Phrynus Marginemaculatus Research Articles

Investigating boundary-geometry use by whip spiders (Phrynus marginemaculatus) during goal-directed navigation.

Previous studies have shown that whip spiders (Amblypygi) can use a variety of cues to navigate to and recognize a home refuge. The current study aimed to determine whether whip spiders were capable of using the boundary geometry of an experimental space (geometric information) to guide goal-directed navigation and to investigate any preferential use of geometric or feature (visual) information. Animals were first trained to find a goal location situated in one corner of a rectangular arena (geometric information) fronting a dark-green-colored wall, which created a brightness contrast with the other three white walls (feature information). Various probe trials were then implemented to determine cue use. It was found that animals were capable of directing their choice behavior towards geometrically correct corners at a rate significantly higher than chance, even when the feature cue was removed. By contrast, choice behavior dropped to random chance when geometric information was removed (test in a square arena) and only feature information remained. Choice behavior was also reduced to chance when geometric and feature information were set in conflict (by moving the feature cue to one of the longer walls in the rectangular arena). The data thus suggest that whip spiders are capable of using geometric information to guide goal-directed navigation and that geometric information is preferred over feature guidance, although a feature cue may set the context for activating geometry-guided navigation. Experimental design limitations and future directions are discussed.

Visual control of refuge recognition in the whip spider Phrynus marginemaculatus.

Amblypygids, or whip spiders, are nocturnally active arachnids which live in structurally complex environments. Whip spiders are excellent navigators thatcan re-locate a home refuge without relying on visual input. Therefore, an open question is whether visual input can control any aspect of whip spider spatial behavior. In the current study, Phrynus marginemaculatus were trained to locate an escape refuge by discriminating between differently oriented black and white stripes placed either on the walls of a testing arena (frontal discrimination) or on the ceiling of the same testing arena (overhead discrimination). Regardless of the placement of the visual stimuli, the whip spiders were successful in learning the location of the escape refuge. In a follow-up study of the overhead discrimination, occluding the median eyes was found to disrupt the ability of the whip spiders to locate the shelter. The data support the conclusion that whip spiders can rely on vision to learn and recognize an escape shelter. We suggest that visual inputs to the brain's mushroom bodies enable this ability.

Elemental enrichment of the exoskeleton of the whip spider Phrynus marginemaculatus (Arachnida: Amblypygi)

Amblypygi is a small order of arachnids that includes the whip spiders. Like other members of the clade Pedipalpi, these arachnids are cryptic predators that use their antenniform appendages to detect prey, and spinose pedipalps for quick prey capture. To date, there is very little information on the composition of their exoskeleton despite its importance in predation and defense. Here, we performed the first analysis of a whip spider exoskeleton using energy-dispersive X-ray spectroscopy (SEM-EDS). Our studies of Phrynus marginemaculatus CL Koch, 1840 were designed to (1) determine if elemental profiles differ between instars and (2) determine if and how elemental profiles of whip spiders differ from other closely related arachnids. We found the whip spider exoskeleton to contain several trace metal elements including calcium, magnesium, manganese, potassium, sodium, and zinc. The diversity and abundance of trace elements is relatively low throughout the exoskeleton of 2nd instars but increases in adults. In particular, the chelicerae and pedipalps are well reinforced with several metal elements, most notably calcium and zinc, which are also present in the tarsal claws. A similar elemental distribution is known for adult whip scorpions (Thelyphonida). In P. marginemaculatus, these metal elements are similarly present in adult exuviae. The elemental enrichment of the whip spider exoskeleton is comparable to that present in other members of the Pedipalpi and Tetrapulmonata, reflecting a relatively conserved profile for the few species that have been examined.

Multisensory integration supports configural learning of a home refuge in the whip spider Phrynus marginemaculatus.

Whip spiders (Amblypygi) reside in structurally complex habitats and are nocturnally active yet display notable navigational abilities. From the theory that uncertainty in sensory inputs should promote multisensory representations to guide behavior, we hypothesized that their navigation is supported by a multisensory and perhaps configural representation of navigational inputs, an ability documented in a few insects and never reported in arachnids. We trained Phrynus marginemaculatus to recognize a home shelter characterized by both discriminative olfactory and tactile stimuli. In tests, subjects readily discriminated between shelters based on the paired stimuli. However, subjects failed to recognize the shelter in tests with either of the component stimuli alone. This result is consistent with the hypothesis that the terminal phase of their navigational behavior, shelter recognition, can be supported by the integration of multisensory stimuli as an enduring, configural representation. We hypothesize that multisensory learning occurs in the whip spiders' extraordinarily large mushroom bodies, which may functionally resemble the hippocampus of vertebrates.

