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Invesigating the effect of environmental sex determination on gene regulation

Supervisor: Ann Kathrin Huylmans

Co-Supervisor: Peter Baumann


Scientific Background:
Males and females are two very different phenotypes that result from the same or almost the same genome. Differences exist in physiology, ornamentation, size, immunity, and behaviour and most of these differences arise due to differential gene expression between the sexes. However, sometimes tight regulation does not let one or both sexes reach their optimum phenotype and this creates sexual conflict. Sex-biased gene expression is considered evidence for sexual conflict in the past. In species with sex chromosomes, sexual conflict between males and females over gene expression can at least partially be resolved via transloctions of genes to the sex chromosomes. However, this is not possible in species with environmental sex determination where males and females share their entire genome. In these species, gene regulation plays an even more pronounced role in the formation of the different phenotypes. One possibility to resolve sexual conflict other than moving genes to the sex chromosomes is the duplication of a gene with subsequent subfunctionalisation. There, one copy can primarily be used in males and the other in females.


PhD Project: Invesigating the effect of environmental sex determination on gene regulation
The hypothesis is that gene duplication and sex-biased or sex-specific expression of the copies is more frequent in species with environmental sex determination than in those with sex chromosomes. Initial data in the lab indicate that this may be the case in the water flea Daphnia. We would like to test this hypothesis more widely using different taxa with environmental sex determination and compare them to related species with genetic sex determination using genomic and transcriptomic data. If this is indeed the case, this would indicate that gene duplication plays an important role in alleviating sexual conflict and that the mode of sex determination can contribute to fast evolution of the gene repertoire and gene regulation.

The Research Traning Group investigates which processes are evolutionarily conserved or subject to change. If environmental sex determination indeed leads to higher rates of gene duplication and subfunctionalisation, we will have identified one of the selective forces that can drastically shape the genome. This project involves the analysis of many different types of omics data on the genome level as well as gene expression data for model and non-model species providing extensive opportunity to learn state-of-the-art techniques from the sampling step all the way to the analysis stage. For this project, Peter Baumann is the co-supervisor. His background in biochemistry, epigenetics, and experience with allele-specific expression wil benefit the project greatly and will also make it possible to identify the molecular changes that accompany the subfunctionalisation and ultimately lead to a change in gene expression. In addition, he has ample experience working with lizards and other reptiles – a group where many species show environmental sex determination.


Publications relevant to this project
Gallach, M., Betrán, E. Intralocus sexual conflict resolved through gene duplication. Trends Ecol Evol 26(5), 222–228 (2011).
Wyman, M.J., Cutter, A.D., Rowe, L. Gene duplication in the evolution of sexual dimorphism. Evolution 66(5), 1556–1566 (2012).
VanKuren, N.W., Long, M. Gene duplicates resolving sexual conflict rapidly evolved essential gametogenesis functions. Nat Ecol Evol 2, 705–712 (2018).