Pit Organs Research Articles

Responses of infrared-sensitive tectal units of the pit viper Crotalus atrox to moving objects.

Rattlesnakes perceive IR radiation with their pit organs. This enables them to detect and strike towards warm-blooded prey even in the dark. In addition, the IR sense allows rattlesnakes to find places for thermoregulation. Animate objects (e.g., prey) tend to move and thus cause moving IR images across the pit membrane. Even when an object is stationary, scanning head movements of rattlesnakes will result in moving IR images across the pit membrane. We recorded the neuronal activity of IR-sensitive tectal neurons of the rattlesnake Crotalus atrox while stimulating the snakes with an IR source that moved horizontally at various velocities. As long as object velocity was low (angular velocity of ~5°/s) IR-sensitive tectal neurons hardly showed any responses. With increasing object velocity though, neuronal activity reached a maximum at ~50°/s. A further increase in object velocity up to ~120°/s resulted in a slight decrease of neuronal activity. Our results demonstrate the importance of moving stimuli for the snake's IR detection abilities: in contrast to fast moving objects, stationary or slowly moving objects will not be detected when the snake is motionless, but might be detected by scanning head movements.

Exceptionally high thermal sensitivity of rattlesnake TRPA1 correlates with peak current amplitude

Extraordinary infrared-sensing ability of snake pit organs closely correlates with rich expression of TRPA1 transcripts in pit-innervating sensory neurons, strongly suggesting that TRPA1 is the molecular basis of the infrared detection. Here, it is shown that temperature coefficient Q10 (the fold current increase over 10°C increase) of rattlesnake TRPA1 heterologously expressed in Xenopus oocytes increases proportionally to current amplitudes when appraised with two independent methods, the canonical Arrhenius plot analysis and newly devised Q10 scanning that assigns Q10 to each recorded temperature point. Moreover, for larger TRPA1 currents, the rise of Q10 from elevation of current sizes was steeper, yielding maximal Q10s up to ~100,000. TRPA1 from boas with less sensitive infrared-sensing ability was also sharply activated by temperature increase in oocytes, while Q10 rise from escalating current amplitudes was moderate compared to rattlesnake TRPA1. In contrast, thermal sensitivity of Drosophila TRPA1 was little dependent on current sizes, indicating that the steeply proportional current amplitude/thermosensitivity relationship is unique to the snake TRPA1s. Taken together, rattlesnake and boa TRPA1s are regulated to generate sufficient thermal sensitivity for infrared detection, providing an interesting context to further study the temperature-dependent activation mechanism of thermo-TRPs.

Eye and pit size are inversely correlated in crotalinae: Implications for selection pressure relaxation.

Mate, prey, and predator recognition often depend on the integration of information from multiple sensory modalities including visual, auditory, and/or olfactory inputs. In Crotalinae, the eyes sense visible light while the pit organs detect infrared (IR) radiation. Previous studies indicate that there is significant overlap between the eye and pit sensory fields and that both senses are involved in recognition processes. This study investigated the relationships between eye and pit sizes in this taxonomic group as a function of phylogeny and habitat. In view of the fact that pit orientation depends largely on snout shape, pit vipers were grouped as follows: 1) arboreal, 2) terrestrial with rounded snout, and 3) terrestrial with pointed snout. The pit orientations and habitant patterns were fully independent of the Crotalinae phylogenetic tree. The phylogenetic generalized least squares model showed that both eye and pit areas were not of significantly phylogenetic relatedness, implying alternatively a strong effect of adaptation on eye and pit sizes. Negative correlations between relative eye and pit areas in terrestrial (both pointed and rounded snouts) and arboreal species were statistically significant. Our results suggest that the eyes and pits function in a complementary fashion such that selection for IR-perception relaxes selection pressures on the visual system and selection for visual discrimination relaxes selection pressures acting on the IR-system.

Denticle-embedded ampullary organs in a Cretaceous shark provide unique insight into the evolution of elasmobranch electroreceptors.

