Programme 2016

Le MEE se tiendra les 6 et 7 juin 2016 à l’amphitéâtre Charles Flahaut de l’Institut de Botanique de Montpellier.

Programme-MEE-2016.pdf

Lundi 6 juin :

  • 8h30 – 9h00 Accueil des participants
  • 9h00-10h00 Cindy Gidoin (CREEC, Montpellier)

Range expansion framework to study evolutionary dynamics of cancer.

The cancer provides a relevant model to use concepts and tools from evolutionary biology to better understand a disease traditionally studied by clinical medicine. In this talk, I will present a modeling approach usually applied to study range expansion of species and that can learn us about evolutionary dynamics of cancer.

During range expansion process, a mutation can surf in the wave front due to genetic drift and reach high frequency in the population. Recently, a theoretical study showed that deleterious mutations can surf and accumulate in the wave front, creating a so-called expansion load. Although the expansion load develops under quite general conditions, its impact on evolutionary processes of expanding populations has been largely unappreciated. More specifically, expansion load has been studied in a homogeneous environment, thus it is yet unclear how this excess of deleterious mutations could affect the adaptation of expanding populations to a new environment. I used an individual-based model to investigate the role of expansion load on adaptation to a new environment. As expected, the expanding populations have a higher genetic diversity than non-expanding species but it is mainly a source of maladaptive individuals leading to a lower mean fitness in the new environment.

Most of the studies focused on range expansion discuss their results in the context of species expansion but similar phenomena can occur during tumor growth which can be considered as a population of abnormal cells expanding its range in the body of its host. In evolutionary medicine context, this study is a theoretical illustration of the potential behavior of cancer face to treatments. I wish this talk can give an overview of how rich is the use of concepts from evolutionary biology to better understand the cancer and potentially raise new medical directions and prevent therapeutic failures

  • 10h00-10h25 Cédric Perret (MIVEGEC, Montpellier)

Impact of the cancer on natural communities : ecological and evolutionnary analysis of a modified prey-predator model.

Les écosystèmes sont des objets encore mal compris et impossible à prédire. L’une des raisons de cette situation inconfortable, pour nous qui en dépendons, tient dans le fait que les écosystèmes ne sont ni tout à fait inertes, ni tout à fait vivants, mais bien une sorte de troisième état encore compris. Une façon de s’attaquer au problème consiste à développer des modèles « intégrés » capables d’articuler entre elles les composantes physicochimiques et biologiques de l’écosystème. Souvent par le passé, de telles tentatives de modélisation intégrées se sont concentrées sur les bilans de matières ou d’énergie de l’écosystème (e.g. approche thermodynamique, (Odum, 1968)), ou sur les réseaux d’interaction des communautés d’espèces (approche biomathématique (Thébault & Loreau, 2006), voire évolutive), mais rarement les deux simultanément.

J’exposerai une autre piste de modélisation intégrée de l’écosystème, s’inspirant de l’approche DS² (pour Système Dynamique avec une Structure Dynamique (Giavitto & Michel, 2003)), et des grammaires sur graphes. En plus d’offrir une formalisation appropriée à la modélisation d’écosystèmes, ces approches permettent de rendre compte de leurs nombreux changements (non stationnaires). Nous savons, en effet, que l’écosystème a de bonnes chances d’être hors-équilibre, et soumis à une certaine « évolution » (certainement très différente de celle de ses populations). De tels modèles ont déjà donné des résultats encourageants sur des paysages (Gaucherel et al., 2012) et je l’illustrerai sur des écosystèmes idéaux tels que des colonies d’insectes sociaux.

  • 10h25-10h55 Pause café
  • 10h55-11h20 John Burley (ISEM, Montpellier)

Effects of tissue architecture on the somatic evolution of cancer – implications for clinical forecasting.

