Roost selection and roost switching of female Bechstein’s bats (Myotis bechsteinii) as a strategy of parasite avoidance

Taking cues from ecological and evolutionary theories to expand the landscape of disgust

Behavioural avoidance of parasites in the environment generates what is known as the 'landscape of disgust' (analogous to the predator-induced 'landscape of fear'). Despite the potential for improving our inference of host-parasite dynamics, three limitations of the landscape of disgust restrict the insight that is gained from current research: (i) many host-parasite systems will not be appropriate for invoking the landscape of disgust framework; (ii) existing research has primarily focused on immediate choices made by hosts on small scales, limiting predictive power, generalizability, and the value of the insight obtained; and (iii) relevant ecological and evolutionary theory has yet to be integrated into the framework, challenging our ability to interpret the landscape of disgust within the context of most host-parasite systems. In this review, we explore the specific requirements for implementing a landscape of disgust framework in empirical systems. We also propose greater integration of habitat selection and evolutionary theories, aiming to generate novel insight, by exploring how the landscape of disgust varies within and across generations, presenting opportunities for future research. Despite interest in the impacts of parasitism on animal movement and behaviour, many unanswered questions remain.

Gastrointestinal parasitic helminths of bats from a cave in Luzon Island, Philippines

Bats are often associated with several zoonotic diseases, including helminth infections. Despite their potential detrimental effects on both human and bat populations, information on helminth parasites of Philippine bats remains scarce. Here, we identify gastrointestinal helminths parasitizing bats collected from a cave complex in Cavinti, Laguna Province, Philippines, determine their prevalence (P) and mean intensity (MI), and investigate relationship of helminth prevalence and intensity with bat host characteristics including sex, diet, age, and roosting habit. We isolated 581 individuals of helminths representing six taxa (three trematodes, two nematodes, one cestode) from the gastrointestinal tract of sampled bats. Helminths were observed in 82 out of 172 bats captured (P = 47.67%), with Miniopteruspaululus having the highest infection rate (P = 91.3%) and highest MI (18 ± 4.5/infected bat). Helminths parasitizing endemic bat species from the Philippines, such as Rhinolophus rufus, Rhinolophus inops, Hipposideros pygmaeus, and Ptenochirus jagori were reported here for the first time. We provide new host records for other helminth species and report the presence of two parasites, Plagiorchis sp. and Toxocara sp., known for their zoonotic potential. These data will contribute to efforts in identifying parasites and diseases harbored by bats in the country and develop additional conservation measures for bats.

Season and host-community composition inside roosts may affect host-specificity of bat flies

Bat flies are one of the most abundant ectoparasites of bats, showing remarkable morphological adaptations to the parasitic habit, while the relationship with their hosts is characterized by a high level of specificity. By collecting bat flies from live hosts, our intention was to elucidate the seasonal differences in bat fly occurrence and to describe factors regulating the level of incipient host specificity. Our results indicate that the prevalence and the intensity of infestation is increasing from spring to autumn for most host species, with significant differences among different fly species. Males showed higher infestation levels than females in autumn, suggesting a non-random host choice by flies, targeting the most active host sex. Bat-bat fly host specificity shows seasonal changes and host choice of bat flies are affected by the seasonal differences in hosts' behavior and ecology, the intensity of infestation and the species composition of the local host community. Nycteribiid bat flies showed lower host specificity in the swarming (boreal autumn) period, with higher prevalence recorded on non-primary hosts. Choosing a non-primary bat host may be an adaptive choice for bat flies in the host's mating period, thus increasing their dispersive ability in a high activity phase of their hosts.

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.

Network and parasitological analyses reveal latitudinal gradient in bats-ectoparasitic fly interactions across the Neotropic

Ecological interactions between parasites and their hosts play a fundamental role in evolutionary processes. Selection pressures are exerted on parasites and their hosts, usually resulting in high levels of specificity. Such is the case of ectoparasitic bat-flies, but how large-scale spatial gradients affect the dynamics of their interactions with their bat hosts is still unknown. In the present study, we investigated interaction patterns between bats and their ectoparasitic flies (Streblidae and Nycteribiidae), both presenting their peak of diversity in the Neotropical region, along a latitudinal gradient. Using network analyses and parasitic indices, grounded on the latitudinal diversity gradient pattern, we evaluated how spatial gradients affect species interactions and parasitic indices at the biogeopraphic scale, with increasing species richness in interaction networks closer to the tropics, leading to increases in network modularity, size, and specialization, and to a decrease in nesting and connectivity. We conducted a literature review, focusing on studies done in the Neotropical region, and own data. We obtained a bat richness of 97 species parasitized by 128 species of ectoparasitic flies, distributed into 57 interaction networks between latitudes 29° S and 19° N in the Neotropic. Network metrics and parasitic indices varied along the latitudinal gradient, with changes in the richness of bats and their ectoparasitic flies and in the structure of their interactions; network specialization, modularity, and connectance increase with latitude, while network size decreases with latitude. Regions closer to the equator had higher parasite loads. Our results show that interaction network metrics present a latitudinal gradient and that such interactions, when observed at a local scale, hide variations that only become perceptible at larger scales. In this way, ectoparasites such as bat flies are not only influenced by the ecology and biology of their hosts, but also by other environmental factors acting directly on their distribution and survival.

