Little Brown Bats (Myotis lucifugus) Recognize Individual Identity of Conspecifics Using Sonar Calls

Bats use sonar calls to locate prey and orient in their environment but they may also be used by conspecifics to obtain information about a caller. Statistical analysis of sonar calls provides evidence that variation carries social information about a caller, including individual identity. We hypothesized that little brown bats (Myotis lucifugus) would be able to recognize individuals given the potential fitness benefits of doing so. We performed playback trials using a habituation‐discrimination design to determine whether little brown bats are able to recognize the individual identity of a caller based on variation in their sonar calls. Each subject bat was played the calls of bat A until they habituated (defined as a 50% decrease from the beginning call rate), then the calls of bat B or a new call sequence of bat A (a control, referred to as bat A’) were played. Each subject received a unique pair of playback recordings (bat A and B) from adult female bats from the same colony (but a different colony from the subject) and the order of trials was randomized. The response measures were habituation time (s) and call rate (calls/s). Within a trial, subjects habituated to calls of bat A and transferred this habituation to the bat A’ sequence. In addition, they increased their call rates when played calls of bat B. Comparing between trials, subjects increased their call rate to the calls of bat B to a greater relative extent than to the calls of bat A’. These results provide the first evidence that bats recognize individual identity of conspecifics (as opposed to discrimination of groups), which has implications for the social interactions of bats.     

Blood and Spleen Response to Isolation and Cold Stress in Little Brown Bats,Myotis lucifugus

Female bats were housed singly or in groups and maintained at 5° or 23 °C. Red blood cell life spans were determined utilizing the disappearance of labeled sodium chromate (Cr⁵¹). Red cell counts, hematocrits, reticulocyte percentages and diameters, white cell differentials, and spleen histology were determined for bats subjected to three weeks of stress treatment. Isolated animals (warm and cold) had significantly lower hematocrits and red cell counts and significantly higher reticulocyte diameters and percentages than grouped bats. Random destruction of erythrocytes was initially higher in isolated bats. In cold and isolated animals the white pulp of the spleen was most reduced in quantity and in proliferative activity. Red pulp became highly engorged with erythrocytes and showed a hypertrophy of reticuloendothelial elements. Higher rates of random destruction are closely correlated with increased splenic erythrophagocytosis. Gold or isolation imposed separately are mild stress factors in little brown bats, while a severe stress response occurs when the two stressors are imposed simultaneously.     

Hibernating Little Brown Myotis (Myotis lucifugus) Show Variable Immunological Responses to White-Nose Syndrome

White-nose syndrome (WNS) is an emerging infectious disease devastating hibernating North American bat populations that is caused by the psychrophilic fungus Geomyces destructans. Previous histopathological analysis demonstrated little evidence of inflammatory responses in infected bats, however few studies have compared other aspects of immune function between WNS-affected and unaffected bats. We collected bats from confirmed WNS-affected and unaffected sites during the winter of 2008–2009 and compared estimates of their circulating levels of total leukocytes, total immunoglobulins, cytokines and total antioxidants. Bats from affected and unaffected sites did not differ in their total circulating immunoglobulin levels, but significantly higher leukocyte counts were observed in bats from affected sites and particularly in affected bats with elevated body temperatures (above 20°C). Bats from WNS-affected sites exhibited significantly lower antioxidant activity and levels of interleukin-4 (IL-4), a cytokine that induces T cell differentiation. Within affected sites only, bats exhibiting visible fungal infections had significantly lower antioxidant activity and levels of IL-4 compared to bats without visible fungal infections. Overall, bats hibernating in WNS-affected sites showed immunological changes that may be evident of attempted defense against G. destructans. Observed changes, specifically elevated circulating leukocytes, may also be related to the documented changes in thermoregulatory behaviors of affected bats (i.e. increased frequencies in arousal from torpor). Alterations in immune function may reflect expensive energetic costs associated with these processes and intrinsic qualities of the immunocapability of hibernating bats to clear fungal infections. Additionally, lowered antioxidant activity indicates a possible imbalance in the pro- versus antioxidant system, may reflect oxidative tissue damage, and should be investigated as a contributor to WNS-associated morbidity and mortality.     