John Burley

The interacting ecological and evolutionary processes that shape tumour progression remain poorly understood. Relatively few mutations (2-10) are generally required for the development of malignancy in cancers. Yet, recent genomic analyses show large variation in the amount of heterogeneity between cancers (ranging in the order of 10’s to 100’s mutations) and the spatial distribution of heterogeneity within cancers. In the emerging field of predictive oncology, measurements of genetic diversity (heterogeneity) from tumour biopsies may be used to forecast tumour progression. A key challenge is to distinguish functional from non-function genetic diversity, which first requires an understanding of underlying processes. A spectrum of evolutionary models of cancer progression have been proposed between two extremes: Neutral evolution characterises the ‘big bang’ model, in which cancer cells possessing early-arising advantageous genotypes (whether by chance or selection) undergo rapid clonal expansion, such that subsequent mutations are unlikely to spread throughout the cancer irrespective of relative fitness. The ‘clonal sweep’ model proposes a more pervasive role of natural selection in cancer progression, where expanding genotypes are iteratively overtaken by beneficial mutations arising from within them. A paradox of ‘big bang’ cancers, which may represent 1/3 of cases, is that tissue architecture in many organs seems to have evolved to limit the rate of spread of cancer cells. The predictability of cancers (via heterogeneity measurements) may hinge on whether neutral evolution or selection operates. I will show how stochastic simulations, based on empirical data, can be used to compare the roles of natural selection versus neutral evolution in cancers. I will examine effects of tissue architecture (the spatial structuring of cell populations, and the degree of resistance to dispersal) on tumour evolution and the accumulation of intra-tumour heterogeneity. Of clinical relevance, I will examine how evolutionary processes and ecological conditions interactively affect the spatial and temporal distribution of phenotypic/genotypic diversity within expanding tumours; and compare the effectiveness of different biopsy strategies for generating forecasts of tumour progression.

  • 11h20-11h45  Coline Canonne (Tour du Valat)

Influence of wintering strategy on lifetime reproductive success of greater flamingos in Camargue.

Canonne C., Pradel R., Béchet A.

Migration may be a way to track optimal conditions at each moment of the life cycle, but it entails costs. The equilibrium between costs and benefits of migration may change over time because of environmental stochasticity and density-dependent factors. Partial migration in a population may be maintained if the pay-offs of the resident and migratory strategies are balanced, implying that the two strategies are ‘evolutionarily stable’. Facultative partial migration has been observed in the Western Mediterranean Greater flamingo population (Phoenicopterus roseus). Some individuals stay nearby their breeding colonies during winter, when others migrate to further destinations over the western Mediterranean including North Africa. To investigate the costs and benefits of different migration strategies we used a 37 years dataset of 2370 Greater flamingos born in the Camargue (France) and resighted during winter all over the Mediterranean. We estimated lifetime reproductive success of individuals depending on their wintering strategy while accounting for imperfect detection and state uncertainty, using up-to-date capture-recapture models implemented in a Bayesian framework via Markov Chain Monte Carlo simulations. Our study suggests that individual quality and breeding site experience are important drivers of partial migration in this species.  Individuals wintering in Spain and Portugal are likely to be more prone to leave the Mediterranean basin system than other. Ongoing development is including breeding attempts made at a Spanish colony in order to understand better the costs and benefits of partial migration in interaction with the high dispersion characterizing this species.

  • 11h45-13h00 Repas
  • 13h00-14h00 Violaine Llaurens (MNHN, Paris)

Evolution of dominance in loci under balancing selection: from models to data.

V. Llaurens, M. Arias, Le Poul Y, Chouteau M, Billiard S and Joron M.

Balancing selection promotes the persistence of polymorphism in adaptive traits within natural populations and can shape the underlying genetic architecture. Polymorphic loci frequently display high frequency of heterozygotes, giving the opportunity to dominance among adaptive alleles to evolve in response to natural selection. Here we used the evolutionary convergence of warning signal in toxic species, i.e. Müllerian mimicry, as an example of strong natural selection. Most species involved in Müllerian mimicry display a single warning signal within population because of selection exerted by predators, fixing the most common signal. However, in the toxic butterfly Heliconius numata, several warning patterns are maintained within localities, and each display high resemblance with distasteful species from different communities. These variations in warning pattern are controlled by a supergene in which each allele encodes for a different mimetic pattern. Heterozygotes might display an intermediate, non-mimetic phenotype, depending on the dominance among alleles. Using experiment in natural populations, we showed how natural selection acts on dominance between mimetic alleles. We then used a theoretical approach to describe the condition of invasion of dominance modifiers, and highlight the putative location and mechanisms of dominance modification. Finally, we investigated variations of dominance in natural populations to understand the molecular mechanisms shaping dominance in polymorphic adaptive loci.

  • 14h00-14h25 Thibaut Latrille (LBBE, Lyon)

The red queen dynamic in the kingdom of recombination.

Latrille Thibault, Laurent Duret, Nicolas Lartillot

In humans and many other species, recombination events cluster into narrow hotspots within the genome. Given the vital role recombination plays in meiosis, we might expect that the positions of these hotspots would be tightly conserved over evolutionary time. However, there is now strong evidence that hotspots of meiotic recombination in humans are transient features of the genome. For example, hotspot locations are not shared between human and chimpanzee. Biased gene conversion in favor of alleles that locally disrupt hotspots is a possible explanation of the short lifespan of hotspots.

