More on the function of the pectines in scorpion navigation

 

There have been a lot of research on the morphology and the functions of the pectines, which is a unique organ found only in scorpions (Solifigae has a similar organ called malleoli or racquet (or racket) organs). Most of the research so far have focused on the "taste function" (the detection of chemical cues), but it also seems that the pectines have a "feeling function" (having mechanosensory abilities). Overall, the pectines help scorpions find food, navigate, avoid predators and find mates.

Hannah Peeples and Douglas Gaffin recently published a study investigating the role of the peg sensilla on scorpion pectines for mechanosensory responses. This is a very technical paper, but as far as I can tell the main conclusion is that pectines use mechanosensory stimuli to navigate in its activity area, to find home to its shelter and to retrieve dropped insect prey.

Abstract:
Scorpions possess midventral touch/taste organs called pectines, which may be important for learning the nuances of the substrate during navigation as well as the detection of pheromones, spermatophores, and food. The pectines possess thousands of minute structures called peg sensilla that are responsive to both chemicals and mechanical deflection of the peg shaft. While much is known about the chemical responsiveness of the pegs, very little is known about their mechanosensory properties. Here we ask if the peg mechanosensory response is “all-or-nothing” or graded depending on the intensity of stimulation. We made electrophysiological recordings of neural activity from individual peg sensilla while deflecting the peg to elicit apparent mechanosensory responses. Our records show the presence of a rapid firing (.100 Hz), quickly adapting waveform that is indicative of a mechanoreceptor and appears to be independent of previously identified chemo-responsive cells. We tested mechanosensory response dynamics in two ways. The first test focused on a shorter-duration touch versus a longer-duration touch, while the second focused on a smaller deflection versus a larger deflection. Both pairs of stimulations (short vs long touch; small vs large touch) produced repeatable and statistically distinct responses in terms of spiking frequency. These results indicate the mechanosensory responses of peg sensilla are graded, which sheds light on the textural resolvability of the pectines and informs models of the type of information that scorpions obtain while assessing surfaces in their environment.

Reference:
Peeples HM, Gaffin DD. An assessment of the mechanosensory responses of peg sensilla on scorpion pectines. The Journal of Arachnology. 2024;52(1):1-8.

Thanks to Matt Simon for informing me about this article and for providing insight about the article!

How does Paruroctonus utahensis find its way home

 

Finding the way home is an important skill for burrowing scorpions like Paruroctonus utahensis (Williams, 1968) (Vaejovidae). There have been some indications that scorpions use a view-based navigational process termed "Navigation by Scene Familiarity", which has been seen in bees and ants. Douglas Gaffin and co-workers have recently published a study where they investigate if scorpions may be guided by tastes and touches acquired via their mid-ventral pectines, instead of or in addition to vision.

The authors have named this form of homing "The Navigation by Chemotextural Familiarity Hypothesis (NCFH)". In their study they find evidence of learning walks during burrowing in Paruroctonus utahensis and they conclude that these putative learning walks, together with recently reported path integration in scorpions, may provide the crucial home-directed information requisite for NCFH. 

Abstract:
The navigation by chemo-textural familiarity hypothesis (NCFH) suggests that scorpions use their midventral pectines to gather
chemical and textural information near their burrows and use this information as they subsequently return home. For NCFH to be viable, animals must somehow acquire home-directed ‘tastes’ of the substrate, such as through path integration (PI) and/or learning walks. We conducted laboratory behavioral trials using desert grassland scorpions (Paruroctonus utahensis). Animals reliably formed burrows in small mounds of sand we provided in the middle of circular, sandlined behavioral arenas. We processed overnight infrared video recordings with a MATLAB script that tracked animal movements at 1–2 s intervals. In all, we analyzed the movements of 23 animals, representing nearly 1500 h of video recording. We found that once animals established their home burrows, they immediately made one to several short, looping excursions away from and back to their burrows before walking greater distances. We also observed similar excursions when animals made burrows in level sand in the middle of the arena (i.e. no mound provided). These putative learning walks, together with recently reported PI in scorpions, may provide the crucial home-directed information requisite for NCFH.

Reference:
Gaffin DD, Munoz MG, Hoefnagels MH. Evidence of learning walks related to scorpion home burrow navigation. J Exp Biol. 2022;225:jeb243947. [Open Access]

Scorpion pectines are probably important in finding the way home

Burrowing scorpions are usually good at finding their way home to their burrows. But how to they manage this? Gaffin and Brayford published a study late in 2017 studying the importance of the pectines in navigation. It has been well known that the pections has chemo- and mechano (vibration) sensitive sensors that are important in reproduction and prey capture, but can they also play a role in navigation?

Their study seems to confirm that the massive amount of peg sensillas on the pectins help the scorpion create a sort of chemical texture map of the area the scorpion moves in. This map can be used to quickly find the way home to the burrow after a successful prey capture.

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 sand’s 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.

Reference:
Gaffin DD, Brayfield BP. Exploring the chemo-textural familiarity hypothesis for scorpion navigation. J Arachnol. 2017;45:265-70. [Open Access]

Thanks to Matt Simon for telling me about this "old", but interesting paper that I seem to have missed when it was published!