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1. Body mass and hibernation microclimate may predict bat susceptibility to white‐nose syndrome

   https://doi.org/10.1002/ece3.7070  

   Haase, Catherine G. ; Fuller, Nathan W. ; Dzal, Yvonne A. ; Hranac, C. Reed ; Hayman, David T. S. ; Lausen, Cori L. ; Silas, Kirk A. ; Olson, Sarah H. ; Plowright, Raina K. ( December 2020 , Ecology and Evolution)

   In multihost disease systems, differences in mortality between species may reflect variation in host physiology, morphology, and behavior. In systems where the pathogen can persist in the environment, microclimate conditions, and the adaptation of the host to these conditions, may also impact mortality. White‐nose syndrome (WNS) is an emerging disease of hibernating bats caused by an environmentally persistent fungus,Pseudogymnoascus destructans. We assessed the effects of body mass, torpid metabolic rate, evaporative water loss, and hibernaculum temperature and water vapor deficit on predicted overwinter survival of bats infected byP. destructans. We used a hibernation energetics model in an individual‐based model framework to predict the probability of survival of nine bat species at eight sampling sites across North America. The model predicts time until fat exhaustion as a function of species‐specific host characteristics, hibernaculum microclimate, and fungal growth. We fit a linear model to determine relationships with each variable and predicted survival and semipartial correlation coefficients to determine the major drivers in variation in bat survival. We found host body mass and hibernaculum water vapor deficit explained over half of the variation in survival with WNS across species. As previous work on the interplay between host and pathogen physiology and the environment has focused on species with narrow microclimate preferences, our view on this relationship is limited. Our results highlight some key predictors of interspecific survival among western bat species and provide a framework to assess impacts of WNS as the fungus continues to spread into western North America.

    

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2. The functional significance of facultative hyperthermia varies with body size and phylogeny in birds

   https://doi.org/10.1111/1365-2435.13274  

   Gerson, Alexander R. ; McKechnie, Andrew E. ; Smit, Ben ; Whitfield, Maxine C. ; Smith, Eric K. ; Talbot, William A. ; McWhorter, Todd J. ; Wolf, Blair O. ; Williams, ed., Tony ( January 2019 , Functional Ecology)

   Facultative hyperthermia, the elevation of body temperature above normothermic levels, during heat exposure, importantly affects the water economy and heat balance of terrestrial endotherms. We currently lack a mechanistic understanding of the benefits hyperthermia provides for avian taxa.

   Facultative hyperthermia has been proposed to minimize rates of water loss via three distinct mechanisms: M1) by maintaining body temperature (T_b) above environmental temperatures (T_e), heat can be lost non‐evaporatively, saving water; M2) by minimizing the thermal gradient whenT_e>T_b, environmental heat gain and evaporative water loss rates are reduced; and M3) by storing heat via increases inT_bwhich reduces evaporative heat loss demands and conserves water.

   Although individuals may benefit from all three mechanisms during heat exposure, the relative importance of each mechanism has not been quantified among species that differ in their body size, heat tolerance and mechanisms of evaporative heat dissipation.

   We measured resting metabolism, evaporative water loss and real‐timeT_bfrom 33 species of birds representing nine orders ranging in mass from 8 to 300 g and estimated the water savings associated with each proposed mechanism. We show that facultative hyperthermia varies in its benefits among species.

   Small songbirds with comparatively low evaporative cooling capacities benefit most from (M1), and hyperthermia maintains a thermal gradient that allows non‐evaporative heat losses. Other species benefited most from (M2) minimizing evaporative losses via a reduced thermal gradient for heat gain at highT_e. We found that (M3), heat storage, only improved the water economy of the sandgrouse, providing little benefit to other species.

   We propose that differences in the frequency and magnitude of hyperthermia will drive taxon‐specific differences in temperature sensitivity of tissues and enzymes and that the evolution of thermoregulatory mechanisms of evaporative heat dissipation may contribute to differences in basal metabolic rate among avian orders.

   Understanding the mechanistic basis of heat tolerance is essential to advance our understanding of the ecology of birds living in hot environments that are warming rapidly, where extreme heat events are already re‐structuring avian communities.

   Aplain language summaryis available for this article.

    

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3. Assessing hybrid vigour using the thermal sensitivity of physiological trade‐offs in tiger salamanders

   https://doi.org/10.1111/1365-2435.14463  

   Burger, Isabella J. ; Carter, Evin T. ; Magner, Lexie M. ; Muñoz, Martha M. ; Sears, Michael W. ; Fitzpatrick, Benjamin M. ; Riddell, Eric A. ( November 2023 , Functional Ecology)

   Hybridization between species affects biodiversity and population sustainability in numerous ways, many of which depend on the fitness of the hybrid relative to the parental species. Hybrids can exhibit fitter phenotypes compared to the parental lineages, and this ‘hybrid vigour’ can then lead to the extinction of one or both parental lines.

