Phenotypic and genotypic variation in the allopolyploid Arabidopsis suecica and its parent species A. thaliana and A. arenosa : an investigation of a possible model for studies of polyploidy and invasiveness

Abstract

Species that possess more than two sets of chromosomes are denoted as polyploids. It is hypothesized that polyploids show high gene redundancy, hybrid vigour and masking of deleterious alleles, and that this make them better at adapting to novel environments because of wider phenotypic response range. It is also speculated that adaptive advantage of polyploidy contributes to invasiveness as there is a trend that polyploids are overrepresented within invasive species. The allopolyploid Arabidopsis suecica and its parent species A. arenosa and A. thaliana were chosen as a model system to investigate relationships between phenotypic plasticity, fitness and genetic variation. In this thesis I try to uncover genetic structures in the study species, and I investigate if A. suecica show higher plasticity and/or fitness than its parent species, if the different species show different levels of genetic diversity and whether A. suecica could work as a model for studying polyploidy and invasiveness.

Three to four wild Norwegian populations of each species were analyzed for phenotypic responses to differences in availability of nutrient and light, while population structure and genetic diversity was assessed through analysis of AFLP markers. The species were separated into genetic and phenotypic clusters with A. suecica being intermediate between its parent species. Clear population structure was inferred in A. thaliana and A. arenosa, while no structure was inferred in A. suecica.

The species exhibited similar phenotypic responses. A. arenosa seemed to have higher phenotypic plasticity and higher genetic diversity than the two other species, probably related to its outbreeding reproduction strategy. Furthermore, a general positive relationship between genetic diversity and phenotypic plasticity was found. Low genetic diversity and more population structure were found in the indigenous, inbreeding A. thaliana. Population spacing might explain the clear genetic structure in A. arenosa, while the lack of structure in A. suecica could be due to coherent populations. When it came to fitness measured as allocation of resources to reproduction, the trend pointed towards A. arenosa having lower fitness under poor environmental conditions. A. suecica, on the other hand, showed the ability to keep up fitness under different environmental conditions, which makes it a promising model for investigating invasiveness and polyploidy. Still, further studies are needed to confirm this.