Connectivity of Alpine newt populations (Ichthyosaura alpestris) exacerbates the risk of Batrachochytrium salamandrivorans outbreaks in European fire salamanders (Salamandra salamandra)

The pathogenic chytrid fungus Batrachochytrium salamandrivorans (Bsal) was introduced from Asia to Europe, most likely via the pet trade. It is currently causing a severe local decline in populations of the European fire salamanders (Salamandra salamandra). Laboratory tests confirmed that all infected individuals succumbed to the disease within two weeks. Furthermore, mass mortality events in the wild were observed in Germany, Belgium and the Netherlands. Some newt species, including the Alpine newt (Ichthyosaura alpestris), can also become infected with Bsal. However, they seem to be ‘tolerant’ and can often survive the disease, but maintain an infectious load, which they could spread among connected populations. It is, therefore, hypothesized that this species functions as a vector of the disease and threatens syntopic populations of susceptible species such as the European fire salamander. To assess the risk of Alpine newts as vectors for Bsal, we sampled 233 individuals from 50 sites in 2017 and performed a genetic population connectivity analysis using microsatellites. The results showed that populations of Alpine newts are not spatially structured, suggesting high gene flow across the study area. Tests for Bsal of all Alpine newts and 150 individuals of two other newt species confirmed five infected individuals. Infected newts can thus function as reservoirs and vectors of Bsal and spread it through dispersal. As a result, the risk of European fire salamander declines in this region is further exacerbated by the connectivity of syntopic Alpine newt populations.