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Sandoval-Herrera NI, Mastromonaco GF, Becker DJ, Simmons NB, Welch KC. Inter- and intra-specific variation in hair cortisol concentrations of Neotropical bats. CONSERVATION PHYSIOLOGY 2021; 9:coab053. [PMID: 34267922 PMCID: PMC8278960 DOI: 10.1093/conphys/coab053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/20/2021] [Revised: 06/13/2021] [Accepted: 07/08/2021] [Indexed: 06/13/2023]
Abstract
Quantifying hair cortisol has become popular in wildlife ecology for its practical advantages for evaluating stress. Before hair cortisol levels can be reliably interpreted, however, it is key to first understand the intrinsic factors explaining intra- and inter-specific variation. Bats are an ecologically diverse group of mammals that allow studying such variation. Given that many bat species are threatened or have declining populations in parts of their range, minimally invasive tools for monitoring colony health and identifying cryptic stressors are needed to efficiently direct conservation efforts. Here we describe intra- and inter-specific sources of variation in hair cortisol levels in 18 Neotropical bat species from Belize and Mexico. We found that fecundity is an important ecological trait explaining inter-specific variation in bat hair cortisol. Other ecological variables such as colony size, roost durability and basal metabolic rate did not explain hair cortisol variation among species. At the individual level, females exhibited higher hair cortisol levels than males and the effect of body mass varied among species. Overall, our findings help validate and accurately apply hair cortisol as a monitoring tool in free-ranging bats.
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Affiliation(s)
- Natalia I Sandoval-Herrera
- Department of Ecology and Evolutionary Biology, University of Toronto, Ontario, M5S 3B2, Canada
- Department of Biological Sciences, University of Toronto Scarborough, Ontario, M1C 1A4, Canada
| | | | - Daniel J Becker
- Department of Biology, University of Oklahoma, Norman, OK 73019, USA
| | - Nancy B Simmons
- Department of Mammalogy, Division of Vertebrate Zoology, American Museum of Natural History, New York, NY, 10024-5102, USA
| | - Kenneth C Welch
- Department of Ecology and Evolutionary Biology, University of Toronto, Ontario, M5S 3B2, Canada
- Department of Biological Sciences, University of Toronto Scarborough, Ontario, M1C 1A4, Canada
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Stidsholt L, Greif S, Goerlitz HR, Beedholm K, Macaulay J, Johnson M, Madsen PT. Hunting bats adjust their echolocation to receive weak prey echoes for clutter reduction. SCIENCE ADVANCES 2021; 7:7/10/eabf1367. [PMID: 33658207 PMCID: PMC7929515 DOI: 10.1126/sciadv.abf1367] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2020] [Accepted: 01/21/2021] [Indexed: 05/27/2023]
Abstract
How animals extract information from their surroundings to guide motor patterns is central to their survival. Here, we use echo-recording tags to show how wild hunting bats adjust their sensory strategies to their prey and natural environment. When searching, bats maximize the chances of detecting small prey by using large sensory volumes. During prey pursuit, they trade spatial for temporal information by reducing sensory volumes while increasing update rate and redundancy of their sensory scenes. These adjustments lead to very weak prey echoes that bats protect from interference by segregating prey sensory streams from the background using a combination of fast-acting sensory and motor strategies. Counterintuitively, these weak sensory scenes allow bats to be efficient hunters close to background clutter broadening the niches available to hunt for insects.
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Affiliation(s)
- Laura Stidsholt
- Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark.