Here, we report a novel type of dermal denticle (or placoid scale), unknown among both living and fossil chondrichthyan fishes, in a Cretaceous lamniform shark. By their morphology and location, these dermal denticles, grouped into clusters in the cephalic region, appear to have been directly associated with the electrosensory ampullary system. These denticles have a relatively enlarged (∼350 μm in diameter), ornamented crown with a small (∼100 μm) asterisk- or cross-shaped central perforation connected to a multi-alveolate internal cavity. The formation of such a complex structure can be explained by the annular coalescence and fusion, around an ampullary vesicle, of several developmental units still at papillary stage (i.e. before mineralization), leading to a single denticle embedding an alveolar ampulla devoid of canal. This differs from larger typical ampullae of Lorenzini with a well-developed canal opening in a pore of the skin and may represent another adaptive response to low skin resistance. Since it has been recently demonstrated that ampullary organs arise from lateral line placodes in chondrichthyans, this highly specialized type of dermal denticle (most likely non-deciduous) may be derived from the modified placoid scales covering the superficial neuromasts (pit organs) of the mechanosensory lateral line system of many modern sharks.

Bionic research of pit vipers on infrared imaging.

The members of viperidae crotalinae (pit viper) family have special pit organs to detect infrared radiation in normal room conditions, whereas most artificial uncooled infrared focal plane arrays (FPAs) operate only in a vacuum chamber. Dissection shows that the pit membrane is a unique substrate-free structure. The temperature rise advantage of this pit organ was verified in comparison with an assumed substrate pit organ (as an artificial FPA structure). Inspired by the pit viper, we introduced this structure to infrared FPA, replacing the conventional substrate FPA. The substrate-free FPA was fabricated by micro-elctromechanical systems (MEMS) process and placed into an infrared imaging system to obtain thermal images of the human body in atmosphere and vacuum working conditions. We show that the infrared capability of the substrate-free pit organ was achieved.

Male mites (Varroa destructor) perceive the female sex pheromone with the sensory pit organ on the front leg tarsi

Varroa destructor males are attracted by a volatile sex pheromone of female mites. We assume that this pheromone is perceived by the sensory pit organ on the front leg tarsi. To test this hypothesis, the front legs of the males were varnished with nail polish. The behavior of the thus treated males toward attractive female mites was analyzed in our mating bioassay and compared to untreated control males and to males with varnished idiosoma. The control males with the varnished idiosoma revealed the same distinct copulation behavior as untreated males whereas the males with the varnished front legs did not show copulation attempts any more. Hence, the sensory pit organ is responsible for the perception of female signals that elicit the copulation behavior. Additionally, a first scanning electron microscopy (SEM) analysis is presented to characterize the male sensory pit organ.

Organotopic organization of the primary Infrared Sensitive Nucleus (LTTD) in the western diamondback rattlesnake (Crotalus atrox)

ABSTRACTPit vipers (Crotalinae) have a specific sensory system that detects infrared radiation with bilateral pit organs in the upper jaw. Each pit organ consists of a thin membrane, innervated by three trigeminal nerve branches that project to a specific nucleus in the dorsal hindbrain. The known topographic organization of infrared signals in the optic tectum prompted us to test the implementation of spatiotopically aligned sensory maps through hierarchical neuronal levels from the peripheral epithelium to the first central site in the hindbrain, the nucleus of the lateral descending trigeminal tract (LTTD). The spatial organization of the anatomical connections was revealed in a novel in vitro whole‐brain preparation of the western diamondback rattlesnake (Crotalus atrox) that allowed specific application of multiple neuronal tracers to identified pit‐organ‐supplying trigeminal nerve branches. After adequate survival times, the entire peripheral and central projections of fibers within the pit membrane and the LTTD became visible. This approach revealed a morphological partition of the pit membrane into three well‐defined sensory areas with largely separated innervations by the three main branches. The peripheral segregation of infrared afferents in the sensory epithelium was matched by a differential termination of the afferents within different areas of the LTTD, with little overlap. This result demonstrates a topographic organizational principle of the snake infrared system that is implemented by maintaining spatially aligned representations of environmental infrared cues on the sensory epithelium through specific neuronal projections at the level of the first central processing stage, comparable to the visual system. J. Comp. Neurol. 522:3943–3959, 2014. © 2014 Wiley Periodicals, Inc.

Organotopic organization of the primary Infrared Sensitive Nucleus (LTTD) in the western diamondback rattlesnake (Crotalus atrox).

