A 21st century approach to study chytrid fungal infections in an amphibian hybrid zone

ongoing

World-wide declines in amphibian populations have led to many local and global extinctions, and are connected to the global spread chytrid fungus (Bd). Because few animals survive infection, Bd poses a strong selection pressure in infected populations. 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. Thus, the first hypothesis postulates that the negative impact of pathogens is higher in hybrid zone populations than in populations comprising a single species. The second hypothesis proposes that the resistance of a hybrid population towards pathogens is strengthened by the coexistence of multiple immune gene variants, in comparison to populations comprising a single species. The two species of yellow-bellied and red-bellied toads (Bombina) are an ideal system to investigate these hypotheses, as 1) their hybrid zone has been well-studied before using various - but few - genetic markers, and 2) toads of these species have previously been found to be infected with Bd. On a side note, the skin microbiome of amphibians is different between healty individuals and individuals infected with Bd. 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. With this action, I aim to investigate the role of hybridisation in pathogen resistance in amphibian populations. I will also explore changes in composition of the amphibian skin microbiome in response to Bd infection. I will use the genus Bombina as a model system - employing 21st century sequencing technology.