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AC K N OW L E D G M E N T S This study was funded by projects: IB20089 from the Consejería de Economía, Ciencia y Agenda Digital of the Junta de Extremadura and Fondo Europeo de Desarrollo Regional, P11-RNM-7038 from Junta de Andalucía, and PR(19_ECO_0070) from Ayudas Fundación BBVA a Equipos de Investigación Científica 2019. MF was supported by a Juan de la Cierva 2017 Formación contract (FJCI-2017-34394) from the Ministry of Science, Innovation and Universities, by the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie (grant agreement No 844285, ‘EpiEcoMod’) and she is currently funded by a Ramón y Cajal postdoctoral contract (RYC2021- 031613-I) from the Spanish Ministry of Science and Innovation (MICINN). JJP was supported by the Fundación Tatiana Pérez de Guzmán el Bueno. JMP was supported by ProyExcel_00049 financed by Proyectos I+D+i of Junta de Andalucía 2021. LGL was supported by Junta de Extremadura (IB20089, Post-Doc grant). JM was supported by a Juan de la Cierva - Formación contract (FJCI-2017-34109) from the Ministry of Science, Innovation and Universities, and he is currently supported by a postdoctoral researcher contract for scientific excellence under the Plan Propio de I+D+i of the Universidad de Castilla - La Mancha (UCLM), co-funded by the European Social Fund Plus (ESF+). LZG was supported by funds from the Hungary's National Research, Development and Innovation Office (K135841, RRF-2.3.1-21-2022- 00006). We also acknowledge the comments of four anonymous reviewers who improved the final version of this manuscript., DATA AVA I L A B I L I T Y S TAT E M E N T Data supporting the conclusions of this study are available in the supplementary material to this article. Any further details are available from the corresponding author on reasonable request., Aim The increasing spread of vector-borne diseases has resulted in severe health concerns for humans, domestic animals and wildlife, with changes in land use and the introduction of invasive species being among the main possible causes for this increase. We explored several ecological drivers potentially affecting the local prevalence and richness of avian malaria parasite lineages in native and introduced house sparrows (Passer domesticus) populations. Location Global. Time period 2002–2019. Major taxa studied Avian Plasmodium parasites in house sparrows. Methods We analysed data from 2,220 samples from 69 localities across all continents, except Antarctica. The influence of environment (urbanization index and human density), geography (altitude, latitude, hemisphere) and time (bird breeding season and years since introduction) were analysed using generalized additive mixed models (GAMMs) and random forests. Results Overall, 670 sparrows (30.2%) were infected with 22 Plasmodium lineages. In native populations, parasite prevalence was positively related to urbanization index, with the highest prevalence values in areas with intermediate urbanization levels. Likewise, in introduced populations, prevalence was positively associated with urbanization index; however, higher infection occurred in areas with either extreme high or low levels of urbanization. In introduced populations, the number of parasite lineages increased with altitude and with the years elapsed since the establishment of sparrows in a new locality. Here, after a decline in the number of parasite lineages in the first 30 years, an increase from 40 years onwards was detected. Main conclusions Urbanization was related to parasite prevalence in both native and introduced bird populations. In invaded areas, altitude and time since bird introduction were related to the number of Plasmodium lineages found to be infecting sparrows., Consejería de Economía, Innovación, Ciencia y Empleo, Junta de Andalucía, Grant/Award Number: P11-RNM-7038, Fundación BBVA, Grant/Award Number: PR(19_ECO_0070, Junta de Extremadura, Grant/Award Number: IB20089 and PO17024, Marie Sklodowska- Curie Actions, Grant/Award Number: 844285, Ministerio de Ciencia, Innovación y Universidades, Grant/Award Number: FJCI-2017-34109 and FJCI-2017-34394, Proyectos I+D+i of Junta de Andalucía 2021, Grant/Award Number: ProyExcel_00049, Universidad de Castilla- La Mancha

