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

Mapping Intimacies ◽

10.1101/750257 ◽

2019 ◽

Author(s):

Catherine G. Haase ◽

Nathan W. Fuller ◽

C. Reed Hranac ◽

David T. S. Hayman ◽

Liam P. McGuire ◽

...

Keyword(s):

Water Loss ◽

Water Conservation ◽

Fungal Growth ◽

Host Adaptation ◽

Evaporative Water Loss ◽

Myotis Lucifugus ◽

Evaporative Water ◽

White Nose Syndrome ◽

Animal Physiology ◽

Fat Stores

AbstractHibernation 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.

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Environmental determinants of total evaporative water loss in birds at multiple temperatures

The Auk ◽

10.1093/auk/ukz069 ◽

2019 ◽

Vol 137 (1) ◽

Cited By ~ 2

Author(s):

Soorim Song ◽

Steven R Beissinger

Keyword(s):

Water Loss ◽

Water Conservation ◽

Heat Dissipation ◽

Natural Habitat ◽

Thermal Conditions ◽

Evaporative Water Loss ◽

Diel Activity ◽

Maximum Temperature ◽

Arid Environments ◽

Evaporative Water

Abstract Endotherms dissipate heat to the environment to maintain a stable body temperature at high ambient temperatures, which requires them to maintain a balance between heat dissipation and water conservation. Birds are relatively small, contain a large amount of metabolically expensive tissue, and are mostly diurnal, making them susceptible to physiological challenges related to water balance and heat dissipation. We compiled total evaporative water loss (TEWL) measurements for 174 species of birds exposed to different temperatures and used comparative methods to examine their relationships with body size, ambient temperature, precipitation, diet, and diel activity cycle. TEWL in the thermoneutral zone (TNZ) was associated primarily with body mass and activity phase. Larger and more active-phase birds, with their higher metabolic rates, lost more water through evaporation than smaller, resting-phase birds, particularly at higher thermal exposures. However, maximum temperature of the natural habitat became an important determinant of TEWL when birds were exposed to temperatures exceeding the TNZ. Species from hotter climates exhibited higher TEWL. Adaptation to arid climates did not restrict evaporative water loss at thermal conditions within the TNZ, but promoted evaporative water loss at exposures above the TNZ. The TEWL of granivores, which ingest food with low water content, differed little from species with other food habitats under all thermal conditions. The effects of environmental covariates of TEWL were dissimilar across thermal exposures, suggesting no evidence for a tradeoff between water conservation in the TNZ and heat dissipation at exposure to higher temperatures. Thus, birds may be able to acclimate when climate change results in the need to increase heat dissipation due to warming, except perhaps in hot, arid environments where species will need to depend heavily upon evaporative cooling to maintain homeothermy.

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White-nose syndrome increases torpid metabolic rate and evaporative water loss in hibernating bats

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00058.2017 ◽

2017 ◽

Vol 313 (6) ◽

pp. R680-R686 ◽

Cited By ~ 17

Author(s):

Liam P. McGuire ◽

Heather W. Mayberry ◽

Craig K. R. Willis

Keyword(s):

Water Loss ◽

Direct Evidence ◽

Evaporative Water Loss ◽

Mechanistic Models ◽

Skin Infections ◽

Pseudogymnoascus Destructans ◽

Free Living ◽

Evaporative Water ◽

White Nose Syndrome ◽

Superficial Skin

Fungal diseases of wildlife typically manifest as superficial skin infections but can have devastating consequences for host physiology and survival. White-nose syndrome (WNS) is a fungal skin disease that has killed millions of hibernating bats in North America since 2007. Infection with the fungus Pseudogymnoascus destructans causes bats to rewarm too often during hibernation, but the cause of increased arousal rates remains unknown. On the basis of data from studies of captive and free-living bats, two mechanistic models have been proposed to explain disease processes in WNS. Key predictions of both models are that WNS-affected bats will show 1) higher metabolic rates during torpor (TMR) and 2) higher rates of evaporative water loss (EWL). We collected bats from a WNS-negative hibernaculum, inoculated one group with P. destructans, and sham-inoculated a second group as controls. After 4 mo of hibernation, TMR and EWL were measured using respirometry. Both predictions were supported, and our data suggest that infected bats were more affected by variation in ambient humidity than controls. Furthermore, disease severity, as indicated by the area of the wing with UV fluorescence, was positively correlated with EWL, but not TMR. Our results provide the first direct evidence that heightened energy expenditure during torpor and higher EWL independently contribute to WNS pathophysiology, with implications for the design of potential treatments for the disease.

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Evaporative Water Loss by Hibernating Little Brown Bats, Myotis lucifugus

Physiological Zoology ◽

10.1086/physzool.65.2.30158262 ◽

1992 ◽

Vol 65 (2) ◽

pp. 443-456 ◽

Cited By ~ 60

Author(s):

Donald W. Thomas ◽

Danielle Cloutier

Keyword(s):

Water Loss ◽

Evaporative Water Loss ◽

Myotis Lucifugus ◽

Evaporative Water ◽

Little Brown Bats

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Does control of insensible evaporative water loss by two species of mesic parrot have a thermoregulatory role?

Journal of Experimental Biology ◽

10.1242/jeb.229930 ◽

2020 ◽

Vol 223 (19) ◽

pp. jeb229930 ◽

Cited By ~ 1

Author(s):

Christine Elizabeth Cooper ◽

Philip Carew Withers ◽

Gerhard Körtner ◽

Fritz Geiser

Keyword(s):

Water Loss ◽

Water Conservation ◽

Arid Zone ◽

Evaporative Water Loss ◽

Primary Role ◽

Physiological Control ◽

Evaporative Water ◽

Ambient Temperatures ◽

Physiological Variables ◽

Regulatory Ability

ABSTRACTInsensible evaporative water loss (EWL) at or below thermoneutrality is generally assumed to be a passive physical process. However, some arid zone mammals and a single arid zone bird can control their insensible water loss, so we tested the hypothesis that the same is the case for two parrot species from a mesic habitat. We investigated red-rumped parrots (Psephotus haematonotus) and eastern rosellas (Platycercus eximius), measuring their EWL, and other physiological variables, at a range of relative humidities at ambient temperatures of 20 and 30°C (below and at thermoneutrality). We found that, despite a decrease in EWL with increasing relative humidity, rates of EWL were not fully accounted for by the water vapour deficit between the animal and its environment, indicating that the insensible EWL of both parrots was controlled. It is unlikely that this deviation from physical expectations was regulation with a primary role for water conservation because our mesic-habitat parrots had equivalent regulatory ability as the arid habitat budgerigar (Melopsittacus undulatus). This, together with our observations of body temperature and metabolic rate, instead support the hypothesis that acute physiological control of insensible water loss serves a thermoregulatory purpose for endotherms. Modification of both cutaneous and respiratory avenues of evaporation may be involved, possibly via modification of expired air temperature and humidity, and surface resistance.

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