Isabelle Olivieri

Local Adaptation and Gene-For-Gene Coevolution in a Metapopulation Model

In several reciprocal cross-infection experiments parasites were found to be significantly more adapted to their local host populations than to hosts from distant populations. We developed a metapopulation model, taking explicit account of both population densities and gene frequencies, to determine the influence of ecological and genetical parameters on the local adaptation of the parasites and on the spatial distribution of resistance and virulence genes. Our results point to the predominant effect of ecological parameters such as parasite growth rate and host and parasite migration rates on coevolutionary outcomes. In particular, the parasites are more likely to be adapted to their local host population than to allopatric hosts when the parasite migration rate is larger than the host migration rate. The opposite should be observed whenever hosts migrate more than parasites.

Metapopulation Genetics and the Evolution of Dispersal

A Markovian extinction model that takes into account age structure of local populations allows consideration of the effects of demography and successional dynamics on the evolution of migration. Analytical expressions for the evolutionarily stable (ES) rates of dispersal are given for cases in which newly recolonized sites attain carrying capacity within a single season. Using a low-fecundity numerical model, we find that an increase of the level of site saturation increases the dispersal rate. Ecological successions and unequal local extinction rates between newly colonized sites and established populations strongly affect the ES dispersal rate. The frequency of genetic modifiers that enhance the rate of dispersal evolves negative correlations with deme age, with high-migration genotypes predominant among colonizers while progressively declining in frequency as a deme ages. This suggests that between-deme selection (colonization) favors migrants while within-deme selection favors low dispersers, which allows the coexistence of types with different dispersal rates. Because of the interaction between the two levels of selection, the relation between the ES dispersal rate and the deme maximal lifetime is nonmonotone. We suggest that life-history traits other than dispersal might also experience antagonistic selective forces at the between- and within-deme levels.

Monitoring adaptive genetic responses to environmental change

Widespread environmental changes including climate change, selective harvesting and landscape alterations now greatly affect selection regimes for most organisms. How animals and plants can adapt to these altered environments via contemporary evolution is thus of strong interest. We discuss how to use genetic monitoring to study adaptive responses via repeated analysis of the same populations over time, distinguishing between phenotypic and molecular genetics approaches. After describing monitoring designs, we develop explicit criteria for demonstrating adaptive responses, which include testing for selection and establishing clear links between genetic and environmental change. We then review a few exemplary studies that explore adaptive responses to climate change in Drosophila, selective responses to hunting and fishing, and contemporary evolution in Daphnia using resurrected resting eggs. We further review a broader set of 44 studies to assess how well they meet the proposed criteria, and conclude that only 23% fulfill all criteria. Approximately half (43%) of these studies failed to rule out the alternative hypothesis of replacement by a different, better‐adapted population. Likewise, 34% of the studies based on phenotypic variation did not test for selection as opposed to drift. These shortcomings can be addressed via improved experimental designs and statistical testing. We foresee monitoring of adaptive responses as a future valuable tool in conservation biology, for identifying populations unable to evolve at sufficiently high rates and for identifying possible donor populations for genetic rescue. Technological advances will further augment the realization of this potential, especially next‐generation sequencing technologies that allow for monitoring at the level of whole genomes.

Live Where You Thrive: Joint Evolution of Habitat Choice and Local Adaptation Facilitates Specialization and Promotes Diversity

We derive a comprehensive overview of specialization evolution based on analytical results and numerical illustrations. We study the separate and joint evolution of two critical facets of specialization—local adaptation and habitat choice—under different life cycles, modes of density regulation, variance‐covariance structures, and trade‐off strengths. A particular feature of our analysis is the investigation of arbitrary trade‐off functions. We find that local‐adaptation evolution qualitatively changes the outcome of habitat‐choice evolution under a wide range of conditions. In addition, habitat‐choice evolution qualitatively and invariably changes the outcomes of local‐adaptation evolution whenever trade‐offs are weak. Even weak trade‐offs, which favor generalists when habitat choice is fixed, select for specialists once local adaptation and habitat choice are both allowed to evolve. Unless trapped by maladaptive genetic constraints, joint evolution of local adaptation and habitat choice in the models analyzed here thus always leads to specialists, independent of life cycle, density regulation, and trade‐off strength, thus raising the bar for evolutionarily sound explanations of generalism. Whether a single specialist or two specialists evolve depends on the life cycle and the mode of density regulation. Finally, we explain why the gradual evolutionary emergence of coexisting specialists requires more restrictive conditions than does their evolutionarily stable maintenance.

