Amphibia-Reptilia 33 (2012): 319-326 The amphibian chytrid fungus in Bavarian populations of Alytes obstetricans: past absence, current presence, and metamorph mortality Susanne Böll 1,∗ , Ursina Tobler 2 , Corina C. Geiger 2 , Günter Hansbauer 3 , Benedikt R. Schmidt 2,4 Abstract. In three Bavarian populations of Alytes obstetricans that were studied for the occurrence of Batrachochytrium dendrobatidis, the pathogen was detected. This is the first account of chytridiomycosis in Bavaria, Germany. Infected tadpoles had low infection loads mostly of 10 1 to 10 2 genome equivalents. Under high-density rearing conditions in the laboratory mortality rates were high after metamorphosis. Some individuals, however, showed no infection with Bd, while others survived metamorphosis in spite of low Bd loads. A new approach was chosen to get historical data on Bd occurrence in one of these populations: skeletochronological phalanx cross sections of 248 individuals that had been collected in the late 1980s were used to analyse the epidermis for chytrid sporangia. No sporangia were detected, thus we conclude that this population was not affected by Bd in the past. Keywords: Alytes obstetricans, Batrachochytrium dendrobatidis, chytridiomycosis, skeletochronological phalanx cross sections. Introduction Chytridiomycosis, a disease caused by the zoosporic fungus Batrachochytrium dendroba- tidis (hereafter Bd), is known to be one of the driving forces of the worldwide amphibian de- cline (Gascon et al., 2007; Skerratt et al., 2007; Fisher, Garner and Walker, 2009). Although the pathogen and disease were originally reported primarily from tropical areas, it is now evi- dent that the pathogen is also widespread in Eu- rope (Bosch, Martinez-Solano and Garcia-Paris, 2001; Garner et al., 2005; Tobler and Schmidt, 2010; Walker et al., 2010; Ohst et al., 2011). It is not known how or when chytridiomyco- sis has spread in Europe. Bd could well be an endemic pathogen with changing host suscep- tibility due to increasing environmental stress 1 - Agency for Population Ecology and Nature Conser- vancy, Gerbrunn, Germany 2 - Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Switzerland 3 - Bavarian Environment Agency (LfU), Augsburg, Ger- many 4 - KARCH, Passage Maximilien-de-Meuron 6, 2000 Neuchâtel, Switzerland ∗ Corresponding author; e-mail: susanneboell@gmail.com (endemic pathogen hypothesis, Rachowicz et al., 2005). However, most authors favour the novel pathogen hypothesis (Rachowicz et al., 2005), arguing that Bd has been recently intro- duced to Europe via global amphibian trade and spread by vector species such as Xenopus laevis and Lithobates catesbeianus (Duffus and Cun- ningham, 2010) or non-native Pelophylax frogs from eastern Europe (Ohst et al., 2011). Yet, re- cent genetic data support both hypotheses, rec- ognizing endemic Bd-lineages as well as a hy- pervirulent global panzootic lineage that is as- sociated with regional epizootics on five conti- nents (Farrer et al., 2011). Susceptibility to Bd varies greatly among am- phibian species (Kilpatrick, Briggs and Daszak, 2010). The common midwife toad, Alytes ob- stetricans, is probably one of the most suscepti- ble species in Europe, most likely because tad- poles overwinter (Bosch, Martinez-Solano and Garcia-Paris, 2001; J. Bielby, personal com- munication). In montane areas of Spain and France where the larval period is even more extended and tadpoles overwinter two or more times (Böll, Scheidt and Uthleb, 2012), fatal outbreaks of chytridiomycosis have been ob- served and have led to dramatic declines of mid- © Koninklijke Brill NV, Leiden, 2012. DOI:10.1163/156853812X651856 Downloaded from Brill.com09/10/2023 12:06:12PM via free access