Thermoperception in the common vampire bat (Desmodus rotundus)

Evolution of olfactory receptor superfamily in bats based on high throughput molecular modelling

The origin of flight and laryngeal echolocation in bats is likely to have been accompanied by evolutionary changes in other aspects of their sensory biology. Of all sensory modalities in bats, olfaction is perhaps the least well understood. Olfactory receptors (ORs) function in recognizing odour molecules, with crucial roles in evaluating food, as well as in processing social information. Here we compare OR repertoire sizes across taxa and apply a new pipeline that integrates comparative genome data with protein structure modelling and then we employ molecular docking techniques with small molecules to analyse OR functionality based on binding energies. Our results suggest a sharp contraction in odorant recognition of the functional OR repertoire during the origin of bats, consistent with a reduced dependence on olfaction. We also compared bat lineages with contrasting different ecological characteristics and found evidence of differences in OR gene expansion and contraction, and in the composition of ORs with different tuning breadths. The strongest binding energies of ORs in non-echolocating fruit-eating bats were seen to correspond to ester odorants, although we did not detect a quantitative advantage of functional OR repertoires in these bats compared with echolocating insectivorous species. Overall, our findings based on molecular modelling and computational docking suggest that bats have undergone olfactory evolution linked to dietary adaptation. Our results from extant and ancestral bats help to lay the groundwork for targeted experimental functional tests in the future.

Modeling of Human Rabies Cases in Brazil in Different Future Global Warming Scenarios

Bat species have been observed to have the potential to expand their distribution in response to climate change, thereby influencing shifts in the spatial distribution and population dynamics of human rabies cases. In this study, we applied an ensemble niche modeling approach to project climatic suitability under different future global warming scenarios for human rabies cases in Brazil, and assessed the impact on the probability of emergence of new cases. We obtained notification records of human rabies cases in all Brazilian cities from January 2001 to August 2023, as reported by the State and Municipal Health Departments. The current and future climate data were sourced from a digital repository on the WorldClim website. The future bioclimatic variables provided were downscaled climate projections from CMIP6 (a global model ensemble) and extracted from the regionalized climate model HadGEM3-GC31-LL for three future socioeconomic scenarios over four periods (2021-2100). Seven statistical algorithms (MAXENT, MARS, RF, FDA, CTA, GAM, and GLM) were selected for modeling human rabies. Temperature seasonality was the bioclimatic variable with the highest relative contribution to both current and future consensus models. Future scenario modeling for human rabies indicated a trend of changes in the areas of occurrence, maintaining the current pace of global warming, population growth, socioeconomic instability, and the loss of natural areas. In Brazil, there are areas with a higher likelihood of climatic factors contributing to the emergence of cases. When assessing future scenarios, a change in the local climatic suitability is observed that may lead to a reduction or increase in cases, depending on the region.

A bifurcation integrates information from many noisy ion channels and allows for milli-Kelvin thermal sensitivity in the snake pit organ

In various biological systems, information from many noisy molecular receptors must be integrated into a collective response. A striking example is the thermal imaging organ of pit vipers. Single nerve fibers in the organ reliably respond to milli-Kelvin (mK) temperature increases, a thousand times more sensitive than their molecular sensors, thermo-transient receptor potential (TRP) ion channels. Here, we propose a mechanism for the integration of this molecular information. In our model, amplification arises due to proximity to a dynamical bifurcation, separating a regime with frequent and regular action potentials (APs), from a regime where APs are irregular and infrequent. Near the transition, AP frequency can have an extremely sharp dependence on temperature, naturally accounting for the thousand-fold amplification. Furthermore, close to the bifurcation, most of the information about temperature available in the TRP channels' kinetics can be read out from the times between consecutive APs even in the presence of readout noise. A key model prediction is that the coefficient of variation in the distribution of interspike times decreases with AP frequency, and quantitative comparison with experiments indeed suggests that nerve fibers of snakes are located very close to the bifurcation. While proximity to such bifurcation points typically requires fine-tuning of parameters, we propose that having feedback act from the order parameter (AP frequency) onto the control parameter robustly maintains the system in the vicinity of the bifurcation. This robustness suggests that similar feedback mechanisms might be found in other sensory systems which also need to detect tiny signals in a varying environment.

Hunting with heat: thermosensory-driven foraging in mosquitoes, snakes and beetles

Animals commonly use thermosensation, the detection of temperature and its variation, for defensive purposes: to maintain appropriate body temperature and to avoid tissue damage. However, some animals also use thermosensation to go on the offensive: to hunt for food. The emergence of heat-dependent foraging behavior has been accompanied by the evolution of diverse thermosensory organs of often exquisite thermosensitivity. These organs detect the heat energy emitted from food sources that range from nearby humans to trees burning in a forest kilometers away. Here, we examine the biophysical considerations, anatomical specializations and molecular mechanisms that underlie heat-driven foraging. We focus on three groups of animals that each meet the challenge of detecting heat from potential food sources in different ways: (1) disease-spreading vector mosquitoes, which seek blood meals from warm-bodied hosts at close range, using warming-inhibited thermosensory neurons responsive to conductive and convective heat flow; (2) snakes (vipers, pythons and boas), which seek warm-blooded prey from ten or more centimeters away, using warmth-activated thermosensory neurons housed in an organ specialized to harvest infrared radiation; and (3) fire beetles, which maximize their offspring's feeding opportunities by seeking forest fires from kilometers away, using mechanosensory neurons housed in an organ specialized to convert infrared radiation into mechanosensory stimuli. These examples highlight the diverse ways in which animals exploit the heat emanating from potential food sources, whether this heat reflects ongoing metabolic activity or a recent lightning strike, to secure a nutritious meal for themselves or for their offspring.

