World-wide declines in amphibian populations have led to many local and global extinctions, and are connected to the global spread of chytrid fungus (Bd). Because few animals survive infection, Bd poses a strong selection pressure in infected populations. In addition, the skin microbiome of amphibians is significantly different between healthy individuals and individuals infected with Bd.
Hybrid zones, where two species meet and reproduce, are an ideal setting for research on adaptation, as different combinations of gene variants are tested. However, two contrasting hypotheses exist on the role of hybridisation in infection resistance. Genetic incompatibilities between diverging populations limit gene flow between closely related species, and cause lower fitness in hybrids. On the other hand, hybrid populations are mixes of the two parental genotypes, therewith increasing the chance of beneficial genes being present. The two species of yellow-bellied toads (Bombina variegata) and fire-bellied toads (Bombina bombina) are an ideal system to investigate evolutionary mechanisms and the two contrasting hypotheses about hybrid population fitness. While chytrid fungus is mostly associated with permanent ponds, where B. bombina prefers to live, it is currently unknown if there are any genes which allow for adaptation for the presence of chytrid in Bombina populations. To date, little is known about the interaction between Bd infection and the skin microbiome, and even less is known about this effect in Bombina. We expect to find genes involved in disease resistance, and uncover differences in the microbiomes of the two species, both in healthy animals and animals carrying the chytrid fungus, on which further projects will be built in the future.