Cutaneous Mechanoreceptor Distribution and Its Relationship to Behavioral Specializations in Squirrels

The relationship between sensory specializations and behavioral specializations in two ecologically distinct species of squirrels was examined. It was predicted that the relative density of receptors in the glabrous forepaw skin of tree squirrels (Sciurus niger), which are skilled climbers and manipulate food items extensively, would be higher than that in ground squirrels (Spermophilus tridecemlineatus), which dig underground burrows. In addition to testing this prediction, several other aspects of the distribution of receptors were quantitatively examined in silver-stained material. As predicted, the relative density of receptors in the glabrous forepaw skin of tree squirrels is significantly higher than that in ground squirrels. Receptors are randomly dispersed and different classes of receptors (corpuscular vs. non-corpuscular) are intermingled in the palmar skin of both species. The proportions of the different classes of receptors do not differ among species.