The evolution of sanguivory in vampire bats: origins and convergences

Blood-feeding (sanguivory) has evolved more than two dozen times among birds, fishes, insects, arachnids, molluscs, crustaceans, and annelids; however, among mammals, it is restricted to the vampire bats. Here, the authors revisit the question of how it evolved in that group. Evidence to date suggests that the ancestors of phyllostomids were insectivorous, and that carnivory, omnivory, and nectarivory evolved among phyllostomids after vampire bats diverged. Frugivory likely also evolved after vampire bats diverged, but the phylogeny is ambiguous on that point. However, vampire bats lack any genetic evidence of a frugivorous past, and the behavioural progression from frugivory to sanguivory is difficult to envision. Thus, the most parsimonious scenario is that sanguivory evolved in an insectivorous ancestor to vampire bats via ectoparasite-eating, wound-feeding, or some combination of the two—all feeding habits found among blood-feeding birds today. Comparing vampire bats with other sanguivores, the authors find several remarkable examples of convergence. Further, it was found that blood-feeding has been ca. 50 times more likely to evolve in a vertebrate lineage than in an invertebrate one. The authors hypothesize that this difference exists because vertebrates are more likely than invertebrates to have the biochemical necessities required to assimilate the components of vertebrate blood.

Thermoconforming rays of the star-nosed mole

The star-nosed mole (Condylura cristata) is renowned for its densely innervated 22 appendage star-like rostrum ('star') specialized for tactile sensation. As a northerly distributed insectivorous mammal exploiting aquatic and terrestrial habitats, these vascularized nasal rays are regularly exposed to cold water and thermally conductive soil, leading us to ask whether the star surface temperature, a proxy for blood flow, conforms to the local ambient temperature to conserve body heat. Alternatively, given the exquisite sensory nature of the star, we posited that the uninsulated rays may be kept warm when foraging to maintain high mechanosensory function. To test these hypotheses, we remotely monitored surface temperatures in wild-caught star-nosed moles. Although the tail acted as a thermal window exhibiting clear vasoconstriction/vasodilation, the star varied passively in surface temperature, with little evidence for thermoregulatory vasomotion. This thermoconforming response may have evolved to minimize conductive heat loss to the water or wet soils when foraging.

Alternative splicing as a source of phenotypic diversity

A major goal of evolutionary genetics is to understand the genetic processes that give rise to phenotypic diversity in multicellular organisms. Alternative splicing generates multiple transcripts from a single gene, enriching the diversity of proteins and phenotypic traits. It is well established that alternative splicing contributes to key innovations over long evolutionary timescales, such as brain development in bilaterians. However, recent developments in long-read sequencing and the generation of high-quality genome assemblies for diverse organisms has facilitated comparisons of splicing profiles between closely related species, providing insights into how alternative splicing evolves over shorter timescales. Although most splicing variants are probably non-functional, alternative splicing is nonetheless emerging as a dynamic, evolutionarily labile process that can facilitate adaptation and contribute to species divergence.

Behavior of Nymphs and Adults of the Black-Legged Tick Ixodes scapularis and the Lone Star Tick Ambylomma americanum in Response to Thermal Stimuli

Ticks use chemical and thermal signals emitted by humans and other vertebrates to locate suitable hosts for a blood meal. Here, we study the behavior of black-legged Ixodes scapularis and the lone star ticks Amblyomma americanum exposed to heat sources held at temperatures near those of vertebrate hosts (32 °C). First, we used a locomotion compensator to test behavioral responses of ticks to an infrared light emitting diode (LED). The servosphere allowed us to measure parameters such as velocity, acceleration, linearity, and orientation. Then a heating element (Peltier) located in one of the extremes of a double-choice vertical rod (flying T), was employed to observe upward movement of the ticks toward such a heat source. While both species oriented toward the LED, only lone star ticks were attracted to the Peltier element while climbing upward. In conclusion, we showed that heat attracted ticks from short distances up to several centimeters on a the servosphere, and those responses differed between the two species of ticks on the flying T. We discuss our results in the context of the ecology of both tick species and their potential in tick survey and management.

