Changes in body condition of hibernating bats support the thrifty female hypothesis and predict consequences for populations with white-nose syndrome

White-nose syndrome, winter duration, and pre-hibernation climate impact abundance of reproductive female bats

White-nose syndrome (WNS) is an infectious disease that disrupts hibernation in bats, leading to premature exhaustion of fat stores. Though we know WNS does impact reproduction in hibernating female bats, we are unsure how these impacts are exacerbated by local climate factors. We compiled data from four southeastern U.S. states and used generalized linear mixed effects models to compare effects of WNS, pre-hibernation climate variables, and winter duration on the number of reproductive females in species across the range of WNS susceptibility. We predicted we would see a decline in the number of reproductive females in WNS-susceptible species, with the effect exaggerated by longer winter durations and pre-hibernation climate variables that lead to reductions in foraging. We found that the number of reproductive females in WNS-susceptible species was positively correlated with pre-hibernation local climate conditions conducive to foraging; however, WNS-susceptible species experienced an overall decline with the presence of WNS and as winter duration increased. Our long-term dataset provides evidence that pre-hibernation climate, specifically favorable summer weather conditions for foraging, greatly influences the reproduction, regardless of WNS status.

Sex-specific heterothermy patterns in wintering captive Microcebus murinus do not translate into differences in energy balance

The physiological mechanisms of responses to stressors are at the core of ecophysiological studies that examine the limits of an organism's flexibility. Interindividual variability in these physiological responses can be particularly important and lead to differences in the stress response among population groups, which can affect population dynamics. Some observations of intersexual differences in heterothermy raise the question of whether there is a difference in energy management between the sexes. In this study, we assessed male and female differences in mouse lemurs (Microcebus murinus), a highly seasonal malagasy primate, by measuring their physiological flexibility in response to caloric restriction and examining the subsequent impact on reproductive success. Using complementary methods aiming to describe large-scale and daily variations in body temperature throughout a 6-month winter-like short-day (SD) period, we monitored 12 males and 12 females, applying chronic 40% caloric restriction (CR) to 6 individuals in each group. We found variations in Tb modulation throughout the SD period and in response to caloric treatment that depended on sex, as females, regardless of food restriction, and CR males, only, entered deep torpor. The use of deeper torpor, however, did not translate into a lower loss of body mass in females and did not affect reproductive success. Captive conditions may have buffered the depth of torpor and minimised the positive effects of torpor on energy savings. However, the significant sex differences in heterothermy we observed may point to physiological benefits other than preservation of energy reserves.

Hibernating female big brown bats (Eptesicus fuscus) adjust huddling and drinking behaviour, but not arousal frequency, in response to low humidity

Many mammals hibernate during winter, reducing energy expenditure via bouts of torpor. The majority of a hibernator's energy reserves are used to fuel brief, but costly, arousals from torpor. Although arousals likely serve multiple functions, an important one is to restore water stores depleted during torpor. Many hibernating bat species require high humidity, presumably to reduce torpid water loss, but big brown bats (Eptesicus fuscus) appear tolerant of a wide humidity range. We tested the hypothesis that hibernating female E. fuscus use behavioural flexibility during torpor and arousals to maintain water balance and reduce energy expenditure. We predicted: (1) E. fuscus hibernating in dry conditions would exhibit more compact huddles during torpor and drink more frequently than bats in high humidity conditions; and (2) the frequency and duration of torpor bouts and arousals, and thus total loss of body mass would not differ between bats in the two environments. We housed hibernating E. fuscus in temperature- and humidity-controlled incubators at 50% or 98% relative humidity (8°C, 110 days). Bats in the dry environment maintained a more compact huddle during torpor and drank more frequently during arousals. Bats in the two environments had a similar number of arousals, but arousal duration was shorter in the dry environment. However, total loss of body mass over hibernation did not differ between treatments, indicating that the two groups used similar amounts of energy. Our results suggest that behavioural flexibility allows hibernating E. fuscus to maintain water balance and reduce energy costs across a wide range of hibernation humidities.

Thinner bats to face hibernation as response to climate warming

One of the principal consequences of climate warming on hibernating mammals could be the loss of optimal conditions for hibernation. Although hibernating mammals, like bats, may be particularly vulnerable to climate warming due to a potential reduction of energy saving during the hibernation, there is a lack of knowledge regarding how they will be affected and how they will respond to this impact. Here, we examine the variation in the body condition of Schreiber's bent-winged bat (Miniopterus schreibersii) to investigate changes in the optimization energy demand. Using a 20-year dataset (1998-2017), we analyse the temporal trends of body condition in three key stages of the hibernation period: onset and end of hibernation and early activity. Our results indicate that body condition at the onset and end of hibernation have decreased significantly over these 20 years. However, despite this lower body condition, the decrease of mass loss rate in the last decade (although not significant) indicate a greater saving of fat reserves. The significant increase in winter temperatures did not affect body condition or reserve depletion, instead, lower body condition was observed with a higher number of days below 0 °C. Unlike other hibernating bat species, the females had lower fat reserves than males in all three periods considered. This study indicates that hibernation energy requirements could be changing as an adaptation to a warmer climate and that hibernating bats can survive the winter by optimizing their lower accumulation of reserves.

Higher antibody titres against Pseudogymnoascus destructans are associated with less white-nose syndrome skin lesions in Palearctic bats

Introduction

Serological tests can be used to test whether an animal has been exposed to an infectious agent, and whether its immune system has recognized and produced antibodies against it. Paired samples taken several weeks apart then document an ongoing infection and/or seroconversion.

Methods

In the absence of a commercial kit, we developed an indirect enzyme-linked immunosorbent assay (ELISA) to detect the fungus-specific antibodies for Pseudogymnoascus destructans, the agent of white-nose syndrome in bats.

Results and Discussion

Samples collected from European Myotis myotis (n=35) and Asian Myotis dasycneme (n=11) in their hibernacula at the end of the hibernation period displayed 100% seroprevalence of antibodies against P. destructans, demonstrating a high rate of exposure. Our results showed that the higher the titre of antibodies against P. destructans, the lower the infection intensity, suggesting that a degree of protection is provided by this arm of adaptive immunity in Palearctic bats. Moreover, P. destructans infection appears to be a seasonally self-limiting disease of Palearctic bats showing seroconversion as the WNS skin lesions heal in the early post-hibernation period.

