Biodiversity and Plant systematics Dr. Nora Walden

Different aspects of phylogenetics and the evolutionary history of the Brassicaceae (mustard family) have been the main focus of my research over the past years. More recently, I have also been fascinated by understanding complex and reticulate evolutionary histories across different timescales, from recent hybridization and polyploidization to deep evolutionary divergence. The Brassicaceae family, with high numbers of recent polyploids and frequent hybridization, offer a great model system to investigate phylogenetic discordance and its potential causes (hybridization, polyploidization, incomplete lineage sorting) and consequences. In addition to phylogenomics, I also use comparative genomics methods and synteny analyses to study the evolution of genes in the context of entire chromosomes. Much of my work has also focused on the evolutionary history of the genus Arabidopsis and on North American Arabidopsis lyrata, mostly using population level sampling and population genetic methods.

Phylogenomics of Arabideae

With around 4000 species in 350 genera, the Brassicaceae are among the most species rich angiosperm families. Over ten percent of Brassicaceae taxa belong to the tribe Arabideae, which among others contains the species rich genera Arabis and Draba. Polyploidization, posing a particular challenge to phylogenetic reconstruction, is common among Arabideae species, and ploidy levels of octaploid and higher are not uncommon in Draba. Using target enrichment data, we reconstruct a robust phylogenetic hypothesis which serves as an anchor for further analyses of morphological evolution through space and time and to study (parallel) evolution of traits (project by Dr. Christiane Kiefer).

Conservation genetics of Nuphar

Nuphar pumila (Nymphaceae) is an aquatic plant with a mostly northern/arctic distribution (Scandinavia, Russia). Populations in Central and Western Europa are regarded as glacial relicts and are threatened by habitat loss through anthropogenic impact as well as introgression from Nuphar lutea, a closely related species. Using ddRAD sequencing we investigate status of introgression and develop molecular markers to monitor the advancement of hybridization for nature conservation.

The evolutionary history of Cardamine bulbifera

Cardamine bulbifera (Brassicaceae) is a dodecaploid species exclusively propagating through bulb-like structures. Despite its seemingly complete absence of sexual reproduction, the species was able to colonize large parts of Europe postglacially. We study the evolutionary history and adaptive potential of this plant using genomic datasets.

Recent speciation of Cochlearia excelsa

Cochlearia excelsa (Brassicaceae) is a highly endangered, cold-adapted small range endemic from the Eastern Alps. It likely diverged from its closest relative, Cochlearia pyrenaica, during the Pleistocene. We use population genomic methods to investigate the dynamics of divergence and gene flow between both species.