Sensory and Cognitive Ecology of Bats

We see stunning morphological diversity across the animal world. Less conspicuous but equally fascinating are the sensory and cognitive adaptations that determine animals’ interactions with their environments and each other. We discuss the development of the fields of sensory and cognitive ecology and the importance of integrating these fields to understand the evolution of adaptive behaviors. Bats, with their extraordinarily high ecological diversity, are ideal animals for this purpose. An explosion in recent research allows for better understanding of the molecular, genetic, neural, and behavioral bases for sensory ecology and cognition in bats. We give examples of studies that illuminate connections between sensory and cognitive features of information filtering, evolutionary trade-offs in sensory and cognitive processing, and multimodal sensing and integration. By investigating the selective pressures underlying information acquisition, processing, and use in bats, we aim to illuminate patterns and processes driving sensory and cognitive evolution.

Functional differences in echolocation call design in an adaptive radiation of bats

All organisms have specialized systems to sense their environment. Most bat species use echolocation for navigation and foraging, but which and how ecological factors shaped echolocation call diversity remains unclear for the most diverse clades, including the adaptive radiation of neotropical leaf-nosed bats (Phyllostomidae). This is because phyllostomids emit low-intensity echolocation calls and many inhabit dense forests, leading to low representation in acoustic surveys. We present a field-collected, echolocation call dataset spanning 35 species and all phyllostomid dietary guilds. We analyze these data under a phylogenetic framework to test the hypothesis that echolocation call design and parameters are specialized for the acoustic demands of different diets, and investigate the contributions of phylogeny and body size to echolocation call diversity. We further link call parameters to dietary ecology by contrasting minimum detectable prey size estimates (MDPSE) across species. We find phylogeny and body size explain a substantial proportion of echolocation call parameter diversity, but most species can be correctly assigned to taxonomic (61%) or functional (77%) dietary guilds based on call parameters. This suggests a degree of acoustic ecological specialization, albeit with interspecific similarities in call structure. Theoretical MDPSE are greatest for omnivores and smallest for insectivores. Omnivores significantly differ from other dietary guilds in MDPSE when phylogeny is not considered, but there are no differences among taxonomic dietary guilds within a phylogenetic context. Similarly, predators of non-mobile/non-evasive prey and predators of mobile/evasive prey differ in estimated MDPSE when phylogeny is not considered. Phyllostomid echolocation call structure may be primarily specialized for overcoming acoustic challenges of foraging in dense habitats, and then secondarily specialized for the detection of food items according to functional dietary guilds. Our results give insight into the possible ecological mechanisms shaping the diversity of sensory systems, and their reciprocal influence on resource use.

Bitter taste receptors of the common vampire bat are functional and show conserved responses to metal ions in vitro

The bitter taste sensation is important to warn mammals of the ingestion of potentially toxic food compounds. For mammals, whose nutrition relies on highly specific food sources, such as blood in the case of vampire bats, it is unknown if bitter sensing is involved in prey selection. By contrast to other bat species, vampire bats exhibit numerous bitter taste receptor pseudogenes, which could point to a decreased importance of bitter taste. However, electrophysiological and behavioural studies suggest the existence of functional bitter taste transmission. To determine the agonist spectra of the three bitter taste receptors that are conserved in all three vampire bat species, we investigated the in vitro activation of Desmodus rotundus T2R1, T2R4 and T2R7. Using a set of 57 natural and synthetic bitter compounds, we were able to identify agonists for all three receptors. Hence, we confirmed a persisting functionality and, consequently, a putative biological role of bitter taste receptors in vampire bats. Furthermore, the activation of the human TAS2R7 by metal ions is shown to be conserved in D. rotundus.

Dogs can sense weak thermal radiation

The dog rhinarium (naked and often moist skin on the nose-tip) is prominent and richly innervated, suggesting a sensory function. Compared to nose-tips of herbivorous artio- and perissodactyla, carnivoran rhinaria are considerably colder. We hypothesized that this coldness makes the dog rhinarium particularly sensitive to radiating heat. We trained three dogs to distinguish between two distant objects based on radiating heat; the neutral object was about ambient temperature, the warm object was about the same surface temperature as a furry mammal. In addition, we employed functional magnetic resonance imaging on 13 awake dogs, comparing the responses to heat stimuli of about the same temperatures as in the behavioural experiment. The warm stimulus elicited increased neural response in the left somatosensory association cortex. Our results demonstrate a hitherto undiscovered sensory modality in a carnivoran species.

The role of past experience in development of feeding behavior in common vampire bats

The life history strategy of common vampire bats (Desmodus rotundus) suggests that learning might play a role in development of their foraging skills. We took advantage of 12 captive births in a study colony of vampire bats to test the role of past experience in two aspects of feeding. First, we compared preferences for blood temperature in 32 wild-born vampire bats versus 11 captive-born vampire bats that had only previously fed on blood of ambient temperature or colder. We found no evidence for a preference in either group for blood presented at 4 °C versus 37 °C. Second, we tested whether captive-born vampire bats with no previous experience of feeding on live animals could successfully feed on a live chicken. Five of 12 naïve captive-born bats were able to bite the chicken and draw blood, but only one bat gained more than 5% of body mass. We were unable to reasonably compare their feeding performance with that of wild-born bats because only two of three wild-born, short-term captive bats fed on the chicken and none of the seven wild-born, long-term captive mothers attempted to feed. This unexpected lack of feeding might be due to a previously reported age-dependent neophobia. When six of the captive-born bats were released in the wild, they appeared to feed successfully because they survived for more than three consecutive nights. We suggest further tests that would better clarify the role of learning in the development of foraging in vampire bats.