Remarkably, Prdm9 has been proposed to be a key determinant of the positioning of recombination hotspots during meiosis, and the most rapidly evolving gene in human. Prdm9 genes often exhibit substantial variation in their numbers of encoded zincfingers, not only between closely related species but also among individuals of a species.

Here, we propose a population genetic model which exhibits hotspots transience while reflecting the PRDM9 features, resulting in a intragenomic red queen dynamic. Our model account for empirical observations regarding the molecular mechanisms of recombination hotspots and the nonrandom targeting of the recombination by PRDM9. We further investigate and compare to known data the diversity of PRDM9, the hotspots turnover and the genome wide disruption of hotspots.

  • 14h25-14h50 Théo Gaboriau (MARBEC, Montpellier)

The influence of plate tectonics on biodiversity gradients: A General Simulation Model of Macroevolution (GSM).

Gaboriau Théo, Leprieur Fabien, Albouy Camille, Pelissier Loic

Understanding the causes of spatial variation in species richness is a major research focus of biogeography and macroecology. Great efforts have been deployed to link environmental and phylogenetic data to patterns of species richness using correlative approaches. However, correlative approaches do not allow quantitative predictions and hardly disentangle alternative hypotheses. Here we present a mechanistic model of dispersion and speciation following the idea of a General Simulation model of macroevolution proposed by Gotelli et al. We used this model to predict longitudinal and latitudinal gradients of coastal fishes diversity. We used plate tectonics as the main predictor of marine biodiversity because it modulated the distribution of shelfal seafloors through continental movement and collision over geological timescales.

  • 14h50-15h10 Pause café
  • 15h10-16h10 Vincent Calcagno (INRA, Nice)

 ESS, fin de l’histoire? Les routes de la diversification dans les modèles écologiques d’interaction entre espèces.

Une question importante en écologie et évolution est de savoir si l’évolution des phénotypes par mutation et sélection naturelle peut conduire à des points où la sélection n’est ni directionnelle ni stabilisante, mais diversifiante. Une telle situation rend possible la formation de lignées distinctes chez les organismes clonaux, et constitue une condition favorable à la spéciation adaptative chez les organismes sexués. L’évolution des phénotypes est souvent modélisée par des méthodes de dynamique adaptative dans les modèles écologiques décrivant la dynamique des populations d’une ou plusieurs espèces en interaction dans une communauté. Je considérerai deux modèles généraux décrivant: (i) la coévolution entre victimes et ennemis naturels (e.g. prédation, parasitisme…) et (ii) la coévolution d’espèces compétitrices coexistant par différents mécanismes de ségrégation de niche. Dans chaque cas, j’étudierai les conditions dans lesquelles l’évolution adaptative des traits mène à des minimums de fitness, ou points de branchement. Je montrerai que ces conditions sont plus fréquentes que les analyses classiques laisseraient penser.

Mardi 7 juin:

  • 8h30-9h00 Accueil des participants
  • 9h00-10h00 Christelle Fraïsse (IST, Vienne, Autriche)

Understanding species formation: a phenotypic approach.

Dobzhansky played a central role in our understanding of speciation by using simple 2-locus fitness landscape models. Over the past 30 years, research in speciation genetics has uncovered many robust patterns in intrinsic reproductive isolation, and fitness landscape models have been useful in interpreting these patterns. Here we examine fitness landscapes based on Fisher’s geometric model. Such landscapes are analogous to models of optimizing selection acting on quantitative traits. We show that Fisher’s model can generate all of the major findings of speciation studies (including “speciation genes” with strong deleterious effects in the sister-species background). Fisher’s model can also explain conflicting empirical results about the rate at which incompatibilities accumulate with genetic divergence. We finally show that the manner in which populations diverge has very little effect on the quality of reproductive isolation that evolves between them.

  • 10h00-10h25 Valentin Thouzeau (MNHN, Paris)

Reconstructing demographic and cultural history of human populations from genetic and linguistic polymorphism data.