Treatment with gut-specific nonsteroidal anti-inflammatory drug attenuates metabolic inflammation but not body mass in fattening ground squirrels

The active season of hibernators corresponds to rapid adiposity in preparation for the next hibernation season. We have previously shown that this dramatic increase in adipose mass is associated with metabolic inflammation similar to what is seen in obesity and metabolic disease. We next sought to determine whether curbing this inflammation at its source (i.e., the gut) would attenuate weight gain in fattening 13-lined ground squirrels (Ictidomys tridecemlineatus). We fed active yearling ground squirrels a diet containing the gut-specific nonsteroidal anti-inflammatory drug mesalazine (5-aminosalicylic acid) for 10 wk. Mesalazine treatment had slight effects on microbial community diversity in the cecum and colon. Not surprisingly, mesalazine treatment decreased inflammatory cytokine levels in the ileum and colon. Mesalazine also decreased proinflammatory and increased anti-inflammatory cytokines in omental white adipose tissue (oWAT). Despite this, body mass was unaffected, and caloric intake increased in mesalazine-treated squirrels, mainly in males. Mass of the primary WAT depot, intra-abdominal WAT (iaWAT), or the highly metabolic oWAT were unaltered by treatment, as was adiposity index. Together, these results suggest that mesalazine treatment has some effects on adiposity in fattening ground squirrels, but this treatment needs to be modified to overcome the strong drive to fatten in this species.NEW & NOTEWORTHY Adiposity and obesity are caused, at least in part, by inflammation of metabolic tissues. Hibernators, like ground squirrels, undergo this same metabolic inflammation during their summer fattening period. We attempted to curb this inflammation, and thus fattening, using mesalazine. We found that mesalazine did curb the inflammation but did not affect fattening, likely due to the strong drive to fatten in hibernators.

Mating in the cold. Prolonged sperm storage provides opportunities for forced copulation by male bats during winter

In a wide range of heterothermic mammals, hibernation interrupts the reproductive cycle by forcing reproductive delays. In hibernating bats with delayed fertilization, an opportunity for sperm competition is enhanced by extending a time-window between copulations and fertilization. In order to achieve greater fertilization success, males are expected to show adaptations for sperm competition by increasing their opportunities for mating over an extended period. We aimed to clarify the physiological and behavioral characteristics of male bats experiencing increased risks of sperm competition. We investigated the characteristics of the reproductive cycle of the little horseshoe bat (Rhinolophus cornutus), and examined whether males retain reproductive physiology related to sexual behavior, and attempt to copulate with females even during the hibernation period. Field observations and histological examinations of the reproductive cycle confirmed that females, having mated in the autumn, store spermatozoa in the uterus during hibernation and give birth in the early summer to just one offspring per year, thus males face a low certainty of successful fertilization. Although their testes regressed rapidly and their testosterone levels were lower during winter than in autumn, males stored motile spermatozoa in their cauda epididymides from autumn throughout the winter. During hibernation, we found that males occasionally aroused from torpor and attempted to mate forcibly with torpid females. Forced copulations appear to increase a male's chances of obtaining a mate while avoiding pre-copulatory female choice. Epididymal sperm storage could be advantageous for males in allowing them to extend their potential mating period even though their testes have regressed. We also found that some hibernating nulliparous females were ready for fertilization in spring after hibernation, whereas few parous females appeared in the same roost. In contrast to males, forced copulations would be maladaptive for females because they cannot opt for higher-quality males while in torpor. Females that have experienced sexual coercion when young may subsequently avoid hibernacula where adult males are present.

Species-specific responses to white-nose syndrome in the Great Lakes region

White-nose syndrome is a fungal disease that is threatening bat populations across North America. The disease primarily affects cave-hibernating bats by depleting fat reserves during hibernation and causing a range of other physiological consequences when immune responses are suppressed. Since it was first detected in 2006, the disease has killed millions of bats and is responsible for extensive local extinctions. To better understand the effects of white-nose syndrome on various bat species, we analyzed summer acoustic survey data collected from 2016 to 2020 at nine US National Parks within the Great Lakes region. We examined the effect that white-nose syndrome, time of the year relative to pup volancy, habitat type, and regional variation (i.e., park) have on the acoustic abundance (i.e., mean call abundance) of six bat species. As expected, little brown bat (Myotis lucifugus) and northern long-eared bat (Myotis septentrionalis), both hibernating species, experienced a significant decline in acoustic abundance following white-nose syndrome detection. We observed a significant increase in acoustic abundance as white-nose syndrome progressed for hoary bats (Lasiurus cinereus) and silver-haired bats (Lasionycteris noctivagans), both migratory species that are not impacted by the disease. Contrary to our predictions, we observed an increase in big brown bat (Eptesicus fuscus; hibernating) acoustic abundance and a decrease in eastern red bat (Lasiurus borealis; migratory) acoustic abundance following the detection of white-nose syndrome. We did not observe any significant changes after the onset of white-nose syndrome in the seasonal patterns of acoustic activity related to pup volancy, suggesting that production or recruitment of young may not be affected by the disease. Our results suggest that white-nose syndrome is affecting the acoustic abundance of certain species; however, these changes may not be a result of reduced reproductive success caused by the disease. In addition, species population dynamics may be indirectly affected by white-nose syndrome as a result of reduced competition or a foraging niche release. We also found that for parks located at higher latitudes, little brown bat and northern long-eared bat were more likely to experience greater declines in acoustic abundance as a result of white-nose syndrome. Our work provides insight into species-specific responses to white-nose syndrome at a regional scale and examines factors that may facilitate resistance or resiliency to the disease.

Sex-biased infections scale to population impacts for an emerging wildlife disease

Demographic factors are fundamental in shaping infectious disease dynamics. Aspects of populations that create structure, like age and sex, can affect patterns of transmission, infection intensity and population outcomes. However, studies rarely link these processes from individual to population-scale effects. Moreover, the mechanisms underlying demographic differences in disease are frequently unclear. Here, we explore sex-biased infections for a multi-host fungal disease of bats, white-nose syndrome, and link disease-associated mortality between sexes, the distortion of sex ratios and the potential mechanisms underlying sex differences in infection. We collected data on host traits, infection intensity and survival of five bat species at 42 sites across seven years. We found females were more infected than males for all five species. Females also had lower apparent survival over winter and accounted for a smaller proportion of populations over time. Notably, female-biased infections were evident by early hibernation and likely driven by sex-based differences in autumn mating behaviour. Male bats were more active during autumn which likely reduced replication of the cool-growing fungus. Higher disease impacts in female bats may have cascading effects on bat populations beyond the hibernation season by limiting recruitment and increasing the risk of Allee effects.

Shifting effects of host physiological condition following pathogen establishment

Understanding host persistence with emerging pathogens is essential for conserving populations. Hosts may initially survive pathogen invasions through pre-adaptive mechanisms. However, whether pre-adaptive traits are directionally selected to increase in frequency depends on the heritability and environmental dependence of the trait and the costs of trait maintenance. Body condition is likely an important pre-adaptive mechanism aiding in host survival, although can be seasonally variable in wildlife hosts. We used data collected over 7 years on bat body mass, infection and survival to determine the role of host body condition during the invasion and establishment of the emerging disease, white-nose syndrome. We found that when the pathogen first invaded, bats with higher body mass were more likely to survive, but this effect dissipated following the initial epizootic. We also found that heavier bats lost more weight overwinter, but fat loss depended on infection severity. Lastly, we found mixed support that bat mass increased in the population after pathogen arrival; high annual plasticity in individual bat masses may have reduced the potential for directional selection. Overall, our results suggest that some factors that contribute to host survival during pathogen invasion may diminish over time and are potentially replaced by other host adaptations.

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.