IntroductionInteractions between the gut microbiome (GM) and the immune system influence host health and fitness. However, few studies have investigated this link and GM dynamics during disease in wild species. Bats (Mammalia: Chiroptera) have an exceptional ability to cope with intracellular pathogens and a unique GM adapted to powered flight. Yet, the contribution of the GM to bat health, especially immunity, or how it is affected by disease, remains unknown.MethodsHere, we examined the dynamics of the Egyptian fruit bats’ (Rousettus aegyptiacus) GM during health and disease. We provoked an inflammatory response in bats using lipopolysaccharides (LPS), an endotoxin of Gram-negative bacteria. We then measured the inflammatory marker haptoglobin, a major acute phase protein in bats, and analyzed the GM (anal swabs) of control and challenged bats using high-throughput 16S rRNA sequencing, before the challenge, 24h and 48h post challenge.ResultsWe revealed that the antigen challenge causes a shift in the composition of the bat GM (e.g., Weissella, Escherichia, Streptococcus). This shift was significantly correlated with haptoglobin concentration, but more strongly with sampling time. Eleven bacterial sequences were correlated with haptoglobin concentration and nine were found to be potential predictors of the strength of the immune response, and implicit of infection severity, notably Weissella and Escherichia. The bat GM showed high resilience, regaining the colony’s group GM composition rapidly, as bats resumed foraging and social activities.ConclusionOur results demonstrate a tight link between bat immune response and changes in their GM, and emphasize the importance of integrating microbial ecology in ecoimmunological studies of wild species. The resilience of the GM may provide this species with an adaptive advantage to cope with infections and maintain colony health.

Bats are particularly interesting vertebrates in their response to pathogens owing to extremes in terms of tolerance and resistance. Oxidation is often a by-product of processes involved in the acute phase response, which may result in antimicrobial or self-damaging effects. We measured the immunological and oxidative status responses of Egyptian fruit bats (Rousettus aegyptiacus) to a simulated bacterial infection using lipopolysaccharide injection. As expected, experimental bats exhibited increases in two humoral immunological markers. However, they surprisingly did not show any effects across two markers of oxidative damage and four antioxidant markers. We propose that this lack of effects on oxidative status may be due to a reduction in cell metabolism through sickness behaviours or given life history traits, such as a long lifespan and a frugivorous diet. Finally, the consistency in the pattern of elevation in haptoglobin and lysozyme between current and previous findings highlights their utility as diagnostic markers for extracellular infections in bats.

Spillover of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) to North American white-tailed deer (Odocoileus virginianus) has been documented. However, it is unclear if this is a phenomenon specific to North American deer or is a broader problem. We evaluated pre and pandemic exposure of German and Austrian deer species using a SARS-CoV-2 pseudoneutralization assay. In stark contrast to North American white-tailed deer, we found no evidence of SARS-CoV-2 exposure.

Immunological responses of hibernating mammals are suppressed at low body temperatures, a possible explanation for the devastating effect of the white-nose syndrome on hibernating North American bats. However, European bats seem to cope well with the fungal causative agent of the disease. To better understand the immune response of hibernating bats, especially against fungal pathogens, we challenged European greater mouse-eared bats (Myotis myotis) by inoculating the fungal antigen zymosan. We monitored torpor patterns, immune gene expressions, different aspects of the acute phase response and plasma oxidative status markers, and compared them with sham-injected control animals at 30 min, 48 h and 96 h after inoculation. Torpor patterns, body temperatures, body masses, white blood cell counts, expression of immune genes, reactive oxygen metabolites and non-enzymatic antioxidant capacity did not differ between groups during the experiment. However, zymosan injected bats had significantly higher levels of haptoglobin than the control animals. Our results indicate that hibernating greater mouse-eared bats mount an inflammatory response to a fungal challenge, with only mild to negligible consequences for the energy budget of hibernation. Our study gives a first hint that hibernating European bats may have evolved a hibernation-adjusted immune response in order to balance the trade-off between competent pathogen elimination and a prudent energy-saving regime., Summary: Our experimental immunological study on European bats provides new information on the functionality of the immune system in hibernation. For this we challenged bats with a fungal antigen and measured different immunological parameters.

S1. Site coordinates and livestock density; S2. Stable isotopes of bats and prey; S3. Multivariate analysis of immune function; S4. Livestock biomass and isotopic distance; S5. Sensitivity to holding time

