Hybrid speciation in Cottus

Hybridization receives attention because of the role that it may play in generating evolutionary novelty. We analyze a lineage of Cottus that has recently invaded vast habitats within the lower River Rhine basin and is thus referred to as invasive Cottus. Genome wide analyses of ancestry show that invasive Cottus are hybrids between Cottus perifretum, most likely from the River Scheldt basin, and Cottus rhenanus from the River Rhine basin.

Cottus from the Dutch lowlands and Belgium (C. perifretum) as well as from tributaries to the River Rhine (C. rhenanus,) have come into secondary contact and given rise to invasive Cottus, a lineage of hybrid origin. Invasive Cottus (center, top individual) have colonized and spread within the lower River Rhine (left) while C. rhenanus (center, bottom individual) are restricted to smaller tributaries as for example the Bröl in North Rhine Westphalia (right) (Pictures: I. Steinmann, A. Hartl). — *Cottus* from the Dutch lowlands and Belgium (*C. perifretum*) as well as from tributaries to the River Rhine (*C. rhenanus*,) have come into secondary contact and given rise to invasive *Cottus,* a lineage of hybrid origin. Invasive *Cottus* (center, top individual) have colonized and spread within the lower River Rhine (left) while *C. rhenanus* (center, bottom individual) are restricted to smaller tributaries as for example the Bröl in North Rhine Westphalia (right) (Pictures: I. Steinmann, A. Hartl).

*Cottus* from the Dutch lowlands and Belgium (*C. perifretum*) as well as from tributaries to the River Rhine (*C. rhenanus*,) have come into secondary contact and given rise to invasive *Cottus,* a lineage of hybrid origin. Invasive *Cottus* (center, top individual) have colonized and spread within the lower River Rhine (left) while *C. rhenanus* (center, bottom individual) are restricted to smaller tributaries as for example the Bröl in North Rhine Westphalia (right) (Pictures: I. Steinmann, A. Hartl).

Invasive Cottus form a distinct genetic group and possess a unique ecological potential, attributed to the process of hybridization. We are studying the genetics of the emerging hybrid lineage in order to learn about the dynamic evolutionary processes during the formation of a hybrid swarm after secondary contact. We are interested in how hybridization may lead to the formation of evolutionary novelty but also in genomic conflicts that would lead to underdominance and hybrid dysgenesis.

Homoploid hybrid speciation can be explained, if hybrid separate spatially and ecologically from their parents. However, intrinsic genetic conflicts and selective forces that affect in the emerging hybrid lineages are poorly understood.

Homoploid hybrid speciation can be explained, if hybrid separate spatially and ecologically from their parents. However, intrinsic genetic conflicts and selective forces that affect in the emerging hybrid lineages are poorly understood.

To explore the genetics of invasive Cottus, we apply massively parallel sequencing, genetic mapping, transciptomics and population genetic analyses. Ancestry informative markers and linkage information are used in population genetic studies of the makeup of the invasive Cottus gene pool. We collaborate with Prof. Dr. Floyd Reed (University of Hawaii, USA) to model the evolution genomic ancestry in hybrid species to derive predictions that can be tested in Cottus. Dr. Fritz Sedlazek and Prof. Dr. Arndt von Haeseler (both University of Vienna, Austria) develop mapping algorithms and software that can map next generation sequencing reads to distant reference genomes. We are collaborating to efficiently map Cottus genomic sequences directly onto the stickleback (Gasterosteus) genome and to develop analysis approaches to study population genomics of hybrid Cottus.

We are interested to document evolution in natural habitats. However, we keep fishes for breeding experiments, genetic mapping and for studies of gene expression in controlled environments. This requires aquaria with a constant supply of fresh water. We can simulate the natural light and temperature cycle and are able to breed Cottus in our fish facilities at the Max-Planck Institute in Plön.