Global warming leads to larger bats with a faster life history pace in the long-lived Bechstein's bat (Myotis bechsteinii)

Whether species can cope with environmental change depends considerably on their life history. Bats have long lifespans and low reproductive rates which make them vulnerable to environmental changes. Global warming causes Bechstein’s bats (Myotis bechsteinii) to produce larger females that face a higher mortality risk. Here, we test whether these larger females are able to offset their elevated mortality risk by adopting a faster life history. We analysed an individual-based 25-year dataset from 331 RFID-tagged wild bats and combine genetic pedigrees with data on survival, reproduction and body size. We find that size-dependent fecundity and age at first reproduction drive the observed increase in mortality. Because larger females have an earlier onset of reproduction and shorter generation times, lifetime reproductive success remains remarkably stable across individuals with different body sizes. Our study demonstrates a rapid shift to a faster pace of life in a mammal with a slow life history.

Warming summers across a 25-year study are linked to larger body sizes in female bats, leading to a switch from a slow-reproducing, long-lived species to a faster pace of life.

Emergence activity at hibernacula differs among four bat species affected by white-nose syndrome

Prior to the introduction of white-nose syndrome (WNS) to North America, temperate bats were thought to remain within hibernacula throughout most of the winter. However, recent research has shown that bats in the southeastern United States emerge regularly from hibernation and are active on the landscape, regardless of their WNS status. The relationship between winter activity and susceptibility to WNS has yet to be explored but warrants attention, as it may enable managers to implement targeted management for WNS-affected species. We investigated this relationship by implanting 1346 passive integrated transponder (PIT) tags in four species that vary in their susceptibility to WNS. Based on PIT-tag detections, three species entered hibernation from late October to early November. Bats were active at hibernacula entrances on days when midpoint temperatures ranged from -1.94 to 22.78°C (mean midpoint temperature = 8.70 ± 0.33°C). Eastern small-footed bats (Myotis leibii), a species with low susceptibility to WNS, were active throughout winter, with a significant decrease in activity in mid-hibernation (December 16 to February 15). Tricolored bats (Perimyotis subflavus), a species that is highly susceptible to WNS, exhibited an increase in activity beginning in mid-hibernation and extending through late hibernation (February 16 to March 31). Indiana bats (M. sodalis), a species determined to have a medium-high susceptibility to WNS, remained on the landscape into early hibernation (November 1 to December 15), after which we did not record any again until the latter portion of mid-hibernation. Finally, gray bats (M. grisescens), another species with low susceptibility to WNS, maintained low but regular levels of activity throughout winter. Given these results, we determined that emergence activity from hibernacula during winter is highly variable among bat species and our data will assist wildlife managers to make informed decisions regarding the timing of implementation of species-specific conservation actions.

One or two pups - optimal reproduction strategies of common noctule females

BACKGROUND

The success of animal reproduction is impacted by a trade-off between energetic costs and mortality associated with immediate vs. future reproductive attempts. The reproductive strategies of European insectivorous bats differ from common mammalian standards due to the use of delayed fertilisation. Phenology of bat reproduction, including length of pregnancy, which may vary in the same species at different latitudes, between years at the same site or between individuals within a colony, is influenced by ecological conditions. To assess factors influencing the course of pregnancy, we evaluated levels of blood progesterone in 20 female common noctule bats Nyctalus noctula. The bats were individually tagged and randomly divided into two groups with different hibernation ending points (i.e. a control group vs. a treatment group with one-week longer hibernation). Following emergence from hibernation, the bats were kept in a wooden box at a stable temperature of 22 °C.

RESULTS

The majority of females gave birth to a single neonate (65%), but one female aborted her pups 2 days before the first successful births of other females. Based on development of progesterone concentration, we were able to define a number of different reproduction strategies, i.e. females with single offspring or twins, and females with supposed resorption of one embryo (embryonic mortality after implantation of the developing fertilised egg). Progesterone levels were much higher in females with two embryos during the first part of gestation and after birth. Progesterone levels were at their highest mid-gestation, with no difference between females carrying one or two foetuses. Length of gestation differed significantly between the two groups, with the longer hibernation (treatment) group having a roughly two-day shorter gestation period.

CONCLUSIONS

Female N. noctula are able to manipulate their litter size to balance immediate and future reproduction success. The estimated gestation length of approx. 49-days appears to be standard for N. noctula, with females optimising their thermoregulatory behaviour to keep the length of gestation as close to the standard as possible.

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.

Long-term individualized monitoring of sympatric bat species reveals distinct species- and demographic differences in hibernation phenology

Background

Hibernation allows species to conserve energy and thereby bridge unfavorable environmental conditions. At the same time, hibernation imposes substantial ecological and physiological costs. Understanding how hibernation timing differs within and between species can provide insights into the underlying drivers of this trade-off. However, this requires individualized long-term data that are often unavailable. Here, we used automatic monitoring techniques and a reproducible analysis pipeline to assess the individualized hibernation phenology of two sympatric bat species. Our study is based on data of more than 1100 RFID-tagged Daubenton’s bats (Myotis daubentonii) and Natterer’s bats (Myotis nattereri) collected over seven years at a hibernaculum in Germany. We used linear mixed models to analyze species-, sex- and age-specific differences in entrance, emergence and duration of the longest continuous period spent in the hibernaculum.

Results

Overall, Daubenton’s bats entered the hibernaculum earlier and emerged later than Natterer’s bats, resulting in a nearly twice as long hibernation duration. In both species, adult females entered earlier and emerged from hibernation later than adult males. Hibernation duration was shorter for juveniles than adults with the exception of adult male Natterer’s bats whose hibernation duration was shortest of all classes. Finally, hibernation timing differed among years, but yearly variations in entrance and emergence timing were not equally shifted in both species.

Conclusions

Our results suggest that even in sympatric species, and across sex and age classes, hibernation timing may be differentially affected by environmental conditions. This highlights the necessity of using individualized information when studying the impact of changing environments on hibernation phenology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-022-01962-6.

Body Mass and Tail Girth Predict Hibernation Expression in Captive Dwarf Lemurs

AbstractHibernation, a metabolic strategy, allows individuals to reduce energetic demands in times of energetic deficits. Hibernation is pervasive in nature, occurring in all major mammalian lineages and geographical regions; however, its expression is variable across species, populations, and individuals, suggesting that trade-offs are at play. Whereas hibernation reduces energy expenditure, energetically expensive arousals may impose physiological burdens. The torpor optimization hypothesis posits that hibernation should be expressed according to energy availability. The greater the energy surplus, the lower the hibernation output. The thrifty female hypothesis, a variation of the torpor optimization hypothesis, states that females should conserve more energy because of their more substantial reproductive costs. Contrarily, if hibernation's benefits offset its costs, hibernation may be maximized rather than optimized (e.g., hibernators with greater fat reserves could afford to hibernate longer). We assessed torpor expression in captive dwarf lemurs, primates that are obligate, seasonal, and tropical hibernators. Across 4.5 mo in winter, we subjected eight individuals at the Duke Lemur Center to conditions conducive to hibernation, recorded estimates of skin temperature hourly (a proxy for torpor), and determined body mass and tail fat reserves bimonthly. Across and between consecutive weigh-ins, heavier dwarf lemurs spent less time in torpor and lost more body mass. At equivalent body mass, females spent more time torpid and better conserved energy than did males. Although preliminary, our results support the torpor optimization and thrifty female hypotheses, suggesting that individuals optimize rather than maximize torpor according to body mass. These patterns are consistent with hibernation phenology in Madagascar, where dwarf lemurs hibernate longer in more seasonal habitats.

