Spatial genetic structure among bat hibernacula along the leading edge of a rapidly spreading pathogen

High Diversity and Low Genetic Differentiation Among Geographic Populations of Myotis yumanensis in Western Canada

Myotis yumanensis is a small insectivorous bat distributed in Western North America and is susceptible to white-nose syndrome, a devastating fungal disease. Effective management of the disease in M. yumanensis requires an understanding of its population structure to identify possible routes and barriers of disease transmission. Here we used nine microsatellite loci to investigate genetic variation among 336 M. yumanensis from 10 locations in Western Canada. Our analyses revealed high genetic diversity and low but statistically significant genetic differentiation among several geographic populations. Interestingly, though geographically it was not the most distant, the Lillooet population showed the highest genetic differentiation from others, suggesting factors other than geographic distance also contributed to gene flow in this species. While white-nose syndrome has been reported in M. yumanensis populations in neighbouring Washington State in the United States of America, as of 2023, the causative pathogen was not detected on the wings of our analyzed 336 M. yumanensis bats in Western Canada. However, continuing monitoring is required to provide the most updated information about the white-nose syndrome status in these populations. The knowledge of M. yumanensis population structure in Western Canada will help develop effective management strategies for protecting this bat species from white-nose syndrome.

Prehibernation swarming in temperate bats: a critical transition between summer activity and hibernation

In this contribution to Dr. Brock Fenton's Festschrift, we briefly reflect on Dr. Fenton's seminal works examining bat swarming behaviour in Ontario and use these reflections as a launch pad to conduct a global review on autumn swarming in bats, and underlying hypotheses to explain this behaviour. Our review frames the swarming period as a time of critical transitions, during which bats must balance multiple life history trade-offs, and we consider how various intrinsic and extrinsic factors may contribute to inter- and intraspecific differences in autumn behaviour. We discuss the transition away from summer residency, including maternity colony breakup, day roosting, and migration during autumn. We review key life history elements of swarming, including mating behaviours and associated reproductive condition, genetic exchange during swarming, and variation among sexes, ages, and species. Finally, we discuss the behaviours and physiological states of bats transitioning from the swarming period to hibernation. Throughout, we identify common patterns and also exceptions. Over 50 years of research has yielded many insights into autumn swarming, but knowledge gaps remain. Future research focus on a greater diversity of species will reveal general principles underlying the transition from summer active season, through the swarming period, and into winter hibernation.

Host traits and environment interact to determine persistence of bat populations impacted by white-nose syndrome

Emerging infectious diseases have resulted in severe population declines across diverse taxa. In some instances, despite attributes associated with high extinction risk, disease emergence and host declines are followed by host stabilisation for unknown reasons. While host, pathogen, and the environment are recognised as important factors that interact to determine host-pathogen coexistence, they are often considered independently. Here, we use a translocation experiment to disentangle the role of host traits and environmental conditions in driving the persistence of remnant bat populations a decade after they declined 70-99% due to white-nose syndrome and subsequently stabilised. While survival was significantly higher than during the initial epidemic within all sites, protection from severe disease only existed within a narrow environmental space, suggesting host traits conducive to surviving disease are highly environmentally dependent. Ultimately, population persistence following pathogen invasion is the product of host-pathogen interactions that vary across a patchwork of environments.

Landscape Genetic Connectivity and Evidence for Recombination in the North American Population of the White-Nose Syndrome Pathogen, Pseudogymnoascus destructans

White-Nose Syndrome is an ongoing fungal epizootic caused by epidermal infections of the fungus, Pseudogymnoascus destructans (P. destructans), affecting hibernating bat species in North America. Emerging early in 2006 in New York State, infections of P. destructans have spread to 38 US States and seven Canadian Provinces. Since then, clonal isolates of P. destructans have accumulated genotypic and phenotypic variations in North America. Using microsatellite and single nucleotide polymorphism markers, we investigated the population structure and genetic relationships among P. destructans isolates from diverse regions in North America to understand its pattern of spread, and to test hypotheses about factors that contribute to transmission. We found limited support for genetic isolation of P. destructans populations by geographic distance, and instead identified evidence for gene flow among geographic regions. Interestingly, allelic association tests revealed evidence for recombination in the North American P. destructans population. Our landscape genetic analyses revealed that the population structure of P. destructans in North America was significantly influenced by anthropogenic impacts on the landscape. Our results have important implications for understanding the mechanism(s) of P. destructans spread.

Population structure, gene flow and relatedness of Natterer’s bats in Northern England

There have been significant declines in population numbers of many bat species in the United Kingdom, including Natterer’s batsMyotis nattereri, over the last century, largely due to anthropogenic changes. The philopatry, which temperate-zone bats often exhibit to their natal landscapes, in combination with anthropogenic threats, can lead to fragmentation, isolation and sub-division of populations. This may result in bottlenecks and declines in genetic diversity. Multi-scaled research is required to disentangle how the variation in the physical traits of bat species (e.g. affecting flight), as well as their social and behavioural traits (e.g. community size, migration, breeding systems), may affect the genetic health of populations and provide a potential buffer against fragmentation. We used microsatellite markers to characterise the genetic diversity and population structure present in Natterer’s bat colonies to determine whether summer roosting bat colonies were spatially differentiated or part of a meta-population. Analyses of population structure and measures of genetic relatedness suggest spatially differentiated populations of bats exhibit long term site fidelity to summer roosting sites, whilst high genetic diversity at sites indicates gene exchange occurs via swarming sites. Natterer’s bats in northern England may travel greater distances to swarming sites than has been previously documented.

