hedging, its study remains mired in conceptual and practical difficulties, compounded by confusion over what constitutes evidence for its existence. Here, I attempt to resolve misunderstandings about bet hedging and its relationship with other modes of response to environmental change, identify the challenges inherent to its study and assess the state of existing empirical evidence. The variety and distribution of plausible Bet-Hedging traits found across 16 phyla in over 100 studies suggest their ubiquity. Thus, bet hedging should be considered a specific mode of response to environmental change. However, the distribution of Bet-Hedging studies across evidence categories—defined according to potential strength—is heavily skewed towards weaker categories, underscoring the need for direct appraisals of the adaptive significance of putative Bet-Hedging traits in nature.

  • Fluctuating natural selection accounts for the evolution of diversification bet hedging
    Proceedings. Biological sciences, 2009
    Co-Authors: Andrew M. Simons
    Abstract:

    Natural environments are characterized by unpredictability over all time scales. This stochasticity is expected on theoretical grounds to result in the evolution of ‘Bet-Hedging’ traits that maximize the long term, or geometric mean fitness even though such traits do not maximize fitness over shorter time scales. The geometric mean principle is thus central to our interpretation of optimality and adaptation; however, quantitative empirical support for bet hedging is lacking. Here, I report a quantitative test using the timing of seed germination—a model diversification Bet-Hedging trait—in Lobelia inflata under field conditions. In a phenotypic manipulation study, I find the magnitude of fluctuating selection acting on seed germination timing—across 70 intervals throughout five seasons—to be extreme: fitness functions for survival are complex and multimodal within seasons and significantly dissimilar among seasons. I confirm that the observed magnitude of fluctuating selection is sufficient to account for the degree of diversification behaviour characteristic of individuals of this species. The geometric mean principle has been known to economic theory for over two centuries; this study now provides a quantitative test of optimality of a Bet-Hedging trait in nature.

  • ENVIRONMENTAL AND GENETIC SOURCES OF DIVERSIFICATION IN THE TIMING OF SEED GERMINATION: IMPLICATIONS FOR THE EVOLUTION OF BET HEDGING
    Evolution; international journal of organic evolution, 2006
    Co-Authors: Andrew M. Simons, Mark O. Johnston
    Abstract:

    Abstract Environmental variation that is not predictably related to cues is expected to drive the evolution of Bet-Hedging strategies. The high variance observed in the timing of seed germination has led to it being the most cited diversification strategy in the theoretical Bet-Hedging literature. Despite this theoretical focus, virtually nothing is known about the mechanisms responsible for the generation of individual-level diversification. Here we report analyses of sources of variation in timing of germination within seasons, germination fraction over two generations and three sequential seasons, and the genetic correlation structure of these traits using almost 10,000 seeds from more than 100 genotypes of the monocarpic perennial Lobelia inflata. Microenvironmental analysis of time to germination suggests that extreme sensitivity to environmental gradients, or microplasticity, even within a homogeneous growth chamber, may act as an effective individual-level diversification mechanism and explains mor...

Frédéric Menu - One of the best experts on this subject based on the ideXlab platform.

  • The Evolution of Bet Hedging in Response to Local Ecological Conditions
    The American naturalist, 2014
    Co-Authors: Etienne Rajon, Emmanuel Desouhant, Mathieu Chevalier, François Débias, Frédéric Menu
    Abstract:

    AbstractGenotypes that hedge their bets can be favored by selection in an unpredictably varying environment. Bet hedging can be achieved by systematically expressing several phenotypes, such as one that readily attempts to reproduce and one that procrastinates in a dormant stage. But how much of each phenotype should a genotype express? Theory predicts that evolving Bet-Hedging strategies depend on local environmental variation, on how the population is regulated, and on exchanges with neighboring populations. Empirically, however, it remains unknown whether bet hedging can evolve to cope with the ecological conditions experienced by populations. Here we study the evolution of Bet-Hedging dormancy frequencies in two neighboring populations of the chestnut weevil, Curculio elephas. We estimate the temporal distribution of demographic parameters together with the form of the relationship between fecundity and population density and use both to parameterize models that predict the Bet-Hedging dormancy freque...