Differential selection of roosts by Eastern Small-footed Myotis (Myotis leibii) relative to rock structure and microclimate

Roost selection by insectivorous bats in temperate regions is presumably influenced by roost microclimates in relation to thermoregulatory strategies, but few studies have included temperature measurements in habitat selection models. Rocky landscape features are an important source of roosts that provide both shelter from predators and beneficial microclimates for bats. Most information about rock-roosting bats has been derived from western North America. We studied microhabitat selection by the Eastern Small-footed Myotis (Myotis leibii) on natural talus slopes and human-made stone structures in the Appalachian Mountains of Virginia and New Hampshire, relative to thermal and structural characteristics of rock crevices. Roosts were located with a combination of radiotelemetry and randomized visual surveys. Roost-switching behavior and structural characteristics of roosts did not appear to be influenced by the methods we used to locate roosts. Compared to random crevices, both sexes selected crevices with narrow openings, likely to provide protection from predators. Reproductive females also selected rocks that were larger and more thermally stable than random crevices, whereas males selected crevices that were structurally similar to random crevices but warmed more during the day. Rock size and other structural characteristics influenced temperatures of roosts and random crevices alike by inhibiting excessive daytime heating and nighttime cooling. Because large rocks were important for reproductive females, and talus slopes with large rocks could be limited, we recommend including rock size as a variable in landscape scale habitat assessments for Eastern Small-footed Myotis. Protecting or managing for habitat features with large rocks that receive high solar exposure could benefit Eastern Small-footed Myotis, and perhaps other rock-roosting species.

Continuous low-intensity predation by owls (Strix aluco) on bats (Nyctalus lasiopterus) in Spain and the potential effect on bat colony stability

Owls prey on bats, but information on owl predation is scarce, its impact on bat mortality is unclear, and reports on behavioural responses, including roost-switching and fission-fusion behaviour, are equivocal. To study the link between owl predation and anti-predator behaviour in bats, we evaluated seven months of video recordings at roosts and the behaviour of 51 passive integrated transponder (PIT)-tagged bats and bats without tags in a geographically isolated colony of greater noctule bats (Nyctalus lasiopterus) in Spain. We found the tawny owl Strix aluco to almost continuously hunt N. lasiopterus, from perches and on the wing, well after the bats emerged at dusk and when they returned to their roosts. We recorded 39 unsuccessful and three successful attacks. Nonetheless, we found no evidence that owl predation modifies bat behaviour. While the bats constituted only a very small proportion of the owls' diet, owl predation accounted for an estimated 30-40% of bat mortality, which may have a significant impact on small, local or isolated bat populations, in particular, and thereby shape regional bat distributions. We hypothesize that low roost availability may also affect the bats' potential response to predation, which could lead to natural predation having an excessive impact on bat populations.

The impact of habitat loss on molecular signatures of coevolution between an iconic butterfly (Alcon blue) and its host plant (Marsh gentian)

Habitat loss is threatening natural communities worldwide. Small and isolated populations suffer from inbreeding and genetic drift, which jeopardize their long-term survival and adaptive capacities. However, the consequences of habitat loss for reciprocal coevolutionary interactions remain poorly studied. In this study, we investigated the effects of decreasing habitat patch size and connectivity associated with habitat loss on molecular signatures of coevolution in the Alcon blue butterfly (Phengaris alcon) and its most limited host, the marsh gentian (Gentiana pneumonanthe). Because reciprocal coevolution is characterized by negative frequency-dependent selection as a particular type of balancing selection, we investigated how signatures of balancing selection vary along a gradient of patch size and connectivity, using single nucleotide polymorphisms (SNPs). We found that signatures of coevolution were unaffected by patch characteristics in the host plants. On the other hand, more pronounced signatures of coevolution were observed in both spatially isolated and in large Alcon populations, together with pronounced spatial variation in SNPs that are putatively involved in coevolution. These findings suggest that habitat loss can facilitate coevolution in large butterfly populations through limiting swamping of locally beneficial alleles by maladaptive ones. We also found that allelic richness (Ar) of the coevolutionary SNPs is decoupled from neutral Ar in the butterfly, indicating that habitat loss has different effects on coevolutionary as compared with neutral processes. We conclude that this specialized coevolutionary system requires particular conservation interventions aiming at generating a spatial mosaic of both connected and of isolated habitat to maintain coevolutionary dynamics.

Mother-to-daughter transmission of hygienic anti-parasite behaviour in mandrills

Social animals are particularly exposed to infectious diseases. Pathogen-driven selection pressures have thus favoured the evolution of behavioural adaptations to decrease transmission risk such as the avoidance of contagious individuals. Yet, such strategies deprive individuals of valuable social interactions, generating a cost-benefit trade-off between pathogen avoidance and social opportunities. Recent studies revealed that hosts differ in these behavioural defences, but the determinants driving such inter-individual variation remain understudied. Using 6 years of behavioural and parasite data on a large natural population of mandrills (Mandrillus sphinx), we showed that, when parasite prevalence was high in the population, females avoided grooming their conspecifics' peri-anal region (PAR), where contagious gastro-intestinal parasites accumulate. Females varied, however, in their propensity to avoid this risky body region: across years, some females consistently avoided grooming it, while others did not. Interestingly, hygienic females (i.e. those avoiding the PAR) were less parasitized than non-hygienic females. Finally, age, dominance rank and grooming frequency did not influence a female's hygiene, but both mother-daughter and maternal half-sisters exhibited similar hygienic levels, whereas paternal half-sisters and non-kin dyads did not, suggesting a social transmission of this behaviour. Our study emphasizes that the social inheritance of hygiene may structure behavioural resistance to pathogens in host populations with potential consequences on the dynamics of infectious diseases.