   In this study, we analysed the relationship between water loss and gas exchange to compare physiological performance among three tiger salamander genotypes—the native California tiger salamander (CTS), the invasive barred tiger salamanders (BTS) and CTS × BTS hybrids across multiple temperatures (13.5°C, 20.5°C and 23.5°C). We developed a new index of performance, the water‐gas exchange ratio (WGER), which we define as the ratio of gas exchange to evaporative water loss (μLVO₂/μL H₂O). The ratio describes the ability of an organism to support energetically costly activities with high levels of gas exchange while simultaneously limiting water loss to lower desiccation risk. We used flow through respirometry to measure the thermal sensitivity of metabolic rate and resistance to water loss of each salamander genotype to compare indices of physiological performance.

   We found that temperature had a significant effect on metabolic rate and resistance to water loss, with both traits increasing as temperatures warmed. Across genotypes, we found that hybrids have a higher WGER than the native CTS, owing to a higher metabolic rate despite having a lower resistance to water loss.

   These results provide a greater insight into the physiological mechanisms driving hybrid vigour and offer a potential explanation for the rapid spread of salamander hybrids. More broadly, our introduction of the WGER may allow for species‐ or lineage‐wide comparisons of physiological performance across changing environmental conditions, highlighting the insight that can be gleaned from multitrait analysis of organism performance.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

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4. Metabolic rates from Bluntnose minnow ( Pimephales notatus ) populations at lower latitudes are more sensitive to changes in temperature than populations at higher latitudes

   https://doi.org/10.1111/eff.12507  

   Beachum, Collin E. ; Michel, Matt J. ; Knouft, Jason H. ( October 2019 , Ecology of Freshwater Fish)

   Predicting the potential effects of changes in climate on freshwater species requires an understanding of the relationships between physiological traits and environmental conditions among populations. While water temperature is a primary factor regulating metabolic rates in freshwater ectotherms, how metabolic rates vary across the species range is unclear. In addition, photoperiod has also been hypothesised to influence metabolic rates in freshwater taxa based on seasonal changes in activity rates. Using an experimental approach, we investigated whether variation in routine metabolic rate (RMR) and sensitivity of RMR to changes in temperature are correlated with local thermal regimes, photoperiods and body mass among ten populations across the geographic range of the Bluntnose minnow (Pimephales notatus), a North American freshwater fish species. Routine metabolic rate data were collected from populations acclimatised to three temperature treatments (9, 18 and 27°C) and correlated with water temperature and photoperiod estimates at collection locations for each population. Routine metabolic rate was negatively correlated with minimum photoperiod at 9°C, negatively correlated with weekly high temperature at 18°C and positively correlated with weekly high temperature at 27°C. Body mass was also a predictor of RMR at each temperature treatment. Thermal sensitivity of RMR was positively correlated with weekly high temperature, indicating that individuals from warmer low latitude populations experienced greater sensitivity of RMR to changes in temperature than individuals from cooler high latitude populations. These results indicate differential responses among populations to variation in temperature and suggest the importance of recognising this variation when characterising responses of freshwater taxa to increases in water temperature.

    

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5. Liver proteome response to torpor in a basoendothermic mammal, Tenrec ecaudatus , provides insights into the evolution of homeothermy

   https://doi.org/10.1152/ajpregu.00150.2021  

   Khudyakov, Jane I. ; Treat, Michael D. ; Shanafelt, Mikayla C. ; Deyarmin, Jared S. ; Neely, Benjamin A. ; van Breukelen, Frank ( October 2021 , American Journal of Physiology-Regulatory, Integrative and Comparative Physiology)

   Many mammals use adaptive heterothermy (e.g., torpor, hibernation) to reduce metabolic demands of maintaining high body temperature ( T b ). Torpor is typically characterized by coordinated declines in T b and metabolic rate (MR) followed by active rewarming. Most hibernators experience periods of euthermy between bouts of torpor during which homeostatic processes are restored. In contrast, the common tenrec, a basoendothermic Afrotherian mammal, hibernates without interbout arousals and displays extreme flexibility in T b and MR. We investigated the molecular basis of this plasticity in tenrecs by profiling the liver proteome of animals that were active or torpid with high and more stable T b (∼32°C) or lower T b (∼14°C). We identified 768 tenrec liver proteins, of which 50.9% were differentially abundant between torpid and active animals. Protein abundance was significantly more variable in active cold and torpid compared with active warm animals, suggesting poor control of proteostasis. Our data suggest that torpor in tenrecs may lead to mismatches in protein pools due to poor coordination of anabolic and catabolic processes. We propose that the evolution of endothermy leading to a more realized homeothermy of boreoeutherians likely led to greater coordination of homeostatic processes and reduced mismatches in thermal sensitivities of metabolic pathways. 

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