Genomic resources and toolkits for developmental study of whip spiders (Amblypygi) provide insights into arachnid genome evolution and antenniform leg patterning

BackgroundThe resurgence of interest in the comparative developmental study of chelicerates has led to important insights, such as the discovery of a genome duplication shared by spiders and scorpions, inferred to have occurred in the most recent common ancestor of Arachnopulmonata (a clade comprising the five arachnid orders that bear book lungs). Nonetheless, several arachnid groups remain understudied in the context of development and genomics, such as the order Amblypygi (whip spiders). The phylogenetic position of Amblypygi in Arachnopulmonata posits them as an interesting group to test the incidence of the proposed genome duplication in the common ancestor of Arachnopulmonata, as well as the degree of retention of duplicates over 450 Myr. Moreover, whip spiders have their first pair of walking legs elongated and modified into sensory appendages (a convergence with the antennae of mandibulates), but the genetic patterning of these antenniform legs has never been investigated.ResultsWe established genomic resources and protocols for cultivation of embryos and gene expression assays by in situ hybridization to study the development of the whip spider Phrynus marginemaculatus. Using embryonic transcriptomes from three species of Amblypygi, we show that the ancestral whip spider exhibited duplications of all ten Hox genes. We deploy these resources to show that paralogs of the leg gap genes dachshund and homothorax retain arachnopulmonate-specific expression patterns in P. marginemaculatus. We characterize the expression of leg gap genes Distal-less, dachshund-1/2 and homothorax-1/2 in the embryonic antenniform leg and other appendages, and provide evidence that allometry, and by extension the antenniform leg fate, is specified early in embryogenesis.ConclusionThis study is the first step in establishing P. marginemaculatus as a chelicerate model for modern evolutionary developmental study, and provides the first resources sampling whip spiders for comparative genomics. Our results suggest that Amblypygi share a genome duplication with spiders and scorpions, and set up a framework to study the genetic specification of antenniform legs. Future efforts to study whip spider development must emphasize the development of tools for functional experiments in P. marginemaculatus.

Distortion of the local magnetic field appears to neither disrupt nocturnal navigation nor cue shelter recognition in the amblypygid Paraphrynus laevifrons

AbstractMany arthropods are known to be sensitive to the geomagnetic field and exploit the field to solve spatial problems. The polarity of the geomagnetic field is used, for instance, as an orientation cue by leafcutter ants as they travel on engineered trails in a rainforest and by Drosophila larvae as they move short distances in search of food. A ubiquitous orientation cue like the geomagnetic field may be especially useful in complex, cluttered environments like rainforests, where the reliability of celestial cues used to navigate in more open environments may be poor. The neotropical amblypygid Paraphrynus laevifrons is a nocturnal arachnid that wanders nightly in the vicinity of its shelter and occasionally travels 30 m or more in the rainforest understory before it returns to its shelter. Here, we conducted a field experiment to determine whether navigation by P. laevifrons is guided by the ambient magnetic field and a complimentary laboratory experiment to assess whether a magnetic anomaly could be used to pinpoint the entrance of a shelter. In the field experiment, subjects were fitted with a radio transmitter and a small, powerful magnet or a similar‐sized brass disk and displaced 10 m from their shelter. The return rate of magnet‐fitted subjects was similar to that of brass‐fitted subjects and to that of subjects in an earlier study fitted with only a radio transmitter. In the laboratory experiment, we trained P. laevifrons with a protocol under which the amblypygid Phrynus marginemaculatus rapidly learns—in 1–14 trials over two daily sessions—to associate an olfactory stimulus with access to a shelter. The conditioned stimulus here was a magnetic anomaly characterized by a high total field intensity and a 180° reversal of the polarity of the ambient magnetic field. The magnetic anomaly‐shelter contingency was not learned in 50 trials conducted over 10 daily sessions. These results imply prima facie that P. laevifrons does not rely on a magnetic compass to locate or recognize a shelter and, perhaps, that the magnetic field cannot be detected, but alternative explanations are discussed.