Valentin Thouzeau, Paul Verdu, Philippe Mennecier, Fédéric Austerlitz

The main aim of my research is to develop methods for analyzing language and genetic polymorphism data in a unified framework, in order to infer the past history of separation, exchanges and admixture among human populations. For this purpose, I have developed a new computer program that simulates simultaneously the evolution of gene and language (cognates) diversities in a set of populations for which both types of data are available. These simulations are then compared to real genetic and cognate polymorphism data, using Approximate Bayesian Computations (ABC) methods to identify the most realistic historical scenarios underlying each type of data, and to infer the corresponding model parameters. So far, we applied this approach to Central Asia, an area where Turkic-Mongol and Indo- Iranian speaking populations historically met, and where our laboratory has already gathered both genetic (sequences, microsatellites, genome-wide genotypes) and language (vocabulary lists, cognates) data.

  • 10h25-10h55 Pause café
  • 10h55-11h20 Marjorie Haond (ISA, Nice / BioSP, Avignon)

Habitat quality and the velocity of spatial population expansion.

Marjorie Haond, Ludovic Mailleret, Thibaut Morel Journel, Lionel Roques, Elodie Vercken

An important prediction of several spatio-temporal models of population dynamics is that habitat quality, defined here as the carrying capacity (K) of the environment, should have no influence on the velocity (v) of a population expansion. Using different modelling frameworks: reaction-diffusion equations to stochastic individual based models (IBM), we show that this prediction is far from being generic.

We review known results on theoretical diffusion models, regarding the dependence between K and v for logistic-like growth functions and we derive some additional results for other growth functions (weak or strong Allee effects). We also report some results for equations describing density-dependent dispersal. Then, using discrete space stochastic models, we investigate the dependence between K and v under different assumptions: no Allee effect, weak and strong Allee effects, and positive density-dependent dispersal.

We show that both models lead to an increasing relationship between v and K in the presence of an Allee effect or of positive density-dependent dispersal. This relationship still holds in the IBMs even when there is no Allee effect or positive density-dependant dispersal. This effect is especially strong when K is small (or close to the Allee threshold in the presence of a strong Allee effect), and tends to become less powerful or negligible when K becomes large. Experiments that we have conduced on minute size wasps Trichogramma chilonis in laboratory microcosms confirm the existence of this positive relationship.

Finally, we discuss how this dependence is related to the pulled/pushed nature of the expansion process.

  • 11h20-11h45 Claire Godineau (ISEM, Montpellier)

Effects of assortative mating for flowering on evolutionary potential in a context of climate change.

Claire Godineau

Plants are under obligate assortative mating for flowering as they can only mate with others flowering at the same time. This phenotypic correlation among individuals creates associations among loci, thus increasing the genetic variance for flowering and potentially promoting the response to selection compared to a trait under random mating. To quantify the effects of assortative mating on the response of flowering to climate change, I compare the adaptive potential for flowering of a population mating assortatively to that of a population artificially forced to mate randomly. I use an individual-based quantitative genetic model for flowering, for plants that have non-overlapping generations, are self-compatible and wind-pollinated. The genetic effects of assortative mating are studied in a single (non-spatialized) population of large and constant size, decreasing genetic drift and demographic stochasticity; migration and phenotypic plasticity are omitted. First results show that stabilizing selection is more efficient under assortative mating than under random mating, and therefore that the adaptive potential of a population under assortative mating is smaller than that of population under random mating. Under assortative mating, positive covariances generated among alleles controlling for flowering increase the genetic variance of the population and expose plants to stronger selection.

  • 11h45-13h00 Repas
  • 13h00-14h00 Céline Casenave (INRA, Montpellier)

Modelling of cyanobacteria blooms dynamics: minimal vs complex dynamic models.

Cyanobacteria (often called blue-green algae) have attracted the interest of the scientific community for a long time. Under specific conditions, cyanobacteria population can grow very quickly and accumulate on the water surface forming scums. This phenomenon, known as algal bloom, has important economic, ecological and health consequences.
Since the 1990s, mathematical models have been developed in order to better understand the dynamics of cyanobacteria population and the formation of blooms. In this presentation, I will introduce the two main categories of models of Harmful Algal Bloom (HAB): the minimal and the complex dynamic models. In the first part, we will see how minimal dynamic models can be used to « examine the likelihood of certain processes generating a HAB » (Franks, 1997). In the second part, the usefulness of “complex dynamic models” will be demonstrated on the particular case of Lake Tai (China). Such models are designed to be used as a virtual reality for the simulation of the whole ecosystem and are therefore generally coupled with a detailed hydrodynamic model and validated on field data.

  • 14h00-14h25 Pierre Quévreux (iEES, Paris)

Nutrient recycling in complex food webs.