  • Adaptive dynamics of dormancy duration variability: evolutionary trade-off and priority effect lead to suboptimal adaptation.
    Evolution, 2009
    Co-Authors: Sébastien Gourbière, Frédéric Menu
    Abstract:

    Many plants, insects, and crustaceans show within-population variability in dormancy length. The question of whether such variability corresponds to a genetic polymorphism of pure strategies or a mixed Bet-Hedging strategy, and how the level of phenotypic variability can evolve remain unknown for most species. Using an eco-genetic model rooted in a 25-year ecological field study of a Chestnut weevil, Curculio elephas, we show that its diapause-duration variability is more likely to have evolved by the spread of a Bet-Hedging strategy than by the establishment of a genetic polymorphism. Investigating further the adaptive dynamics of diapause-duration variability, we find two unanticipated patterns of general interest. First, there is a trade-off between the ability of Bet-Hedging strategies to persist on an ecological time scale and their ability to invade. The optimal strategy (in terms of persistence) cannot invade, whereas suboptimal bet-hedgers are good invaders. Second, we describe an original evolutionary dynamics where each Bet-Hedging strategy (defined by its rate of prolonged diapause) resists invasion by all others, so that the first type of bet-hedger to appear persists on an evolutionary time scale. Such "evolutionary priority effect" could drive the evolution of maladapted levels of diapause-duration variability.

  • Variability in diapause duration in the chestnut weevil: mixed ESS, genetic polymorphism or bet‐hedging?
    Oikos, 2003
    Co-Authors: Bertrand Soula, Frédéric Menu
    Abstract:

    Within-generation variability in diapause duration can be viewed either as a mixed Evolutionary Stable Strategy (ESS), a genetic polymorphism of pure strategies, or as Bet-Hedging. Diapause variability expressed by a single genotype that maximizes mean geometric fitness at the cost of mean arithmetic fitness is a Bet-Hedging strategy. Bet-Hedging differs from mixed ESS and stable genetic polymorphism of pure strategies because in these latter the expected pay-offs for all phenotypes are equal. In insects, individuals with a prolonged diapause (long cycle) lose at least one reproductive opportunity and suffer lower survival before reproduction than those with a short diapause (short cycle). If long-cycle individuals compensate this cost by better adult performance, the compensation leads to a trade-off which could result in mixed ESS or genetic polymorphism of pure strategies since the overall fitness of the two morphs may be similar. In this paper, we show that in the chestnut weevil Curculio elephas adult performance, measured as sex ratio, longevity, weight, and realized fecundity of females, are similar in individuals emerged after one and two years. Long-cycle morphs emerge slightly before short-cycle ones but this eventual advantage for fertility probably does not compensate higher larval mortality and missed reproductive opportunity in long-cycle phenotypes. Therefore, the cost associated with prolonged diapause cannot be completely compensated for by a better adult performance. From these results, and previous data, we conclude that variability in diapause duration cycle is better explained as Bet-Hedging than mixed ESS or genetic polymorphism of pure strategies.

  • Bet-Hedging for variability in life cycle duration: bigger and later-emerging chestnut weevils have increased probability of a prolonged diapause.
    Oecologia, 2002
    Co-Authors: Frédéric Menu, Emmanuel Desouhant
    Abstract:

    Diversified Bet-Hedging for life cycle duration is defined as within-generation variability in cycle length expressed by a single genotype maximising mean geometric fitness. Such plasticity is not predictive, i.e. it is not a response to cues from the environment that has a predictive value for the decision at hand. In evolutionary terms, diversified Bet-Hedging is perceived as an adaptation to environmental stochasticity. However, clear evidence of Bet-Hedging is scarce and exists only for a few desert plant species and one desert bee. In temperate insects, diversified Bet-Hedging for life cycle duration has been suspected in the chestnut weevil, but proximate factors responsible for individual variation are still unknown. From field experiments, we show that the frequency of the long cycle depends on larval weight and on the date when a larva abandons the fruit, but not on larval burying depth in the soil. Since the two first factors are known to depend on food and temperature and cannot lead to predictive plasticity, we give evidence of bet hedging in this temperate species. Indeed, despite a cost associated with prolonged diapause (extra mortality and loss of reproductive opportunity), a previous study showed that plasticity for life cycle duration, such as discussed in this paper, maximises mean geometric fitness and persistence probability in the chestnut weevil. We propose the hypothesis that the variation in life cycle duration depends on individual variability of metabolic resources such as lipids.

María José Carmona - One of the best experts on this subject based on the ideXlab platform.

  • Experimental evolution of bet hedging in rotifer diapause traits as a response to environmental unpredictability
    Oikos, 2017
    Co-Authors: Eva Tarazona, Eduardo M. García-roger, María José Carmona
    Abstract:

    The adaptive response of organisms to unpredictable environments is increasingly recognized as a central topic in fundamental and applied evolutionary ecology. Selection due to environmental unpredictability can act on multiple traits of an organism's life cycle to reduce the impact of high environmental variance. The aim of this research was to study how unpredictability selects for diapause traits: 1) the timing of sex (a proxy of the timing of diapausing egg production), and 2) the diapausing egg hatching fraction (a proxy of diapause duration). We used an experimental evolution approach with the facultative sexual rotifer Brachionus plicatilis. Laboratory populations experiencing two contrasting regimes of environmental fluctuation (predictable versus unpredictable) evolved divergently over a short time span (< 77 days). The populations under the unpredictable regime showed an earlier initiation of sexual reproduction and a lower hatching fraction of diapausing eggs than populations under the predictable regime. These findings demonstrate empirically the existence of Bet-Hedging strategies in B. plicatilis regarding both traits, consistent with theoretical predictions of Bet-Hedging evolution under conditions of unpredictable environmental variance. Given that scenarios of increased environmental variability are expected to occur in the near future, a comprehensive understanding of the role of Bet-Hedging strategies is necessary for predicting population responses to environmental change.