Insight on segregation distortions in two intraspecific crosses between annual species of Medicago (Leguminosae)

Abstract About 40% (α=0.05) of the PCR-derived markers scored in a Medicago truncatula and M. tornata intraspecific cross departed from Mendelian expectations at α=0.05. This proportion is among the highest ever documented in the literature, notably for intraspecific crosses. Estimations of DNA amount were also implemented for the parental genotypes or parental lines, and significant variations were observed. Our results suggest that the parental genotypes have diverged for quite a while, and we propose that the level of distortion we documented is correlated with the genome size difference we measured.

DIVERGENT EVOLUTION OF DISPERSAL IN A HETEROGENEOUS LANDSCAPE

The evolution of dispersal is investigated in a landscape of many patches with fluctuating carrying capacities and spatial heterogeneity in temporal fluctuations. Although asynchronous temporal fluctuations select for dispersal, spatial heterogeneity in the distribution of fluctuating environmental variables selects against it. We find evolutionary branching in dispersal rate leading to the evolutionarily stable coexistence of a high‐ and a low‐dispersal phenotype. We study how the opposing forces of selection for and against dispersal change with the relative size and the environmental qualities of the source and sink habitats. Our results suggest that the evolution of dispersal dimorphism could be a first step towards speciation and local adaptation.

Evolution of Migration Rate and Other Traits: The Metapopulation Effect

Publisher Summary This chapter focuses on metapopulation evolutionary models and metapopulation effect. Metapopulation evolutionary models focus on the evolutionary consequences of population extinctions and recolonizations. In these models, the emphasis is on the selective pressures created by population turnover within a metapopulation. The focus is on the evolution of particular traits, whose genetic determinism is usually unknown. Metapopulation evolutionary models are mostly used to study the evolution of migration rate. It is shown that the demographic functioning of metapopulations creates intrinsic emergent properties that influence the evolution of major biological traits, such as migration rate. This chapter also shows that the processes determining the migration rate in a metapopulation are specific to the very functioning of the metapopulation (the metapopulation effect) and interacting with the processes determining the evolution of most significant life-history traits. These processes result in a partial adaptation of the metapopulation to its landscape. This adaptation is incomplete because the processes involved act between genes at both the population and the metapopulation levels. Thus, they necessarily involve frequency dependence; and therefore, Fishers fundamental theorem of natural selection does not apply at the metapopulation level.

The genetics of transient populations: Research at the metapopulation level

The metapopulation concept allows us to generate new models, in which each single local population is in disequilibrium (from both demographic and genetic points of view) but the whole is stable. We review recent empirical and theoretical results showing the relevance of the metapopulation level, in particular for understanding the evolution of those traits that do not experience the same selective forces during the different demographic stages of each local population.

Neglect of Genetic Diversity in Implementation of the Convention on Biological Diversity

Genetic diversity is the foundation for all biological diversity; the persistence and evolutionary potential of species depend on it. World leaders have agreed on the conservation of genetic diversity as an explicit goal of the Convention on Biological Diversity (CBD). Nevertheless, actions to protect genetic diversity are largely lacking. With only months left to the 2010-biodiversity target, when the 191 parties to the CBD have agreed on achieving a significant reduction of the rate of biodiversity loss, gene-level diversity is still not being monitored, and indicators and thresholds that can be used to devise strategies to conserve this important component of biodiversity are missing. Immediate action is needed to ensure that genetic diversity is not neglected in conservation targets beyond 2010.

Ribosomal External and Internal Transcribed Spacers: Combined Use in the Phylogenetic Analysis of Medicago (Leguminosae)

Abstract. We have estimated the potential phylogenetic utility of the ribosomal external transcribed spacer (ETS) from the nuclear ribosomal region. The ETS was sequenced from 13 annual Medicago (Fabaceae) species upstream a highly conserved motive which was found among many different organisms. In the genus Medicago, the ETS was found to evolve 1.5 times faster than the internal transcribed spacer and to be 1.5 times more informative. Reduced ribosomal maturation process constraints on ETS are proposed to explain the different evolutionary rates between the two spacers. Maximal phylogenetic resolution and support was obtained when the two spacers were analyzed together. No incongruence between the two spacers was found and ETS appears to be a valuable source of information for solidifying ITS plant phylogeny. The phylogeny obtained in Medicago suggests that none of the three subsections included in the study is monophyletic.