Sociality, Parasites, and Pathogens in Bats

Improving the science and practice of using artificial roosts for bats

Worldwide, artificial bat roosts (e.g., bat boxes, bark mimics, bat condos) are routinely deployed for conservation, mitigation, and community engagement. However, scant attention has been paid to developing best practices for the use of artificial roosts as conservation tools. Although bats readily occupy artificial roosts, occupancy and abundance data are misleading indicators of habitat quality. Lacking information on bat behavior, health, and fitness in artificial roosts, their conservation efficacy cannot be adequately validated. We considered the proximal and ultimate factors, such as evolutionarily reliable cues, that may prompt bats to preferentially use and show fidelity to suboptimal artificial roosts even when high-quality alternatives are available. Possible negative health and fitness consequences for artificial roost inhabitants include exposure to unstable and extreme microclimates in poorly designed roosts, and vulnerability to larger numbers of ectoparasites in longer lasting artificial roosts that house larger bat colonies than in natural roosts. Bats using artificial roosts may have lower survival rates if predators have easy access to roosts placed in conspicuous locations. Bats may be lured into occupying low-quality habitats if attractive artificial roosts are deployed on polluted urban and agricultural landscapes. To advance the science behind artificial bat roosts, we present testable research hypotheses and suggestions to improve the quality of artificial roosts for bats and decrease risks to occupants. Because continued loss of natural roosts may increase reliance on alternatives, such as artificial roosts, it is imperative that this conservation practice be improved.

Bat cellular immunity varies by year and dietary habit amidst land conversion

Monitoring the health of wildlife populations is essential in the face of increased agricultural expansion and forest fragmentation. Loss of habitat and habitat degradation can negatively affect an animal's physiological state, possibly resulting in immunosuppression and increased morbidity or mortality. We sought to determine how land conversion may differentially impact cellular immunity and infection risk in Neotropical bats species regularly infected with bloodborne pathogens, and to evaluate how effects may vary over time and by dietary habit. We studied common vampire bats (Desmodus rotundus), northern yellow-shouldered bats (Sturnira parvidens) and Mesoamerican mustached bats (Pteronotus mesoamericanus), representing the dietary habits of sanguivory, frugivory and insectivory respectively, in northern Belize. We compared estimated total white blood cell count, leukocyte differentials, neutrophil to lymphocyte ratio and infection status with two bloodborne bacterial pathogens (Bartonella spp. and hemoplasmas) of 118 bats captured in a broadleaf, secondary forest over three years (2017-2019). During this period, tree cover decreased by 14.5% while rangeland expanded by 14.3%, indicating increasing habitat loss and fragmentation. We found evidence for bat species-specific responses of cellular immunity between years, with neutrophil counts significantly decreasing in S. parvidens from 2017 to 2018, but marginally increasing in D. rotundus. However, the odds of infection with Bartonella spp. and hemoplasmas between 2017 and 2019 did not differ between bat species, contrary to our prediction that pathogen prevalence may increase with land conversion. We conclude that each bat species invested differently in cellular immunity in ways that changed over years of increasing habitat loss and fragmentation. We recommend further research on the interactions between land conversion, immunity and infection across dietary habits of Neotropical bats for informed management and conservation.

Effects of host state and body condition on parasite infestation of bent-wing bats

BACKGROUND

Ectoparasites inhabit the body surface or outgrowths of hosts and are usually detrimental to host health and wellbeing. Hosts, however, vary in quality and may lead ectoparasites to aggregate on preferred hosts, resulting in a heterogeneous distribution of parasite load among hosts.

RESULTS

We set out to examine the effects of host individual state and body condition on the parasite load of multiple nycteribiid and streblid bat flies and Spinturnix wing mites on eastern bent-wing bats Miniopterus fuliginosus in a tropical forest in southern Taiwan. We detected a high parasite prevalence of 98.9% among the sampled bats, with nearly 75% of the bats harboring three or more species of parasites. The parasite abundance was higher in the wet season from mid spring to early fall, coinciding with the breeding period of female bats, than in the dry winter season. In both seasonal periods, the overall parasite abundance of adult females was higher than that of adult males. Among the bats, reproductive females, particularly lactating females, exhibited a higher body condition and were generally most infested. The Penicillidia jenynsii and Nycteribia parvula bat flies showed a consistent female-biased infection pattern. The N. allotopa and Ascodipteron speiserianum flies, however, showed a tendency towards bats of a moderate to higher body condition, particularly reproductive females and adult males.

CONCLUSIONS

We found an overall positive correlation between parasite abundance and reproductive state and body condition of the host and female-biased parasitism for M. fuliginosus bats. However, the effects of body condition and female-biased infestation appear to be parasite species specific, and suggest that the mobility, life history, and potential inter-species interactions of the parasites may all play important roles.