Free-Ranging Little Brown Myotis (Myotis lucifugus) Heal from Wing Damage Associated with White-Nose Syndrome

White-nose syndrome (WNS) is having an unprecedented impact on hibernating bat populations in the eastern United States. While most studies have focused on widespread mortality observed at winter hibernacula, few have examined the consequences of wing damage that has been observed among those bats that survive hibernation. Given that WNS-related wing damage may lead to life-threatening changes in wing function, we tested the hypothesis that reduced abundance of free-ranging little brown myotis (Myotis lucifugus) with severe wing damage as the summer progresses is due to healing of wing tissue. Photographs of captured and recaptured adult females were examined for wing damage and healing rates were calculated for each category of wing damage index (WDI = 0–3). We found that free-ranging bats with severe wing damage were able to heal to a lower WDI score within 2 weeks. Bats with the most severe wing damage had faster healing rates than did individuals with less damage. We also found a significant relationship between body condition and WDI for adult females captured in the early weeks of the active season. Our results support the hypothesis that some bats can heal from severe wing damage during the active season, and thus may not experience increased mortality associated with reduced functions of wings. We urge researchers and wildlife managers to use caution when interpreting data on WDI to assess the impact of WNS on bat populations, especially during the later months of the active season.     

Host,Pathogen, and Environmental Characteristics Predict White-Nose Syndrome Mortality in Captive Little Brown Myotis (Myotis lucifugus)

An estimated 5.7 million or more bats died in North America between 2006 and 2012 due to infection with the fungus Pseudogymnoascus destructans (Pd) that causes white-nose syndrome (WNS) during hibernation. The behavioral and physiological changes associated with hibernation leave bats vulnerable to WNS, but the persistence of bats within the contaminated regions of North America suggests that survival might vary predictably among individuals or in relation to environmental conditions. To investigate variables influencing WNS mortality, we conducted a captive study of 147 little brown myotis (Myotis lucifugus) inoculated with 0, 500, 5 000, 50 000, or 500 000 Pd conidia and hibernated for five months at either 4 or 10°C. We found that female bats were significantly more likely to survive hibernation, as were bats hibernated at 4°C, and bats with greater body condition at the start of hibernation. Although all bats inoculated with Pd exhibited shorter torpor bouts compared to controls, a characteristic of WNS, only bats inoculated with 500 conidia had significantly lower survival odds compared to controls. These data show that host and environmental characteristics are significant predictors of WNS mortality, and that exposure to up to 500 conidia is sufficient to cause a fatal infection. These results also illustrate a need to quantify dynamics of Pd exposure in free-ranging bats, as dynamics of WNS produced in captive studies inoculating bats with several hundred thousand conidia may differ from those in the wild.     

Population Genetic Structure Within and among Seasonal Site Types in the Little Brown Bat (Myotis lucifugus) and the Northern Long-Eared Bat (M. septentrionalis)

During late summer and early autumn, temperate bats migrate from their summering sites to swarming sites, where mating likely occurs. However, the extent to which individuals of a single summering site migrate to the same swarming site, and vice versa, is not known. We examined the migratory connectivity between summering and swarming sites in two temperate, North American, bat species, the little brown bat (Myotis lucifugus) and the northern long-eared bat (Myotis septentrionalis). Using mitochondrial and microsatellite DNA markers, we examined population structuring within and among summering and swarming sites. Both species exhibited moderate degrees of mitochondrial DNA differentiation (little brown bat: F_ST(SWARMING)= 0.093, F_ST(SWARMING)= 0.052; northern long-eared bat: F_ST(SWARMING)= 0.117, F_ST(SWARMING)= 0.043) and little microsatellite DNA differentiation among summering and among swarming sites. Haplotype diversity was significantly higher at swarming sites than summering sites, supporting the idea that swarming sites are comprised of individuals from various summering sites. Further, pairwise analyses suggest that swarming sites are not necessarily comprised of only individuals from the most proximal summering colonies.     

Fishing Long-Fingered Bats (Myotis capaccinii) Prey Regularly upon Exotic Fish

The long-fingered bat Myotis capaccinii is a European trawling bat reported to feed on fish in several Mediterranean locations, but the ecological circumstances of this behavior have not yet been studied. To elucidate the importance of fishing in this bat''s diet, we evaluated the frequency and seasonal variation of fish remains in 3,000 fecal pellets collected from M. capaccinii at a nursery roost in Dénia (Eastern Iberian Peninsula) in 2008, 2009, and 2010. Fish consumption occurred evenly throughout the year. All otoliths found in feces were identified as belonging to the surface-feeding fish Gambusia holbrooki. Measuring otoliths, we estimated that the mean size of consumed fish was significantly smaller than the mean measured for available fish, suggesting that the long-fingered bat''s relatively small body may constrain its handling of larger prey. Of note, one bat had eaten 15 fish, showing that fish may be a locally or seasonally important trophic resource for this species. By capturing 15 bats and radio-tracking the four with the most fish remains in their droppings, we also identified fishing areas, including a single fishing ground comprising several ponds within a golf course. Ponds hold a high density of G. holbrooki, suggesting that the amount of fish at the water surface may be the principal factor triggering fishing. The observed six-fold increase in percentage of consumed fish across the study period may be related to recent pond-building in the area. We discuss whether this quick behavioral response is a novel feature of M. capaccinii or an intrinsic feature that has erupted and faded locally along the species'' history.     

