Disentangling interactions among mercury, immunity, and infection in a Neotropical bat community

Abstract

381. Contaminants such as mercury are pervasive and can have immunosuppressive effects on 39 wildlife. Impaired immunity could be important for forecasting pathogen spillover risks, 40 as many land-use changes that generate mercury contamination can also bring wildlife 41 reservoir hosts into close contact with humans and domestic animals. However, the 42 interactions between contaminants, immunity, and infection are difficult to study in 43 natural systems, and empirical tests of possible directional relationships remain rare. 44 2. We capitalized on extreme mercury variation in a diverse Neotropical bat community in 45 Belize to test association between contaminants, immunity, and infection. By comparing 46 a previous dataset of bats sampled in 2014 with new data from 2017, we first confirmed 47 bat species with more aquatic prey in their diet had higher fur mercury. We then tested 48 covariation between mercury and cellular immunity and determined if such relationships 49 mediated associations between mercury and common bacterial pathogens (hemoplasmas 50 and Bartonella). Lastly, as bat ecology can dictate exposure to mercury and pathogens, 51 we also assessed species-specific patterns in these mercury-infection relationships. 52 3. Across the bat community, individuals with higher mercury had fewer neutrophils but not 53 lymphocytes, suggesting stronger associations with innate immunity. However, the odds 54 of infection for both pathogens were generally lowest in bats with high mercury, and 55 relationships between mercury and immunity did not mediate infection patterns. When 56 considering species-specific relationships between mercury and infection, mercury was 57 associated with especially low odds for Pteronotus mesoamericanus and Dermanura 58 phaeotis for hemoplasmas. Yet for Bartonella, mercury was associated with particularly 59 low odds in the genus Pteronotus but especially high odds within the Stenodermatinae.60 4. Synthesis and application: Lower infection risk in bats with high mercury despite weaker 61 innate defense suggests contaminant-driven loss of pathogen habitat (i.e., anemia) or 62 vector mortality as possible causal mechanisms. Strong positive associations between 63 mercury and Bartonella in the Stenodermatinae, however, alongside negative 64 associations between mercury and neutrophils in this clade, suggest these bats could be 65 especially vulnerable to immunosuppression. Greater attention to these potential causal 66 pathways could help disentangle the complex relationships between environmental 67 contaminants, immunity, and infection in natural systems and forecast disease risks. 68 69Wildlife are commonly exposed to a range of contaminants that are ubiquitous in the 70 environment, including heavy metals, organic compounds, and pesticides (Smith et al., 2007).

Worldwide occurrence of haemoplasmas in wildlife: Insights into the patterns of infection, transmission, pathology and zoonotic potential

“…Similarly, high food availability in urban areas was suggested to explain lower haemoplasma prevalence in rodents compared to those in forest fragments owing to more robust immune defence or to less frequent aggressive interactions from reduced food competition (Gonçalves et al, 2020). Lastly, Neotropical bats with higher dietary exposure to mercury, a heavy metal, generally had lower odds of haemoplasma infection, suggesting that contaminants might eliminate bacterial habitat through anaemia or cause mortality of possible arthropod vectors (Becker, Speer, Korstian, et al, 2020).…”

Disentangling interactions among mercury, immunity and infection in a Neotropical bat community

“…Data are available via the Dryad Digital Repository https://doi.org/10.5061/dryad.70rxwdbwb (Becker, Speer, Korstian, et al, 2020).…”

Avian influenza antibody prevalence increases with mercury contamination in wild waterfowl

“…inflammation [9,38–41]) and the adaptive immune response (e.g. lymphocyte production [38,42,43], antibody titres [10]). Both innate and adaptive immunity influence the probability and severity of influenza infection [44,45], so mercury contamination could affect the prevalence of influenza infection and its impacts waterfowl populations.…”

“…MeHg can also alter immune function in mammals and birds [37], including compromising both the innate immune response (e.g. inflammation [9,38–41]) and the adaptive immune response (e.g. lymphocyte production [38,42,43], antibody titres [10]).…”