Comparative landscape genetics reveals differential effects of environment on host and pathogen genetic structure in Tasmanian devils (Sarcophilus harrisii) and their transmissible tumour

Genetic structure in host species is often used to predict disease spread. However, host and pathogen genetic variation may be incongruent. Understanding landscape factors that have either concordant or divergent influence on host and pathogen genetic structure is crucial for wildlife disease management. Devil facial tumour disease (DFTD) was first observed in 1996 and has spread throughout almost the entire Tasmanian devil geographic range, causing dramatic population declines. Whereas DFTD is predominantly spread via biting among adults, devils typically disperse as juveniles, which experience low DFTD prevalence. Thus, we predicted little association between devil and tumour population structure and that environmental factors influencing gene flow differ between devils and tumours. We employed a comparative landscape genetics framework to test the influence of environmental factors on patterns of isolation by resistance (IBR) and isolation by environment (IBE) in devils and DFTD. Although we found evidence for broad-scale costructuring between devils and tumours, we found no relationship between host and tumour individual genetic distances. Further, the factors driving the spatial distribution of genetic variation differed for each. Devils exhibited a strong IBR pattern driven by major roads, with no evidence of IBE. By contrast, tumours showed little evidence for IBR and a weak IBE pattern with respect to elevation in one of two tumour clusters we identify herein. Our results warrant caution when inferring pathogen spread using host population genetic structure and suggest that reliance on environmental barriers to host connectivity may be ineffective for managing the spread of wildlife diseases. Our findings demonstrate the utility of comparative landscape genetics for identifying differential factors driving host dispersal and pathogen transmission.

Widespread gene flow between oceans in a pelagic seabird species complex

Global-scale gene flow is an important concern in conservation biology as it has the potential to either increase or decrease genetic diversity in species and populations. Although many studies focus on the gene flow between different populations of a single species, the potential for gene flow and introgression between species is understudied, particularly in seabirds. The only well-studied example of a mixed-species, hybridizing population of petrels exists on Round Island, in the Indian Ocean. Previous research assumed that Round Island represents a point of secondary contact between Atlantic (Pterodroma arminjoniana) and Pacific species (Pterodroma neglecta and Pterodroma heraldica). This study uses microsatellite genotyping and tracking data to address the possibility of between-species hybridization occurring outside the Indian Ocean. Dispersal and gene flow spanning three oceans were demonstrated between the species in this complex. Analysis of migration rates estimated using bayesass revealed unidirectional movement of petrels from the Atlantic and Pacific into the Indian Ocean. Conversely, structure analysis revealed gene flow between species of the Atlantic and Pacific oceans, with potential three-way hybrids occurring outside the Indian Ocean. Additionally, geolocation tracking of Round Island petrels revealed two individuals travelling to the Atlantic and Pacific. These results suggest that interspecific hybrids in Pterodroma petrels are more common than was previously assumed. This study is the first of its kind to investigate gene flow between populations of closely related Procellariiform species on a global scale, demonstrating the need for consideration of widespread migration and hybridization in the conservation of threatened seabirds.

Prelude to a panzootic: Gene flow and immunogenetic variation in northern little brown myotis vulnerable to bat white-nose syndrome

The fungus that causes bat white-nose syndrome (WNS) recently leaped from eastern North America to the Pacific Coast. The pathogen’s spread is associated with the genetic population structure of a host ( Myotis lucifugus). To understand the fine-scale neutral and immunogenetic variation among northern populations of M. lucifugus, we sampled 1142 individuals across the species’ northern range. We used genotypes at 11 microsatellite loci to reveal the genetic structure of, and directional gene flow among, populations to predict the likely future spread of the pathogen in the northwest and to estimate effective population size ( Ne). We also pyrosequenced the DRB1-like exon 2 of the class II major histocompatibility complex (MHC) in 160 individuals to explore immunogenetic selection by WNS. We identified three major neutral genetic clusters: Eastern, Montane Cordillera (and adjacent sampling areas), and Haida Gwaii, with admixture at intermediate areas and significant substructure west of the prairies. Estimates of Ne were unexpectedly low (289–16 000). Haida Gwaii may provide temporary refuge from WNS, but the western mountain ranges are not barriers to its dispersal in M. lucifugus and are unlikely to slow its spread. Our major histocompatibility complex (MHC) data suggest potential selection by WNS on the MHC, but gene duplication limited the immunogenetic analyses.