Unusual echolocation behaviour of the common sword-nosed bat Lonchorhina aurita: an adaptation to aerial insectivory in a phyllostomid bat?

Most insectivorous bat species in the Neotropical family Phyllostomidae glean insects from ground, water or vegetation surfaces. They use similar and stereotypical echolocation calls that are generally very short (less than 1-3 ms), multi-harmonic and frequency-modulated (FM). By contrast, the common sword-nosed bat, Lonchorhina aurita, which has the longest noseleaf in the entire phyllostomid family, produces distinctly different echolocation calls. They are composed of a constant frequency (CF) component with a peak frequency of 45 kHz, followed by a short FM down-sweep at the end. With a mean call duration of 6.6 ms (max. 8.7 ms) when flying in the open they have the longest echolocation calls reported from phyllostomid bats. In cluttered environments, the CF-component is very short. In open habitats, however, L. aurita can emit pure CF-calls without the terminal FM-component. We also recorded in the field a distinct terminal group that closely resembles the feeding buzzes of aerial hawking bat species from other bat families. This is the first time the echolocation call design of L. aurita is presented. In addition, we contrast the echolocation behaviour of individuals flying in open and confined situations. Our results suggest that the unique echolocation system of L. aurita represents an adaptation to aerial hawking, a very unusual hunting mode within the phyllostomid family.

Nighttime Ecology: The "Nocturnal Problem" Revisited

The existence of a synthetic program of research on what was then termed the "nocturnal problem" and that we might now call "nighttime ecology" was declared more than 70 years ago. In reality, this failed to materialize, arguably as a consequence of practical challenges in studying organisms at night and instead concentrating on the existence of circadian rhythms, the mechanisms that give rise to them, and their consequences. This legacy is evident to this day, with consideration of the ecology of the nighttime markedly underrepresented in ecological research and literature. However, several factors suggest that it would be timely to revive the vision of a comprehensive research program in nighttime ecology. These include (i) that the study of the ecology of the night is being revolutionized by new and improved technologies; (ii) suggestions that, far from being a minor component of biodiversity, a high proportion of animal species are active at night; (iii) that fundamental questions about differences and connections between the ecology of the daytime and the nighttime remain largely unanswered; and (iv) that the nighttime environment is coming under severe anthropogenic pressure. In this article, I seek to reestablish nighttime ecology as a synthetic program of research, highlighting key focal topics and questions and providing an overview of the current state of understanding and developments.

Assessing changing weather and the El Niño Southern Oscillation impacts on cattle rabies outbreaks and mortality in Costa Rica (1985-2016)

BACKGROUND

Rabies is a major zoonotic disease affecting humans, domestic and wildlife mammals. Cattle are the most important domestic animals impacted by rabies virus in the New World, leading to thousands of cattle deaths per year and eliciting large economic losses. In the New World, virus transmission in cattle is primarily associated with Desmodus rotundus, the common vampire bat. This study analyses the association of weather fluctuations and the El Niño Southern Oscillation (ENSO), with the occurrence and magnitude, in terms of associated mortality, of cattle rabies outbreaks. Data from the 100 cattle rabies outbreaks recorded between 1985 and 2016 in Costa Rica were analyzed. Periodograms for time series of rabies outbreaks and the El Niño 4 index were estimated. Seasonality was studied using a seasonal boxplot. The association between epidemiological and climatic time series was studied via cross wavelet coherence analysis. Retrospective space-time scan cluster analyses were also performed. Finally, seasonal autoregressive time series models were fitted to study linear associations between monthly number of outbreaks, monthly mortality rates and the El Niño 4 index, temperature, and rainfall.

RESULTS

Large rabies mortality occurred towards the Atlantic basin of the country. Outbreak occurrence and size were not directly associated with ENSO, but were sensitive to weather variables impacted by ENSO. Both, ENSO phases and rabies outbreaks, showed a similar 5 year period in their oscillations. Cattle rabies mortality and outbreak occurrence increased with temperature, whereas outbreak occurrence decreased with rainfall. These results suggest that special weather conditions might favor the occurrence of cattle rabies outbreaks.

CONCLUSIONS

Further efforts are necessary to articulate the mechanisms underpinning the association between weather changes and cattle rabies outbreaks. One hypothesis is that exacerbation of cattle rabies outbreaks might be mediated by impacts of weather conditions on common vampire bat movement and access to food resources on its natural habitats. Further eco-epidemiological field studies could help to understand rabies virus transmission ecology, and to propose sound interventions to control this major veterinary public health problem.