Pit vipers (Crotalinae) have a specific sensory system that detects infrared radiation with bilateral pit organs in the upper jaw. Each pit organ consists of a thin membrane, innervated by three trigeminal nerve branches that project to a specific nucleus in the dorsal hindbrain. The known topographic organization of infrared signals in the optic tectum prompted us to test the implementation of spatiotopically aligned sensory maps through hierarchical neuronal levels from the peripheral epithelium to the first central site in the hindbrain, the nucleus of the lateral descending trigeminal tract (LTTD). The spatial organization of the anatomical connections was revealed in a novel in vitro whole-brain preparation of the western diamondback rattlesnake (Crotalus atrox) that allowed specific application of multiple neuronal tracers to identified pit-organ-supplying trigeminal nerve branches. After adequate survival times, the entire peripheral and central projections of fibers within the pit membrane and the LTTD became visible. This approach revealed a morphological partition of the pit membrane into three well-defined sensory areas with largely separated innervations by the three main branches. The peripheral segregation of infrared afferents in the sensory epithelium was matched by a differential termination of the afferents within different areas of the LTTD, with little overlap. This result demonstrates a topographic organizational principle of the snake infrared system that is implemented by maintaining spatially aligned representations of environmental infrared cues on the sensory epithelium through specific neuronal projections at the level of the first central processing stage, comparable to the visual system.

Evaporative respiratory cooling augments pit organ thermal detection in rattlesnakes

Rattlesnakes use their facial pit organs to sense external thermal fluctuations. A temperature decrease in the heat-sensing membrane of the pit organ has the potential to enhance heat flux between their endothermic prey and the thermal sensors, affect the optimal functioning of thermal sensors in the pit membrane and reduce the formation of thermal "afterimages", improving thermal detection. We examined the potential for respiratory cooling to improve strike behaviour, capture, and consumption of endothermic prey in the South American rattlesnake, as behavioural indicators of thermal detection. Snakes with a higher degree of rostral cooling were more accurate during the strike, attacking warmer regions of their prey, and relocated and consumed their prey faster. These findings reveal that by cooling their pit organs, rattlesnakes increase their ability to detect endothermic prey; disabling the pit organs caused these differences to disappear. Rattlesnakes also modify the degree of rostral cooling by altering their breathing pattern in response to biologically relevant stimuli, such as a mouse odour. Our findings reveal that low humidity increases their ability to detect endothermic prey, suggesting that habitat and ambush site selection in the wild may be influenced by external humidity levels as well as temperature.

The mechanoreceptors on the endophytic ovipositor of the dragonfly Aeshna cyanea (Odonata, Aeshnidae)

This study investigates the mechanoreceptors located on the cutting valvulae of the ovipositor of the dragonfly Aeshna cyanea (Aeshnidae), using both SEM and TEM, with the aim of providing an overview of the sensory equipment of an odonatan endophytic ovipositor. Four kinds of sensilla have been described. Notwithstanding their different external and internal morphology, they show features typical of mechanoreceptors. Three of them are evident along the external surface of the two cutting valvulae in the form of sub-spherical pegs, pit organs type 1 (holes) and pit organs type 2 (depressions), these last are similar to amphinematic scolopidia, while the fourth type is represented by subintegumental mononematic scolopidia having no direct relationship with the cuticle. In spite of their structural differences, the morphology of the described mechanoreceptors is consistent with performing a main role in allowing the perception of compression/stretching of the thick cuticle of the valvulae and their bending due to the pressure acting on the distal end of the ovipositor during substrate penetration. Such an organization is coherent with the need of endophytic Odonata to be able to evaluate the stiffness of the plant where to lay eggs.

Fine structure and primary sensory projections of sensilla located in the labial-palp pit organ of Helicoverpa armigera (Insecta)

The fine structure and primary sensory projections of sensilla located in the labial-palp pit organ of the cotton bollworm Helicoverpa armigera (Insecta, Lepidoptera) are investigated by scanning electron and transmission electron microscopy combined with confocal laser scanning microscopy. The pit organ located on the third segment of the labial palp is about 300 μm deep with a 60-μm-wide opening, each structure containing about 1200 sensilla. Two sensillum types have been found, namely hair-shaped and club-shaped sensilla, located on the upper and lower half of the pit, respectively. Most sensilla possess a single dendrite. The dendrite housed by the club-shaped sensilla is often split into several branches or becomes lamellated in the outer segment. As reported previously, the sensory axons of the sensilla in the labial pit organ form a bundle entering the ipsilateral side of the subesophageal ganglion via the labial palp nerve and project to three distinct areas: the labial pit organ glomerulus in each antennal lobe, the subesophageal ganglion and the ventral nerve cord. In the antennal lobe, the labial pit organ glomerulus is innervated by sensory axons from the labial pit organ only; no antennal afferents target this unit. One neuron has been found extending fine processes into the subesophageal ganglion and innervating the labial palp via one branch passing at the base of the labial palp nerve. The soma of this assumed motor neuron is located in the ipsilateral cell body layer of the subesophageal ganglion. Our results provide valuable knowledge concerning the neural circuit encoding information about carbon dioxide and should stimulate further investigations directed at controlling pest species such as H. armigera.