Population genetics as a tool to elucidate pathogen reservoirs: Lessons from Pseudogymnoascus destructans, the causative agent of White-Nose disease in bats

Emerging infectious diseases pose a major threat to human, animal, and plant health. The risk of species-extinctions increases when pathogens can survive in the absence of the host. Environmental reservoirs can facilitate this. However, identifying such reservoirs and modes of infection is often highly challenging. In this study, we investigated the presence and nature of an environmental reservoir for the ascomycete fungus Pseudogymnoascus destructans, the causative agent of White-Nose disease. Using 18 microsatellite markers, we determined the genotypic differentiation between 1497 P. destructans isolates collected from nine closely situated underground sites where bats hibernate (i.e., hibernacula) in Northeastern Germany. This approach was unique in that it ensured that every isolate and resulting multilocus genotype was not only present, but also viable and therefore theoretically capable of infecting a bat. The distinct distribution of multilocus genotypes across hibernacula demonstrates that each hibernaculum has an essentially unique fungal population. This would be expected if bats become infected in their hibernaculum (i.e., the site they spend winter in to hibernate) rather than in other sites visited before they start hibernating. In one hibernaculum, both the walls and the hibernating bats were sampled at regular intervals over five consecutive winter seasons (1062 isolates), revealing higher genotypic richness on walls compared to bats and a stable frequency of multilocus genotypes over multiple winters. This clearly implicates hibernacula walls as the main environmental reservoir of the pathogen, from which bats become reinfected annually during the autumn.

Sharing roosts but not ectoparasites: high host-specificity in bat flies and wing mites of Miniopterus schreibersii and Rhinolophus ferrumequinum (Mammalia: Chiroptera)

Schreiber’s bent-winged bat Miniopterus schreibersii and the greater horseshoe bat Rhinolophus ferrumequinum are widespread and common cavernicolous species across southern Europe that host numerous specialized ectoparasite species. The objective of this study was to characterize the species assemblage, genetic diversity, and host specificity of bat flies (Nycteribiidae, Diptera) and wing mites (Spinturnicidae, Acari) found on these bat hosts in Serbia and Bosnia and Herzegovina. Notably, while bat flies lay puparia on the cave walls and can thus be transmitted indirectly, wing mites require direct body contact for transmission. Morphological identification and sequencing of a 710-bp fragment of cytochrome oxidase I gene of 207 bat flies yielded 4 species, 3 on M. schreibersii and 1 on R. ferrumequinum. Sequencing of a 460-bp small subunit ribosomal RNA fragment, in all 190 collected wing mites revealed 2 species, 1 per host. In no case was a parasite associated with 1 host found on the other host. Species and genetic diversity of flies were higher in M. schreibersii, likely reflecting their host’s larger colony sizes and migratory potential. Mite species of both hosts showed similarly low diversity, likely due to their faster life history and lower winter survival. Our findings highlight a remarkably high host-specificity and segregation of ectoparasite species despite direct contact among their hosts in the roost, suggesting a defined host preference in the investigated ectoparasite species. Furthermore, the differences in ectoparasite genetic diversity exemplify the interplay between host and parasite life histories in shaping parasite population genetic structure.

Prevalence of Gastrointestinal Parasites in the Frugivorous and the Insectivorous Bats in Southcentral Nepal

Bats are the only active flying placental mammals and are traditionally classified into mega- and microbats, which are, respectively, herbivorous and insectivorous in feeding habit. Though deforestation, habitat destruction, natural calamities, illegal hunting, and climate changes are the challenging threats for bats, the role of existing gastrointestinal (GI) parasites have not been evaluated yet in Nepal. Thus, the current study aims to determine the prevalence of GI parasites in bats from the Shaktikhor area at the Chitwan district of Southcentral Nepal. From July 2018 to February 2019, a total of 60 fecal samples of bats (30 from frugivorous bats and 30 from the insectivorous bats) were collected. These samples were preserved at 2.5% potassium dichromate solution. The fecal examination was carried out by the direct wet mount, concentrations, acid-fast staining, and sporulation techniques. Overall results showed the prevalence rate of 80% GI parasites. The parasites detected in the insectivorous bats were Ascarid spp., Capillarid sp., Cryptosporidium sp., Eimeria spp., Entamoeba sp., Giardia sp., Hymenolepis spp., Isospora sp., Oxyurid sp., Strongyle, and Strongyloides sp. In contrast, Eimeria sp., Entamoeba sp., and Hymenolepis sp. were detected in the frugivorous bats. Based on a wide diversity of parasite richness and parasitic concurrency measured by the prevalence rates, we suggest that GI parasitism might be a threatening factor in the insectivorous bats in the current study area.