The proposal was submitted under the title: “POREXPAN: Local adaptation of plant POpulations during Range EXPANsions: the effect on life-history traits and genetic variability” by the following members of the Network:
Centre for Ecological Research (Maria Mayol & Miquel Riba), Barcelona – Spain
National Institute for Agricultural and Food Research and Technology (Santiago C. González-Martínez), Madrid – Spain
University of Lausanne (John Pannell), Lausanne – Switzerland
National Research Council (G. Giuseppe Vendramin), Firenze – Italy
Here is the Abstract:
The analysis and forecasting of the impact of global change on biodiversity rarely incorporate the effects of evolutionary changes and past demographic history of species and their populations. However, there is growing evidence that they can have broad impacts on species
range, community composition and ecosystem services, with potential consequences for human health and welfare. Thus, the scope of current ecological models to support action-taking is severely limited. The dilemma posed to organisms by current trends of global (climate) change is simple: (i) to adjust to new conditions and/or (ii) to shift their ranges tracking favorable environments. Evidence for evolution in response to climate change is accumulating, and there is also ample evidence that current climate change is driving the expansion of numerous plant and animal populations towards higher elevations and latitudes. Though dispersal and adaptation are often presented as alternative mechanisms, both interact in complex ways. First, natural selection operates on complex, integrated phenotypes, so evolutionary predictions for individual traits may fail under conflicting selective pressures.
Second, range shifts usually involve new selective pressures to which individuals and populations are confronted. The interplay among these new selective pressures with demography, and how they affect relevant life-history traits during range-shifts is currently unknown. Third, demographic processes linked to range expansions might pose additional constraints on the evolutionary potential of species and populations on their expanding ranges. In particular, strong and consecutive bottlenecks during range expansions can reduce fitness in
colonization-front populations because of limited genetic variability and the accumulation of deleterious mutations (expansion load). In this project, we propose to investigate the effects of range expansions on life-history traits and genetic variability (adaptive potential) using two non-model plant species, Leontodon taraxacoides and Mercurialis annua, along postglacial expansion routes. Both species are particularly well suited for experimentation and genomic analyses since they are short-lived (annual), have known breeding systems and relatively small genomes, and extensive genomic resources are already available. Our approach includes: 1) the assessment of the genetic basis of the phenotypic variability in key life-history traits (dispersal ability, growth, reproductive effort, phenology, and defense response) and their correlations, through common garden experiments; 2) the characterization of signatures of range expansions in genes and gene networks associated with key adaptive traits and, particularly, the level of accumulation of deleterious mutations in colonization fronts (i.e. expansion load); 3) the association of genes and gene networks with adaptive traits measured in common gardens to determine their molecular basis and provide a first insight on the genetic architecture of life-history traits in the context of range expansions. Our approach will allow us to test current theory on evolutionary consequences of range expansions at both molecular and quantitative trait levels, to identify candidate genes and traits associated with colonization of new environments, and to evaluate the evolutionary potential of expanded populations for future adaptation.
Over 3,000 microsatellite sequences have been made available for marker development by Katie Ridou, the bioinformatician responsible of Mercurialis genome assembly. These sequences include only microsatellite regions with enough flanking sequence to design 20-bp PCR primers. Jonathan El Assad is using standard methods to PCR-test several primer pairs in a diverse panel of diploid Mercurialis annua covering its full range. The target is to develop a set of about 20 microsatellites that could be used in 2-3 multiplexes. This tool would be very useful to increase our understanding of Mercurialis annua demographic history and to evaluate the levels of inbreeding in current experimental evolution and quantitative genetics experiments.
Diploid Mercurialis annua from Central and Western Europe was the result of long-range colonization from ancestral populations in the eastern Mediterranean basin. Colonization-front populations are expected to have reduced fitness due to sequential bottlenecks during colonization. To test up to which point fitness in these populations can be increased by heterosis, polycrosses between different colonization-front populations in France, Spain and UK and between them and ancestral populations in Greece and Turkey are currently being performed at the UNIL greenhouses. This seed material will be used in a quantitative genetic experiment to be installed in Switzerland (under Atlantic/continental climate) and Spain (under Mediterranean climate) in spring 2015.
Crossing scheme and open “boxes” used for crosses at UNIL
Mercurialis annua hexaploid hermaphrodites typically resemble females in their inflorescence architecture, bearing their subsessile inflorescences on the leaf axils. Males, on the other hand, produce a large amount of flowers displayed along long peduncles that protrude above the canopy. Given that Mercurialis annua is a wind pollinated species, peduncles provide important benefits for pollen dispersal. So if males show this adaptation, why hermaphrodites don’t? Excitingly, several populations of hermaphrodites bearing male-like peduncles have been recently found in eastern Spain. They co-occur in the same range as previously known hermaphrodites, and this discovery poses a number of exciting questions relevant to the ecology of wind pollination: What are the fitness consequences of bearing male flowers on peduncles? Do genes coding for peduncles have pleiotropic effects? Are there trade-offs with other fitness traits? What is the genetic architecture of inflorescence architecture? Are males less likely to invade pedunculate hermaphrodite populations? Will pedunculate hermaphrodite populations expand their range? We are currently addressing these questions by phenotypic and molecular characterization, controlled crosses and mating array experiments.
Pedunculated M. annua hermaphrodites from eastern Spain
In the last weeks, Myriam Heuertz and Santiago C. González-Martínez developed different educational activities aimed at promotion of scientific thinking among children, in the framework of their respective Marie Curie Fellowships (in Fribourg and Lausanne). Hermaphrodite, male and female plants of Mercurialis annua were used to illustrate the incredible variety of plant mating systems, even within species. The distinctive Mercurialis male inflorescence was easily identified by the children, who were surprised that plants could have variation in their ways to produce offspring. This was continued by discussing in easy-to-understand terms how differences in mating system can have important consequences in plant evolution.
Learning about separated sexes in plants
Preliminary analyses for the gene flow experiment have been completed. This experiment, conducted by postdoc Anne-Marie Labouche, considers the effects of pollen limitation and pollen competition on offspring number and quality as a function of plant density. Apart from demonstrating pollen limitation in Mercurialis, the experiment showed larger pollen flow distances than expected and several other interesting features related to M. annua mating system.
Experimental arrays of wind-pollinated Mercurialis annua, in which distance from a pollen source regulates the intensity of pollen competition.