The evolution of a bat population with white-nose syndrome (WNS) reveals a shift from an epizootic to an enzootic phase.

BACKGROUND: White-nose Syndrome (WNS) is a mycosis caused by a cutaneous infection with the fungus Pseudogymnoascus destructans (Pd). It produces hibernation mortality rates of 75-98% in 4 bats: Myotis lucifugus, M. septentrionalis, M. sodalis, and Perimyotis subflavus. These high mortality rates were observed during the first several years after the arrival of P. destructans at a hibernation site. Mortality is caused by a 60% decrease in torpor bout duration, which results in a premature depletion of depot fat prior to spring. RESULTS: Little is known about the long-term effects of Pd on torpor and mortality, thus we conducted a 9-year study on M. lucifugus at 5 of the hibernation sites where Pd first appeared in North America during the winter of 2007-08. The M. lucifugus hibernating at one of these sites one year after the arrival of Pd (2008-09) had: a) a mean torpor bout duration of 7.6 d, b) no depot fat reserves by March, and c) an apparent over-winter mortality rate of 88%. The M. lucifugus hibernating at this same site 6-9 years after the arrival of Pd, in contrast, had: a) a mean torpor bout duration of 14.7 d, b) depot fat remaining in March, and c) an apparent mortality rate of 50%. The number of M. lucifugus hibernating at 2 of these sites has consistently increased since 2010 and is now more than 3.0-fold higher than the number remaining after the winter of 2008-09. CONCLUSIONS: These findings indicate that this population of M. lucifugus has evolved mechanisms to hibernate well in the presence of Pd, thus reducing over-winter mortality.

The Antifungal Properties of Epidermal Fatty Acid Esters: Insights from White-Nose Syndrome (WNS) in Bats.

Numerous free fatty acids (FFAs) are known to have potent antifungal effects. The mammalian epidermis contains both FFAs and multiple classes of fatty acid esters, including 1-monoacylglycerols and wax esters. We thus hypothesized that wax esters and 1-monoacylglycerols composed of antifungal fatty acids would also have antifungal properties. We tested this hypothesis by examining the effects of 1-monoacylglycerols, 1,3-diacylglycerols, and wax esters on the growth of Pseudogymnoascus destructans (Pd), the fungus that causes White-nose Syndrome (WNS) in North American bats by invading their epidermis. Laboratory experiments with Pd cultures demonstrated that: (a) three 1-monoacylglycerols (1-monopalmitolein, 1-monoolein, and 1-monolinolein), as well as, (b) two wax esters, behenyl oleate and behenyl palmitoleate, profoundly inhibit Pd growth. The normal growth cycle of Pd was interrupted by addition of two cholesterol esters to the media as well. A bat species resistant to cutaneous Pd infections has these 1-monoacylglycerols in the epidermis, and another Pd resistant bat species has these wax esters in the sebum, thus cutaneous lipid composition is one factor which enables some bats to avoid WNS. Our experiments also revealed that the fatty acid esters which inhibit Pd growth are not hydrolyzed by the lipases secreted by this fungus, whereas the esters that do not inhibit Pd growth are hydrolyzed.

The effects of epidermal fatty acid profiles, 1-oleoglycerol, and triacylglycerols on the susceptibility of hibernating bats to Pseudogymnoascus destructans.

White Nose Syndrome (WNS) greatly increases the over-winter mortality of little brown (Myotis lucifugus), Indiana (M. sodalis), northern (M. septentrionalis), and tricolored (Perimyotis subflavus) bats, and is caused by cutaneous infections with Pseudogymnoascus destructans (Pd). Big brown bats (Eptesicus fuscus) are highly resistant to Pd infections. Seven different fatty acids (myristic, pentadecanoic, palmitic, palmitoleic, oleic, and, linoleic acids) occur in the wing epidermis of both M. lucifugus and E. fuscus, 4 of which (myristic, palmitoleic, oleic, and, linoleic acids) inhibit Pd growth. The amounts of myristic and linoleic acids in the epidermis of M. lucifugus decrease during hibernation, thus we predicted that the epidermal fatty acid profile of M. lucifugus during hibernation has a reduced ability to inhibit Pd growth. Laboratory Pd growth experiments were conducted to test this hypothesis. The results demonstrated that the fatty acid profile of M. lucifugus wing epidermis during hibernation has a reduced ability to inhibit the growth of Pd. Additional Pd growth experiments revealed that: a) triacylglycerols composed of known anti-Pd fatty acids do not significantly affect growth, b) pentadecanoic acid inhibits Pd growth, and c) 1-oleoglycerol, which is found in the wing epidermis of E. fuscus, also inhibits the growth of this fungus. Analyses of white adipose from M. lucifugus also revealed the selective retention of oleic and linoleic acids in this tissue during hibernation.

The Effects of Cutaneous Fatty Acids on the Growth of Pseudogymnoascus destructans, the Etiological Agent of White-Nose Syndrome (WNS).