Review of studies about bat-fly interactions inside roosts, with observations on partnership patterns for publications

Pressures from anthropogenic disturbances have triggered a wealth of studies focusing on the assessment and mitigation of the negative impacts of these disturbances on inter and intraspecific ecological interactions, including bats and bat flies in their roosts. The heterogeneity of research methods employed for these studies and the scientific imbalance between countries may constrain advances and the consolidation of the knowledge on this subject. We reviewed the literature regarding bat and bat-ectoparasite interactions in roosts assessing global research trends and patterns of author collaborative work to be able to identify key questions for future studies and potential initiatives to improve the knowledge on this subject. Current information available has mostly come from the Americas and is predominantly focused on the recognition and description of parasite-host interactions between bats and bat flies. Our findings suggest the value of increasing collaboration for future research, as several countries with largely diverse environments and high organismal richness are disconnected from the countries that produce the most publications in this area, and/or have low records of publications. These regions are in the Global South, mostly in South American and African countries. We suggest that more collaborative networks may increase scientific production in the area, and that investing in local research development and enhancing partnerships for publications may strengthen the field. These research programs and collaborations are key for the development of conservation strategies for bats and bat flies, for their roosts, and for understanding bat and bat-ectoparasite interactions.

Demographic characteristics shape patterns of dawn swarming during roost switching in tree-dwelling Daubenton's bat

Frequent roost switching in fission-fusion societies of tree-dwelling bats is closely associated with swarming behaviour entailing ritualised night-time displays around the roost tree and/or at the roost entrance to signal its actual location, particularly immediately prior to sunrise. However, effects of demographic characteristics of individuals in this social behaviour remain unanswered. Using passive integrated transponders (PIT) and automatic readers, we recorded swarming activity of members of a Daubenton's bat (Myotis daubentonii) maternity colony in the vicinity of their roosts. In total, 59,622 activity events of 281 PIT-tagged individuals were recorded on ten monitored roosts during three summer seasons. We found a gradual increase of swarming activity from midnight to sunrise in old adult females, whereas young females and juveniles primarily swarmed later at dawn. We attribute this difference to the learning status of younger bats, which are not yet able to perform a defined pattern of swarming activity, whereas older bats likely take a more active role in signalling the position of the roost. Old males exhibited the least swarming activity at maternity roosts, which mostly occurred between crepuscular periods, presumably due to their solitary lives. A negative correlation between genetic distance and swarming activity suggests an important role of kinship in the formation of the maternity colony as well as group cohesion during roost switching.

Long-term field studies in bat research: importance for basic and applied research questions in animal behavior

Animal species differ considerably in longevity. Among mammals, short-lived species such as shrews have a maximum lifespan of about a year, whereas long-lived species such as whales can live for more than two centuries. Because of their slow pace of life, long-lived species are typically of high conservation concern and of special scientific interest. This applies not only to large mammals such as whales, but also to small-sized bats and mole-rats. To understand the typically complex social behavior of long-lived mammals and protect their threatened populations, field studies that cover substantial parts of a species' maximum lifespan are required. However, long-term field studies on mammals are an exception because the collection of individualized data requires considerable resources over long time periods in species where individuals can live for decades. Field studies that span decades do not fit well in the current career and funding regime in science. This is unfortunate, as the existing long-term studies on mammals yielded exciting insights into animal behavior and contributed data important for protecting their populations. Here, I present results of long-term field studies on the behavior, demography, and life history of bats, with a particular focus on my long-term studies on wild Bechstein's bats. I show that long-term studies on individually marked populations are invaluable to understand the social system of bats, investigate the causes and consequences of their extraordinary longevity, and assess their responses to changing environments with the aim to efficiently protect these unique mammals in the face of anthropogenic global change.

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.

Mother bats facilitate pup navigation learning

Learning where to forage and how to navigate to foraging sites are among the most essential skills that infants must acquire. How they do so is poorly understood. Numerous bat species carry their young in flight while foraging. This behavior is costly, and the benefits for the offspring are not fully clear. Using GPS tracking of both mothers and bat pups, we documented the pups' ontogeny from being non-volant to foraging independently. Our results suggest that mothers facilitate learning of navigation, assisting their pups with future foraging, by repeatedly placing them on specific trees and by behaving in a manner that seemed to encourage learning. Once independent, pups first flew alone to the same sites that they were carried to by their mothers, following similar routes used by their mothers, after which they began exploring new sites. Notably, in our observations, pups never independently followed their mothers in flight but were always carried by them, suggesting that learning occurred while passively being transported upside down.

