Douglas D. Gaffin

Behavioral evidence of pheromonal signaling in desert grassland scorpions Paruroctonus utahensis

Abstract Behavioral evidence suggests that, in some scorpion species, females deposit a pheromone that attracts mates. To date, however, no pheromone has been identified. The goal of our study was to isolate a pheromone from female desert grassland scorpions, Paruroctonus utahensis (Williams, 1968) (Scorpiones:Vaejovidae). We took in situ cuticular washes from female P. utahensis in a chloroform-methanol solution; the extract stratified into aqueous and organic layers. In controlled laboratory experiments, most males exposed to female extract (aqueous and organic fractions combined) exhibited pre-courtship behavior, whereas those exposed to the solvent control (2∶1 chloroform-methanol) showed no change in behavior. When extract fractions were separately tested, males initiated pre-courtship behavior when exposed to the organic fraction but not when exposed to the aqueous fraction. These data are the first experimental evidence of a female pheromone in this species and are important early steps toward characterizing any scorpion pheromone.

A new approach to examining scorpion peg sensilla: the mineral oil flood technique

Abstract All scorpions possess jointed, ventral appendages called pectines. These organs have chemosensory, peg-shaped sensilla that detect substrate-borne chemicals. Previous physiological studies show that neurons within peg sensilla respond to an assortment of volatile organic chemical stimulants blown across the sensillar opening. We developed an improved method of chemical stimulant delivery called the mineral oil flood technique to further investigate the neural circuitry of scorpion pectines. The new mineral oil flood technique allows us to deliver chemical stimulants directly to individual sensilla by introducing a polar, liquid substance under non-polar mineral oil. Unlike previous methods of stimulant delivery, the mineral oil flood technique allows for precise control over the duration of direct contact between a liquid stimulant of known concentration and a sensillum.

Insect-inspired navigation algorithm for an aerial agent using satellite imagery

Humans have long marveled at the ability of animals to navigate swiftly, accurately, and across long distances. Many mechanisms have been proposed for how animals acquire, store, and retrace learned routes, yet many of these hypotheses appear incongruent with behavioral observations and the animals’ neural constraints. The “Navigation by Scene Familiarity Hypothesis” proposed originally for insect navigation offers an elegantly simple solution for retracing previously experienced routes without the need for complex neural architectures and memory retrieval mechanisms. This hypothesis proposes that an animal can return to a target location by simply moving toward the most familiar scene at any given point. Proof of concept simulations have used computer-generated ant’s-eye views of the world, but here we test the ability of scene familiarity algorithms to navigate training routes across satellite images extracted from Google Maps. We find that Google satellite images are so rich in visual information that familiarity algorithms can be used to retrace even tortuous routes with low-resolution sensors. We discuss the implications of these findings not only for animal navigation but also for the potential development of visual augmentation systems and robot guidance algorithms.

Autonomous Visual Navigation of an Indoor Environment Using a Parsimonious, Insect Inspired Familiarity Algorithm

The navigation of bees and ants from hive to food and back has captivated people for more than a century. Recently, the Navigation by Scene Familiarity Hypothesis (NSFH) has been proposed as a parsimonious approach that is congruent with the limited neural elements of these insects’ brains. In the NSFH approach, an agent completes an initial training excursion, storing images along the way. To retrace the path, the agent scans the area and compares the current scenes to those previously experienced. By turning and moving to minimize the pixel-by-pixel differences between encountered and stored scenes, the agent is guided along the path without having memorized the sequence. An important premise of the NSFH is that the visual information of the environment is adequate to guide navigation without aliasing. Here we demonstrate that an image landscape of an indoor setting possesses ample navigational information. We produced a visual landscape of our laboratory and part of the adjoining corridor consisting of 2816 panoramic snapshots arranged in a grid at 12.7-cm centers. We show that pixel-by-pixel comparisons of these images yield robust translational and rotational visual information. We also produced a simple algorithm that tracks previously experienced routes within our lab based on an insect-inspired scene familiarity approach and demonstrate that adequate visual information exists for an agent to retrace complex training routes, including those where the path’s end is not visible from its origin. We used this landscape to systematically test the interplay of sensor morphology, angles of inspection, and similarity threshold with the recapitulation performance of the agent. Finally, we compared the relative information content and chance of aliasing within our visually rich laboratory landscape to scenes acquired from indoor corridors with more repetitive scenery.

