Exploring the Distribution of the Spreading Lethal Salamander Chytrid Fungus in Its Invasive Range in Europe - A Macroecological Approach

Abstract

The chytrid fungus Batrachochytrium salamandrivorans (Bsal) is a dangerous pathogen to salamanders and newts. Apparently native to Asia, it has recently been detected in Western Europe where it is expected to spread and to have dramatic effects on naïve hosts. Since 2010, Bsal has led to some catastrophic population declines of urodeles in the Netherlands and Belgium. More recently, it has been discovered in additional, more distant sites including sites in Germany. With the purpose to contribute to a better understanding of Bsal, we modelled its potential distribution in its invasive European range to gain insights about the factors driving this distribution. We computed Bsal Maxent models for two predictor sets, which represent different temporal resolutions, using three different background extents to account for different invasion stage scenarios. Beside 'classical' bioclimate, we employed weather data, which allowed us to emphasize predictors in accordance with the known pathogen's biology. The most important predictors as well as spatial predictions varied between invasion scenarios and predictor sets. The most reasonable model was based on weather data and the scenario of a recent pathogen introduction. It identified temperature predictors, which represent optimal growing conditions and heat limiting conditions, as the most explaining drivers of the current distribution. This model also predicted large areas in the study region as suitable for Bsal. The other models predicted considerably less, but shared some areas which we interpreted as most likely high risk zones. Our results indicate that growth relevant temperatures measured under laboratory conditions might also be relevant on a macroecological scale, if predictors with a high temporal resolution and relevance are used. Additionally, the conditions in our study area support the possibility of a further Bsal spread, especially when considering that our models might tend to underestimate the potential distribution of Bsal.

Fig 1. Western Europe study region.

First noted Bsal outbreaks are indicated by black and subsequent records by white triangles. Elevational range (grey scales, light to dark: 28–1,050 m a.s.l.), borders (bold lines), rivers (thin lines), some major cities (normal font) and low mountain range names (sloped font) are shown.

Fig 2. Predictions into the study region for the different Bsal SDMs.

Predicted suitability maps (top) with corresponding presence-absence maps (below) for the different models. High suitability and presences are indicated in red, low suitability and absences in grey. Bsal presences are indicated by black triangles.

Fig 3. Average predictions of all Bsal SDMs.

Average predicted suitability map (left) and presence-absence map (right) of all models. High values are indicated in red, low values in grey. Bsal presences are indicated by black triangles.