Mixed-species groups in bats: non-random roost associations and roost selection in neotropical understory bats

BACKGROUND

Mixed-species groups in animals have been shown to confer antipredator, foraging and other benefits to their members that may provide selective advantages. In most cases, however, it is unclear whether functional benefits are a principal driver of heterospecific groups, or whether groups simply result from simultaneous exploitation of common resources. Mixed-species groups that form independently of environmental conditions may, however, evidence direct benefits of species associations. Bats are among the most gregarious mammals, with sometimes thousands of individuals of various species roosting communally. Despite numerous potential functional benefits of such mixed-species roosting groups, interspecific attraction has never been shown. To explore alternative explanations for mixed-species roosting, we studied roost selection in a speciose neotropical understory bat community in lowland rainforest in Costa Rica. Long term roost data were recorded over 10 years in a total of 133 roosts comprising both natural roosts and structurally uniform artificial roosts. We modelled bat roost occupancy and abundance in each roost type and in forest and pasture habitats to quantify the effects of roost- and environmental variability.

RESULTS

We found that bat species presence in natural roosts is predictable from habitat and structural roost parameters, but that the presence and abundance of other bat species further modifies roost choice. One third of the 12 study species were found to actively associate with selected other bat species in roosts (e.g. Glossophaga commissarisi with Carollia sowelli). Other species did not engage in communal roosting, which in some cases indicates a role for negative interspecific interactions, such as roost competition.

CONCLUSIONS

Mixed-species roosting may provide thermoregulatory benefits, reduce intraspecific competition and promote interspecific information transfer, and hence some heterospecific associations may be selected for in bats. Overall, our study contributes to an improved understanding of the array of factors that shape diverse tropical bat communities and drive the dynamics of heterospecific grouping in mammals more generally.

Associations between Afrotropical bats, eukaryotic parasites, and microbial symbionts

Skin is the largest mammalian organ and the first defensive barrier against the external environment. The skin and fur of mammals can host a wide variety of ectoparasites, many of which are phylogenetically diverse, specialized, and specifically adapted to their hosts. Among hematophagous dipteran parasites, volatile organic compounds (VOCs) are known to serve as important attractants, leading parasites to compatible sources of blood meals. VOCs have been hypothesized to be mediated by host‐associated bacteria, which may thereby indirectly influence parasitism. Host‐associated bacteria may also influence parasitism directly, as has been observed in interactions between animal gut microbiota and malarial parasites. Hypotheses relating bacterial symbionts and eukaryotic parasitism have rarely been tested among humans and domestic animals, and to our knowledge have not been tested in wild vertebrates. In this study, we used Afrotropical bats, hematophagous ectoparasitic bat flies, and haemosporidian (malarial) parasites vectored by bat flies as a model to test the hypothesis that the vertebrate host microbiome is linked to parasitism in a wild system. We identified significant correlations between bacterial community composition of the skin and dipteran ectoparasite prevalence across four major bat lineages, as well as striking differences in skin microbial network characteristics between ectoparasitized and nonectoparasitized bats. We also identified links between the oral microbiome and presence of malarial parasites among miniopterid bats. Our results support the hypothesis that microbial symbionts may serve as indirect mediators of parasitism among eukaryotic hosts and parasites.

see also the Perspective by Kelly A. Speer

Environmental and individual determinants of fecal avoidance in semi-free ranging woolly monkeys (Lagothrix lagotricha poeppigii)

OBJECTIVES

Parasite selection pressures have driven the evolution of numerous behavioral defenses in host species, but recent studies revealed individual variation in their expression. As little is known about the factors causing heterogeneity among individuals in infection-avoidance behaviors, we investigated in woolly monkeys (Lagothrix lagotricha poeppigii) the influence of several environmental and individual characteristics on the tendency to avoid food contaminated by soil and by their own and conspecifics' feces.

MATERIALS AND METHODS

We conducted feeding tests on 40 semi-free ranging individuals rescued from the pet trade. Using generalized linear mixed models, we investigated the effect of season, sex, age, dominance rank, and exposure to non-natural living conditions on feeding decisions.

RESULTS

Woolly monkeys did not avoid soil-contaminated food and equally avoided food contaminated by their own and conspecifics' feces. Individuals varied greatly in their level of fecal avoidance. Only females exhibited strong avoidance of fecally contaminated food, but adapted their behavior to food availability, highlighting the trade-off between nutritional intake and parasite avoidance. Additionally, low-ranking females, less competitive over food resources, exhibited lower avoidance than dominant ones. Juveniles were more cautious than adults, possibly to compensate for a higher parasite susceptibility. Finally, we reported an unknown effect of exposure to non-natural living conditions on behavioral defenses, as animals kept as household pets for an extended period apparently lost their ability to avoid fecally contaminated food.

CONCLUSION

We argue that striving to understand variation in infection-avoidance behaviors in natural populations is crucial to predict disease spread and inform conservation policies.