Pierre Quévreux, Élisa Thébault and Sébastien Barot

The understanding of how food-webs work and how they man-
age to persist along time has been being one of the main  questions in ecology for decades. A lot of progress have been done, especially this last decade, and many mechanisms  have been identified to promote food-web stability.  But most of recent studies largely ignore one fundamental process of ecosystemfunctioning : nutrients are recycled by ecomposers and flow again in the food-web regarding on two paths : the green and the brown food-web. Our objective is to add the well documented process of nutrient recycling in food-web modelling to test the consequences of such an important process in ecosystem’s stability. Food webs are here modelled by a set of ordinary differential equations which represents a size structured food web containing scores of interacting species. The simplest representation of nutrient recycling is implemented in such a model: nutrient are excreted either as mineral nutrient or as detritus decomposed
at a fixed rate. The importance of nutrient recycling and its effects are also compared with the effects of nutrient enrichment. The main result of this study is that nutrient recycling only acts as an additional source of nutrient and not as a bottom-up effect increasing primary productivity when the top-down control applied by consumers is strong. This is due to the stability of recycling: even if species abundance varies a lot along time, the amount of recycled nutrient stays constant.

  • 14h25-14h50 Rémi Patin (CEFE, Montpellier)

Decision-making on space use negates dilution effect on vigilance.

Rémi Patin, Daniel Fortin, Cédric Sueur, Simon Chamaillé-Jammes

Common responses to predation are grouping, increased vigilance and shifts in space-use. Most models of predator-prey interactions focus on the link between grouping and vigilance while it is known that these responses also interact with space-use. In addition, in groups, decisions about space-use may be more or less shared across group members. We integrated these different aspects in a model of prey foraging under predation risk. Prey are allowed to use vigilance and space use to deal with the trade off between predation and starvation risk. We obtained optimal prey behaviour for single individuals or, to account for the possible influence of dilution, individuals of a group having a despotic leader. We found that, in contrast with non-spatialised models, vigilance is not always lower in groups than in single individuals. This happened because individuals benefiting from dilution sometimes choose to spend more time in risky patches.  Moreover, within a group, an individual following a despotic leader may sometimes have a reduced vigilance, but this is caused by the need to maintain a higher condition to cope with uncertainty in future space-use, rather than a benefit from dilution. This suggests that the studies of anti-predator behaviour need to better bring together vigilance and space use, accounting for decision-making processes occurring within groups.

  • 14h50-15h10 Pause Café
  • 15h10-16h10 Sébastien Dutreuil (Université Paris 1 Panthéon-Sorbonne, IHPST)

A quoi servent les modèles abstraits ou décrivant des situations fictives ? Quelques leçons du modèle Daisyworld

A partir d’un cas d’étude, le modèle Daisyworld, et en m’appuyant sur une littérature désormais riche en philosophie des sciences sur les modèles, je préciserai le rôle et le statut de certains types de modèles : les modèles abstraits et ceux décrivant une situation fictive.

Je commencerai par présenter le modèle Daisyworld, un modèle singulier né dans le contexte de l’élaboration de l’hypothèse Gaïa et ayant eu une influence importante dans les pratiques de modélisation en sciences de l’environnement au cours des dernières décennies. Après une brève présentation des questionnements scientifiques qui ont fait naître ce modèle et auxquels il a contribué à répondre, puis un exposé des relations complexes qu’il a entretenu avec l’écologie et la biologie de l’évolution, j’examine en détail une controverse épistémologique qui a surgi au sein de la littérature théorique consacrée à Daisyworld et l’hypothèse Gaïa. Ce modèle a été critiqué parce qu’il était trop abstrait et parce qu’il décrivait des situations fictives, ne correspondant à aucune situation réelle et concrète. Il a ainsi été jugé moins intéressant soit que d’autres pratiques scientifiques (expérimentation), soit que d’autres types de modèles (moins abstraits, décrivant des situations réelles). J’examine en détail la portée de ces critiques et montre qu’elles reposent sur une conception par trop étroite aussi bien de l’activité scientifique que des pratiques de modélisation.

Cela m’amène in fine à élargir la perspective et à discuter de la place des modèles comme activité scientifique différant d’autres activités (expérience et test d’hypothèse empirique, classification, enquête historique, etc.) et à élaborer une typologie des modèles suivant leurs rôles (à quoi servent-ils ? quels types de connaissances permettent-ils de produire ?) et suivant leurs statuts (pourquoi avons-nous confiance dans tel ou tel type de modèle ? quelles procédures nous confèrent une certaine confiance dans les résultats produits par les modèles ?).

  • 16h10-17h30 Atelier