The tradeoff between torpor use and reproduction in little brown bats (Myotis lucifugus)

In mammals, reproduction, especially for females is energetically demanding. Therefore, during the reproductive period females could potentially adjust patterns of thermoregulation and foraging in concert to minimise the energetic constraints associated with pregnancy and lactation. We assessed the influence of pregnancy, lactation, and post-lactation on torpor use and foraging behaviour by female little brown bats, Myotis lucifugus. We measured thermoregulation by recording skin temperature and foraging by tracking bats which carried temperature-sensitive radio-tags. We found that individuals, regardless of reproductive condition, used torpor, but the patterns of torpor use varied significantly between reproductive (pregnant and lactating) females and post-lactating females. As we predicted, reproductive females entered torpor for shorter bouts than post-lactating females. Although all females used torpor frequently, pregnant females spent less time in torpor, and maintained higher skin temperatures than either lactating or post-lactating females. This result suggests that delayed offspring development which has been associated with torpor use during pregnancy, may pose a higher risk to an individual’s reproductive success than reduced milk production during lactation. Conversely, foraging behaviour of radio-tagged bats did not vary with reproductive condition, suggesting that even short, shallow bouts of torpor produce substantial energy savings, likely obviating the need to spend more time foraging. Our data clearly show that torpor use and reproduction are not mutually exclusive and that torpor use (no matter how short or shallow) is an important means of balancing the costs of reproduction for M. lucifugus.     

Post-Pleistocene range expansion of the recently imperiled eastern little brown bat (Myotis lucifugus lucifugus) from a single southern refugium

Myotis lucifugus, once among the most widespread and common bats in North America, has been forecast to be extirpated east of the Rockies in as few as 16 years by the spread of white-nose syndrome. Recent genetic research has demonstrated that this species is paraphyletic and part of a broader species complex; however, only one lineage (Myotis lucifugus lucifugus [M. l. lucifugus]) is present in eastern North America. I used molecular tools and niche modeling to validate this and investigate the role that historical biogeography has played in the phylogenetic and population genetic structure of this species to determine if the eastern subspecies represents an evolutionarily distinct population.To establish the genetic structure within M. l. lucifugus, I densely sampled maternity colonies in Minnesota and sequenced 182 individuals for a portion of cytochrome b. Phylogenetic reconstruction and a haplotype network were used to infer the relationships among mitochondrial haplotypes. Population growth statistics were calculated to determine if there was evidence of significant expansion, and an environmental niche model (ENM) was constructed based on conditions during the last glacial maximum (LGM) to illustrate potential glacial refugia. All individuals derived from a single mitochondrial lineage. Genetic evidence points to population growth starting approximately 18 kya. ENM results show that there was likely a single large southern refugium extending across the southeastern United States and possibly several isolated refugia in western North America. Myotis lucifugus lucifugus likely maintained both a large range and a large population during the peaks of the glacial cycles, and its population appears to have expanded following the retreat of the Laurentide ice sheet. This imperiled lineage likely diverged in isolation from other members of the M. lucifugus/western long-eared Myotis during the Pleistocene.     

Sperm-epithelium relationships in relation to the time of insemination in little brown bats (Myotis lucifugus)

Copulation lasted for up to 46 min in little brown bats. Spermatozoa were stored in both the uterus and the utero-tubal junction, although intimate relationships between spermatozoa and the epithelium were particularly evident in the utero-tubal junction, and were established at the beginning of the period of sperm storage. Polymorphonuclear leucocytes were present in all uteri irrespective of whether or not they had been inseminated but were not generally present in the utero-tubal junction or oviduct. Engulfment of spermatozoa by the epithelial cells of the utero-tubal junction and by polymorphonuclear leucocytes in the uterine glands was evident soon after copulation. It is suggested that this may effect the removal of defective spermatozoa and allow luminal spermatozoa access to the spatially restricted storage sites. Uninseminated female bats attempted to elicit copulation from torpid males, and were also observed adjacent to copulating pairs. Female bats also uttered copulation calls.