Encroachment of humans into pristine habitats is a major threat to biodiversity. We found that some paleotropical bat species from disturbed forests suffered from chronic stress and an impaired immune system, suggesting that allostatic overload may play a pivotal role in the extinction of wildlife species., Anthropogenic habitat disturbance is a major threat to biodiversity worldwide. Yet, before population declines are detectable, individuals may suffer from chronic stress and impaired immunity in disturbed habitats, making them more susceptible to pathogens and adverse weather conditions. Here, we tested in a paleotropical forest with ongoing logging and fragmentation, whether habitat disturbance influences the body mass and immunity of bats. We measured and compared body mass, chronic stress (indicated by neutrophil to lymphocyte ratios) and the number of circulating immune cells between several bat species with different roost types living in recovering areas, actively logged forests, and fragmented forests in Sabah, Malaysia. In a cave-roosting species, chronic stress levels were higher in individuals from fragmented habitats compared with conspecifics from actively logged areas. Foliage-roosting species showed a reduced body mass and decrease in total white blood cell counts in actively logged areas and fragmented forests compared with conspecifics living in recovering habitats. Our study highlights that habitat disturbance may have species-specific effects on chronic stress and immunity in bats that are potentially related to the roost type. We identified foliage-roosting species as particularly sensitive to forest habitat deterioration. These species may face a heightened extinction risk in the near future if anthropogenic habitat alterations continue.

Supplementary figures and tables showing model averaging results, full model comparison, site and year effects on bat hair THg, relationships between sampling year and bat immunity, and temporal patterns in rainfall across years.

The immune system imposes costs that may have to be traded against investment of resources in other costly life-history traits. Yet, it is unknown if a trade-off between immunity and longevity occurs in free-ranging mammals. Here, we tested if age and survival, two aspects associated with longevity, are linked to immune parameters in an 8 g bat species. Using a combination of cross-sectional and longitudinal data, we assessed whether total white blood cell (WBC) counts, bacterial killing ability of the plasma (BKA) and immunoglobulin G (IgG) concentration change with age. Furthermore, we asked if these immune parameters impose costs resulting in decreased survival probabilities. We found that WBC counts decreased with age both within and among individuals. IgG concentrations were higher in older individuals, but did not change with age within individuals. Furthermore, individuals with above average WBC counts or IgG concentration had lower probabilities to survive the next six months. High WBC counts and IgG concentrations may reflect infections with parasites and pathogens, however, individuals that were infected with trypanosomes or nematodes showed neither higher WBC counts or IgG concentrations, nor was infection connected with survival rates. BKA was higher in infected compared with uninfected bats, but not related to age or survival. In conclusion, cellular (WBC) and humoral (IgG) parts of the immune system were both connected to age and survival, but not to parasite infections, which supports the hypothesis that energetically costly immunological defences are traded against other costly life-history traits, leading to a reduced lifespan in this free-ranging mammal.

Simple Summary The arctic fox is the only native terrestrial mammal in Iceland. The population comprises both “coastal” and “inland” fox ecotypes, with regard to food resources. Because of the relatively low biodiversity within arctic ecosystems and the involvement of the species in both marine and terrestrial ecosystems, the Icelandic arctic fox population could serve as sentinels for the overall ecosystem health of Iceland. After screening the samples from 60 foxes for tick-/vector-borne pathogens, this study reports the near-absence (very low prevalence) of these pathogens in Icelandic arctic foxes in 2011–2012. Taking into account the broad range of target microorganisms analyzed here, as well as the warming climate and increasing presence of the vector Ixodes ricinus in Iceland, our results will be very useful as baseline data for comparison in future monitoring of the emergence of ticks and tick-borne diseases in this country. Abstract The arctic fox (Vulpes lagopus) is the only native terrestrial mammal in Iceland. While red foxes (V. vulpes) are known to be epidemiologically important carriers of several vector-borne pathogens in Europe, arctic foxes have never been evaluated in a similar context on this continent. This has become especially relevant in the last decade, considering the establishing populations of the tick species Ixodes ricinus in Iceland. In this study, liver DNA extracts of 60 arctic foxes, hunted between 2011–2012, were molecularly screened for vector-borne protozoan parasites (Trypanosomatidae, Babesia, Theileria, Hepatozoon) and bacteria (Anaplasma, Ehrlichia, Rickettsia, Borrelia, hemotropic Mycoplasma). One sample was real-time qPCR positive for Anaplasma phagocytophilum, though this positivity could not be confirmed with sequencing. Samples were negative for all other tested vector-borne pathogens. Results of this study indicate that, except for A. phagocytophilum, Icelandic arctic foxes were apparently “not yet infected” with vector-borne pathogens in 2011–2012, or their infections were “below the detection limit” of applied methods. Taking into account the broad range of target microorganisms analyzed here, as well as the warming climate and increasing presence of the vector I. ricinus in Iceland, our results will be very useful as baseline data for comparison in future monitoring of the emergence of ticks and tick-borne diseases in this country.