Colour vision variation in leaf-nosed bats (Phyllostomidae): Links to cave roosting and dietary specialization

Bats are a diverse radiation of mammals of enduring interest for understanding the evolution of sensory specialization. Colour vision variation among species has previously been linked to roosting preferences and echolocation form in the suborder Yinpterochiroptera, yet questions remain about the roles of diet and habitat in shaping bat visual ecology. We sequenced OPN1SW and OPN1LW opsin genes for 20 species of leaf-nosed bats (family Phyllostomidae; suborder Yangochiroptera) with diverse roosting and dietary ecologies, along with one vespertilionid species (Myotis lavali). OPN1LW genes appear intact for all species, and predicted spectral tuning of long-wavelength opsins varied among lineages. OPN1SW genes appear intact and under purifying selection for Myotis lavali and most phyllostomid bats, with two exceptions: (a) We found evidence of ancient OPN1SW pseudogenization in the vampire bat lineage, and loss-of-function mutations in all three species of extant vampire bats; (b) we additionally found a recent, independently derived OPN1SW pseudogene in Lonchophylla mordax, a cave-roosting species. These mutations in leaf-nosed bats are independent of the OPN1SW pseudogenization events previously reported in Yinpterochiropterans. Therefore, the evolution of monochromacy (complete colour blindness) has occurred in both suborders of bats and under various evolutionary drivers; we find independent support for the hypothesis that obligate cave roosting drives colour vision loss. We additionally suggest that haematophagous dietary specialization and corresponding selection on nonvisual senses led to loss of colour vision through evolutionary sensory trade-off. Our results underscore the evolutionary plasticity of opsins among nocturnal mammals.

Testing the sensory trade-off hypothesis in New World bats

Detection of evolutionary shifts in sensory systems is challenging. By adopting a molecular approach, our earlier study proposed a sensory trade-off hypothesis between a loss of colour vision and an origin of high-duty-cycle (HDC) echolocation in Old World bats. Here, we test the hypothesis in New World bats, which include HDC echolocators that are distantly related to Old World HDC echolocators, as well as vampire bats, which have an infrared sensory system apparently unique among bats. Through sequencing the short-wavelength opsin gene (SWS1) in 16 species (29 individuals) of New World bats, we identified a novel SWS1 polymorphism in an HDC echolocator: one allele is pseudogenized but the other is intact, while both alleles are either intact or pseudogenized in other individuals. Strikingly, both alleles were found to be pseudogenized in all three vampire bats. Since pseudogenization, transcriptional or translational changes could separately result in functional loss of a gene, a pseudogenized SWS1 indicates a loss of dichromatic colour vision in bats. Thus, the same sensory trade-off appears to have repeatedly occurred in the two divergent lineages of HDC echolocators, and colour vision may have also been traded off against the infrared sense in vampire bats.

Bioinspired Infrared Sensing Materials and Systems

Bioinspired engineering offers a promising alternative approach in accelerating the development of many man-made systems. Next-generation infrared (IR) sensing systems can also benefit from such nature-inspired approach. The inherent compact and uncooled operation of biological IR sensing systems provides ample inspiration for the engineering of portable and high-performance artificial IR sensing systems. This review overviews the current understanding of the biological IR sensing systems, most of which are thermal-based IR sensors that rely on either bolometer-like or photomechanic sensing mechanism. The existing efforts inspired by the biological IR sensing systems and possible future bioinspired approaches in the development of new IR sensing systems are also discussed in the review. Besides these biological IR sensing systems, other biological systems that do not have IR sensing capabilities but can help advance the development of engineered IR sensing systems are also discussed, and the related engineering efforts are overviewed as well. Further efforts in understanding the biological IR sensing systems, the learning from the integration of multifunction in biological systems, and the reduction of barriers to maximize the multidiscipline collaborations are needed to move this research field forward.

TRPs et al.: a molecular toolkit for thermosensory adaptations

The ability to sense temperature is crucial for the survival of an organism. Temperature influences all biological operations, from rates of metabolic reactions to protein folding, and broad behavioral functions, from feeding to breeding, and other seasonal activities. The evolution of specialized thermosensory adaptations has enabled animals to inhabit extreme temperature niches and to perform specific temperature-dependent behaviors. The function of sensory neurons depends on the participation of various types of ion channels. Each of the channels involved in neuronal excitability, whether through the generation of receptor potential, action potential, or the maintenance of the resting potential have temperature-dependent properties that can tune the neuron's response to temperature stimuli. Since the function of all proteins is affected by temperature, animals need adaptations not only for detecting different temperatures, but also for maintaining sensory ability at different temperatures. A full understanding of the molecular mechanism of thermosensation requires an investigation of all channel types at each step of thermosensory transduction. A fruitful avenue of investigation into how different molecules can contribute to the fine-tuning of temperature sensitivity is to study the specialized adaptations of various species. Given the diversity of molecular participants at each stage of sensory transduction, animals have a toolkit of channels at their disposal to adapt their thermosensitivity to their particular habitats or behavioral circumstances.