Sensory organs of the antenna of two Fannia species (Diptera: Fanniidae)

The latrine fly (Fannia scalaris) and lesser house fly (Fannia canicularis) are ubiquitous fanniid species of forensic and medical importance. The external morphology of sensilla on the antennae is studied using a stereoscopic microscope and scanning electron microscope, and the internal structure of the antennae is revealed by paraffin sections under the light microscope and laser scanning confocal microscope. Only grooved bristles are found on the scape and pedicel. Four major types of surface sensilla are found on the antennal funiculus and are classified as: (a) trichoid sensilla, (b) two subtypes of basiconic sensilla, (c) clavate sensilla, and (d) coeloconic sensilla. Density of each sensilla type of the two species is calculated. A remarkable difference is observed that the higher density of clavate sensilla occurs on the posteroventral surface in F. scalaris, whereas they are on the anterodorsal surface in F. canicularis. Several cuticular depressions that were previously known as "olfactory pits" are observed on the funiculus of both species. Combining with previous studies, they are suggested to be classified into two types: pit and sacculus. Pit is single-chambered and filled with one type of sensilla, whereas the sacculus is a multi-chambered pit organ containing several types of sensilla. Surprisingly, the pits observed in our study are mostly situated at the lateral region of the antennal funiculus, whereas in other flies, they are found on the posteroventral or anterodorsal surface of antennal funiculus. In addition, the sacculus found in our study houses only basiconic-like sensilla, which is remarkably different from other findings. Moreover, observation under light microscope indicates that previous data of the complexity and the number of the "olfactory pits," which are an important type of efficient sensory convergence, could be underestimated. Thus, more precise methods such as paraffin section or transmission electron microscope are suggested for further study.

Antennal sensilla of head of poultry shaft louse, Menopon gallinae (Phthiraptera, Insecta, Menoponidae, Amblycera)

Phthirapteran ectoparasites (lice) are very small arthropodan creature which spend their life on different mammalian and avian host body. Many morphological features of these tiny creatures are not visible under simple microscopic study and hence scanning electron microscopic (SEM) study is required for specific details. Antennal sensillum is also one of the special features located on anterior part of the head of the louse. The present study on the sample specimen of poultry louse, Menopon gallinae (Phthiraptera : Amblycera) showed presence of a small, ovoid scape and pedicel (broad cup-like structure having narrower base) seen in antennal sensilla under SEM. In addition to sensory setae, sense organ was present on terminal segment. Tuft organ contain 6/7 small peg like structure. Pit organ was also visible at the sub-terminal area of fourth segment. Presence of any structure resembling coeloconic chaemo-receptor was not observed on any flagellar sub-segment of M. gallinae.

The mechanosensory lateral line system in two species of wobbegong shark (Orectolobidae)

Comparative studies of the mechanosensory lateral line (MLL) have provided valuable insights into the predatory, escape and navigation behaviours of teleost and elasmobranch fishes. Recent work on the MLL in elasmobranchs has focused on canal morphology and pore topography in batoid species, with considerably less detailed examination of the canal system of sharks. In this study, the spatial arrangement of MLL canals and pit organs, and the morphology of the sensory neuromasts, are described for two species of wobbegong shark: the spotted wobbegong Orectolobus maculatus and the ornate wobbegong O. ornatus. Wobbegongs are benthic species that employ an ambush feeding strategy, and it is hypothesised that the MLL will be adapted for both these ecological traits. The spatial distribution of the MLL system in both species is broadly similar to other elasmobranchs, with a dorsal concentration of canals and pit organs that is ideally suited for detecting water flow over the top of the head. This arrangement may facilitate the detection of prey and predators swimming above and in front of the shark. The non-pored canals positioned directly above the mouth may be used as mechanotactile receptors to optimise ‘touch’ sensation when feeding. Wobbegong canal and pit organ neuromast hair cell morphology is typical of other sharks; however, canal neuromast sensory tissue differs from other elasmobranch species in that it is not continuous throughout the canals. The study provides evidence that the MLL system of wobbegong sharks is well adapted for their rather unique feeding mode and benthic lifestyle.