Comparative analysis of the boundary layer filtering of odor signals in the amblypygid (whip spider) species Paraphrynus laevifrons and Phrynus marginemaculatus

Amblypygids use a pair of modified walking legs (antenniform) as chemosensory and mechanosensory appendages. At the tip of these legs are covered in chemosensory sensilla, which the animals use to sample odor stimuli in their environment by moving the antenniform leg through the air. We designed a set of experiments to measure the filtering effect that aerodynamic boundary layers have on the temporal and spatial structure of chemical stimuli. In addition, two different species of amblypygids (Paraphrynus laevifrons and Phrynus marginemaculatus) that live in two distinct habitats were used for a comparative analysis. Pulses of a tracer molecule were quantified at different distances and flow velocities using an electrochemical detection system. Temporal attributes of the chemical pulses were extracted and were statistically compared across velocities, distances from the appendage, and the two species. Overall, the boundary layer significantly decreased the concentration and increased the duration of pulses for both species. This filtering effect was more pronounced for P. marginemaculatus than P. laevifrons, as the chemical signal was lower in concentration and longer in duration at any distance from the antenniform leg. It is speculated that the difference in boundary layer filtering, as a function of appendage morphology, is tuned to the different types of odor plumes in these animals’ native habitats.

Self-derived chemical cues support home refuge recognition in the whip spider Phrynus marginemaculatus (Amblypygi: Phrynidae)

Whip spiders (Class Arachnida: Order Amblypygi) are hypothesized to use multimodal sensory inputs to navigate back to their diurnal shelter after a night of activity, and chemical cues are thought to be involved. In two experiments, we investigated whether self-deposited chemical cues on a substrate could be used for shelter recognition by Phrynus marginemaculatus C.L. Koch, 1840. When given a choice, individual P. marginemaculatus spent more time in a shelter that contained filter paper it had previously contacted compared to a shelter with filter paper never contacted. In the second experiment, subjects showed no significant preference for a shelter that contained filter paper they had contacted compared to a shelter with filter paper that had been contacted by a conspecific. The data support the hypothesis that during the last stage of nightly navigation to their refuge, detection of self-deposited chemical cues, likely mediated by contact chemoreceptors, may facilitate home refuge recognition by P. marginemaculatus.

Nocturnal navigation by whip spiders: antenniform legs mediate near-distance olfactory localization of a shelter

Navigation by terrestrial arthropods that wander away from a shelter in search of food or mates in uncluttered environments invariably relies on path integration mechanisms, which provide distance and direction information used to compute a straight-line return trajectory. Navigation in cluttered habitats is more typically visually guided, even in species that are nocturnal. Nocturnal, tropical arachnids in the order Amblypygi, however, depend neither on path integration nor on vision to navigate and are hypothesized to instead rely on highly sensitive olfactory structures. The distal articles of their antenniform legs are covered with receptors that presumably bind the odour stimuli thought to control, at least in part, their impressive ability to relocate a shelter after they wander in a rainforest understory. To test the hypothesis that olfactory inputs from the antenniform legs support their near-distance ability to localize a shelter, we conducted a laboratory experiment with the amblypygid Phrynus marginemaculatus in which an olfactory cue (with contact chemoreception precluded) identified the location of a shelter, the position of which was varied as subjects were trained. Localization of a shelter was readily learned and performance was fully retained over a 2-week period in which subjects were not trained. Localization of the odour-cued shelter declined markedly, however, when the distal articles of the antenniform legs were amputated. Moreover, the residual discrimination ability displayed by subjects when they were subsequently retrained depended on how many olfactory receptors had been removed. The results clearly demonstrate that odour cues can support near-distance goal localization and that receptors on the antenniform legs are the locus of the peripheral neural transduction necessary when odour is used to identify the position of a shelter.

Island biogeography and ecological modeling of the amblypygid Phrynus marginemaculatus in the Florida Keys archipelago.

AimThe biogeography of terrestrial organisms across the Florida Keys archipelago is poorly understood. We used population genetics and spatioecological modeling of the Amblypygi Phrynus marginemaculatus to understand the genetic structure and metapopulation dynamics of Keys populations that are otherwise isolated by human development and ocean.LocationThe Florida Keys archipelago and mainland Florida.MethodsWe sequenced a 1,238 bp fragment of mtDNA for 103 individuals of P. marginemaculatus from 13 sites in the Florida Keys and South Florida, binned into four regions. We used population genetic analyses to understand the population structure of the species throughout its US range. Furthermore, we used ecological modeling with climate, habitat, and human development data to develop habitat suitability estimates for the species.ResultsWe found clear genetic structure between localities. The Lower Keys, in particular, support populations separate from those in other regions studied. Ecological modeling and genetic analyses showed the highest habitat suitability and genetic isolation in the Lower Keys, but urban development across the species range has resulted in the loss of most historical habitat.Main conclusionsA mainland‐metapopulation model best fits P. marginemaculatus gene flow patterns in the Florida Keys and mainland. Ocean currents likely play a role in metapopulation dynamics and gene flow for terrestrial Keys species like P. marginemaculatus, and genetic patterns also matched patterns consistent with geologic history. Suitable habitat, however, is limited and under threat of human destruction. The few remaining pockets of the most suitable habitat tend to occur in parks and protected areas. We argue that conservation efforts for this species and others in the terrestrial Florida Keys would benefit from a deeper understanding of the population genetic structure and ecology of the archipelago.

