Leppälä, Johanna - Genetics of speciation

Research

Johanna Leppala in a forest environmentPlants commonly have strategies for both sexual and asexual reproduction. These reproductive functions do not evolve independently, but asexual reproduction e.g. through clonality, has consequences for sexual reproduction, typically by relaxing selection for sexual traits and allowing mutational degeneration in genes related to sexual functions. In my research, I am interested in both sexual and asexual reproduction of plants.

Related to sexual reproduction, I study genetics of speciation – i.e. genes involved in development of reproductive isolation. I have been using hybrids within and between outcrossing Arabidopsis species (A. lyrata, A. halleri and A. arenosa) to investigate reproductive barriers. Species barriers commonly manifest themselves as reduced hybrid viability and/or fertility. In these Arabidopsis species, reduction of hybrid pollen fertility is one of the first barriers to emerge between incipient species. Therefore, my main focus is on pollen related traits.

Three microscopy images of pollen grains of a hybrid between Arabidopsis speciesLeft: Light microscopy image of pollen grains of a hybrid between Arabidopsis species. Middle: DAPI staining (blue) of the same pollen grains, showing stained nuclei in two of the pollen grains, whereas two pollen grains (in the middle) remain unstained, as the cells are dead and DNA has degraded. Right: Scanning electron microscopy (SEM) image of pollen grains of a hybrid between Arabidopsis species: two smaller pollen grains in the middle are inviable.

Regarding asexual reproduction, my main interest is in clonality and its relation to sexual reproduction. Vegetative reproduction is typically associated with longevity and perenniality, and it can also be seen as a survival strategy, in conditions where sexual recruitment is low. Clonality has consequences for sexual reproduction, typically by relaxing selection for sexual traits and allowing mutational degeneration in genes related to sexual functions. The genetic basis of clonality has remained unknown, as the model plants of genetics are typically annuals. I use European aspen (Populus tremula) and Arabidopsis lyrata, as model species to study clonality and its genetic basis. In addition, I aim to identify whether clonality has affected sexual functions, specifically pollen quality and flowering frequency in these species.

Flowering Arabidopsis lyrata on the left side and Aspen trees with freshly green leaves photographed from below on the right.Left: Arabidopsis lyrata in Höga Kusten, Sweden. Right: Aspen clones in a forest in Bjurholm.

Read more about Johanna Leppälä's research