Reduced Performance of Prey Targeting in Pit Vipers with Contralaterally Occluded Infrared and Visual Senses

Both visual and infrared (IR) senses are utilized in prey targeting by pit vipers. Visual and IR inputs project to the contralateral optic tectum where they activate both multimodal and bimodal neurons. A series of ocular and pit organ occlusion experiments using the short-tailed pit viper (Gloydius brevicaudus) were conducted to investigate the role of visual and IR information during prey targeting. Compared with unoccluded controls, snakes with either both eyes or pit organs occluded performed more poorly in hunting prey although such subjects still captured prey on 75% of trials. Subjects with one eye and one pit occluded on the same side of the face performed as well as those with bilateral occlusion although these subjects showed a significant targeting angle bias toward the unoccluded side. Performance was significantly poorer when only a single eye or pit was available. Interestingly, when one eye and one pit organ were occluded on opposite sides of the face, performance was poorest, the snakes striking prey on no more than half the trials. These results indicate that, visual and infrared information are both effective in prey targeting in this species, although interference between the two modalities occurs if visual and IR information is restricted to opposite sides of the brain.

Antennal sensillar equipment in closely related predatory wasp species (Hymenoptera: Philanthinae) hunting for different prey types

Despite its potential value in phylogenetic and ecological studies, the morphology of antennal sensilla has rarely been compared quantitatively within the Apoidea. Here, through a scanning electron microscopy analysis, we provide an inventory of different types of antennal sensilla and compare their morphology across 10 species of predatory wasps (Crabronidae: Philanthinae) including species that hunt exclusively either on beetles or on bees to feed their larvae. A sensilla-free area was found on the apical flagellomer of all but two species, and its shape and size appear to be useful for separating Philanthini from Cercerini within the subfamily. A total of eight types of sensilla (sensilla placoidea, sensilla basiconica, two types of pit organs, sensilla coelocapitula and three types of sensilla trichoidea) were found in all species, and an additional rarer type (grooved peg sensilla) was found only in three bee-hunting species and for first time in the genus Cerceris. Certain morphological features confirmed the separation of the apoid wasps from the rest of the Apoidea (i.e., bees). A cluster analysis based on the sizes of the different types of sensilla suggested that, overall, sensilla morphology is not a useful taxonomic tool, and thus, other factors likely determine interspecific variability. One candidate factor is the prey type, given some differences in the presence, density, size and distribution of certain types of olfactory sensilla between beetle-hunters and bee-hunters. This hypothesis needs to be further tested quantitatively using a larger species set, more individuals per species, additional sensilla features, and a correction for phylogeny.

Morphological structure and peripheral innervation of the lateral line system in the Siberian sturgeon (Acipenser baerii)

Light and scanning electron microscopy (SEM) were used to study the epidermal lateral line system of the Siberian sturgeon (Acipenser baerii Brandt, 1869). This system consists of mechanoreceptive neuromasts, ampullae and the electroreceptive organ. The neuromasts are located in 5 pairs of cephalic and 1 pair of trunk canals and superficially in the middle and posterior pit lines that lie dorsomedially along the top of the skull immediately adjacent to the otic ampullae field. Both canal neuromasts and pit organ superficial neuromasts have opposite polarized hair cells that are parallel along the axis of the canal and pit line, respectively. However, they differ in both size and shape and in the density and length of the hair bundles. The ampullae are confined on the head, adjacent to the neuromast lines. The morphological structure of the ampullae in the Siberian sturgeon is similar to the ampullae in elasmobranchs and other primitive fish. Nevertheless, it has a relatively large mucus-filled ampulla, and a shorter and narrower canal leading to a small opening to the outer epidermal surface. We also present new information concerning the peripheral innervation of lateral line receptors in sturgeons. The receptors of the lateral line system are innervated by 2 pairs of cranial nerves: anterior and posterior lateral line nerves. The peripheral processes of the anterior lateral line nerve form superficial ophthalmic, buccal, otic and anteroventral rami. The peripheral processes of the posterior lateral line nerve form middle, supratemporal and lateral rami.