Analysis of astrovirus transmission pathways in a free-ranging fission-fusion colony of Natterer’s bats (Myotis nattereri)

Abstract

Bats are a diverse and widespread order of mammals. They fulfill critical ecosystem roles but may also act as reservoirs and spreaders for zoonotic agents. Consequently, many recent studies have focused on the potential of bats to spread diseases to other animals and to humans. However, virus transmission networks within bat colonies remain largely unexplored. We studied the detection rate and transmission pathway of astroviruses in a free-ranging Natterer’s bat colony (Myotis nattereri) that exhibits a high fission-fusion dynamic. Based on automatic roost monitoring data of radio-frequency identification tagged bats, we assessed the impact of the strength of an individual’s roosting associations with all other colony members (weighted degree), and the number of roost sites (bat boxes) an individual used—both being proxies for individual exposure risk—on the detected presence of astrovirus-related nucleic acid in individual swab samples. Moreover, we tested to which degree astrovirus sequence types were shared between individuals that frequently roosted together, as proxy for direct transmission risk, and between bats sharing the same roost sites in close temporal succession, as proxy for indirect transmission risk. Neither roosting associations nor the number of different roost sites had an effect on detected virus presence in individual bats. Transmission network data suggest that astroviruses are transmitted both via direct and indirect contact, implying that roost sites pose a risk of astrovirus infection for several days after the bats leave them. Our study offers novel insights in the presence and transmission of viruses within social networks of bat colonies.

Significance statement

Bats provide many ecosystem services but have moved into the focus of virological research as potential carriers of zoonotic disease agents. However, the sparse information available about virus transmission within bat colonies is solely based on simulated transmission data. In this field study, we examined the daily roosting behavior in a wild bat colony in relation to the presence of viruses in individual colony members. Our findings suggest that astroviruses are transmitted by direct contact and via contaminated roost sites. Bats typically defecate in their roost sites, and astroviruses can remain infectious in feces for several days. The here observed virus diversity and roosting behavior suggest that bats can contract astroviruses even if they use contaminated roost sites days after infected individuals have left. This study provides first-time insights in the transmission of astroviruses within bat colonies in the wild.

An agent-based algorithm resembles behaviour of tree-dwelling bats under fission-fusion dynamics

Utilization of computational approach in the study of social behaviour of animals is increasing and we attempted such an approach in our study of tree-dwelling bats. These bats live in highly dynamic fission-fusion societies that share multiple roosts in a common home range. The key behavioural component associated with complex and non-centralized decision-making processes in roost switching is swarming around potential locations in order to recruit members to the new roost. To understand roost switching dynamics of bat groups in their natural environment, we employed a computational model, the SkyBat, which is based on swarm algorithm, to model this process. In a simulated environment of this agent-based model, we replicated natural fission-fusion dynamics of the Leisler's bat, Nyctalus leisleri, groups according to predefined species and habitat parameters. Spatiotemporal patterns of swarming activity of agents were similar to bats. The number of simulated groups formed prior to sunrise, the mean number of individuals in groups and the roost height did not differ significantly from data on a local population of bats collected in the field. Thus, the swarm algorithm gave a basic framework of roost-switching, suggesting possible applications in the study of bat behaviour in rapidly changing environments as well as in the field of computer science.

Seasonal changes and the influence of tree species and ambient temperature on the fission-fusion dynamics of tree-roosting bats

Abstract

Many species of bats live in dynamic associations in which individuals aggregate or split into smaller or larger groups, moving between roost sites, but factors influencing group size and roost switching decisions in bats living in fission-fusion societies are poorly understood. To test the extent to which fission-fusion dynamics are species-specific and shaped by environmental factors, we radio-tracked two closely related species: noctule bats Nyctalus noctula and Leisler’s bats N. leisleri in well-preserved, old-growth stands of the Białowieża Forest, where roost availability and diversity is high and bats can potentially freely exhibit fission-fusion behaviour. We estimated the number of bats per roost and noted the tree species selected as roost sites. We evaluated the influence of ambient temperature and roost tree species on bat group size and the process of roost switching, and their seasonal component. Our results revealed that bat group size showed species-specific differences in seasonal variation, relationship to ambient temperature and tree species. The number of noctule bats emerging from a roost was relatively stable with a weak tendency to decrease during the breeding season while the number of Leisler’s bats emerging from a roost increased when the juveniles started to be volant. Group size of noctule bats increased with ambient temperature. Leisler’s bats formed smaller colonies in oaks and ashes than in other tree species. Roost switching rate was associated with ambient temperature and tree species selected by the bats. The bats changed roosts more frequently when the minimum ambient temperature increased, and less often in ashes than in oaks and other tree species. Our results show that bat group size and roost switching behaviour are shaped by both environmental factors and the stage of reproduction.

Significance statement

Environmental factors may affect group size and roost switching behaviour of bats forming fission-fusion associations, but this is expected to vary depending on body size, environmental conditions, as well as seasonally. Few studies have explored this behaviour in tree-dwelling bats and examined how it differs between species. Here, we studied the group size dynamics and the process of roost switching in closely related bat species living in well-preserved, European old-growth forests, for which the knowledge of these patterns is particularly poor. We demonstrate for the first time that bat group size and roost switching rate relates to roost tree species selected by bats, the ambient temperature and varies seasonally, and that these effects are species-specific. The results point out the importance of the availability of suitable roost trees providing a range of microclimatic conditions for maintaining efficient fission-fusion dynamics throughout the reproductive period.