Contaminant exposure as an additional stressor to bats affected by white-nose syndrome: current evidence and knowledge gaps

Bats are exposed to numerous threats including pollution and emerging diseases. In North America, the fungal disease white-nose syndrome (WNS) has caused declines in many bat species. While the mechanisms of WNS have received considerable research attention, possible influences of contaminants have not. Herein, we review what is known about contaminant exposure and toxicity for four species whose populations have been severely affected by WNS (Myotis sodalis, M. septentrionalis, M. lucifugus, and Perimyotis subflavus) and identify temporal and spatial data gaps. We determine that there is limited information about the effects of contaminants on bats, and many compounds that have been detected in these bat species have yet to be evaluated for toxicity. The four species examined were exposed to a wide variety of contaminants; however, large spatial and knowledge gaps limit our ability to evaluate if contaminants contribute to species-level declines and if contaminant exposure exacerbates infection by WNS.

Disparate roost sites drive intraspecific physiological variation in a Malagasy bat

Many species are widely distributed and individual populations can experience vastly different environmental conditions over seasonal and geographic scales. With such a broad ecological reality, datasets with limited spatial and temporal resolution may not accurately represent a species and could lead to poorly informed management decisions. Because physiological flexibility can help species tolerate environmental variation, we studied the physiological responses of two separate populations of Macronycteris commersoni, a bat widespread across Madagascar, in contrasting seasons. The populations roost under the following dissimilar conditions: either a hot, well-buffered cave or within open foliage, unprotected from the local weather. We found that flexible torpor patterns, used in response to prevailing ambient temperature and relative humidity, were central to keeping energy budgets balanced in both populations. While bats’ metabolic rate during torpor and rest did not differ between roosts, adjusting torpor frequency, duration and timing helped bats maintain body condition. Interestingly, the exposed forest roost induced extensive use of torpor, which exceeded the torpor frequency of overwintering bats that stayed in the cave for months and consequently minimised daytime resting energy expenditure in the forest. Our current understanding of intraspecific physiological variation is limited and physiological traits are often considered to be fixed. The results of our study therefore highlight the need for examining species at broad environmental scales to avoid underestimating a species’ full capacity for withstanding environmental variation, especially in the face of ongoing, disruptive human interference in natural habitats.

Cold arousal - A mechanism used by hibernating bats to reduce the energetic costs of disturbance

During the season of hibernation, temperate bats alternate between prolonged bouts of torpor with reduced body temperature and short arousals with a return to normothermy. Hibernating bats are sensitive to non-tactile stimuli and arouse following changes in microclimatic conditions or disturbance from other bats, potential predators, or humans. Here, we used temperature data loggers to register the skin temperature of 38 Myotis myotis bats over two winters (between January and March), during which regular visits were made to the hibernaculum. Two kinds of arousal were observed, normothermic (T_sk > 25 °C) and cold (T_sk < 15 °C). Although bats responded to the presence of a researcher by arousals of both kinds, cold arousals were more frequent (63.8%). We found that mass loss was not affected by the number of disturbances, however it was in positive relationship with the mass at the beginning of the observation and differed between sex and age categories. Furthermore normothermic bats crawling among cluster-mates initiated arousal cascades, which mainly consisted of cold arousals. We failed to detect any effect of age or sex on the number of arousals initiated by normothermic individuals. Warming by only a few degrees requires less energy than a normothermic arousal and we propose it is sufficient to activate the sensory system in order to assess the relevance of external stimuli. Our results indicate that cold arousals reflect a physiological and behavioural adaptation aimed at avoiding the energetic costs of disturbance that can lead to depletion of fat reserves.

The effects of housing density on mouse thermal physiology depend on sex and ambient temperature

Objective

To improve understanding of mouse energy homeostasis and its applicability to humans, we quantitated the effects of housing density on mouse thermal physiology in both sexes.

Methods

Littermate wild type and Brs3-null mice were single- or group- (three per cage) housed and studied by indirect calorimetry with continuous measurement of core body temperature, energy expenditure, physical activity, and food intake.

Results

At 23 °C, below thermoneutrality, single-housed males had a lower body temperature and unchanged metabolic rate compared to group-housed controls. In contrast, single-housed females maintained a similar body temperature to group-housed controls by increasing their metabolic rate. With decreasing ambient temperature below 27 °C, only group-housed mice decreased their heat conductance, likely due to huddling, thus interfering with the energy expenditure vs ambient temperature relationship described by Scholander. In a hot environment (35 °C), the single-housed mice were less heat stressed. Upon fasting, single-housed mice had larger reductions in body temperature, with male mice having more torpor episodes of similar duration and female mice having a similar number of torpor episodes that lasted longer. Qualitatively, the effects of housing density on thermal physiology of Brs3-null mice generally mimicked the effects in controls.

Conclusions

Single housing is more sensitive than group housing for detecting thermal physiology phenotypes. Single housing increases heat loss and amplifies the effects of fasting or a cold environment. Male and female mice utilize different thermoregulatory strategies to respond to single housing.

• Changing housing density changes thermal physiology and metabolic rate.

• Singly housed mice are more affected by fasting and by cold temperatures.

• Single housing is more sensitive than group housing for detecting thermal phenotypes.

• Certain principles of thermal physiology are masked by group housing.

• Male and female mice respond differently to single housing.

Similar hibernation physiology in bats across broad geographic ranges

Species with broad geographic ranges may experience varied environmental conditions throughout their range leading to local adaptation. Variation among populations reflects potential adaptability or plasticity, with implications for populations impacted by disease, climate change, and other anthropogenic influences. However, behavior may counteract divergent selection among populations. We studied intraspecific variation in hibernation physiology of Myotis lucifugus (little brown myotis) and Corynorhinus townsendii (Townsend's big-eared bat), two species of bats with large geographic ranges. We studied M. lucifugus at three hibernacula which spanned a latitudinal gradient of 1500 km, and C. townsendii from 6 hibernacula spread across 1200 km latitude and 1200 km longitude. We found no difference in torpid metabolic rate among populations of either species, nor was there a difference in the effect of ambient temperature among sites. Evaporative water loss was similar among populations of both species, with the exception of one C. townsendii pairwise site difference and one M. lucifugus site that differed from the others. We suggest the general lack of geographic variation is a consequence of behavioral microhabitat selection. As volant animals, bats can travel relatively long distances in search of preferred microclimates for hibernation. Despite dramatic macroclimate differences among populations, hibernating bats are able to find preferred microclimate conditions within their range, resulting in similar selection pressures among populations spread across wide geographic ranges.

