BIOADAPT - Adaptation - des gènes aux populations.Génétique et biologie de l'adaptation aux stress et aux perturbations

Adaptation of Fragmented Freshwater species Assemblages In Rapidly-changing environmentS – AFFAIRS

Understanding the response of a community of species to the constraints of a fragmentes

Animal communities respond to change by losing/gaining species or by evolutionary change within species. Understanding such processes is crucial now that climate and land use are being rapidly modified by man. We will study these processes in Antillean freshwaters.

Freshwater ecosystems as models of fragmented habitats exposed to multiple human-induced stresses

Human activities exert considerable pressure on ecosystems, through climate change, species introductions and anthropisation. Freshwater habitats, such as ponds and lakes, are particularly exposed. Freshwater faunas and floras react to change at several levels : (i) within species, selection favors genotypes adapted to the new constraints (ii) within communities, some species increase in abundance while others decrease, depending on their biological traits. Our objective is to better understand and predict these two interdependent responses, the evolutionary and the ecological. We study a model community : the freshwater snails of french Antilles. <br /> Freshwater habitats typically present themselves as small fragments (such as ponds) submitted to unstable water levels. Animal populations living there are often subject to extinction-recolonisation cycles. One of our challenges is to distinguish long-term change from this rapid, natural turnover. This issue is common to many other systems. Thus, our methodological developments may serve many other research programs trying to predict ecosystemic responses to global change. <br />

Our approach relies on a large amount of fieldwork, with an annual survey of species and habitat characteristics in more than 200 sites in both Martinique and Guadeloupe. These results will be added on top of previously accumulated long-term data, generating an exceptionnally large dataset. We will develop cutting-edge statistical methods to analyse these data and quantify species dynamics in naturally fragmented freshwater habitats (local population extinctions, colonisation of new habitats, competitive interactions among species, invasion dynamics). We will also follow genetic changes in populations of a few target-species through molecular genetics and meaure of traits in common environment (laboratory). All results willl be used to produce a predictive model of the response of communities to climate modifiations and species introductions.

Major results
We modelled the metapopulation dynamics of around 15 species in the studied community. This methodology allows us to predict what these species will become, who will be maintained and who will decline, in the face of global changes and bioinvasions. Our genetic data reveal the persistance of populations during pond dessication, while individuals are buried in the ground and cannot be found. In addition, we show, on one model system, that resident species can quickly evolve to adopt life-history traits that favor coexistence with introduced species. At a larger scale, our models show that some level of initial diversity is usually necessary to start a process of evolutionary diversification of species ; this autocatalytic effect explains previous observations on the history of insular communities as well as on experimental communities. In general, our results have far-reaching implications for the study of spatially fragmented communities submitted to global change.

We have elaborated a new metod to precisely estimate extinction and colonisation rates in a network of populations (metapopulation). The originality o our approach is to take into account non-detectable forms of organisms such as seeds or inactive life stages. This methodology will be useful to field eciologists that frequently face this problem.

To date, this project has resulted in 10 publications in high-impact international journals (such as American Naturalist and Nature communications). Review papers (in Advances in Ecological Research, Oikos) have replaced our result in a more general framework. We also transferred expertise to (i) environmental policy institutions (ex. Guadeloupe natural Park) through conferences and common field sessions ; (ii) a naturalist-oriented public, via a book published jointly by the Museum d’Histoire Naturelle and the environemental-assesment agency Biotope.

We will study how fragmented systems (metapopulations and metacommunities) adapt to climate change and bioinvasions. The specificity of these systems is that diversity is regulated at the landscape scale by perturbations that result in local turnovers of genotypes and species. The fitness of a genotype emerges from its ability to colonize new patches, to compete with others within patches, and to avoid extinction during perturbation. Equilibria due to tradeoffs among these abilities are compromised by global change, which modifies both the rate of perturbation and the competitive environment (through the arrival of invasive species). Given the increasing importance of fragmented habitats, understanding how communities and species evolve in response to such changes is a major goal.
We focus on small tropical freshwater habitats, (ponds and streams) in the Antilles. They are naturally fragmented and are exposed to dramatic climate change, resulting in increased frequency of desiccation events (perturbation). At the same time many invasive species have spread in these habitats. Our first major objective is to decompose adaptation in these systems by quantifying colonisation ability, resistance to perturbation and competitiveness in a set of species in a community, and/or a set of genotypes in a species. Thus we will explain past changes, and predict future changes, in the frequency of these species/genotypes, i.e. the adaptive trajectory of the community/species in response to increased perturbation rates and bioinvasions. To this end we will rely on exceptional datasets: yearly surveys performed for >14yr in Guadeloupe ponds / Martinique rivers. The Guadeloupe ponds harbour communities of freshwater molluscs (similar in their life habits) while Martinique rivers mainly contains one species (Melanoides tuberculata) which is parthenogenetic and is composed of a set of morphologically identifiable clones. These clones compete with each other, providing a large-scale evolutionary experiment at the scale of the island. Using state-of-the-art bayesian patch-occupancy models, as well as more innovative analysis based on graph-theory, we will model the temporal trajectories of these systems. These results will potentially have a large impact because no such analysis has ever been done on a n-species or n-genotype system, highlighting a big gap between theory and field studies. In parallel, we will concentrate our efforts on laboratory measures of life-history and drought-resistance traits to uncover the phenotypic and genetic architecture of colonization, resistance and competition abilities.
We will also adress how trait evolution might affect coexistence by looking at rapid evolution of traits in a pair of related species (Physa acuta and P. marmorata), one of which is a recent invader, and the other a local species. Theoretical models will be made to understand which pairs (or communities) of species or genotypes are not only ecologically, but also evolutionarily stable, and how character displacement may (or not) take place in the competition-colonisation-resistance phenotype space. This theory will be applied to a two-species subset (one invasive, one indigenous) of our data in Guadeloupe. We will perform a phenotypic scan by looking for rapid local adaptation to new perturbation regimes in the invasive species; and rapid character displacement in the local species when the invader arrives.
This project brings together a pluridisciplinary consortium (ecology, quantitative and molecular genetics, mathematical modeling), with a good equilibrium between Empiricists and theorists, field ecology and lab experiments, evolutionary genetics and community ecology. The competences of the different members are highly complementary, and most of them have collaborated and written joint papers in the past.

Project coordinator

Monsieur Patrice DAVID (Laboratoire public)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

CBGP Centre de Biologie pour le Gestion des Populations
CNRS CNRS
ISA Institut Sophia Agrobiotech
CRIOBE Centre de Recherches Insulaires et Observatoire de l'Environnement
ASCONIT ASCONIT Consultants

Help of the ANR 339,174 euros
Beginning and duration of the scientific project: September 2012 - 42 Months

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