Ascospore release in apple scab underlies infrared sensation

The agent of apple scab disease (Venturia inaequalis) is the most common pathogen in apple cultivation. Its ascospores are released in spring, mainly during daylight hours and triggered by rain events. To investigate the causes of diurnal rhythm of ascospore dissemination of the apple scab fungus ascospore releases were examined continuously with spore traps in the orchard and with laboratory assays. One of the spore traps was illuminated at night with different light sources in each year during 2011-2015. The laboratory assays were performed with different light sources with varying wavelengths and intensities. In field and laboratory conditions only light including infrared radiation stimulated ascospore release, but not with light in the visible spectrum only. Artificial illumination during night was correlated with an increase of up to 46 % of ascospores released overnight in the field. We proved that infrared radiation induces V. inaequalis to release its spores. This is the first report in which spore discharge could be stimulated during night under field conditions.

Vampire bats exhibit evolutionary reduction of bitter taste receptor genes common to other bats

The bitter taste serves as an important natural defence against the ingestion of poisonous foods and is thus believed to be indispensable in animals. However, vampire bats are obligate blood feeders that show a reduced behavioural response towards bitter-tasting compounds. To test whether bitter taste receptor genes (T2Rs) have been relaxed from selective constraint in vampire bats, we sampled all three vampire bat species and 11 non-vampire bats, and sequenced nine one-to-one orthologous T2Rs that are assumed to be functionally conserved in all bats. We generated 85 T2R sequences and found that vampire bats have a significantly greater percentage of pseudogenes than other bats. These results strongly suggest a relaxation of selective constraint and a reduction of bitter taste function in vampire bats. We also found that vampire bats retain many intact T2Rs, and that the taste signalling pathway gene Calhm1 remains complete and intact with strong functional constraint. These results suggest the presence of some bitter taste function in vampire bats, although it is not likely to play a major role in food selection. Together, our study suggests that the evolutionary reduction of bitter taste function in animals is more pervasive than previously believed, and highlights the importance of extra-oral functions of taste receptor genes.

Independent losses of visual perception genes Gja10 and Rbp3 in echolocating bats (Order: Chiroptera)

A trade-off between the sensory modalities of vision and hearing is likely to have occurred in echolocating bats as the sophisticated mechanism of laryngeal echolocation requires considerable neural processing and has reduced the reliance of echolocating bats on vision for perceiving the environment. If such a trade-off exists, it is reasonable to hypothesize that some genes involved in visual function may have undergone relaxed selection or even functional loss in echolocating bats. The Gap junction protein, alpha 10 (Gja10, encoded by Gja10 gene) is expressed abundantly in mammal retinal horizontal cells and plays an important role in horizontal cell coupling. The interphotoreceptor retinoid-binding protein (Irbp, encoded by the Rbp3 gene) is mainly expressed in interphotoreceptor matrix and is known to be critical for normal functioning of the visual cycle. We sequenced Gja10 and Rbp3 genes in a taxonomically wide range of bats with divergent auditory characteristics (35 and 18 species for Gja10 and Rbp3, respectively). Both genes have became pseudogenes in species from the families Hipposideridae and Rhinolophidae that emit constant frequency echolocation calls with Doppler shift compensation at high-duty-cycles (the most sophisticated form of biosonar known), and in some bat species that emit echolocation calls at low-duty-cycles. Our study thus provides further evidence for the hypothesis that a trade-off occurs at the genetic level between vision and echolocation in bats.

Hearing in American leaf-nosed bats. IV: the Common vampire bat, Desmodus rotundus

We behaviorally determined the audiograms of three Common vampire bats (Phyllostomidae, Desmodus rotundus), a species specialized to exist exclusively on blood. The bats were trained to respond to pure tones in a conditioned suppression/avoidance procedure for a blood reward and a mild punisher for failures to detect the tones. Common vampire bats have a hearing range from 716 Hz to 113 kHz at a level of 60 dB. Their best hearing is at 20 kHz where they are slightly more sensitive than other bats, and they have a second peak of good sensitivity at 71 kHz. They have unusually good sensitivity to low frequencies compared to other bats, but are less sensitive to low frequencies than most mammals. Selective pressures affecting high-frequency hearing in bats and mammals in general are discussed.

Ecological correlates of cortisol levels in two bat species with contrasting feeding habits

The immediate release of adrenal glucocorticoids can be crucial for an animal's survival when facing a stressor, but constantly elevated or exceptionally high glucocorticoid levels are usually detrimental for health. Although baseline and maximal secretion of glucocorticoids are regulated within narrow ranges within species, plasma glucocorticoid levels vary largely across vertebrates. We asked what ecological factors affect baseline plasma cortisol levels (CortI) and maximum levels (CortMax) following a physiological challenge through administration of adrenocorticotropic hormone (ACTH). Specifically, we studied whether seasonal fluctuations in food abundance correlate with the capacity of cortisol increases in two phyllostomid bat species with contrasting feeding habits: the sanguinivorous vampire bat (Desmodus rotundus) and the frugivorous short-tailed fruit bat (Carollia perspicillata). Both species coexist in habitats with various levels of seasonality (dry and rainforest). On a seasonal basis, resource abundance is more stable for vampire than for fruit bats, but previous studies suggested that daily foraging success may vary more for vampire than for fruit bats. CortI and CortMax varied seasonally in C. perspicillata from dry and rainforests, with the exception of CortMax in rainforest bats. Although we expected food availability to be stable year-round for vampire bats, we found CortI and CortMax of vampires to be higher during the rainy season than during the dry season. Also, we found CortMax to be higher in vampires from the rainforest than in those from the dry forest. CortMax of vampires were among the highest measured for a free-ranging mammal; a pattern that could be related to the species' vulnerability to starvation. We conclude that food availability modulates cortisol levels in free-ranging species that face seasonally fluctuating resources; in species, however, that benefit from food which is constantly abundant, other factors than food may become more important in modulating cortisol levels.

