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Abstract Resistance and tolerance allow organisms to cope with potentially life-threatening pathogens. Recently introduced pathogens initially induce resistance responses, but natural selection favors the development of tolerance, allowing for a commensal relationship to evolve. Mycosis by Pseudogymnoascus destructans, causing white-nose syndrome (WNS) in Nearctic hibernating bats, has resulted in population declines since 2006. The pathogen, which spread from Europe, has infected species of Palearctic Myotis for a longer period. We compared ecologically relevant responses to the fungal infection in the susceptible Nearctic M. lucifugus and less susceptible Palearctic M. myotis, to uncover factors contributing to survival differences in the two species. Samples were collected from euthermic bats during arousal from hibernation, a naturally occurring phenomenon, during which transcriptional responses are activated. We compared the whole-transcriptome responses in wild bats infected with P. destructans hibernating in their natural habitat. Our results show dramatically different local transcriptional responses to the pathogen between uninfected and infected samples from the two species. Whereas we found 1526 significantly upregulated or downregulated transcripts in infected M. lucifugus, only one transcript was downregulated in M. myotis. The upregulated response pathways in M. lucifugus include immune cell activation and migration, and inflammatory pathways, indicative of an unsuccessful attempt to resist the infection. In contrast, M. myotis appears to tolerate P. destructans infection by not activating a transcriptional response. These host-microbe interactions determine pathology, contributing to WNS susceptibility, or commensalism, promoting tolerance to fungal colonization during hibernation that favors survival. Graphic abstract

A Cylindrocarpon species with up to 10 microm wide, straight and predominantly 3-septate macroconidia, subglobose to ovoidal microconidia and chlamydospores, is described as Cyl. pauciseptatum. It is most similar to Cyl. austrodestructans but no chlamydospores and microconidia are formed in the latter. Similar macroconidia also occur in Cyl. theobromicola, which forms oval to ellipsoidal microconidia at least sparsely and has slightly curved macroconidia, and Cyl. destructans var. crassum, which forms abundant 1-celled microconidia. DNA sequence data of the internal transcribed spacer regions 1 and 2 plus the 5.8S rDNA and the partial beta-tubulin gene were used for phylogenetic inferences. Cylindrocarpon pauciseptatum and Cyl. macrodidymum are monophyletic and are closely related to other species of Cylindrocarpon sensu stricto including members of the Cyl. destructans (teleomorph, Neonectria radicicola) species complex, which accommodates Cyl. liriodendri (teleomorph, Neon. liriodendri), Cyl. destructans var. crassum and Cyl. austrodestructans (teleomorph, Neonectria austroradicicola comb. nov.). Cylindrocarpon theobromicola is distantly related to species of Cylindrocarpon sensu stricto or Neonectria sensu stricto. It clustered among cylindrocarpon-like species with curved macroconidia, of which some belong to the Neon. mammoidea group. Relatively voluminous cells in sporodochial conidiophores of Cyl. theobromicola resembled those described for Campylocarpon, which is closely related to members of the Neon. mammoidea group including Cyl. theobromicola. Cylindrocarpon pauciseptatum has been isolated from roots of Vitis spp. in South-eastern Europe (Slovenia) as well as New Zealand, where it also occurs on roots of Erica melanthera.