Group Vuilleumier
Metapopulation ecology and genetics

Our aim is to answer fundamental theoretical questions on the genetics, ecology and evolution of populations. Our research focuses on understanding

(i) Gene dynamics and fixation in heterogeneous environments, e.g. fixation when selection, population sizes, extinction and migration rates are heterogeneous

(ii) Dynamics of genetic diversity and evolutionary consequences e.g. impact of large scale environmental changes on genetic diversity, implications for the reconstruction of populations’ demographic and evolutionary history from genetic data

(iii) Dispersal in heterogeneous environment e.g. dispersal and behaviour, dispersal asymmetries, coexistence of dispersal strategies, evolution of metapopulation structure

(iv) Persistence in heterogeneous and disturbed environments e.g. disturbance and habitat aggregation, control of invasive species

(v) Evolution of reproduction systems e.g. male to female heterogamety, parthenogenesis from sexual population, transition in number of self-incompatible loci.

Work in collaboration with Prof. N. Perrin, Dr. J. Yearsley and Prof J. Goudet.

Understanding the dynamics of genetic components in biological compartments (individual, population, metapopulation) has direct relevance for understanding species adaptation to novel environments and changing environment. It is thus also of major interest for several present day health, agricultural or conservation challenges.
Vuilleumier et al. (2008) demonstrate that fixation of a novel mutant genotype can be strongly enhanced by spatial heterogeneities in selection (e.g. selective pressure) and be fastened by the occurrence of extinction processes (disturbances, control). Moreover, Vuilleumier et al. (2010) demonstrate that in structured population, assumptions on the pattern (stepping-stone, island) and type of migration models (e.g. source-sink, balanced) have drastic consequences on the fate of selected mutants. Spatial localization of newly arising mutations, patterns of selection and type of migration assumed (asymmetric, bottleneck) have been shown to have strong impacts on the likeliness of new genetic component fixation. Given the extreme sensitivity of fixation probability to characteristics of dispersal, they highlight the importance of making explicit the assumptions underlying migration models.

Genetic diversity is essential for population survival and adaptation to changing environments. Demographic processes (e.g. bottleneck and expansion) and spatial structure (e.g. migration, number and size of populations) are known to shape the patterns of genetic diversity of populations. However, the impact of temporal changes in migration on genetic diversity has been seldom considered, although such events might be the norm. Indeed, during the millions years of a species life-time, repeated events of isolation and reconnection of populations occurred. Geological and climatic events alternately isolated and reconnected habitats. In this context, we analyse the dynamics of genetic diversity after an abrupt change in migration.
N. Alcala and S. Vuilleumier demonstrate that during transient dynamics, genetic diversity can reach unexpectedly high values that can be maintained over thousands of generations. We also investigate the genetic and evolutionary consequences of such processes and how it can affect the reconstruction of populations’ demographic and evolutionary history from genetic data.

Work in collaboration with Dr. R. Metzger, Dr. Fontanillas and Prof. N. Perrin.

Dispersal and behavior: Dispersal strongly depends on how a species interacts with its environment and on its dispersal behaviour and strategies. S. Vuilleumier has developed a spatially-explicit and individual-based dispersal model to simulate complex interactions between individuals and the environment (Vuilleumier and Metzger 2006). Then, she analyzed the influence of environmental heterogeneities and species behaviour on dispersal, and their combined impact on metapopulation dynamics (Vuilleumier and Perrin 2006). Subsequently, she analyzed the relationships between the “ecological” distance -accounting for species movement behaviour and environmental characteristics- and genetic distances between populations of the greater white-toothed shrew (Vuilleumier and Fontanillas 2007).

Work in collaboration with Prof H.P. Possingham, Prof. B. Bolker and Dr. O. Levêque,

Dispersal asymmetries: Despite considerable evidence showing that dispersal between habitat populations is often asymmetric (e.g. directional dispersing agent, variation in habitat quality, spatial structure of the environment, social interaction), most models used to estimate population persistence assume symmetric dispersal. Vuilleumier and Possingham (2006) demonstrate that assuming symmetric dispersal when dispersal is actually asymmetric lead to a wrong estimation of metapopulation persistence in more than 50%. However, under a directional bias of 25% in dispersal strength, persistence is lightly affected (Vuilleumier et al. 2010a). Vuilleumier et al. (2010a) also demonstrates that strong local connectivity whithin metapopulation (as expected in river networks) provides the highest persistence compared to systems that allow large scale circulation (as expected in ocean).

