Evolution of biological populations during and after range expansions
During range expansions, an expanding population is necessarily faced with new environmental conditions that require new local adaptations. These may be achieved if there is a sufficient amount of “useful” standing genetic variation in the source population, provided that at least a proportion of this useful variation is brought to new areas by founders. The latter condition may not be met if the expansion is led by small founder populations due to random genetic drift, and this may halt the expansion . However, it has been suggested that range expansions may be boosted by plasticity – ability of a single genotype to produce different phenotypes when faced with different environments . Specifically, adaptive plasticity improves the ability of an individual to cope with a new environment, thus effectively weakening natural selection. However, exploiting plasticity induces energetic costs for individuals, and there must also be a limiting range of environmental conditions where a plastic response may be expressed. In turn, this suggests that adaptive plasticity alone is not sufficient to assure successful range expansions, both in terms of the short- and long-term survival and function of a population in a given ecosystem. Instead, expanding populations must also evolve some degree of local genetic adaptation. To date, however, we lack knowledge and understanding of how local genetic adaptation evolves during range expansions in the face of the joint effect of genetic drift (repeated founder events), selection and plasticity. Delivering this knowledge is the key aim of this project.
In addition, the project aims at bringing together the research on range expansions and speciation, that have traditionally been pursued separately from each other, even though the two are highly related. An expanding population faced with new environmental conditions will evolve population differentiation. This may result in the establishment of locally divergent ecotypes with partial reproductive isolation (unless gene flow is too strong). Over time, reproductive isolation may be strengthened, thus allowing the initially established ecotypes to progress towards different species (speciation). Despite this simple expectation, research on range expansions and speciation have mainly been pursued separately from each other. Thus, the contribution of the processes acting during range expansions to speciation is not yet understood. This project has a potential to deliver new knowledge in this direction, thereby significantly improving our understanding of speciation.
Overall, this project has a potential to deliver new insights into the mechanisms of local adaptation, and to improve our knowledge regarding species’ distributions and re-distributions.
The project will primarily involve mathematical modelling (individual-based computer simulations). This project is partly financed by the Hasselblad Foundation: Grant for Female Scientists to Marina Rafajlović, and by the Swedish Research Council Formas (grant awarded to Kerstin Johannesson and Marina Rafajlović).
1. Polechová, J. 2018. Is the sky the limit? On the expansion threshold of a species’ range. Plos. Biol. 16(6): e2005372.
2. Chevin, L.-M., R. Lande, and G. M. Mace. 2010. Adaptation, plasticity, and extinction in a changing environment: towards a predictive theory. PLoS Biol. 8: e1000357.