Karrenberg lab: Our research
Research projects
Sex chromosome evolution
The evolution of separate sexes is of fundamental importance in biology. Sex-determining mechanisms are highly variable and sex chromosomes often degenerate; however, the underlying evolutionary mechanisms are unclear. Theoretical studies predict that sex chromosome evolution is governed by sex ratio selection and/or by different forms of genetic conflict, for example between males and females or between cytoplasm and nucleus. Empirical evidence for these predictions is scarce, in part because the best-studied systems are animals with ancient sex chromosomes.
This project investigates a plant family with separate sexes (Salicaeae, willows and poplars) where a high turnover of nascent sex chromosomes has been suggested and sex ratio bias is common, to understand the evolution of sex determining region and sex chromosomes. We use mostly genomic approaches, but also field surveys and greenhouse experiments with the dwarf willow Salix herbacea.
Model for the evolution of recombination suppression on the W -chromosome of Salix herbacea
Repeated evolution of dwarfism in arctic and alpine environment
Altitudinal gradients encompass steep cimatic clines, for example, in temperature. Species that occur over a wide range of altitudes may therefore have adapted to altitude across their different populations. We tested this hypothesis using in the model plant Arabidopsis thaliana. In particular, we investigated whether small stature at high altitude ("alpine dwarfism") is adaptive and how genetic drift and natural selection may interact to produce trait clines along altitude.
High-altitude environments are not only chanracterized by extreme conditions but also by a high heterogeneity in microhabitats, often association with the duration on snow cover. Our resarch shows that such micro-heterogeniety may allow the dwraf willow Salix herbacea to maintain variation wiithin popouluations and increase the species's potential to cope with changing conditions.
Female dwarf willow in cultivation
Sampling a dwarf willow in its natural habitat
Speciation
Lineage divergence and the formation of new species generate biodiversity. We study speciation mechanisms in two hybridizing sister species of campions, Silene latifolia and S. dioica and in willows (Salix),where hybridization is common. Both genera have separate sexes and sex chromosomes which is rare in plants. Our main questions include:
- How is cross-compatibility associated with genetic divergence and past gene flow?
- How are reproductive barriers controlled genetically and what is the role of sex chromosomes in this process
Lineage divergence with a reduction in gene flow (arrows) over time
Range dynamics: the roles of genetic variation, adaptation and plasticity
The range of a species results from their ecological amplitude and from interactions with other species, as well as from adaptive differentiation phenotypic plasticity across heterogeneous conditions. Understanding range dynamics is vital for predicting shifts in the species ranges due to changing conditions.
We investigate climatic effects on species ranges using distribution modelling of communities and individual species in sand vegetation. We are further part of a collaborative research project led by John Pannell (University of Lausanne, Switzerland), addressing range dynamics and the underlying genetic mechanisms with multi-site transplant experiments (https://ecorama.github.io/). For these experiments, we use the annual mercury (Mercurialis annua) as a model species. In relation to this project, we investigate adaptative differentiation in seed germination and seed dormancy throughout the range of Mercurialis annua in growth chamber experiments.
Transplant experiment with Mercurialis annua