Work in collaboration with Dr. L. Büchi

Coexistence of dispersal strategies: The diversity of dispersal strategies in a metacommunity results from the combined effect of numerous evolutionary and ecological forces: Kin competition, life history traits, the heterogeneity and structure of the environment. In this context Büchi and Vuilleumier (2012) used a unifying modeling approach to contrast the combined effects of species traits (adult survival, specialization), environmental heterogeneity and structure (spatial autocorrelation, habitat availability) and disturbance on the selected, maintained and coexisting dispersal strategies in heterogeneous metacommunities. Their results unify apparently contradictory previous results and demonstrate that spatial structure, disturbance and adult survival determine the success and diversity of coexisting dispersal strategies in competing metacommunities.

Evolution of metapopulation structure: N. Alcala and S. Vuilleumier are currently investigating how can evolve the rate of individual exchanges between populations (source-sink and the balanced migration) and delineate the conditions under which some metapopulation structures are more likely to emerge (the stepping-stone or island model) and which dispersal distance distributions are expected. Various forms of habitats distributions, heterogeneity in selection and fragmentation are investigated (Alcala and Vuilleumier, in prep).

Work in collaboration with Prof H.P. Possingham, Dr. C. Wilcox and Dr. B. Cairns

Disturbance and spatial aggregation: S. Vuilleumier has developed a stochastic, spatially-explicit model to analyze how metapopulation persistence is affected by different regimes of spread of disturbance looking at various spatial configurations and connectivity patterns (Vuilleumier et al. 2007a). With this model, S. Vuilleumier and H. Possingham also investigating how spatial and temporal variation in extinction risk and colonization impact the persistence of species and the conditions for which habitat aggregation or random distribution can favour species persistence (Vuilleumier and Possingham, 2012).

Work in collaboration with Dr. J. Yearsley and Prof. A Buttler

Invasive species: The effect of heterogeneous environments upon the dynamics of invasion and the eradication or control of an invasive species is poorly understood; S. Vuilleumier and co-workers investigated how the probability of eradication and the time for invasion or eradication are affected by spatial heterogeneity in a species' growth rate. Then, they studied the effect of control program strategies (e.g. species specificity, spatial scale, detection efficiency and local eradication efficiency) on the success and time of eradication (Vuilleumier et al., 2010).

Work in collaboration with Prof. O. Seehausen and Prof. R. Lande.

Male to female heterogamety: In Vuilleumier et al. (2007b) we investigated the conditions under which dominant female-determining gene W can invade and become fixed in the population, changing the population from male to female heterogamety. We found that the interaction of sex-ratio selection and random genetic drift causes W to be fixed among females more often than a comparable neutral conditions (Vuilleumier et al. 2007b)

Work in collaboration with Dr. T, Schwander and Prof. B.J. Crespi

To parthenogenesis from sexual population: Understanding how new phenotypes evolve is challenging because intermediate stages in transitions from ancestral to derived phenotypes often remain elusive. In Schwander et al. (2010), we describe and evaluate a new mechanism facilitating the transition from sexual reproduction to parthenogenesis. Using an analytical model, we show that if females are mate-limited, it can result in the loss of males through a positive feedback mechanism. Empirical data from Timema populations provide evidence for this simple mechanism through which parthenogenesis can evolve rapidly in a sexual population.

Work in collaboration with Dr. Hélène Niculita-Hirzel

Transition in number of self-incompatible loci: Self-incompatibility (SI), a reproductive system broadly present in plants, chordates, fungi and protists, might be controlled by one or several multiallelic loci. How a transition in the number of SI loci can occur and the consequences of such event on population’s genetics and dynamics have no theoretical basis. We provide an analytical description of two mechanisms of transition: the linkage of the two SI loci (scenario 1) and the loss of one SI capacity (scenario 2) within a mating type of a two SI loci population. We show that invasion of a population by such a mating type depends on the new mating type’s potential fitness reduction, the allelic diversity of SI loci and recombination between the two SI loci in the invaded population. Moreover, under scenario 1, it also depends on the frequency of the SI alleles caught in a single SI locus. We demonstrate that following invasion, complete transition in the reproductive system occurs systematically only under scenario 2. Interestingly, this event was associated with a drastic reduction in mating type number.