Temperature alone is insufficient to understand hibernation energetics

Energy conservation has long been a focal point in hibernation research. A long-standing assumption is that ambient temperature (Ta) largely defines the rate of energy expenditure because of well-known relationships between Ta, metabolic rate and frequency of arousal from torpor. Body condition and humidity also affect energy expenditure but are usually considered secondary factors. We held tricolored bats (Perimyotis subflavus) in captivity under multiple environmental conditions to directly compare the importance of Ta, fat mass and humidity for hibernation energy expenditure. Fat mass was the best predictor of female mass loss, followed by Ta and humidity. However, males had less fat and adopted a more energetically conservative hibernation strategy. Our results demonstrate that understanding the evolution of behavior, physiology and ecology of hibernation requires disentangling the relative contributions of multiple drivers of hibernation energetics, and that Ta is not always the most important factor driving energy expenditure.

Hepatic lipid signatures of little brown bats (Myotis lucifugus) and big brown bats (Eptesicus fuscus) at early stages of white-nose syndrome

White-nose syndrome (WNS) is an emergent wildlife fungal disease of cave-dwelling, hibernating bats that has led to unprecedented mortalities throughout North America. A primary factor in WNS-associated bat mortality includes increased arousals from torpor and premature fat depletion during winter months. Details of species and sex-specific changes in lipid metabolism during WNS are poorly understood and may play an important role in the pathophysiology of the disease. Given the likely role of fat metabolism in WNS and the fact that the liver plays a crucial role in fatty acid distribution and lipid storage, we assessed hepatic lipid signatures of little brown bats (Myotis lucifugus) and big brown bats (Eptesicus fuscus) at an early stage of infection with the etiological agent, Pseudogymnoascus destructans (Pd). Differences in lipid profiles were detected at the species and sex level in the sham-inoculated treatment, most strikingly in higher hepatic triacylglyceride (TG) levels in E. fuscus females compared to males. Interestingly, several dominant TGs (storage lipids) decreased dramatically after Pd infection in both female M. lucifugus and E. fuscus. Increases in hepatic glycerophospholipid (structural lipid) levels were only observed in M. lucifugus, including two phosphatidylcholines (PC [32:1], PC [42:6]) and one phosphatidylglycerol (PG [34:1]). These results suggest that even at early stages of WNS, changes in hepatic lipid mobilization may occur and be species and sex specific. As pre-hibernation lipid reserves may aid in bat persistence and survival during WNS, these early perturbations to lipid metabolism could have important implications for management responses that aid in pre-hibernation fat storage.

Determinants of defence strategies of a hibernating European bat species towards the fungal pathogen Pseudogymnoascus destructans

Pseudogymnoascus destructans (Pd), the causative agent of white-nose syndrome in North America, has decimated bat populations within a decade. The fungus impacts bats during hibernation when physiological functions, including immune responses, are down-regulated. Studies have shown that Pd is native to Europe, where it is not associated with mass mortalities. Moreover, genomic and proteomic studies indicated that European bats may have evolved an effective immune defence, which is lacking in North American bats. However, it is still unclear which defence strategy enables European bats to cope with the pathogen. Here, we analyzed selected physiological and immunological parameters in torpid, Pd infected European greater mouse-eared bats (Myotis myotis) showing three different levels of infection (asymptomatic, mild and severe symptoms). From a subset of the studied bats we tracked skin temperatures during one month of hibernation. Contrasting North American bats, arousal patterns remained unaffected by Pd infections in M. myotis. In general, heavier M. myotis aroused more often from hibernation and showed less severe disease symptoms than lean individuals; most likely because heavy bats were capable of reducing the Pd load more effectively than lean individuals. In the blood of severely infected bats, we found higher gene expression levels of an inflammatory cytokine (IL-1β), but lower levels of an acute phase protein (haptoglobin), reactive oxygen metabolites (ROMs) and plasma non-enzymatic antioxidant capacity (OXY) compared to conspecifics with lower levels of infection. We conclude that M. myotis, and possibly also other European bat species, tolerate Pd infections during torpor by using selected acute phase response parameters at baseline levels, yet without arousing from torpor and without synthesizing additional immune molecules.

Population dynamics of little brown bats (Myotis lucifugus) at summer roosts: Apparent survival, fidelity, abundance, and the influence of winter conditions

White-nose syndrome (WNS) has caused the death of millions of bats, but the impacts have been more difficult to identify in western North America. Understanding how WNS, or other threats, impacts western bats may require monitoring other roosts, such as maternity roosts and night roosts, where bats aggregate in large numbers.Little brown bats (Myotis lucifugus) are experiencing some of the greatest declines from WNS. Estimating survival and understanding population dynamics can provide valuable data for assessing population declines and informing conservation efforts.We conducted a 5-year mark-recapture study of two M. lucifugus roosts in Colorado. We used the robust design model to estimate apparent survival, fidelity, and abundance to understand population dynamics, and environmental covariates to understand how summer and winter weather conditions impact adult female survival. We compared the fidelity and capture probability of M. lucifugus between colonies to understand how bats use such roosts.Overwinter survival increased with the number of days with temperatures below freezing (β > 0.100, SE = 0.003) and decreased with the number of days with snow cover (β < -0.40, SE < 0.13). Adult female fidelity was higher at one maternity roost than the other. Overwinter and oversummer adult female survival was high (>0.90), and based on survival estimates and fungal-swabbing results, we believe these populations have yet to experience WNS.Recapture of M. lucifugus using antennas that continuously read passive integrated transponder tags allows rigorous estimation of bat population parameters that can elucidate trends in abundance and changes in survival. Monitoring populations at summer roosts can provide unique population ecology data that monitoring hibernacula alone may not. Because few adult males are captured at maternity colonies, and juvenile males have low fidelity, additional effort should focus on understanding male M. lucifugus population dynamics.

Vocal performance reflects individual quality in male Great Himalayan leaf-nosed bats (Hipposideros armiger)

Signals containing parameter trade-offs are likely to be honest indicators of signaler quality because they are difficult to produce. Signals with a trill-rate/bandwidth trade-off have been described for many songbird species, one mouse, and one non-human primate species. However, there were no reports about whether there is a vocal performance trade-off in social calls of bats. This study investigated (1) a possible vocal performance trade-off in territorial calls of male Great Himalayan leaf-nosed bats, Hipposideros armiger, recorded from 9 locations in south China, and (2) the relationships between vocal performance (vocal deviation and consistency) and caller's quality (body mass) to determine whether vocal performance honestly indicates a caller's quality. Vocal deviation measures the deviation of a call relative to an extreme call and vocal consistency measures the spectral consistency across a string of syllables. Our results showed a significant negative correlation between syllable repetition rate and frequency bandwidth, suggesting a vocal performance trade-off similar to the one in songbirds. Further, there was a significant negative relationship between body mass and vocal deviation, but no significant correlation between body mass and vocal consistency. This study provides the first empirical evidence for a vocal performance trade-off of social calls in bats, and the potential for the level of performance to indicate caller quality.