Effects of fungal infection on the survival of parasitic bat flies

Background

Parasites are able to alter numerous aspects of their hosts’ life history, behaviour and distribution. One central question in parasitology is to determine the degree of impact that parasites have on their hosts. Laboulbeniales (Fungi: Ascomycota) are ectoparasitic fungi of arthropods. Even though these fungi are widely distributed, little is known about their ecology and their possible physiological effects on their hosts. We used a highly specific bat fly-fungi association to assess the effect of these fungal parasites on their dipteran hosts.

Methods

We collected bat flies (Diptera: Nycteribiidae) belonging to two species, Nycteribia schmidlii and Penicillidia conspicua from their bat host Miniopterus schreibersii (Chiroptera: Miniopteridae). We experimentally tested the effect of infection on the lifespan of bat flies.

Results

The prevalence of Laboulbeniales fungi was 17.9% in N. schmidlii and 64.8% in P. conspicua. Two fungi species were identified, Arthrorhynchus eucampsipodae and A. nycteribiae, both showing strict host specificity with N. schmidlii and P. conspicua, respectively. We found that fungal infection reduced by half the survival rate of P. conspicua regardless of sex, whereas N. schmidlii was not affected by the infection. Moreover, the intensity of infection showed negative correlation with the lifespan of P. conspicua.

Conclusions

To our knowledge, this is the first indication that fungal infection can alter bat fly survival and thus may play a significant role in the population dynamics of these bat ectoparasites.

Social calls of Myotis nattereri during swarming: Call structure mirrors the different behavioral context

Swarming is a characteristic behavior of bats that occurs in different social contexts. We studied the swarming behavior of Myotis nattereri at a maternity colony and at an autumn swarming site in South-West Germany by using synchronized sound and video recordings. Swarming was always associated with social vocalizations consisting of four frequently occurring call types. Call type A was a short call with a broadband steep-shallow-steep downward frequency modulation. Call type B consisted of two elements beginning with a broadband upward hooked element followed by a steep frequency modulated element. Call type C showed a characteristic rapid downward-upward-downward frequency modulation. Call type D was a long sinusoidal trill-like call with high variability in signal structure. All call types were recorded at the maternity colony, as well as at the autumn swarming site, but the incidence of each call type differed distinctly between the study sites. At the maternity roost, type A calls were most commonly produced. We found evidence for an individual signature in this call type and suggest that this social call has the function of a contact call in Natterer’s bats. At the autumn swarming site, type D calls were the most common social calls; in contrast, this call type was recorded only twice at the maternity roost. The occurrence of trills mainly at the autumn swarming site and their high variability suggests that trills function as male advertisement calls in M. nattereri.

Hygienic personalities in wild grey mouse lemurs vary adaptively with sex

Detecting the risk of infection and minimizing parasite exposure represent the first lines of host defence against parasites. Individuals differ in the expression of these behavioural defences, but causes of such variation have received little empirical attention. We therefore experimentally investigated the effects of several individual and environmental factors on the expression level of faecal avoidance in the context of feeding, drinking, sleeping and defecating in a wild primate population. We found a strong sex bias in the expression level of anti-parasite behaviours of grey mouse lemurs (Microcebus murinus), with only females strongly avoiding contaminated food, water and nests, and exhibiting selective defecation. Our results further suggest that individuals adapted their protective behaviours according to variation in intrinsic and ecological factors that may influence the cost-benefit balance of behavioural defences. Overall, individuals exhibited high consistency of investment in protective behaviours across behavioural contexts and time, suggesting that grey mouse lemurs exhibit different hygienic personalities. Finally, the global hygienic score was negatively correlated with faecal-orally transmitted parasite richness, suggesting that variation in behavioural defence has fitness consequences. We suggest that integrating inter-individual variation in behavioural defences in epidemiological studies should improve our ability to model disease spread within populations.

Flexible roost selection by Gould’s wattled bats (Chalinolobus gouldii) using bat boxes in an urban landscape

Bat boxes are often used as a conservation tool in human-disturbed landscapes across Australia; however, to assess their effectiveness we need to understand the factors influencing their occupancy by insectivorous bats. We investigated roost selection by Gould’s wattled bat (Chalinolobus gouldii) using 76 bat boxes, comprising six designs, across three sites in suburban Melbourne, Australia. We conducted monthly surveys for a year and recorded the physical characteristics of each box. Five species of bats were recorded but Gould’s wattled bats dominated box occupancy year-round at all three sites. Group sizes ranged from 1 to 58 individuals, with maternity colonies forming over summer. There was little consistency in the use of selection criteria by Gould’s wattled bats when choosing a bat box as a day roost, with considerable variability across sites and seasons, highlighting the flexibility in roost site selection by this widespread, adaptable species. Our findings show that bat boxes can be an effective tool for providing supplementary roosts for Gould’s wattled bats in urbanised landscapes. However, little is known about the impact on the whole bat community, especially disturbance-sensitive taxa, of artificially increasing roosting resources for common species.