Development of site fidelity in the nocturnal amblypygid, Phrynus marginemaculatus.

Amblypygids are capable of navigation in the complex terrain of rainforests in near complete darkness. Path integration is unnecessary for successful homing, and the alternative mechanisms by which they navigate have yet to be elucidated. Here, our aims were to determine whether the amblypygid Phrynus marginemaculatus could be trained to reliably return to a target shelter in a laboratory arena-indicating goal recognition-and to document changes in behavior associated with the development of fidelity. We recorded nocturnal movements and space use by individuals over five nights in an arena in which subjects were provided with two shelters that differed in quality. The target shelter, unlike the alternative shelter, shielded subjects from light in daylight hours. Individuals consistently exited and returned to a shelter each night and from the third night onward chose the target shelter more often than the alternative shelter. Indeed, on the fifth night, every subject chose the target shelter. This transition was associated with changes in movement and space use in the arena. Notably, the movement features of outbound and inbound paths differed but did not change across nights. Individuals were also characterized by distinct behavioral strategies reflecting candidate homing mechanisms.

Evidence for air movement signals in the agonistic behaviour of a nocturnal arachnid (order Amblypygi).

Many arthropods possess filiform hair sensilla (termed trichobothria in arachnids), which are extremely sensitive detectors of medium particle displacement. Electrophysiological evidence in some taxa suggests that these sensilla can detect air particle displacements resulting from intraspecific communication signals. However, it has not yet been shown for any species that the air particle displacements detected by the filiform hairs are themselves perceived as a ‘signal’ (i.e. that individuals make behavioural decisions based upon the responses of these organs to the displays of conspecifics). We investigate the agonistic behaviour of the whip spider Phrynus marginemaculatus and the role of its trichobothria in receiving agonistic signals. Whip spiders have extremely elongated ‘antenniform’ first legs, which they vibrate close to their opponents during agonistic interactions, inducing air movements that excite their opponents' trichobothria. We find that ablation of the trichobothria causes significant increases in: (I) contest duration, and (II) the probability of contest escalation past aggressive displays to physical fighting. Therefore, in the absence of air movement-sensitive sensilla, contest assessment is impaired. This suggests that whip spiders exploit true air movement signals during agonistic interactions, and that these are received by the trichobothria. Furthermore, these results indicate that, in whip spiders, such signals help mitigate the cost of agonistic interaction.

Prey capture by the whip spider Phrynus marginemaculatus C.L. Koch

Abstract Whip spiders (Arachnida, Amblypygi) are little-studied arachnids with enlarged spiny pedipalps and elongated “antenniform” forelegs. These antenniform legs contain at least seven giant sensory neurons with no known behavioral function. Here we use high-speed cinematography to describe the prey capture behavior of the whip spider Phrynus marginemaculatus C.L. Koch 1840, in order to examine how these giant neurons might be involved. When presented with a prey item (a cricket), a whip spider first accurately aims one of its antenniform legs in the prey's direction. Next, the whip spider orients its body to the prey item and approaches, placing one antenniform leg tip on either side of the prey. The whip spider may remain relatively still in this position for some time, before opening its pedipalps in preparation for a strike and then rapidly swinging its antenniform legs away from the prey item and striking at it with its pedipalps. In common with previous studies, our results show that giant neuron...

Tactile learning by a whip spider, Phrynus marginemaculatus C.L. Koch (Arachnida, Amblypygi)

The ability of animals to learn and remember underpins many behavioural actions and can be crucial for survival in certain contexts, for example in finding and recognising a habitual refuge. The sensory cues that an animal learns in such situations are to an extent determined by its own sensory specialisations. Whip spiders (Arachnida, Amblypygi) are nocturnal and possess uniquely specialised sensory systems that include elongated 'antenniform' forelegs specialised for use as chemo- and mechanosensory feelers. We tested the tactile learning abilities of the whip spider Phrynus marginemaculatus in a maze learning task with two tactile cues of different texture--one associated with an accessible refuge, and the other with an inaccessible refuge. Over ten training trials, whip spiders got faster and more accurate at finding the accessible refuge. During a subsequent test trial where both refuges were inaccessible, whip spiders searched for significantly longer at the tactile cue previously associated with the accessible refuge. Using high-speed cinematography, we describe three distinct antenniform leg movements used by whip spiders during tactile examination. We discuss the potential importance of tactile learning in whip spider behaviour and a possible role for their unique giant sensory neurons in accessing tactile information.

