The evolution of complexity–The impact of progenetic evolution on the genome of a small worm

Animals are multicellular organisms comprising a variety of different body plans. They can be as simple and sessile as sponges or as complex and mobile as humans. With a body length of less than 0.5 mm some (e.g., small marine worms like gastrotrichs) are even smaller than certain unicellular organisms. While tremendous progress has been achieved in recent years regarding the phylogeny of animals due to the application of genome-scale data, many questions concerning animal evolution remain contentious including, among others, the evolution of complexity within Bilateria. Bilateria comprises all animals except sponges, jellyfishes, placozoans and comb jellies. Based on development-biological studies of large-sized and more complex animals it has been proposed that complex suits of character traits evolved early in animal evolution and have been simplified several times independently, for example, in gastrotrichs. On the other hand, recent phylogenetic studies using genome-scale data (i.e., phylogenomics) support the traditional view that early evolution in Bilateria progressed from simple to complex. The aim of this master project is to contribute to this debate by studying a neglected, but crucial aspect in this debate: the evolution of small-sized, simple-bodied animals.

Stygocapitella subterranea. Courtesy of Günter Purschke (University of Osnabrück). The adult stage of this species resembles the juvenile form of another annelid group.

Progenetic evolution (or progenesis) is an evolutionary process often invoked to explain secondary simplification of small-sized animals. Simply put, progenesis is an evolutionary process where sexual maturation occurs faster than somatic development (non-sexual development) and growth. Instead of a more complex adult stage, the new species resembles the juvenile or larval stage of the ancestor. While the general principles of progenetic evolution are clearly defined little is known about the actual impact of progenetic evolution on the genomes of the affected animals.

Progenetic evolution has also been invoked in the discussion about evolution of complexity. The evolution of many simple-organized animals groups like gastrotrichs, which are traditionally considered to show an ancestral, simple body plan, are in the new hypothesis regarded as secondarily simplified animals by progenetic evolution. However, this conclusion is contentious regarding all animal groups, which are crucial in the debate about the evolution of complexity in Bilateria. On the other hand, knowledge about the impact of progenetic evolution on genomes of known secondarily simplified animal groups could provide independent evidence for secondary simplification in dubious cases.

Aim of this Master project:

The major aim of this Master project is to assess the impact of the progenetic evolution on the genome of small-sized, simple-bodied annelid worm Stygocapitella subterranea. Stygocapitella subterranea originated hundreds of millions years ago and inhabits the same environments as the crucial small-sized animal groups, which are crucial in the debate about complexity in animals. Hence, Stygocapitella subterranea shares similar environmental selection pressures over a comparable time frame. Therefore, The results of this project can provide the basis for follow-up projects focusing on these crucial taxa addressing if they are secondarily simplified or not.



First, the student will be involved in the assemblage, annotation and description of the genome. Third, the generated data will be used to assess the following hypotheses about the impact of progenetic evolution by comparing the genome to published genomes of other invertebrate genomes. (1) Genes, which are expressed in late developmental stages across the animal kingdom and in closely related species, are lacking in the genome of Stygocapitella subterranea. (2) Genes involved in sexual maturity, however, are not affected in this way. (3) The genome of Stygocapitella subterranea is more compact or has a lower gene content than the other genomes.


Supervision and teaching

The student will be supervised by Torsten Struck, Jose Cerca de Oliveira and Russell Orr (all NHM Oslo). You will be provided with a broad training in different aspects of biology, which includes, among others, metazoan evolution, comparative genomics, sequencing techniques, phylogenetic reconstruction and bioinformatics. All of these techniques are state-of-the-art techniques, which are relevant for both academic and non-academic positions. As methods, which were developed for cancer research, and genomics are employed this also includes positions in the medical field.

For further inquiries feel free to contact Torsten Struck.

Torsten Struck -

José Cerca de Oliveira –


Publisert 12. apr. 2018 07:23 - Sist endret 7. feb. 2020 16:26

Omfang (studiepoeng)