POREXPAN

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. Though adaptation and dispersal 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. 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.