A new tip-recording method to test scorpion pecten chemoresponses to water-soluble stimulants

On the ventral surface of all scorpions are jointed appendages called pectines, which possess thousands of sensory sensilla. Researchers have electrophysiologically examined these peg sensilla in the past, providing evidence for their chemosensitivity and intra-peg synaptic interactions. However, limits to extracellular recording and chemical stimulation have impeded further research. In this study, we develop and apply a new tip-recording technique for stimulating and recording peg neurons. Relative to previous methods in pecten electrophysiology, this technique allows for very fast and efficient data assembly. Using it, we captured sensilla chemoresponses to aqueous stimulants. We see utility in this method for advancing our understanding of sensory physiology; specifically, we suggest this technique may be useful for physiological assays on scorpion and other arthropod chemoreceptors, such as insect and crustacean gustatory sensilla.

Determination of in-lab site fidelity and movement patterns of Paruroctonus utahensis (Scorpiones: Vaejovidae)

Abstract Many animals build homes to which they return after excursions. However, the sensory and motor mechanisms that animals use to home are poorly understood. Sand scorpions, including Paruroctonus utahensis (Williams 1968), make burrows from which they emerge to hunt at night. These scorpions spend most of their surface time within about a meter of their burrow. Our goal was to create a laboratory environment conducive to scorpion homing behavior. Specifically, our objectives were to verify in-lab burrow use similar to field observations and to characterize scorpion movements in these artificial environments. Tests occurred in circular, sand-filled arenas (65 cm diam); in the center of each was a shelter (a small jar lid with openings for the scorpions to enter). We used IR cameras to film all trials from above in a room with a 14:10 hour light-dark cycle. Animals were tested over a 7-day period for their tendency to establish and return to their shelters on a normal day/night cycle. Time-in-shelter percentages showed significant evidence of shelter use, consistent with their normal burrow use in the field. In the second experiment, we wrote a MATLAB program to automatically track several hours of videotaped scorpion nocturnal movements. Animals spent most of their time along the arena walls but made intermittent forays across the arena center. When they returned to their shelters, their movements appeared to be direct and deliberate. This behavioral set-up will be useful in future attempts to deduce the sensory information these animals use to return to their burrows.

Analysis of sensory processing in scorpion peg sensilla

Abstract Primary chemosensory afferents within each peg sensillum on scorpion pectines contain a dense plexus of synaptic contacts of unknown importance to informational processing within this simple sensory structure. These connections probably contribute to the processing of chemical signals from the substrate to the encoded pattern of spike activity ascending the pectinal nerves to the CNS. A key finding of earlier studies of this system was the apparent existence of strong and long-lasting inhibitory interactions between one identifiable unit – type “B” cells – and at least two other sensory neurons – identified as “A1” and “A2” – cells within the same sensillum. Because peripheral synaptic interactions are rarely observed between primary sensory neurons, it is important to reject the alternative non-synaptic mechanism to account for the unusual spike waveform of inhibitory B units, namely, that it is derived from coincident discharge of the A1 and A2 units it is presumed to inhibit. High resolution waveform analysis of two or more units firing in close temporal proximity (within about 5 ms) showed unequivocally that type B units occur within the post excitatory period when the A units would be refractory to re-excitation. Furthermore, the number of these B/A1 or B/A2 doublets was in line with the number predicted for the observed spontaneous firing frequency of the B, A1, and A2 units in the peg. This analysis corroborates the original conclusion that B unit activity is the electrophysiological signature of an inhibitory processing event, one that strikingly transforms the information encoded and passed from each peg sensillum to the central nervous system.

