About Hannes


I am a biologist interested in all sorts of life-related phenomena. Being a botanist at heart, I have worked (and published) on Historical Geobotany, Pollen Analysis, Molecular Systematics, Cytogenetics, and Epigenetics of Giant Genomes.

In 2014, I ventured to start a PhD on Population Genetics, Hybridisation, and Sex Chromosome Evolution in an amazing grasshopper, Podisma pedestris. This allows me to apply my knowledge acquired in the plant world, and it challenges me to go beyond that every day.

I enjoy scripting in python, R, and Julia; and I am a keen microscopist. In my spare time I enjoy nature and music. Recently I started learning French: “Tu as un joli canard.” I hope I will manage to take it a bit further…

My PhD project

My PhD is on hybridisation and sex chromosome evolution. As a model I use Podisma pedestris, an alpine grasshopper species, which has two races differing in their sex chromosome systems. Interracial hybrids are viable but they show a seriously reduced fitness, presumably representing an obstacle to gene flow between the races. The sex chromosomes (which are the basis of the race classification) seem to contribute little to the low hybrid fitness observed, suggesting there must be other differences. I am using methods like high-throughput DNA sequencing (HTS), fluorescent microscopy, and computer modelling to find what makes the difference between P. pedestris’ races.

The chromosomal races

The ancestral (original) state of P. pedestris’ sex chromosomes is an X0 system. That means unlike in humans there is no Y-chromosome. Females have two X and males have only one.

The other race has a neo-X/neo-Y system created by an autosome-to-X fusion. This fusion created a big neo-X (fused X) and left behind a former autosome that is now limited to males. The left-over former autosome is thought to be evolving Y-chromosomal features (hence it is called neo-Y). For instance, we observe reduced recombination between the neo-Y and its homologous bit of the neo-X. See the figure below for an overview.

In the hybrid zone, the neo-Y can potentially occur in females, allowing us to ask whether there is sexually antagonistic selection acting on it. Being “Natural Laboratories”, in which crossing has happened for thousands of generations, hybrid zones are invaluable sources of data which could not be produced in the lab. Unfortunately there is no marker known for the Y at this point. I am addressing questions like:


The figure above shows the sex-chromosomal configurations possible in P. pedestris. The ancestral X-chromosome is shown in red, a pair of autosomes is blue, the fused X is a red and blue compound, and the neo-Y is blue with dots.

Male karyotypes are shown in the top row, female ones in the bottom. The ancestral configuration is shown on the left, followed by the fused karyotype. The figure’s right-hand half shows all possible hybrid karyotypes. Note it is possible for neo-Y-chromosomes to occur in hybrid females.