Ganglion-specific splicing of TRPV1 underlies infrared sensation in vampire bats

Vampire bats (Desmodus rotundus) are obligate blood feeders that have evolved specialized systems to suit their unique sanguinary lifestyle ^1–3. Chief among such adaptations is the ability to detect infrared radiation as a means of locating hot spots on warm-blooded prey. Among vertebrates, only vampire bats, boas, pythons, and pit vipers are capable of detecting infrared radiation ^1,4. In each case, infrared heat is detected by trigeminal nerve fibers that innervate specialized pit organs on the animal’s face ^5–10. Thus, vampire bats and snakes have taken thermosensation to the extreme by developing specialized systems for detecting infrared radiation. As such, these creatures provide a window into the molecular and genetic mechanisms underlying evolutionary tuning of thermoreceptors in a species or cell type specific manner. Previously, we have shown that snakes co-opt a non-heat sensitive channel (vertebrate TRPA1) to produce an infrared detector ⁶. Here we show that vampire bats tune an already heat sensitive channel (TRPV1) by lowering its thermal activation threshold to ~30°C. This is achieved through alternative splicing of TRPV1 transcripts to produce a channel with a truncated C-terminal cytoplasmic domain. Remarkably, these splicing events occur exclusively in trigeminal ganglia (TG), and not dorsal root ganglia (DRG), thereby maintaining a role for TRPV1 as a detector of noxious heat in somatic afferents. This reflects a unique organization of the bat TRPV1 gene that we show to be characteristic of Laurasiatheria mammals (cows, dogs, and moles), supporting a close phylogenetic relationship with bats. These findings reveal a unique molecular mechanism for physiological tuning of thermosensory nerve fibers.

Infrared-sensitive pit organ and trigeminal ganglion in the crotaline snakes

The infrared (IR) receptors in the pit organ of crotaline snakes are very sensitive to temperature. The sensitivity to IR radiation is much greater in crotaline snakes than in boid snakes because they have a thermosensitive membrane suspended in a pair of pits that comprise the pit organ. The vasculature of the pit membrane, which is located near IR-sensitive terminal nerve masses, the IR receptors, supplies the blood necessary to provide cooling and the energy and oxygen that the IR receptors require. The ophthalmic and maxillary branches of the trigeminal nerve innervate the pit membrane. In crotaline snakes, the trigeminal ganglion (TG) is divided into the ophthalmic and maxillomandibular ganglia; a prominent septum further separates the two divisions of the maxillomandibular ganglion. The TG neurons in the ophthalmic ganglion and the maxillary division of the maxillomandibular ganglion relay IR sensation to the brain. This article reviews the IR-sensitive pit organ and trigeminal sensory system structures in crotaline snakes.

Infrared radiation from hot cones on cool conifers attracts seed-feeding insects

Foraging animals use diverse cues to locate resources. Common foraging cues have visual, auditory, olfactory, tactile or gustatory characteristics. Here, we show a foraging herbivore using infrared (IR) radiation from living plants as a host-finding cue. We present data revealing that (i) conifer cones are warmer and emit more near-, mid- and long-range IR radiation than needles, (ii) cone-feeding western conifer seed bugs, Leptoglossus occidentalis (Hemiptera: Coreidae), possess IR receptive organs and orient towards experimental IR cues, and (iii) occlusion of the insects' IR receptors impairs IR perception. The conifers' cost of attracting cone-feeding insects may be offset by occasional mast seeding resulting in cone crops too large to be effectively exploited by herbivores.

Biological infrared imaging and sensing

A variety of thermoreceptors are present in animals and insects, which aid them in hunting, feeding and survival. Infrared (IR) imaging pit organs in Crotaline and Boid snakes enable them to detect, locate and apprehend their prey by detecting the IR radiation they emit. IR pit organs of common vampire bats (Desmodus rotundus) enable them to detect IR radiation emitted by blood-rich locations on homeothermic prey. The beetle Melanophila acuminata locates forest fires by IR-detecting pit organs in order to lay their eggs in freshly killed conifers. Thermoreceptors located in the wings and antennae of darkly pigmented butterflies (Pachliopta aristolochiae and Troides rhadamathus plateni) protect them from heat damage while sun basking. Blood-sucking bugs (Triatoma infestans) are speculated to possess thermoreceptors, which enable them to perceive the radiant heat emitted by homeothermic prey and estimate its temperature at a distance. This is a review of the diverse types of biological thermoreceptors, their structure and function, and how electron microscopy has been instrumental in determining their ultrastructure.