| | - Stefan Greif
- Department of Zoology, Tel Aviv University, Tel Aviv, Israel
- Acoustic and Functional Ecology, Max Planck Institute for Ornithology, Seewiesen, Germany
| | - Holger R Goerlitz
- Acoustic and Functional Ecology, Max Planck Institute for Ornithology, Seewiesen, Germany
| | - Kristian Beedholm
- Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark
| | - Jamie Macaulay
- Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark
| | - Mark Johnson
- Aarhus Institute of Advanced Studies, Aarhus University, Aarhus, Denmark
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Genzel D, Yartsev MM. The fully automated bat (FAB) flight room: A human-free environment for studying navigation in flying bats and its initial application to the retrosplenial cortex. J Neurosci Methods 2020; 348:108970. [PMID: 33065152 DOI: 10.1016/j.jneumeth.2020.108970] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2020] [Revised: 09/23/2020] [Accepted: 10/07/2020] [Indexed: 10/23/2022]
Abstract
BACKGROUND Bats can offer important insight into the neural computations underlying complex forms of navigation. Up to now, this had been done with the confound of the human experimenter being present in the same environment the bat was navigating in. NEW METHOD We, therefore, developed a novel behavioral setup, the fully automated bat (FAB) flight room, to obtain a detailed and quantitative understanding of bat navigation flight behavior while studying its relevant neural circuits, but importantly without human intervention. As a demonstration of the FAB flight room utility we trained bats on a four-target, visually-guided, foraging task and recorded neural activity from the retrosplenial cortex (RSC). RESULTS We find that bats can be efficiently trained and engaged in complex, multi-target, visuospatial behavior in the FAB flight room. Wireless neural recordings from the bat RSC during the task confirm the multiplexed characteristics of single RSC neurons encoding spatial positional information, target selection, reward obtainment and the intensity of visual cues used to guide navigation. COMPARISON WITH EXISTING METHODS In contrast to the methods introduced in previous studies, we now can investigate spatial navigation in bats without potential experimental biases that can be easily introduced by active physical involvement and presence of experimenters in the room. CONCLUSIONS Combined, we describe a novel experimental approach for studying spatial navigation in freely flying bats and provide support for the involvement of bat RSC in aerial visuospatial foraging behavior.
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Affiliation(s)
- Daria Genzel
- Helen Wills Neuroscience Institute, UC Berkeley, Berkeley, 94720, United States; Department of Bioengineering, UC Berkeley, Berkeley, 94720, United States
| | - Michael M Yartsev
- Helen Wills Neuroscience Institute, UC Berkeley, Berkeley, 94720, United States; Department of Bioengineering, UC Berkeley, Berkeley, 94720, United States.
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Gordon R, Ivens S, Ammerman LK, Fenton MB, Littlefair JE, Ratcliffe JM, Clare EL. Molecular diet analysis finds an insectivorous desert bat community dominated by resource sharing despite diverse echolocation and foraging strategies. Ecol Evol 2019; 9:3117-3129. [PMID: 30962885 PMCID: PMC6434550 DOI: 10.1002/ece3.4896] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2018] [Revised: 12/12/2018] [Accepted: 12/13/2018] [Indexed: 01/05/2023] Open
Abstract
Interspecific differences in traits can alter the relative niche use of species within the same environment. Bats provide an excellent model to study niche use because they use a wide variety of behavioral, acoustic, and morphological traits that may lead to multi-species, functional groups. Predatory bats have been classified by their foraging location (edge, clutter, open space), ability to use aerial hawking or substrate gleaning and echolocation call design and flexibility, all of which may dictate their prey use. For example, high frequency, broadband calls do not travel far but offer high object resolution while high intensity, low frequency calls travel further but provide lower resolution. Because these behaviors can be flexible, four behavioral categories have been proposed: (a) gleaning, (b) behaviorally flexible (gleaning and hawking), (c) clutter-tolerant hawking, and (d) open space hawking. Many recent studies of diet in bats use molecular tools to identify prey but mainly focus on one or two species in isolation; few studies provide evidence for substantial differences in prey use despite the many behavioral, acoustic, and morphological differences. Here, we analyze the diet of 17 sympatric species in the Chihuahuan desert and test the hypothesis that peak echolocation frequency and behavioral categories are linked to differences in diet. We find no significant correlation between dietary richness and echolocation peak frequency though it spanned close to 100 kHz across species. Our data, however, suggest that bats which use both gleaning and hawking strategies have the broadest diets and are most differentiated from clutter-tolerant aerial hawking species.