Long-term patterns of cave-exiting activity of hibernating bats in western North America

Understanding frequency and variation of cave-exiting activity after arousal from torpor of hibernating bats is important for bat ecology and conservation, especially considering white-nose syndrome. In winter from 2011 to 2018, we acoustically monitored, and counted in hibernacula, two species of conservation concern-western small-footed myotis (Myotis ciliolabrum) and Townsend's big-eared bats (Corynorhinus townsendii)-in 9 caves located in important habitat for these species in western North America. We investigated if cave-exiting activity differed by species, cave, number of hibernating bats, moon phase, and weather variables. Both species exited hibernacula during all winter months, but most activity occurred in March followed by November. Although we counted almost 15 times more Townsend's big-eared bats during hibernacula surveys, we documented western small-footed myotis exiting caves 3 times more than Townsend's big-eared bats. Cave-exiting activity increased with increasing number of hibernating bats, but more so for western small-footed myotis. Both species of bats were active during warm weather and low wind speeds. Western small-footed myotis were more active during colder temperatures, higher wind speeds, and greater change in barometric pressure than Townsend's big-eared bats. Our results provide a long-term dataset of cave-exiting activity after arousal from torpor during hibernation for these species before the arrival of white-nose syndrome.

Characteristics of Caves Used by Wintering Bats in a Subtropical Environment

Many cave-roosting bats are declining in number throughout their range because of multiple threats, including disease, disturbance by humans, and habitat loss. Successful conservation of cave-roosting bats requires an understanding of the roles of microclimate, cave structure, and the surrounding landscape on the distribution and abundance of bats, and in particular, the use of winter cave roosts. Cave bats have been well studied in temperate climates, but we know little about these bats in subtropical climates. From 2015 to 2017, we conducted 399 winter surveys of 162 caves in Florida to evaluate factors affecting the presence and abundance of bats at cave roosts. We also determined whether temperatures at these cave roosts were suitable for Pseudogymnoascus destructans, the fungus that causes white-nose syndrome. Across all 3 y, we detected three species of bats: tricolored bat Perimyotis subflavus in 126 (77.8%) caves, southeastern myotis Myotis austroriparius in 51 (31.5%) caves, and a single Rafinesque's big-eared bat Corynorhinus rafinesquii. We analyzed the presence of both tricolored bats and southeastern myotis in caves by using mixed-effects models with a binomial distribution and the number of tricolored bats by using generalized linear mixed-effects models with a Poisson error distribution. Tricolored bat presence was significantly and positively influenced by a cooler cave surface temperature, larger cave entrance size, a single entrance, and the presence of solution holes. Tricolored bat abundance increased in longer, cooler caves that had solution holes, a single, unobstructed entrance, and had no signs of flooding. Southeastern myotis presence was positively associated with longer, domed caves. To be most effective, conservation efforts in subtropical climates should focus on caves with the identified characteristics. More than 90% of caves surveyed each year had a cave interior surface temperature below the upper critical growth limit for P. destructans (19.8°C), indicating that most Florida caves are suitable for growth of P. destructans. Therefore, regular monitoring of winter bat populations in subtropical caves may be important for detecting P. destructans and white-nose syndrome.

Using mounting, orientation, and design to improve bat box thermodynamics in a northern temperate environment

Wildlife managers design artificial structures, such as bird houses and bat boxes, to provide alternative nesting and roosting sites that aid wildlife conservation. However, artificial structures for wildlife may not be equally efficient at all sites due to varying climate or habitat characteristics influencing thermal properties. For example, bat boxes are a popular measure employed to provide compensatory or supplementary roost sites for bats and educate the public. Yet, bat boxes are often thermally unstable or too cold to fulfill reproductive females needs in northern temperate environments. To help improve the thermodynamics of bat boxes, we tested the effect of (1) three mountings, (2) four orientations, and (3) twelve bat box designs on the internal temperature of bat boxes. We recorded temperatures in bat boxes across a climate gradient at seven sites in Quebec, Canada. Bat boxes mounted on buildings had warmer microclimates at night than those on poles and those facing east warmed sooner in the morning than those facing west or south. Our best new model based on passive solar architecture (Ncube PH1) increased the time in the optimal temperature range (22–40 °C) of targeted species by up to 13% compared to the most commonly used model (Classic 4-chamber) when mounted on a building with an east orientation (other designs presented in the Supplementary Information). Based on bioenergetic models, we estimated that bats saved up to 8% of their daily energy using the Ncube PH1 compared to the Classic 4-chamber when mounted on a building with an east orientation. We demonstrate that the use of energy-saving concepts from architecture can improve the thermal performance of bat boxes and potentially other wildlife structures as well.

On the modulation and maintenance of hibernation in captive dwarf lemurs

In nature, photoperiod signals environmental seasonality and is a strong selective "zeitgeber" that synchronizes biological rhythms. For animals facing seasonal environmental challenges and energetic bottlenecks, daily torpor and hibernation are two metabolic strategies that can save energy. In the wild, the dwarf lemurs of Madagascar are obligate hibernators, hibernating between 3 and 7 months a year. In captivity, however, dwarf lemurs generally express torpor for periods far shorter than the hibernation season in Madagascar. We investigated whether fat-tailed dwarf lemurs (Cheirogaleus medius) housed at the Duke Lemur Center (DLC) could hibernate, by subjecting 8 individuals to husbandry conditions more in accord with those in Madagascar, including alternating photoperiods, low ambient temperatures, and food restriction. All dwarf lemurs displayed daily and multiday torpor bouts, including bouts lasting ~ 11 days. Ambient temperature was the greatest predictor of torpor bout duration, and food ingestion and night length also played a role. Unlike their wild counterparts, who rarely leave their hibernacula and do not feed during hibernation, DLC dwarf lemurs sporadically moved and ate. While demonstrating that captive dwarf lemurs are physiologically capable of hibernation, we argue that facilitating their hibernation serves both husbandry and research goals: first, it enables lemurs to express the biphasic phenotypes (fattening and fat depletion) that are characteristic of their wild conspecifics; second, by "renaturalizing" dwarf lemurs in captivity, they will emerge a better model for understanding both metabolic extremes in primates generally and metabolic disorders in humans specifically.

The Torpid State: Recent Advances in Metabolic Adaptations and Protective Mechanisms†

Torpor and hibernation are powerful strategies enabling animals to survive periods of low resource availability. The state of torpor results from an active and drastic reduction of an individual's metabolic rate (MR) associated with a relatively pronounced decrease in body temperature. To date, several forms of torpor have been described in all three mammalian subclasses, i.e., monotremes, marsupials, and placentals, as well as in a few avian orders. This review highlights some of the characteristics, from the whole organism down to cellular and molecular aspects, associated with the torpor phenotype. The first part of this review focuses on the specific metabolic adaptations of torpor, as it is used by many species from temperate zones. This notably includes the endocrine changes involved in fat- and food-storing hibernating species, explaining biomedical implications of MR depression. We further compare adaptive mechanisms occurring in opportunistic vs. seasonal heterotherms, such as tropical and sub-tropical species. Such comparisons bring new insights into the metabolic origins of hibernation among tropical species, including resistance mechanisms to oxidative stress. The second section of this review emphasizes the mechanisms enabling heterotherms to protect their key organs against potential threats, such as reactive oxygen species, associated with the torpid state. We notably address the mechanisms of cellular rehabilitation and protection during torpor and hibernation, with an emphasis on the brain, a central organ requiring protection during torpor and recovery. Also, a special focus is given to the role of an ubiquitous and readily-diffusing molecule, hydrogen sulfide (H2S), in protecting against ischemia-reperfusion damage in various organs over the torpor-arousal cycle and during the torpid state. We conclude that (i) the flexibility of torpor use as an adaptive strategy enables different heterothermic species to substantially suppress their energy needs during periods of severely reduced food availability, (ii) the torpor phenotype implies marked metabolic adaptations from the whole organism down to cellular and molecular levels, and (iii) the torpid state is associated with highly efficient rehabilitation and protective mechanisms ensuring the continuity of proper bodily functions. Comparison of mechanisms in monotremes and marsupials is warranted for understanding the origin and evolution of mammalian torpor.