ANATOMY AND PHYSIOLOGY OF GIANT NEURONS IN THE ANTENNIFORM LEG OF THE AMBLYPYGID PHRYNUS MARGINEMACULATUS

Amblypygids have modified front legs that are not used for locomotion, but rather to probe the environment in the manner of antennae. These elongate, motile sense organs are referred to as antenniform legs. We have found remarkable replication in structure and function of giant neurons in the antenniform leg of the amblypygid Phrynus marginemaculatus C. L. Koch 1841 when compared with other amblypygids. These neurons have such large diameter axons (several m) that their action potentials can be recorded outside the cuticle. Their cell bodies are found in the periphery, in the distal-most segments of the antenniform leg, centimeters away from the central nervous system. Primary afferents from sense organs on the antenniform leg synapse onto some of the giant fibers in these distal segments of the leg. Standard histological techniques and a novel whole mount preparation were used to identify the location of giant cell bodies within the antenniform leg. We found several new cell bodies in segments 10-20, three of which were predicted by previous electrophysiological studies of another amblypygid, Hetero- phrynus elaphus Pocock 1903. Electrophysiology was used to show that the structure and function of four of the giant neurons, GN1, 2, 6, and 7, is very similar in P. marginemaculatus and H. elaphus. Hetero- phrynus elaphus inhabits humid tropical forests in South America while P. marginemaculatus individuals were collected from a pine rock hammock in the Florida Keys, USA. The similarity of findings in species with such distinct habitats suggests that the giant neurons are required for basic neuromechanical operation of these extended limbs, and are not subject to intense selection via ecological factors.

AN EXAMINATION OF AGONISTIC INTERACTIONS IN THE WHIP SPIDER PHRYNUS MARGINEMACULATUS (ARACHNIDA, AMBLYPYGI)

Abstract Intraspecific interactions in adult whip spiders (Phrynus marginemaculatus) were investigated in a laboratory setting to quantify agonistic interactions and to determine predictors of contest outcome. Males were initially paired with size-symmetric or size-asymmetric opponents to assess the effect of size symmetry on contests. Three weeks later, the same males were paired with either the same opponent, or a different opponent to determine whether or not individuals remember earlier encounters. Finally, we quantified aspects of female-female contests. Agonistic encounters between males are characterized by varying degrees of pedipalpal opening, elevation displays, and rapid flicking (∼ 29 Hz) of the antenniform leg. Duration of elevation displays was a predictor of contest outcome, with individuals being more likely to win if they held an elevated posture for longer than their opponent during the contest. Relative size influenced both contest duration and weight loss, with contests between size-sy...

SOCIAL BEHAVIOR IN AMBLYPYGIDS, AND A REASSESSMENT OF ARACHNID SOCIAL PATTERNS

Abstract Aggregation, extended mother-offspring-sibling interactions, and complex social behaviors are extremely rare among arachnids. We report and quantify for the first time in Amblypygi prolonged mother-offspring-sibling associations, active aggregation, and frequent “amicable” (tolerant, nonaggressive) tactile interactions in two species: Phrynus marginemaculatus C.L. Koch 1840 (Phrynidae) and Damon diadema (Simon, 1876) (Phrynichidae). Sociality is characterized by frequent contact and tolerance, and infrequent agonism until sexual maturity in D. diadema and into adulthood in P. marginemaculatus. We experimentally examined potential benefits and costs affecting aggregation: risk of predation, preferred habitats and prey availability. Only increased predation risk decreased nearest-neighbor distances and increased maternal vigilance. Individuals aggregated on a variety of surface textures and locations that varied daily, rather than aggregating only on preferred microhabitats. Manipulation of prey ab...

Surviving the flood: plastron respiration in the non-tracheate arthropod Phrynus marginemaculatus (Amblypygi: Arachnida)

Specimens of Phrynus marginemaculatus can remain responsive when submerged in water for more than 24 hours. Behavioral data indicate that P. marginemaculatus utilizes dissolved oxygen from the surrounding water. Scanning electron miscroscopy and light microscope sections show cuticular modifications for plastron respiration. All previous examples of plastron respiration have involved animals with tracheal systems, but amblypygids respire through the use of two pairs of book lungs. This study provides the first example of plastron respiration not only in the order Amblypygi, but also, in any non-tracheate arthropod.