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Affiliation(s)
- Rowena Gordon
- School of Biological and Chemical SciencesQueen Mary University of LondonLondonUK
| | - Sally Ivens
- School of Biological and Chemical SciencesQueen Mary University of LondonLondonUK
| | | | - M. Brock Fenton
- Department of BiologyUniversity of Western OntarioLondonOntarioCanada
| | - Joanne E. Littlefair
- School of Biological and Chemical SciencesQueen Mary University of LondonLondonUK
- Department of BiologyMcGill UniversityMontréalQuébecCanada
| | - John M. Ratcliffe
- Department of BiologyUniversity of Toronto MississaugaMississaugaOntarioCanada
| | - Elizabeth L. Clare
- School of Biological and Chemical SciencesQueen Mary University of LondonLondonUK
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Luo J, Macias S, Ness TV, Einevoll GT, Zhang K, Moss CF. Neural timing of stimulus events with microsecond precision. PLoS Biol 2018; 16:e2006422. [PMID: 30365484 PMCID: PMC6221347 DOI: 10.1371/journal.pbio.2006422] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2018] [Revised: 11/07/2018] [Accepted: 10/10/2018] [Indexed: 12/29/2022] Open
Abstract
Temporal analysis of sound is fundamental to auditory processing throughout the animal kingdom. Echolocating bats are powerful models for investigating the underlying mechanisms of auditory temporal processing, as they show microsecond precision in discriminating the timing of acoustic events. However, the neural basis for microsecond auditory discrimination in bats has eluded researchers for decades. Combining extracellular recordings in the midbrain inferior colliculus (IC) and mathematical modeling, we show that microsecond precision in registering stimulus events emerges from synchronous neural firing, revealed through low-latency variability of stimulus-evoked extracellular field potentials (EFPs, 200–600 Hz). The temporal precision of the EFP increases with the number of neurons firing in synchrony. Moreover, there is a functional relationship between the temporal precision of the EFP and the spectrotemporal features of the echolocation calls. In addition, EFP can measure the time difference of simulated echolocation call–echo pairs with microsecond precision. We propose that synchronous firing of populations of neurons operates in diverse species to support temporal analysis for auditory localization and complex sound processing. We routinely rely on a stopwatch to precisely measure the time it takes for an athlete to reach the finish line. Without the assistance of such a timing device, our measurement of elapsed time becomes imprecise. By contrast, some animals, such as echolocating bats, naturally perform timing tasks with remarkable precision. Behavioral research has shown that echolocating bats can estimate the elapsed time between sonar cries and echo returns with a precision in the range of microseconds. However, the neural basis for such microsecond precision has remained a puzzle to scientists. Combining extracellular recordings in the bat’s inferior colliculus (IC)—a midbrain nucleus of the auditory pathway—and mathematical modeling, we show that microsecond precision in registering stimulus events emerges from synchronous neural firing. Our recordings revealed a low-latency variability of stimulus-evoked extracellular field potentials (EFPs), which, according to our mathematical modeling, was determined by the number of firing neurons and their synchrony. Moreover, the acoustic features of echolocation calls, such as signal duration and bandwidth, which the bat dynamically modulates during prey capture, also modulate the precision of EFPs. These findings have broad implications for understanding temporal analysis of acoustic signals in a wide range of auditory behaviors across the animal kingdom.
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Affiliation(s)
- Jinhong Luo
- Department of Psychological and Brain Sciences, Johns Hopkins University, Baltimore, Maryland, United States of America
- * E-mail: (JL); (CFM)
| | - Silvio Macias
- Department of Psychological and Brain Sciences, Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Torbjørn V. Ness
- Faculty of Science and Technology, Norwegian University of Life Sciences, Ås, Norway
| | - Gaute T. Einevoll
- Faculty of Science and Technology, Norwegian University of Life Sciences, Ås, Norway
- Department of Physics, University of Oslo, Oslo, Norway
| | - Kechen Zhang
- Department of Biomedical Engineering, Johns Hopkins School of Medicine, Baltimore, Maryland, United States of America
| | - Cynthia F. Moss
- Department of Psychological and Brain Sciences, Johns Hopkins University, Baltimore, Maryland, United States of America
- * E-mail: (JL); (CFM)
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Accurate sound localization behavior in a gleaning bat, Antrozous pallidus. Sci Rep 2018; 8:13457. [PMID: 30194319 PMCID: PMC6128894 DOI: 10.1038/s41598-018-31606-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Accepted: 08/20/2018] [Indexed: 11/08/2022] Open
Abstract
Acute auditory processing in bats is typically associated with echolocation. A subset of bats, called gleaners, listens to prey-generated noise to hunt surface-dwelling prey. Gleaners depend less on echolocation to hunt and, therefore, accurate localization of prey-generated noise is necessary for foraging success. Here we studied azimuth sound localization behavior in the pallid bat, a gleaning bat in which spatial encoding has been studied extensively. We tested pallid bats on a relatively difficult open loop task (single sound, duration ≤ 200 ms). The bats were trained to face the midline when stimulus was presented, and this was confirmed with video analysis. Bats localized broadband noise (5-30 kHz) from 1 out of 11 speakers spaced evenly across the horizontal plane of the frontal sound field. Approach to the correct speaker was rewarded. Pallid bats show accurate localization near the midline with mean errors between 3-6°. Remarkably, the accuracy does not decline significantly at peripheral locations with bats averaging <~7° error upto 72° off midline. Manipulation of stimulus bandwidth shows that higher frequencies (20-30 kHz) are necessary for accurate localization. Comparative studies of gleaning bats will reveal convergent adaptations across auditory systems for non-echolocation-based behaviors in bats.