Validation of quantitative magnetic resonance as a non-invasive measure of body composition in an Australian microbat

Body composition (the total amount of fat mass, lean mass, minerals and water that constitute the body) is an important measure for understanding an animal’s physiology, ecology and behaviour. Traditional measures of body composition require the animal to either be placed under anaesthetic, which is invasive and can be high-risk, or be euthanised, preventing the ability to perform repeated measures on the same individual. We aimed to validate quantitative magnetic resonance (QMR) as a non-invasive measure of body composition by comparing QMR scans with chemical carcass analysis (CCA) in Gould’s wattled bats (Chalinolobus gouldii). In addition, we compared a commonly used microbat body condition index (residuals of mass by forearm length) to CCA. We found that QMR is an accurate method of estimating body condition in Gould’s wattled bats after calibration with regression equations, and the condition index could accurately predict lean and water mass but was a poor predictor of fat mass. Using accurate, non-invasive, repeatable measures of body condition may have important implications for ecological research in the face of changing environments.

Estrogen-sensitive medial preoptic area neurons coordinate torpor in mice

Homeotherms maintain a stable internal body temperature despite changing environments. During energy deficiency, some species can cease to defend their body temperature and enter a hypothermic and hypometabolic state known as torpor. Recent advances have revealed the medial preoptic area (MPA) as a key site for the regulation of torpor in mice. The MPA is estrogen-sensitive and estrogens also have potent effects on both temperature and metabolism. Here, we demonstrate that estrogen-sensitive neurons in the MPA can coordinate hypothermia and hypometabolism in mice. Selectively activating estrogen-sensitive MPA neurons was sufficient to drive a coordinated depression of metabolic rate and body temperature similar to torpor, as measured by body temperature, physical activity, indirect calorimetry, heart rate, and brain activity. Inducing torpor with a prolonged fast revealed larger and more variable calcium transients from estrogen-sensitive MPA neurons during bouts of hypothermia. Finally, whereas selective ablation of estrogen-sensitive MPA neurons demonstrated that these neurons are required for the full expression of fasting-induced torpor in both female and male mice, their effects on thermoregulation and torpor bout initiation exhibit differences across sex. Together, these findings suggest a role for estrogen-sensitive MPA neurons in directing the thermoregulatory and metabolic responses to energy deficiency.

Sex-Specific Response to Caloric Restriction After Reproductive Investment in Microcebus murinus: An Integrative Approach

In seasonal environments, males and females usually maintain high metabolic activity during the whole summer season, exhausting their energy reserves. In the global warming context, unpredictability of food availability during summer could dramatically challenge the energy budget of individuals. Therefore, one can predict that resilience to environmental stress would be dramatically endangered during summer. Here, we hypothesized that females could have greater capacity to survive harsh conditions than males, considering the temporal shift in their respective reproductive energy investment, which can challenge them differently, as well as enhanced flexibility in females' physiological regulation. We tackled this question on the gray mouse lemur (Microcebus murinus), focusing on the late summer period, after the reproductive effort. We monitored six males and six females before and after a 2-weeks 60% caloric restriction (CR), measuring different physiological and cellular parameters in an integrative and comparative multiscale approach. Before CR, females were heavier than males and mostly characterized by high levels of energy expenditure, a more energetic mitochondrial profile and a downregulation of blood antioxidants. We observed a similar energy balance between sexes due to CR, with a decrease in metabolic activity over time only in males. Oxidative damage to DNA was also reduced by different pathways between sexes, which may reflect variability in their physiological status and life-history traits at the end of summer. Finally, females' mitochondria seemed to exhibit greater flexibility and greater metabolic potential than males in response to CR. Our results showed strong differences between males and females in response to food shortage during late summer, underlining the necessity to consider sex as a factor for population dynamics in climate change models.

Phenology of reproductive condition varies with age and spring weather conditions in male Myotis daubentonii and M. nattereri (Chiroptera: Vespertilionidae)

We examine the extent to which intrinsic and extrinsic factors influence reproductive phenology in male bats at the population level. Using data from thirteen breeding seasons (2006-2018), encompassing the reproductive histories of 1546 Myotis daubentonii and 530 M. nattereri males, we compare rates of sexual maturation and the temporal distribution of phases of spermatogenesis between juvenile (born that season) and adult (born in previous seasons) males. We found that (i) higher proportions of M. daubentonii (50.81%) than M. nattereri (12.85%) became sexually mature as juveniles, (ii) the proportion of juveniles in reproductive condition per annum was influenced by spring weather conditions, (iii) in both species males that reached puberty as juveniles had higher body mass, on average, than immature juveniles, (iv) older males (aged ≥4 years old) commenced spermatogenesis earlier than young adult males (aged 1-3 years old), whilst juveniles that commenced spermatogenesis did so later in the year than adults, in both species, and (v) M. daubentonii commenced and completed spermatogenesis earlier than M. nattereri in the equivalent age class. Our findings suggest that selection pressure exists for early mating readiness and synchronisation with female receptivity.

Decimated little brown bats show potential for adaptive change

The degree to which species can rapidly adapt is key to survival in the face of climatic and other anthropogenic changes. For little brown bats (Myotis lucifugus), whose populations have experienced declines of over 90% because of the introduced fungal pathogen that causes white-nose syndrome (WNS), survival of the species may ultimately depend upon its capacity for adaptive change. Here, we present evidence of selectively driven change (adaptation), despite dramatic nonadaptive genomic shifts (genetic drift) associated with population declines. We compared the genetic makeups of wild survivors versus non-survivors of WNS, and found significant shifts in allele frequencies of genes associated with regulating arousal from hibernation (GABARB1), breakdown of fats (cGMP-PK1), and vocalizations (FOXP2). Changes at these genes are suggestive of evolutionary adaptation, given that WNS causes bats to arouse with unusual frequency from hibernation, contributing to premature depletion of fat reserves. However, whether these putatively adaptive shifts in allele frequencies translate into sufficient increases in survival for the species to rebound in the face of WNS is unknown.

