Professional Education


  • Bachelor of Science, Tel-Aviv University (2011)
  • Master of Science, Tel-Aviv University (2013)
  • Doctor of Philosophy, Tel-Aviv University (2016)

Stanford Advisors


Current Research and Scholarly Interests


Microbial evolution, evolution of the mutation and recombination rate, fitness landscapes

All Publications


  • Condition-dependent sex: who does it, when and why? PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES Ram, Y., Hadany, L. 2016; 371 (1706)

    Abstract

    We review the phenomenon of condition-dependent sex-where individuals' condition affects the likelihood that they will reproduce sexually rather than asexually. In recent years, condition-dependent sex has been studied both theoretically and empirically. Empirical results in microbes, fungi and plants support the theoretical prediction that negative condition-dependent sex, in which individuals in poor condition are more likely to reproduce sexually, can be evolutionarily advantageous under a wide range of settings. Here, we review the evidence for condition-dependent sex and its potential implications for the long-term survival and adaptability of populations. We conclude by asking why condition-dependent sex is not more commonly observed, and by considering generalizations of condition-dependent sex that might apply even for obligate sexuals.This article is part of the themed issue 'Weird sex: the underappreciated diversity of sexual reproduction'.

    View details for DOI 10.1098/rstb.2015.0539

    View details for Web of Science ID 000383507000011

    View details for PubMedID 27619702

  • The probability of improvement in Fisher's geometric model: A probabilistic approach THEORETICAL POPULATION BIOLOGY Ram, Y., Hadany, L. 2015; 99: 1-6

    Abstract

    Fisher developed his geometric model to support the micro-mutationalism hypothesis which claims that small mutations are more likely to be beneficial and therefore to contribute to evolution and adaptation. While others have provided a general solution to the model using geometric approaches, we derive an equivalent general solution using a probabilistic approach. Our approach to Fisher's geometric model provides alternative intuition and interpretation of the solution in terms of the model's parameters: for mutation to improve a phenotype, its relative beneficial effect must be larger than the ratio of its total effect and twice the difference between the current phenotype and the optimal one. Our approach provides new insight into this classical model of adaptive evolution.

    View details for DOI 10.1016/j.tpb.2014.10.004

    View details for Web of Science ID 000348892700001

    View details for PubMedID 25453607

  • Stress-induced mutagenesis and complex adaptation PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES Ram, Y., Hadany, L. 2014; 281 (1792)

    Abstract

    Because mutations are mostly deleterious, mutation rates should be reduced by natural selection. However, mutations also provide the raw material for adaptation. Therefore, evolutionary theory suggests that the mutation rate must balance between adaptability-the ability to adapt-and adaptedness-the ability to remain adapted. We model an asexual population crossing a fitness valley and analyse the rate of complex adaptation with and without stress-induced mutagenesis (SIM)-the increase of mutation rates in response to stress or maladaptation. We show that SIM increases the rate of complex adaptation without reducing the population mean fitness, thus breaking the evolutionary trade-off between adaptability and adaptedness. Our theoretical results support the hypothesis that SIM promotes adaptation and provide quantitative predictions of the rate of complex adaptation with different mutational strategies.

    View details for DOI 10.1098/rspb.2014.1025

    View details for Web of Science ID 000341095900010

    View details for PubMedID 25143032

  • Dispersing away from bad genotypes: the evolution of Fitness-Associated Dispersal (FAD) in homogeneous environments BMC EVOLUTIONARY BIOLOGY Gueijman, A., Ayali, A., Ram, Y., Hadany, L. 2013; 13

    Abstract

    Dispersal is a major factor in ecological and evolutionary dynamics. Although empirical evidence shows that the tendency to disperse varies among individuals in many organisms, the evolution of dispersal patterns is not fully understood. Previous theoretical studies have shown that condition-dependent dispersal may evolve as a means to move to a different environment when environments are heterogeneous in space or in time. However, dispersal is also a means to genetically diversify offspring, a genetic advantage that might be particularly important when the individual fitness is low. We suggest that plasticity in dispersal, in which fit individuals are less likely to disperse (Fitness-Associated Dispersal, or FAD), can evolve due to its evolutionary advantages even when the environment is homogeneous and stable, kin competition is weak, and the cost of dispersal is high.Using stochastic simulations we show that throughout the parameter range, selection favors FAD over uniform dispersal (in which all individuals disperse with equal probability). FAD also has significant long-term effects on the mean fitness and genotypic variance of the population.We show that FAD evolves under a very wide parameter range, regardless of its effects on the population mean fitness. We predict that individuals of low quality will have an increased tendency for dispersal, even when the environment is homogeneous, there is no direct competition with neighbors, and dispersal carries significant costs.

    View details for DOI 10.1186/1471-2148-13-125

    View details for Web of Science ID 000321461500001

    View details for PubMedID 23777293

  • THE EVOLUTION OF STRESS-INDUCED HYPERMUTATION IN ASEXUAL POPULATIONS EVOLUTION Ram, Y., Hadany, L. 2012; 66 (7): 2315-2328

    Abstract

    Numerous empirical studies show that stress of various kinds induces a state of hypermutation in bacteria via multiple mechanisms, but theoretical treatment of this intriguing phenomenon is lacking. We used deterministic and stochastic models to study the evolution of stress-induced hypermutation in infinite and finite-size populations of bacteria undergoing selection, mutation, and random genetic drift in constant environments and in changing ones. Our results suggest that if beneficial mutations occur, even rarely, then stress-induced hypermutation is advantageous for bacteria at both the individual and the population levels and that it is likely to evolve in populations of bacteria in a wide range of conditions because it is favored by selection. These results imply that mutations are not, as the current view holds, uniformly distributed in populations, but rather that mutations are more common in stressed individuals and populations. Because mutation is the raw material of evolution, these results have a profound impact on broad aspects of evolution and biology.

    View details for DOI 10.1111/j.1558-5646.2012.01576.x

    View details for Web of Science ID 000305945400025

    View details for PubMedID 22759304