Laboulbeniales (Fungi: Ascomycota) infection of bat flies (Diptera: Nycteribiidae) from Miniopterus schreibersii across Europe

BACKGROUND

Bat flies (Diptera: Nycteribiidae and Streblidae) are obligate, blood-sucking ectoparasites of bats with specialized morphology, life-cycle and ecology. Bat flies are occasionally infected by different species of Laboulbeniales (Fungi: Ascomycota), microscopic fungal ectoparasites belonging to three genera: Arthrorynchus spp. are restricted to the Eastern Hemisphere, while species of Gloeandromyces and Nycteromyces occur on Neotropical bat flies. Little is known about the distribution and host specificity of Arthrorynchus spp. on bat flies. In this study, we focused on sampling bat flies from the cave-dwelling bat species Miniopterus schreibersii. Bat and ectoparasite collection took place in Albania, Croatia, Hungary, Italy, Portugal, Slovakia, Spain and Switzerland. Flies were inspected for Laboulbeniales infections.

RESULTS

Six hundred sixty seven bat flies of five species were collected: Nycteribia latreillii, N. pedicularia, N. schmidlii, Penicillidia conspicua, and P. dufourii. Laboulbeniales infection was observed on 60 specimens (prevalence = 9%). Two Laboulbeniales species, Arthrorhynchus eucampsipodae and A. nycteribiae, were present on three bat fly species. All observations of A. eucampsipodae were on N. schmidlii, and A. nycteribiae was present on P. conspicua and P dufourii. Arthrorhynchus eucampsipodae is, for the first time, reported from Slovakia and Spain. Arthrorhynchus nycteribiae represents a new country record for Portugal and Slovakia. There were no significant differences among infection rates in different countries. Females of N. schmidlii showed a higher infection rate than males with an observable trend (P = 0.0502). No sex differences in infection rate for P. conspicua and P. dufourii were detected. Finally, thallus density was significantly lower in N. schmidlii compared to P. conspicua and P. dufourii.

CONCLUSIONS

With this study, we contribute to the knowledge of the geographical distribution and host specificity of Laboulbeniales fungi associated with ectoparasitic bat flies within Europe. We discuss parasite prevalence and host specificity in the light of our findings and the available literature. Penicillidia conspicua is unambiguously the main host species for A. nycteribiae based on our and previous findings. Differences in parasite intensity and sex-biased infections of the fungi are possible depending on the species.

Sleeping site ecology, but not sex, affect ecto- and hemoparasite risk, in sympatric, arboreal primates (Avahi occidentalis and Lepilemur edwardsi)

Background

A central question in evolutionary parasitology is to what extent ecology impacts patterns of parasitism in wild host populations. In this study, we aim to disentangle factors influencing the risk of parasite exposure by exploring the impact of sleeping site ecology on infection with ectoparasites and vector-borne hemoparasites in two sympatric primates endemic to Madagascar. Both species live in the same dry deciduous forest of northwestern Madagascar and cope with the same climatic constraints, they are arboreal, nocturnal, cat-sized and pair-living but differ prominently in sleeping site ecology. The Western woolly lemur (Avahi occidentalis) sleeps on open branches and frequently changes sleeping sites, whereas the Milne-Edward’s sportive lemur (Lepilemur edwardsi) uses tree holes, displaying strong sleeping site fidelity. Sleeping in tree holes should confer protection from mosquito-borne hemoparasites, but should enhance the risk for ectoparasite infestation with mites and nest-adapted ticks. Sex may affect parasite risk in both species comparably, with males bearing a higher risk than females due to an immunosuppressive effect of higher testosterone levels in males or to sex-specific behavior. To explore these hypotheses, ectoparasites and blood samples were collected from 22 individuals of A. occidentalis and 26 individuals of L. edwardsi during the dry and rainy season.

Results

L. edwardsi, but not A. occidentalis, harbored ectoparasites, namely ticks (Haemaphysalis lemuris [Ixodidae], Ornithodoros sp. [Argasidae]) and mites (Aetholaelaps trilyssa, [Laelapidae]), suggesting that sleeping in tree holes promotes infestation with ectoparasites. Interestingly, ectoparasites were found solely in the hot, rainy season with a prevalence of 75% (N = 16 animals). Blood smears were screened for the presence and infection intensity of hemoparasites. Microfilariae were detected in both species. Morphological characteristics suggested that each lemur species harbored two different filarial species. Prevalence of microfilarial infection was significantly lower in L. edwardsi than in A. occidentalis. No significant difference in infection intensity between the two host species, and no effect of season, daytime of sampling or sex on prevalence or infection intensity was found. In neither host species, parasite infection showed an influence on body weight as an indicator for body condition.

Conclusions

Our findings support that sleeping site ecology affects ectoparasite infestation in nocturnal, arboreal mammalian hosts in the tropics, whereas there is no significant effect of host sex. The influence of sleeping site ecology to vector-borne hemoparasite risk is less pronounced. The observed parasite infections did not affect body condition and thus may be of minor importance for shaping reproductive fitness. Findings provide first evidence for the specific relevance of sleeping site ecology on parasitism in arboreal and social mammals. Further, our results increase the sparse knowledge on ecological drivers of primate host-parasite interactions and transmission pathways in natural tropical environments.

Electronic supplementary material

The online version of this article (10.1186/s12983-017-0228-7) contains supplementary material, which is available to authorized users.

