I am an evolutionary biologist interested in the origins and consequences of sex.

Origin and maintenance of sex

Sexual reproduction and the associated recombination of the parental genomes can be costly compared to asexual reproduction. Nevertheless, sex is ubiquitous across the tree of life, which remains an elusive mystery of evolutionary biology. Sex could be common because recombination confers benefits compensating its costs or because the origin of asexuality is constrained. However, investigations of both potential explanations are hindered by the lack of genetic resources in the asexual species studied to date. In my Postdoc project at the Max-Planck Institute for Multidisciplinary Sciences I am using the planarian Schmidtea mediterranea as a model to study sexual system evolution. Usually studied for its amazing regenerative abilities and pluripotent stem cells, S. mediterranea also occurs in distinct sexually and asexually reproducing strains. However, this asset remains largely unexplored concerning the evolutionary importance of sex, mainly for a lack of high-quality genome assemblies. We have recently overcome this bottleneck via a chromosome-scale genome assembly of both strains. Using these data, I am conducting extensive comparative genomic analysis to probe the causes and consequences of asexuality in Schmidtea mediterranea.

Flatworm biodiversity & sexual trait evolution

During my PhD project I collected molecular and morphological data on 145 species of Macrostomum flatworms. My work uncovered 94 species that are likely new to science, representing an ~50% increase in the number of known species in this genus. I also described several novel sexual traits that likely are important characters shaping Macrostomum evolution and I published taxonomic descriptions of three particularly interesting species. Based on the phylogenetic and morphological data I created, I then conducted a large-scale comparative analysis. I found that hypodermic insemination, an extreme type of mating, evolved independently at least 13 times representing approximately 30% of all such origins across the Metazoa. I also showed that hypodermic insemination coincides with a drastic convergence of genital and sperm morphology. This remarkable case of convergent evolution shows that sexual selection is a powerful force shaping macroevolutionary patterns in hermaphrodites. I further showed that hypodermic insemination is associated with reduced sperm competition as indicated in a shift in sex allocation. Transcriptome-based estimates of heterozygosity suggest that this shift in sex allocation is due to an increase likelihood of selfing in hypodermically inseminating species.

Rate of molecular evolution

Based on de novo assembled transcriptomes, I investigated the rate of molecular evolution of reproduction-related proteins. I could demonstrate, for the first time in flatworms that reproduction-related genes evolve at a faster rate as indicate by both protein divergence and homology detection failure. I have collaborated with Dr. Axel Wiberg to extend these findings to more species finding positive selection on reproduction-related genes throughout the genus. Additionally, we found signature of relaxed selection in species with hypodermic insemination suggesting that a switch in mating behavior has a genome wide effect.