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Razak K. Adaptations for Substrate Gleaning in Bats: The Pallid Bat as a Case Study. BRAIN, BEHAVIOR AND EVOLUTION 2018; 91:97-108. [DOI: 10.1159/000488873] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2018] [Accepted: 03/26/2018] [Indexed: 11/19/2022]
Abstract
Substrate gleaning is a foraging strategy in which bats use a mixture of echolocation, prey-generated sounds, and vision to localize and hunt surface-dwelling prey. Many substrate-gleaning species depend primarily on prey-generated noise to hunt. Use of echolocation is limited to general orientation and obstacle avoidance. This foraging strategy involves a different set of selective pressures on morphology, behavior, and auditory system organization of bats compared to the use of echolocation for both hunting and navigation. Gleaning likely evolved to hunt in cluttered environments and/or as a counterstrategy to reduce detection by eared prey. Gleaning bats simultaneously receive streams of echoes from obstacles and prey-generated noise, and have to segregate these acoustic streams to attend to one or both. Not only do these bats have to be exquisitely sensitive to the soft, low frequency sounds produced by walking/rustling prey, they also have to precisely localize these sounds. Gleaners typically use low intensity echolocation calls. Such stealth echolocation requires a nervous system that is attuned to low intensity sound processing. In addition, landing on the ground to hunt may bring gleaners in close proximity to venomous prey. In fact, at least 2 gleaning bat species are known to hunt highly venomous scorpions. While a number of studies have addressed adaptations for echolocation in bats that hunt in the air, very little is known about the morphological, behavioral, and neural specializations for gleaning in bats. This review highlights the novel insights gleaning bats provide into bat evolution, particularly auditory pathway organization and ion channel structure/function relationships. Gleaning bats are found in multiple families, suggesting convergent evolution of specializations for gleaning as a foraging strategy. However, most of this review is based on recent work on a single species – the pallid bat (Antrozous palli dus) – symptomatic of the fact that more comparative work is needed to identify the mechanisms that facilitate gleaning behavior.
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Topography of sound level representation in the FM sweep selective region of the pallid bat auditory cortex. Hear Res 2018; 367:137-148. [PMID: 29853324 DOI: 10.1016/j.heares.2018.05.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/08/2018] [Revised: 05/17/2018] [Accepted: 05/23/2018] [Indexed: 11/21/2022]
Abstract
Sound level processing is a fundamental function of the auditory system. To determine how the cortex represents sound level, it is important to quantify how changes in level alter the spatiotemporal structure of cortical ensemble activity. This is particularly true for echolocating bats that have control over, and often rapidly adjust, call level to actively change echo level. To understand how cortical activity may change with sound level, here we mapped response rate and latency changes with sound level in the auditory cortex of the pallid bat. The pallid bat uses a 60-30 kHz downward frequency modulated (FM) sweep for echolocation. Neurons tuned to frequencies between 30 and 70 kHz in the auditory cortex are selective for the properties of FM sweeps used in echolocation forming the FM sweep selective region (FMSR). The FMSR is strongly selective for sound level between 30 and 50 dB SPL. Here we mapped the topography of level selectivity in the FMSR using downward FM sweeps and show that neurons with more monotonic rate level functions are located in caudomedial regions of the FMSR overlapping with high frequency (50-60 kHz) neurons. Non-monotonic neurons dominate the FMSR, and are distributed across the entire region, but there is no evidence for amplitopy. We also examined how first spike latency of FMSR neurons change with sound level. The majority of FMSR neurons exhibit paradoxical latency shift wherein the latency increases with sound level. Moreover, neurons with paradoxical latency shifts are more strongly level selective and are tuned to lower sound level than neurons in which latencies decrease with level. These data indicate a clustered arrangement of neurons according to monotonicity, with no strong evidence for finer scale topography, in the FMSR. The latency analysis suggests mechanisms for strong level selectivity that is based on relative timing of excitatory and inhibitory inputs. Taken together, these data suggest how the spatiotemporal spread of cortical activity may represent sound level.
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