Prey targeting by the infrared-imaging snake Python molurus: effects of experimental and congenital visual deprivation

Boid and crotaline snakes possess two distinct types of organ evolved to image radiant electromagnetic energy: the lateral eye, which responds to visible light, and the pit organ, which responds to infrared radiation. While infrared imaging may allow accurate predatory targeting in complete absence of visual information, both infrared and visual information are probably normally involved in prey targeting. We examined the roles of vision and infrared imaging in Python molurus predatory performance under conditions of (1) high visual contrast; (2) very low visual contrast; (3) complete blinding; (4) experimental monocular occlusion; and (5) congenital monocularity. Normally sighted pythons were equally successful at targeting white (BALB/c) and black (C57BL6/J) mice (Mus domesticus) against a black background. Binocularly occluded snakes exhibited strike angles and distances similar to non-occluded snakes, but exhibited lower strike success, suggesting that high visible contrast is not required for accurate targeting, but that precise targeting depends to some degree upon visual information. Strike angles, distances and latencies were indistinguishable between snakes subjected to experimental monocular occlusion and normally sighted snakes. However, snakes congenitally lacking one eye preferentially targeted on the sighted side. Thus, accurate targeting of highly mobile homeothermic prey by Python can be accomplished with little or no visual information, but performance can be affected by complete visual deprivation or by alteration of visual input during development. The developmental effects of early visual deprivation in this system provide a novel opportunity to investigate the neural integration of two electromagnetic radiation-imaging systems in a single animal.

The anatomy and fine structure of the echidna Tachyglossus aculeatus snout with respect to its different trigeminal sensory receptors including the electroreceptors

The gross anatomy and nerve supply of the bill of echidna (Tachyglossus aculeatus) is described in relation to its function as an outstanding sensory organ. The sensory innervation of the skin of the echidna snout was investigated by means of frontal serial sections, after decalcification of the specimens. A comprehensive light and electron microscopic description of the location and fine structure of cutaneous sensory receptors of the trigeminal system was made by this means. The encapsulated and non-encapsulated Ruffini receptors, the types of other free receptors in the connective tissue and the Merkel cell receptor do not differ morphologically from those of higher mammals, whereas the pacinian-like corpuscle shows a unique organization of its outer core. This is composed of large perineural cells containing a unique reticulum of parallel-orientated endoplasmic membranes. Lamellated corpuscles, seen in isolation or in association with push rods, are numerous in the snout and in the tip of the tongue of echidna. Push rod receptor organs occur in the hairless skin of the bill with a very dense array at its rostral end and in the pseudopalatal ridges. Gland duct receptors are restricted to the skin adjacent to the nostrils and the mouth opening, including the pseudopalatal plates. Only about one quarter of the total number of 400 seromucous glands receive a sensory innervation of their intraepidermal duct segment. Within each innervated gland two types of receptor terminals are identified. The distributions of the different receptor types are mapped for different regions of the skin, the mucous membrane of the nasal and oral vestibule and the tip of the tongue. The fine structure of nerve terminals is discussed from a comparative anatomical point of view, and some speculations are made about possible transduction processes that underlie the known electrophysiological properties. The sensory organs such as the "push rod" and "gland duct receptor", and most of their sensory terminals, are less differentiated in echidna snout than in the platypus (Ornithorhynchus anatinus) bill.

Analysis of cold and warm receptor activity in vampire bats and mice

The response characteristics of facial thermoreceptors of the common vampire bat and of the mouse have been quantitatively studied. Cold receptors were identified in bat and mouse; warm receptors were only established in the bat. Cold and warm receptor populations of the two species share most of their properties with facial thermoreceptor populations of various mammalian species investigated so far. The temporal pattern of activity of cold receptors of the mouse corresponded to that observed in cats, dogs and monkeys: impulse groups at lower, and beating activity at higher temperatures. At maintained temperature, no impulse groups were initiated in cold receptors of the bat. However, cooling steps from various initial temperatures induced a transient grouped discharge in both cold receptor populations. A discharge in regular groups of impulses was occasionally generated in warm receptors of the bat at maintained temperatures and following warming steps. The data indicate that the temperature dependence of periodic activity in warm receptors is not as uniform as it is in cold receptors. It is concluded that cyclic processes are involved in sensory transduction of both warm and cold receptors, and that this cyclic behavior seems to be a general property of thermoreceptors of presumably all vertebrate species.

A suspected infrared-recipient nucleus in the brainstem of the vampire bat, Desmodus rotundus

We discovered in the brainstem of infrared-sensitive vampire bats, Desmodus rotundus, a specific nucleus not known in other species of bats. Because it corresponded in location and histological features to the infrared nucleus of infrared-sensitive snakes, we suggest the probability of its being part of the infrared processing system of vampire bats.