White Nose Syndrome (WNS) greatly increases the over-winter mortality of little brown (Myotis lucifugus), Indiana (Myotis sodalis), northern (Myotis septentrionalis), and tricolored (Perimyotis subflavus) bats. It is caused by a cutaneous infection with the fungus Pseudogymnoascus destructans (Pd). Big brown bats (Eptesicus fuscus) are much more resistant to cutaneous infection with Pd, however. We thus conducted analyses of wing epidermis from hibernating E. fuscus and M. lucifugus to determine their fatty acid compositions, and laboratory Pd culture experiments at 4.0-13.4°C to determine the effects of these fatty acids on Pd growth. Our analyses revealed that the epidermis of both bat species contain the same 7 fatty acid types (14:0, 15:0, 16:0. 16:1, 18:0, 18:1, & 18:2), but the epidermis of M. lucifugus contains: a) more stearic (18:0) acid, b) less palmitoleic (16:1) acid, c) less myristic (14:0) acid, and, d) less oleic (18:1) acid than that of E. fuscus. The growth of Pd was inhibited by: a) myristic and stearic acids at 10.5-13.4°C, but not at 4.0-5.0°C, b) oleic acid at 5.0-10.6°C, c) palmitoleic acid, and, d) linoleic (18:2) acid at 5.0-10.6°C. One set of factors that enables E. fuscus to better resist cutaneous P. destructans infections (and thus WNS) therefore appears to be the relatively higher myristic, palmitoleic, and oleic acid contents of the epidermis.

The resistance of a North American bat species (Eptesicus fuscus) to White-nose Syndrome (WNS).

White-nose Syndrome (WNS) is the primary cause of over-winter mortality for little brown (Myotis lucifugus), northern (Myotis septentrionalis), and tricolored (Perimyotis subflavus) bats, and is due to cutaneous infection with the fungus Pseudogymnoascus (Geomyces) destructans (Pd). Cutaneous infection with P. destructans disrupts torpor patterns, which is thought to lead to a premature depletion of body fat reserve. Field studies were conducted at 3 WNS-affected hibernation sites to determine if big brown bats (Eptesicus fuscus) are resistant to Pd. Radio telemetry studies were conducted during 2 winters to determine the torpor patterns of 23 free-ranging E. fuscus hibernating at a site where Pd occurs. The body fat contents of free-ranging E. fuscus and M. lucifugus during hibernation at 2 different WNS-affected sites were also determined. The numbers of bats hibernating at the same site was determined during both: a) 4-7 years prior to the arrival of Pd, and, b) 2-3 years after it first appeared at this site. The torpor bouts of big brown bats hibernating at a WNS-affected site were not significantly different in length from those previously reported for this species. The mean body fat content of E. fuscus in February was nearly twice that of M. lucifugus hibernating at the same WNS-affected sites during this month. The number of M. lucifugus hibernating at one site decreased by 99.6% after P. destructans first appeared, whereas the number of E. fuscus hibernating there actually increased by 43% during the same period. None of the E. fuscus collected during this study had any visible fungal growth or lesions on their skin, whereas virtually all the M. lucifugus collected had visible fungal growth on their wings, muzzle, and ears. These findings indicate that big brown bats are resistant to WNS.

Frequent arousal from hibernation linked to severity of infection and mortality in bats with white-nose syndrome.

White-nose syndrome (WNS), an emerging infectious disease that has killed over 5.5 million hibernating bats, is named for the causative agent, a white fungus (Geomyces destructans (Gd)) that invades the skin of torpid bats. During hibernation, arousals to warm (euthermic) body temperatures are normal but deplete fat stores. Temperature-sensitive dataloggers were attached to the backs of 504 free-ranging little brown bats (Myotis lucifugus) in hibernacula located throughout the northeastern USA. Dataloggers were retrieved at the end of the hibernation season and complete profiles of skin temperature data were available from 83 bats, which were categorized as: (1) unaffected, (2) WNS-affected but alive at time of datalogger removal, or (3) WNS-affected but found dead at time of datalogger removal. Histological confirmation of WNS severity (as indexed by degree of fungal infection) as well as confirmation of presence/absence of DNA from Gd by PCR was determined for 26 animals. We demonstrated that WNS-affected bats aroused to euthermic body temperatures more frequently than unaffected bats, likely contributing to subsequent mortality. Within the subset of WNS-affected bats that were found dead at the time of datalogger removal, the number of arousal bouts since datalogger attachment significantly predicted date of death. Additionally, the severity of cutaneous Gd infection correlated with the number of arousal episodes from torpor during hibernation. Thus, increased frequency of arousal from torpor likely contributes to WNS-associated mortality, but the question of how Gd infection induces increased arousals remains unanswered.

Dietary fatty acid composition and the hibernation patterns in free-ranging arctic ground squirrels.

Laboratory experiments have demonstrated that the amount of polyunsaturated fatty acids (PUFAs) in the diet before hibernation influences patterns of mammalian torpor. The hibernation ability of ground squirrels is greatest (longest torpor bouts, greatest number of animals entering torpor) when the PUFA content of their fall diets is 33-74 mg/g, under laboratory conditions. The extent to which natural fall diets both (a) vary in PUFA content and (b) influence the torpor patterns of free-ranging populations of hibernating mammals is unknown, however. We conducted a 3-yr study on the diet PUFA contents and subsequent hibernation patterns of free-ranging arctic ground squirrels (Spermophilus parryii) in the Brooks Range of Alaska. We found that the PUFA contents of fall diets varied more than threefold among individuals. Our study also revealed that arctic ground squirrels that consumed a moderate-PUFA (33-74 mg/g) diet had (a) longer torpor bouts, (b) fewer arousals from torpor, (c) shorter arousal periods, (d) more days in torpor, and (e) greater probability of persisting in the population than those that consumed a high-PUFA (>74 mg/g) diet during the fall. No animals were demonstrated to have consumed a diet representing low-PUFA (<33 mg/g) values. Our study is therefore the first to demonstrate that estimated dietary PUFA levels of a free-ranging hibernator influence subsequent torpor patterns.