External temperature and distance from nearest entrance influence microclimates of cave and culvert-roosting tri-colored bats (Perimyotis subflavus)

Many North American bat species hibernate in both natural and artificial roosts. Although hibernacula can have high internal climate stability, they still retain spatial variability in their thermal regimes, resulting in various "microclimates" throughout the roost that differ in their characteristics (e.g., temperature and air moisture). These microclimate components can be influenced by factors such as the number of entrances, the depth of the roost, and distance to the nearest entrance of the roost. Tri-colored bats are commonly found roosting in caves in winter, but they can also be found roosting in large numbers in culverts, providing the unique opportunity to investigate factors influencing microclimates of bats in both natural and artificial roost sites. As tri-colored bats are currently under consideration for federal listing, information of this type could be useful in aiding in the conservation and management of this species through a better understanding of what factors affect the microclimate near roosting bats. We collected data on microclimate temperature and microclimate actual water vapor pressure (AWVP) from a total of 760 overwintering tri-colored bats at 18 caves and 44 culverts. Using linear mixed models analysis, we found that variation in bat microclimate temperatures was best explained by external temperature and distance from nearest entrance in both caves and culverts. External temperature had a greater influence on microclimate temperatures in culverts than caves. We found that variation in microclimate AWVP was best explained by external temperature, distance from nearest entrance, and proportion from entrance (proportion of the total length of the roost from the nearest entrance) in culvert-roosting bats. Variation in microclimate AWVP was best explained by external temperature and proportion from entrance in cave-roosting bats. Our results suggest that bat microclimate temperature and AWVP are influenced by similar factors in both artificial and natural roosts, although the relative contribution of these factors differs between roost types.

Incorporating evaporative water loss into bioenergetic models of hibernation to test for relative influence of host and pathogen traits on white-nose syndrome

Hibernation consists of extended durations of torpor interrupted by periodic arousals. The ‘dehydration hypothesis’ proposes that hibernating mammals arouse to replenish water lost through evaporation during torpor. Arousals are energetically expensive, and increased arousal frequency can alter survival throughout hibernation. Yet we lack a means to assess the effect of evaporative water loss (EWL), determined by animal physiology and hibernation microclimate, on torpor bout duration and subsequent survival. White-nose syndrome (WNS), a devastating disease impacting hibernating bats, causes increased frequency of arousals during hibernation and EWL has been hypothesized to contribute to this increased arousal frequency. WNS is caused by a fungus, which grows well in humid hibernaculum environments and damages wing tissue important for water conservation. Here, we integrated the effect of EWL on torpor expression in a hibernation energetics model, including the effects of fungal infection, to determine the link between EWL and survival. We collected field data for Myotis lucifugus, a species that experiences high mortality from WNS, to gather parameters for the model. In saturating conditions, we predicted healthy bats experience minimal mortality. Infected bats, however, suffer high fungal growth in highly saturated environments, leading to exhaustion of fat stores before spring. Our results suggest that host adaptation to humid environments leads to increased arousal frequency from infection, which drives mortality across hibernaculum conditions. Our modified hibernation model provides a tool to assess the interplay between host physiology, hibernaculum microclimate, and diseases such as WNS on winter survival.

Male long-distance migrant turned sedentary; The West European pond bat (Myotis dasycneme) alters their migration and hibernation behaviour

During autumn in the temperate zone, insectivorous male bats face a profound energetic challenge, as in the same period they have to make energy choices related to hibernation, mating and migration. To investigate these energetic trade-offs, we compared the body mass of male and female pond bats (Myotis dasycneme) through the summer season, characterized the known hibernacula in terms of male or female bias, and subsequently compared their population trend during two study periods, between 1930–1980 and 1980–2015. Towards the end of summer, males began losing weight whilst females were simultaneously accumulating fat, suggesting that males were pre-occupied with mating. We also found evidence for a recent adaptation to this energetic trade-off, males have colonised winter roosts in formerly unoccupied areas, which has consequently led to a change in the migration patterns for the male population of this species. As male bats do not assist in raising offspring, males have ample time to restore their energy balance after hibernation. Our results suggest that choosing a hibernacula closer to the summer range not only decreases energy cost needed for migration, it also lengthens the mating season of the individual male. Our findings have important conservation implications, as male and female biased hibernation assemblages may differ critically in terms of microclimate preferences.

Male and female bats differ in their use of a large urban park

Understanding how wildlife respond to ever-encroaching urbanization is of great concern. Bats are the second-most speciose mammalian order and while many appear to be urban adapted, we currently have a limited understanding of their demography and habitat use within urban environments. Using a combination of captures to obtain demographic data, radio-telemetry to examine foraging and roosting behaviour, and data on diet and prey availability, we examined how big brown bats (Eptesicus fuscus), a synurbic species, use an urban green space (High Park) in Canada’s largest city centre, Toronto. We found that adult males outnumbered adult females more than two to one and that males were found throughout the park, while females were concentrated in an area with greater access to water, but lower prey availability. We also found that bats of both sexes were in poorer body condition than reported for other non-urban areas, including a site within southern Ontario. Our data suggest that High Park may not provide adequate resources for reproductive females as they were never found roosting in the park and beetles, their preferred prey, were limited. Although previous studies suggest urban green spaces may offer refuge to bats, most have not considered sex-specific responses to urbanization as they have largely been based on acoustic surveys. Our study therefore highlights the importance of considering demographic differences in response to urbanization to better inform urban management plans and green space development.

Activity Patterns of Cave-Dwelling Bat Species During Pre-Hibernation Swarming and Post-Hibernation Emergence in the Central Appalachians

In North America, bat research efforts largely have focused on summer maternity colonies and winter hibernacula, leaving the immediate pre- and post-hibernation ecology for many species unstudied. Understanding these patterns and processes is critical for addressing potential additive impacts to White-nose Syndrome (WNS)-affected bats, as autumn is a time of vital weight gain and fat resources are largely depleted in early spring in surviving individuals. Our study sought to examine autumn and spring bat activity patterns in the central Appalachian Mountains around three hibernacula to better understand spatio-temporal patterns during staging for hibernation and post-hibernation migration in the post-WNS environment. From early September through November 2015 and 2016, and from early March through April 2016 and 2017, we assessed the effects of distance to hibernacula and ambient conditions on nightly bat activity for Myotis spp. and big brown bats (Eptesicus fuscus) using zero-crossing frequency division bat detectors near cave entrances and 1 km, 2 km, and 3 km distant from caves. Following identification of echolocation calls, we used generalized linear mixed effects models to examine patterns of activity across the landscape over time and relative to weather. Overall bat activity was low at all sample sites during autumn and spring periods except at sites closest to hibernacula. Best-supported models describing bat activity varied, but date and ambient temperatures generally appeared to be major drivers of activity in both seasons. Total activity for all species had largely ceased by mid-November. Spring bat activity was variable across the sampling season, however, some activity was observed as early as mid-March, almost a month earlier than the historically accepted emergence time regionally. Current timing of restrictions on forest management activities that potentially remove day-roosts near hibernacula when bats are active on the landscape may be mismatched with actual spring post-hibernation emergence. Adjustments to the timing of these restrictions during the spring may help to avoid potentially additive negative impacts on WNS-impacted bat species.