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

Animals are faced with a range of ecological constraints that shape their behavioural decisions. Habitat features that affect resource abundance will also have an impact, especially as regards spatial distribution, which will in turn affect associations between the animals. Here we utilised a network approach, using spatial and genetic data, to describe patterns in use of space (foraging sites) by free-ranging Egyptian fruit bats (Rousettus aegyptiacus) at the Dakhla Oasis in Egypt. We observed a decrease in home range size during spring, when food availability was lowest, which was reflected by differences in space sharing networks. Our data showed that when food was abundant, space sharing networks were less connected and more related individuals shared more foraging sites. In comparison, when food was scarce the bats had few possibilities to decide where and with whom to forage. Overall, both networks had high mean degree, suggesting communal knowledge of predictable food distribution.

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Roosts provide bats with place for daytime sheltering, protection from weather and predators, mating, and social interaction. Movements between multiple roosts are often necessary, either due to limited roost life, changes in roost conditions or demands at different times of the year. Information transfer is an important contributor to day-roosting behaviour and typically exhibits non-random social assortment dynamics. Some individuals appear to explore and share roost discoveries more often than others, though it remains unclear whether associations are stronger between close relatives than less related individuals. In the present study, network analysis, in combination with genetic and spatial data, was used to explore the roosting behaviour of Egyptian fruit bats (Rousettus aegyptiacus) within an isolated deme. Our results showed that the roosts had distinct core-periphery structure. The core of the winter roost network was represented by only two roosts, while in spring, the season of food scarcity, the core was represented by multiple roosts, suggesting their potential role as centres, where information about roosts and foraging sites is exchanged. We found no relationship between relatedness and roost sharing over two seasons. These results provide strong support that Egyptian fruit bats do not roost preferentially with relatives, in contrast to many animal populations where individuals preferentially associate with kin.