Body temperatures of hibernating little brown bats reveal pronounced behavioural activity during deep torpor and suggest a fever response during white-nose syndrome

Hibernating animals use torpor [reduced body temperature (T _b) and metabolic rate] to reduce energy expenditure during winter. Periodic arousals to normal T _b are energetically expensive, so hibernators trade off arousal benefits against energetic costs. This is especially important for bats with white-nose syndrome (WNS), a fungal disease causing increased arousal frequency. Little brown bats (Myotis lucifugus) with WNS show upregulation of endogenous pyrogens and sickness behaviour. Therefore, we hypothesized that WNS should cause a fever response characterized by elevated T _b. Hibernators could also accrue some benefits of arousals with minimal T _b increase, thus avoiding full arousal costs. We compared skin temperature (T _sk) of captive Myotis lucifugus inoculated with the WNS-causing fungus to T _sk of sham-inoculated controls. Infected bats re-warmed to higher T _sk during arousals which is consistent with a fever response. Torpid T _sk did not differ. During what we term "cold arousals", bats exhibited movement following T _sk increases of only 2.2 ± 0.3 °C, compared to >20 °C increases during normal arousals. Cold arousals occurred in both infected and control bats, suggesting they are not a pathophysiological consequence of WNS. Fever responses are energetically costly and could exacerbate energy limitation and premature fat depletion for bats with WNS. Cold arousals could represent an energy-saving mechanism for both healthy and WNS-affected bats when complete arousals are unnecessary or too costly. A few cold arousals were observed mid-hibernation, typically in response to disturbances. Cold arousals may, therefore, represent a voluntary restriction of arousal temperature instead of loss of thermoregulatory control.

Evidence of ‘sickness behaviour’ in bats with white-nose syndrome

Many animals change behaviour in response to pathogenic infections. White-nose syndrome (WNS) is a fungal skin disease causing rapid declines of North American bats. Infection with Pseudogymnoascus destructans causes hibernating bats to arouse from torpor too often, potentially causing starvation. Mechanisms underlying increased arousals are not understood but fungal invasion of the wings could trigger thirst to relieve fluid loss or grooming to relieve skin irritation. Alternatively, bats might exhibit ‘sickness behaviour’, a suite of responses to infection that save energy. We quantified behaviours of healthy and experimentally inoculated little brown bats (Myotis lucifugus) that could reflect active (i.e., drinking, grooming) or inactive (i.e., sickness behaviour) responses to infection. Infected bats groomed less and were less likely to visit their water dish compared to controls. These results are consistent with research suggesting that P. destructans causes sickness behaviour which could help bats compensate for energetic costs associated with infection.

Population genetic structure of a common host predicts the spread of white-nose syndrome, an emerging infectious disease in bats

Landscape complexity influences patterns of animal dispersal, which in turn may affect both gene flow and the spread of pathogens. White-nose syndrome (WNS) is an introduced fungal disease that has spread rapidly throughout eastern North America, causing massive mortality in bat populations. We tested for a relationship between the population genetic structure of the most common host, the little brown myotis (Myotis lucifugus), and the geographic spread of WNS to date by evaluating logistic regression models of WNS risk among hibernating colonies in eastern North America. We hypothesized that risk of WNS to susceptible host colonies should increase with both geographic proximity and genetic similarity, reflecting historical connectivity, to infected colonies. Consistent with this hypothesis, inclusion of genetic distance between infected and susceptible colonies significantly improved models of disease spread, capturing heterogeneity in the spatial expansion of WNS despite low levels of genetic differentiation among eastern populations. Expanding our genetic analysis to the continental range of little brown myotis reveals strongly contrasting patterns of population structure between eastern and western North America. Genetic structure increases markedly moving westward into the northern Great Plains, beyond the current distribution of WNS. In western North America, genetic differentiation of geographically proximate populations often exceeds levels observed across the entire eastern region, suggesting infrequent and/or locally restricted dispersal, and thus relatively limited opportunities for pathogen introduction in western North America. Taken together, our analyses suggest a possibly slower future rate of spread of the WNS pathogen, at least as mediated by little brown myotis.

Host demographic predicts ectoparasite dynamics for a colonial host during pre-hibernation mating

Parasite dynamics can be mediated by host behaviours such as sociality, and seasonal changes in aggregation may influence risk of parasite exposure. We used little brown bats (Myotis lucifugus) captured during the autumn mating/swarming period to test the hypothesis that seasonal and demographic-based variation in sociality affect ectoparasitism. We predicted that ectoparasitism would: (1) be higher for adult females and young of the year (YOY) than adult males because of female coloniality; (2) increase for adult males throughout swarming because of increasing contact with females; (3) decrease for adult females and YOY throughout swarming because of reduced coloniality and transmission of individual ectoparasites to males; (4) be similar for male and female YOY because vertical transmission from adult females should be similar. Ectoparasitism was lowest for adult males and increased for males during swarming, but some effects of demographic were unexpected. Contrary to our prediction, ectoparasitism increased for adult females throughout swarming and YOY males also hosted fewer ectoparasites compared with adult and YOY females. Interestingly, females in the best body condition had the highest parasite loads. Our results suggest that host energetic constraints associated with future reproduction affect pre-hibernation parasite dynamics in bats.