  • Modes, mechanisms and evidence of bet hedging in rotifer diapause traits
    Hydrobiologia, 2016
    Co-Authors: Eduardo M. García-roger, María José Carmona, Manuel Serra
    Abstract:

    In this contribution, we review our knowledge on Bet-Hedging strategies associated with rotifer diapause. First, we describe the ecological scenario under which bet hedging is likely to have evolved in three diapause-related traits in monogonont rotifer populations: (1) the timing of sex (because diapausing eggs are produced via sexual reproduction), (2) the sexual reproduction ratio (i.e. the fraction of sexually reproducing females) and (3) the timing of diapausing egg hatching. Then, we describe how to discriminate among Bet-Hedging modes and discuss which modes and mechanisms better fit the variability observed in these traits in rotifers. Finally, we evaluate the strength of the empirical evidence for bet hedging in the scarce studies available, and we call for the need of research at different levels of biological complexity to fully understand bet hedging in rotifer diapause.

  • Bet‐hedging in diapausing egg hatching of temporary rotifer populations – A review of models and new insights
    International Review of Hydrobiology, 2014
    Co-Authors: Eduardo M. García-roger, Manuel Serra, María José Carmona
    Abstract:

    Habitat unpredictability is a local adaptation factor shaping life-history traits in rotifer populations. It may select for the evolution of Bet-Hedging through risk-spreading strategies in diapausing egg hatching. This means that a fraction of diapausing eggs in wild populations do not hatch even when the conditions are favorable for population growth. Thus, there is a remaining fraction of viable diapausing eggs standing in the sediments for longer periods. According to theory, it is expected that the incidence of Bet-Hedging strategies for diapausing egg hatching will be higher in more uncertain habitats. Here, we review the major predictions derived from theoretical models applied to the case of monogonont rotifers. In the simplest “bad versus good season” models, the highest environmental uncertainty occurs when the probability of a good season is 0.5, and then the optimal hatching fraction is 0.5 too, implying maximum variance in hatching (i.e., maximum Bet-Hedging). However, there is still little evidence to support this prediction. This is most likely due to the lack of long-term data of habitat fluctuations and the difficulties in identifying and analyzing Bet-Hedging strategies, as well as the potential to confound genetic variation and phenotypic plasticity. Moreover, we provide new evidence supporting the occurrence of Bet-Hedging strategies associated with diapausingegghatchingin theBrachionus plicatilisspecies complex. Ouranalysessuggesta gradient of predictability in the habitats of these rotifers, and the existence of a significant positive correlation between the hatching fraction of diapausing eggs and an index of habitat predictability.

Luke Holman - One of the best experts on this subject based on the ideXlab platform.

  • Bet hedging via multiple mating: A meta-analysis.
    Evolution; international journal of organic evolution, 2015
    Co-Authors: Luke Holman
    Abstract:

    Polyandry has been hypothesized to allow females to "bet hedge" against mating only with unsuitable mates, reducing variance in offspring fitness between members of a polyandrous lineage relative to a single-mating one. Theoretically, this reduction in fitness variance could select for polyandrous genotypes even when polyandry carries a direct cost, especially in small populations. However, this hypothesis is controversial and difficult to test empirically. Here, I apply a novel simulation model to 49 published empirical datasets, and quantify the potential selective advantage of multiple mating via reduced offspring fitness variance. For a wide range of assumptions, including those that most favor the evolution of bet hedging, I show that any fitness gains are meager. The variance in offspring quality caused by mate identity does not appear to be high enough for bet hedging to drive the evolution of polyandry.

  • bet hedging via polyandry a comment on mating portfolios bet hedging sexual selection and female multiple mating
    Proceedings of The Royal Society B: Biological Sciences, 2015
    Co-Authors: Jonathan M Henshaw, Luke Holman
    Abstract:

    Garcia-Gonzalez et al. [[1][1]] conducted an original and elegant experiment examining whether fertilization of a female's eggs by multiple males (polyandry) can provide fitness benefits via ‘Bet-Hedging’ (i.e. due to decreased variance in offspring fitness). The authors measured these benefits