Amongst tetrapods, mechanoreceptors on the feet establish a sense of body placement and help to facilitate posture and biomechanics. Mechanoreceptors are necessary for stabilizing the body while navigating through changing terrains or responding to a sudden change in body mass and orientation. Lizards such as the leopard gecko (Eublepharis macularius) employ autotomy – a voluntary detachment of a portion of the tail, to escape predation. Tail autotomy represents a natural form of significant (and localized) mass loss. Semmes-Weinstein monofilaments were used to investigate the effect of tail autotomy (and subsequent tail regeneration) on tactile sensitivity of each appendage of the leopard gecko. Prior to autotomy, we identified site-specific differences in tactile sensitivity across the ventral surfaces of the hindlimbs, forelimbs, and tail. Repeated monofilament testing of both control (tail-intact) and tail loss geckos had a significant sensitization effect (i.e., decrease in tactile threshold over time) in all regions of interest except the palmar surfaces of the forelimbs in post-autotomy geckos, compared to baseline testing. Although the regenerated tail is not an exact replica of the original, tactile sensitivity is shown to be effectively restored at this site. Re-establishment of tactile sensitivity on the ventral surface of the regenerate tail points towards a (continued) role in predator detection. 

Geckos were placed in a clear plexiglass chamber (0.35 x 0.295 x 0.315 m) mounted on a raised, perforated (~10 mm diameter) platform. A mirror suspended at an oblique angle below the perforated platform was used to direct the monofilaments through the perforations. A video camera (Panasonic SDR-H85) was mounted outside the chamber to record the trials, and the front of the chamber was covered with a dark partition, to blind the gecko to the presence of the experimenter. Geckos were acclimated to the testing chamber for one hour prior to the start of each testing session. 

Cutaneous sensitivity was tested using Semmes-Weinstein monofilaments at six sites of interest: the palmar surface of each manus (forelimbs), plantar surface of each pes (hindlimbs), and ventral surfaces of the base (proximal) and tip (distal) of the tail. Monofilaments each have a nylon fiber of varying diameters that are calibrated to buckle at a known force when applied perpendicularly to a surface. For each site, monofilaments were applied through the perforated platform in an area roughly corresponding to the middle of a testing site, until buckling occurred. After which, it was maintained in position for approximately one second, before removed. To determine cutaneous sensitivity threshold, monofilaments were applied in an ascending series starting with a 0.091 g filament until a positive response was scored. A withdrawal response from the gecko was regarded as positive when the application of the monofilament resulted in lifting of the appendage from the platform during application. When no withdrawal response was observed, the application was deemed negative, and the subsequent gram monofilament was applied. This process was repeated until a positive withdrawal response was observed. The smallest gram monofilament that evoked a positive response was recorded as the sensitivity threshold (hereafter, threshold). Threshold testing for each site was repeated (test and re-test), and averaged. The order of site testing was chosen opportunistically (pseudorandomly), as sites of interest could only be tested when they were placed over the perforations in the raised platform (within the chamber). Monofilament testing was only administered when the gecko was motionless, with all four feet contacting the platform.

Data for gecko #15 on November 11th is missing.