Sociality influences thermoregulation and roost switching in a forest bat using ephemeral roosts

In summer, many temperate bat species use daytime torpor, but breeding females do so less to avoid interferences with reproduction. In forest-roosting bats, deep tree cavities buffer roost microclimate from abrupt temperature oscillations and facilitate thermoregulation. Forest bats also switch roosts frequently, so thermally suitable cavities may be limiting. We tested how barbastelle bats (Barbastella barbastellus), often roosting beneath flaking bark in snags, may thermoregulate successfully despite the unstable microclimate of their preferred cavities. We assessed thermoregulation patterns of bats roosting in trees in a beech forest of central Italy. Although all bats used torpor, females were more often normothermic. Cavities were poorly insulated, but social thermoregulation probably overcomes this problem. A model incorporating the presence of roost mates and group size explained thermoregulation patterns better than others based, respectively, on the location and structural characteristics of tree roosts and cavities, weather, or sex, reproductive or body condition. Homeothermy was recorded for all subjects, including nonreproductive females: This probably ensures availability of a warm roosting environment for nonvolant juveniles. Homeothermy may also represent a lifesaver for bats roosting beneath loose bark, very exposed to predators, because homeothermic bats may react quickly in case of emergency. We also found that barbastelle bats maintain group cohesion when switching roosts: This may accelerate roost occupation at the end of a night, quickly securing a stable microclimate in the newly occupied cavity. Overall, both thermoregulation and roost-switching patterns were satisfactorily explained as adaptations to a structurally and thermally labile roosting environment.

Sociality, Parasites, and Pathogens in Bats

Little is known about the ecology of many of the parasites and pathogens affecting bats, but host social behavior almost certainly plays an important role in bat-parasite dynamics. Understanding parasite dynamics for bats is important from a human public health perspective because of their role as natural reservoirs for recent high-profile emerging zoonotic pathogens (e.g. Ebola, Hendra) and from a bat conservation perspective because of the recent emergence of white-nose syndrome (WNS) in North America highlighting the potential population impacts of parasites and pathogens. Although some bat species are among the most gregarious of mammals, species vary widely in terms of their social behavior and this variation could influence pathogen transmission and impacts. Here, we review the literature on links between bat social behavior and parasite dynamics. Using standardized search terms in Web of Science, we identified articles that explicitly tested or discussed links between some aspect of bat sociality and parasite transmission or host population impacts. We identified social network analysis, epidemiological modeling, and interspecific comparative analyses as the most commonly used methods to quantify relationships between social behavior and parasite-risk in bats while WNS, Hendra virus, and arthropod ectoparasites were the most commonly studied host-parasite systems. We summarize known host-parasite relationships in these three systems and propose testable hypotheses that could improve our understanding of links between host sociality and parasite-dynamics in bats.

Swarming behaviour associated with group cohesion in tree-dwelling bats

Group living of social species increases the individual survival rate and enhances optimal exploitation of resources within their environment. Groups of cryptic tree-dwelling bats perform frequent roost switching on relatively long distances, whereas groups are temporarily disintegrated during foraging that precedes moving into new roost. In this study, we attempted to elucidate a mechanism in which group members can select new roost from a large set of potential roosting sites without disintegration of the whole group. Exploring the activity at the front of the tree hollows, recorded by automatic infrared monitors, we found that the swarming activity of Leisler's bats was performed during the whole night and was concentrated before the civil twilight at occupied roosts. A generalized linear model revealed significant positive association between the group size and swarming activity while season had negative but smaller effect. As bats swarmed the whole night also at sites that were less occupied or even unoccupied, we suggest that members of a bat colony selected new roost from a potentially larger set of available roosting sites. Thus, we propose a possible signalling role of swarming as a threshold behaviour that ensures group cohesion during roost switching.

Managing Conflict between Bats and Humans: The Response of Soprano Pipistrelles (Pipistrellus pygmaeus) to Exclusion from Roosts in Houses

Conflict can arise when bats roost in human dwellings and householders are affected adversely by their presence. In the United Kingdom, the exclusion of bats from roosts can be licensed under exceptional circumstances to alleviate conflict, but the fate of excluded bats and the impact on their survival and reproduction is not well understood. Using radio-tracking, we investigated the effects of exclusion on the soprano pipistrelle Pipistrellus pygmaeus, a species that commonly roosts in buildings in Europe. Exclusions were performed under licence at five roosts in England in spring, when females were in the early stages of pregnancy. Following exclusion, all bats found alternative roosts and colonies congregated in nearby known roosts that had been used by radio-tagged bats prior to exclusion. We found no difference in roosting behaviour before and after exclusion. Both the frequency of roost switching and the type of roosts used by bats remained unchanged. We also found no change in foraging behaviour. Bats foraged in the same areas, travelled similar distances to reach foraging areas and showed similar patterns of habitat selection before and after exclusion. Population modelling suggested that any reduction in survival following exclusion could have a negative impact on population growth, whereas a reduction in productivity would have less effect. While the number of soprano pipistrelle exclusions currently licensed each year is likely to have little effect on local populations, the cumulative impacts of licensing the destruction of large numbers of roosts may be of concern.