Anomalous Infrared Taxis of an Aquatic Animal, the Giant Jellyfish Nemopilema nomurai (Scyphozoa, Rhizostomeae)

Remote sensing of thermal radiation (infrared wavelengths) has been reported only in some terrestrial animals and is known to have significant physiological and ecological meaning. In aquatic animals, however, it has not even been discussed because water almost completely absorbs infrared (IR) wavelengths, and such sensitivity has been regarded as useless in aquatic environments. Here we report, for the first time, an anomalous behavior—swimming toward an IR-radiating source—in an aquatic animal, the giant jellyfish, Nemopilema nomurai. Experiments were performed with laboratory-reared juvenile medusae of Nemopilema in a small experimental chamber. In all 52 trials, the majority (average: 78.3%; variation: 63.3%– 94.3%) of the medusae gathered on the IR-irradiated half of the chamber. Near-IR (850/940 nm) and visible light neither attracted the medusae nor induced taxis. A series of results indicated that the juveniles of Nemopilema tended to flock toward a mass of warmer water. Although the exact physiological and ecological meaning of this behavior is uncertain, it might be possible to consider infrared taxis as one of the behaviors in marine ecosystems. It may thus be useful to re-examine the swarming behavior reported in some jellyfish species from the viewpoint of IR taxis. Infrared (IR) sensitivity is known to be mediated by the so-called pit organs, which enable crotaline and boid snakes to apprehend homeothermic prey (1–7) and vampire bats to detect IR radiation from blood-rich locations (8, 9). Moreover, similar mechanisms have been reported in some insects such as fine debris species of beetle (10–13), bloodsucking bugs (14), and some butterflies (15, 16). In aquatic animals, however, little is known about the IR sensitivity. This is the first report to describe an anomalous IR-tactic behavior in the giant jellyfish, Nemopilema nomurai, living in an aquatic environment. Nemopilema nomurai Kishinouye 1922 is one of the largest scyphozoan jellyfish, measuring 1–2 m in diameter and weighing 100–200 kg. Massive blooms of this species have occurred almost annually since 2002, severely affecting coastal fisheries in the Sea of Japan. The life cycle of N. nomurai has been well established by us and our coworkers (17, 18), so the juvenile medusae are easily available. We thus used laboratory-reared juveniles (extended bell diameter, 8–15 mm) to examine the IR sensitivity of N. nomurai. The experimental chamber (width 30 cm, length 24 cm, height 16 cm) used to test IR sensitivity was made from transparent acryl resin plate (5 mm thick). It was filled with seawater to a depth of 3.5 cm and 20 to 35 juvenile individuals were added. The distribution of the medusae in the chamber was monitored by photographing them from above with a photographic strobe every 30 or 60 min. The IR wavelengths were obtained from a tungsten-filament lamp (40 W) by passing the light through a long-pass filter (50% cut-on at 990 nm; LIO-990, Asahi Spectra Co. Ltd.). The tungsten-filament lamp was fixed in a lightproof aluminum housing with a window, where the long-pass filter was mounted. All possible heat sources, except for the IR-wavelength source, were excluded from around the experimental chamber. Near-IR wavelengths, 940 and 850 nm, were obtained from two types of 1.2-W LEDs, LB12WP01 and LC12-WP01 (Ebisu Electronics Co. Ltd.), reReceived 1 August 2011; accepted 20 October 2011. * To whom correspondence should be addressed. E-mail: ohtsu@ life.shimane-u.ac.jp Reference: Biol. Bull. 221: 243–247. (December 2011) © 2011 Marine Biological Laboratory

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.

Development of pit organs and behaviour during early ontogeny of the Chinese sturgeon (Acipenser sinensis)

Development of pit organs and behaviour during early ontogeny of the Chinese sturgeon (Acipenser sinensis) By L. X. Li, Y. Chai, Q. W. Wei and C. X. Xie Key Laboratory of Freshwater Fish Germplasm Resources and Biotechnology, the Ministry of Agriculture of PRC, Yangtze River Research Institute, Chinese Academy of Fishery Sciences, Jingzhou, China; College of Animal Science Yangtze University, Jingzhou, China; College of Fisheries Huazhong Agricultural University, Wuhan, China