Exploring the chemo-textural familiarity hypothesis for scorpion navigation

Abstract The navigation by scene familiarity hypothesis provides broad explanatory power for how bees and ants navigate from the hive to distant food sources and back. The premise is that the visual world is decomposed into pixelated matrices of information that are stored and readdressed as the insects retrace learned routes. Innate behaviors in these insects (including learning walks/flights and path integration) provide the important goal-directed views to allow the initial retracing (i.e., the insect must learn the scene while moving toward the goal because everything looks different while moving away). Scorpion navigation may use a similar premise, with the chemical and textural features of the environment substituting for visual input. Scorpion pectines support thousands of chemo- and mechano-sensitive units called peg sensilla, each containing at least 10 energetically expensive sensory neurons. We have long wondered why pectines have so many pegs and associated neurons. Many sand scorpions emerge onto the surface from their home burrows at night to pursue insect prey and somehow find their way back to their burrows. Based on the measured resolution of peg sensilla, we have calculated that sufficient information exists in sands texture to enable scorpions to retrace previously experienced paths with little to no chance of confusion. Preliminary evidence of learning walks and path integration in scorpions is also congruent with the navigation by chemo-textural familiarity hypothesis.

Comparative Morphology and Functional Significance of Setae Called Papillae on the Pedipalps of Male Camel Spiders (Arachnida: Solifugae)

ABSTRACT Some male camel spiders (Arachnida: Solifugae) in the families Eremobatidae, Karschiidae, and Solpugidae have clusters of specialized conical or acuminate setae called papillae, on the ventral surface of the metatarsus of the pedipalps. We compared the overall structure of the papillae found on representatives of the three families using scanning electron microscopy (SEM). We examined the ultrastructure of these setae using transmission electron microscopy (TEM). We also used extracellular electrophysiological recording techniques to examine the electrical properties of these sensory structures and test the hypotheses that they function as mechanoreceptors, olfactory receptors, and chemoreceptors.Wefound similarities in the structure of papillae among genera within a family or distinct family-level differences in structure. Thus, the papillae are phylogenetically informative; similar within family but differing between families. TEM results demonstrated the cuticular wall of a papilla is divided into three sublayers: endo-, meso-, and exocuticle. Mechanoreceptive dendrites are evident at the base of the setal shaft. Other dendrites innervate the shaft of the papilla and penetrate through the cuticular layers near the setal apex. Two SEM images show what appear to be pores on the branches of the papillae, and we found what appears to be a pore tubule extending from the distal portion of the dendrites through the exocuticular layer. Electrophysiological data support the hypothesis that the papillae function as mechanoreceptors and provide no support for chemosensory, thermoregulatory, or hygroreceptive functions. Our data suggest that the papillae function as mechanoreceptors and may also function as chemoreceptors.

Electrophysiology of Scorpion Peg Sensilla

We describe a modification of an existing tip-recording technique1,2 for electrophysiologically investigating short, peg-like sensory sensilla3,4. On the mid-ventral surface of all scorpions are two appendages called pectines, which have dense fields of mechano- and chemosensory peg sensilla5,6. One method for assessing chemoresponsiveness of these sensilla uses a tungsten electrode for extracellularly recording neural activity within a sensillum as a volatile odorant is introduced to the sensory field5,7. The limitations of this method include slow data collection and uncontrolled stimulant introduction to, and removal from, the peg field. To overcome these limitations, we developed a new tip-recording technique that uses nonpolar mineral oil as a medium through which to deliver water-based tastants to individual peg sensilla8,9. We have successfully applied this method to obtain sensillar chemoresponses to citric acid, ethanol, and salt. Here we describe the experimental protocol for such a study9. We think this new method may be useful for studying the response properties of other arthropod chemosensory systems, including those of insects10, 11 and crustaceans12.