We aim to describe the genetic signature at expanding range margins and to understand to what extent populations and species can adapt to new environmental conditions triggered by recent climate change, as well as understand the role of marginal populations for the long term persistence of adaptive genetic variation.
Populations at range limits are currently thought to be poorly adapted and genetically depauperate in comparison to central populations, and are not thought to contribute greatly to adaptation and persistence of the species to which they belong. However, these predictions have rarely been tested and are contradicted by other, parallel lines of research suggesting that marginal and isolated populations at range limits can be important drivers of innovation and speciation. Under current conditions of climate change and rapidly shifting geographic ranges among many species, it is increasingly important to reconcile these disparate lines of research and empirically address the adaptive potential of phenotypic and genetic changes that occur at the limits of expanding ranges.
The research subject: the damselfly Ischnura elegans
Our research subject is the damselfly Ischnura elegans, which is the subject of a long-term research project led by Erik Svensson focusing on evolutionary and population genetic consequences of intrasexual selection, polymorphism, and life history. This species is characterized by a large and expanding geographic range, in which traits such as female morph frequency and body size, and patterns of selection on these traits, are known to exhibit strong clinal variation.
Methods and evaluation
Using a combination of genome-wide genetic methods (RAD-tag sequencing), RNA visualization of heat-shock protein expression, population genetics and ecological niche modeling, field observations, and temperature-exposure experiments, we specifically plan to evaluate the role of environmental and genetic effects on temperature tolerances within the species. We will evaluate how these causes vary by a population’s physical proximity to the expanding northern range limits. Individual, realized temperature tolerances are key predictors of climatic niche occupation. However, it is unknown how these tolerances will evolve. We will evaluate how selection for changes in temperature tolerances at expanding range limits are affected by population-genetic effects of gene flow and genetic drift. Characterizing the effects of this interaction among selection, gene flow, and drift will help us predict adaptive changes in temperature tolerance and niche evolution under climate change.
We will furthermore examine how these genetic changes are impacted by and impact dynamics of sexual selection, including female morph frequency and mating harassment.