Nothing is more practical than a good theory
– Ludwig Boltzmann
As population geneticists we do indeed spend most of our time doing one of two things: describing the genetic structure of populations or theorizing on the evolutionary forces acting on populations. Our questions often stem from the latter (either from our own work or from others work), we then try to test them using one of the experimental systems we are familiar with and generally end up with more questions and, sometimes, partial answers. Below we describe some of our forays into the intricate world of experimental evolutionary biology.
Capsella is becoming a strong model genus in plant evolutionary biology. Our work has primarily focussed the tetraploid shepherd’s purse, Capsella bursa-pastoris. The shepherd’s purse, an unassuming selfing weed, is one of the most common plant on Earth, but its diploid relatives aren’t: the outcrossing C. grandiflora is confined to the mountains of Northern Greece and Albania and the selfing C. orientalis and C. rubella are found in Central Asian steppes and around the Mediterranean Sea, respectively. Why is that so? In which way are the tetraploid better fit than its diploid counterparts, especially the selfing ones? We are addressing these questions by using a combination of genomic studies, common garden experiments, competition experiments and field studies.
This work is financed by grants from the Swedish Research Council, the Scilife Lab and the Erik Philip Sörensen Foundation.
Our main focus in spruce has been on local adaptation. Using parallel clines in Norway and Siberian spruce we have identified strong candidate genes related to phenology; in particular our work established the involvement of FTL2 in the control of budset variation. This was established by using clinal variation in SNP frequency in both Scandinavia and Siberia as well as in gene expression. Furthermore, and quite uniquely, in a parallel study FTL2 was transformed in Norway spruce by Ulf Lagercrantz’s group and its involvement in budset confirmed.
We have currently three ongoing projects on Norway spruce. The three projects are also related to local adaptation but are carried out on different scales and focus on different aspects. Two of them focus on the Swedish breeding population. Part of the plus trees used to establish the breeding population in southern Sweden were introduced from Germany, Belarus, Poland. Using next generation sequencing we are currently genotyping all the plus trees of the Swedish breeding population. After establishing which trees are descendants of introduced ones, which trees are admixed and which are from local origins we will compare their offspring. Those have been tested in numerous progeny tests and therefore we can compare their performance with that of offspring of local populations. We are also part of a large EU project , GENTREE, where we shall genotype and phenotype seven species, including Norway spruce, sampled across Europe and Russia. These data will be used to ask question on population history and local adaptation. Finally, we have recently studied the establishment of the large hybrid zone between Norway and Siberian spruces.
These projects are supported by Formas, SSF and EU FP7.
Since our first study in 2004, we have been working on hybridization, introgression and phylogeography of birch species. Early work was based on chloroplast polymorphism but we have now moved to nuclear variation. While chloroplast DNA suggested that hybridization and introgression was rife among birch species, a recent survey with SSR show clear delineation of the species. Recently we have also been involved in the genome sequencing project of Betula pendula, which was completed by colleagues at the University of Helsinki. Birch will also be studied within the GENTREE project.
Support: Formas, EU FP7.
All the work on poplars stem from a cooperation with Liu Jianquan at Sichuan University. It revolves around adaptation to drought of Populus euphratica and Populus pruinosa and their speciation. This is a large-scale genome resequencing project led by Liu Jianquan. Populus pruinosa occurs only in central Asia whereas Populus Euphratica range extends from NW China to Morocco. We have also a small project on the conservation of Populus Euphratica in Morocco and Algeria,
Support: Swedish Research Council (Research Links).