Histological Variation in Plethodontid Digital Surfaces [University of Findlay]

Abstract

Despite numerous investigations into the morphology and function of toe pads in many species, most notably anurans and geckonids, there is relatively little knowledge on salamander digit morphology. To date, toe morphology in salamanders has been limited to Desmognathus fuscus, Ambystoma maculatum, Bolitoglossa sp., and Aneides aeneus. The limited studies to date have shown variation inter- and intra-specifically but have not investigated numerous taxa within a given family which may provide deeper insights into the causes of variation (phylogenetic vs ecological pressures). Therefore, to test hypotheses concerning the presence of variation in the ventral digital surface of plethodontid salamanders, we plan to use various microscopy methodologies to view the ventral surface of the digital tips of three species from three different genera within the Plethodontidae: Desmognathus, Eurycea, and Plethodon. Toe pads will be characterized grossly using scanning electron microscopy, histologically using light microscopy, and ultrastructurally using transmission electron microscopy. Preliminary results suggest that all three species investigated display enlarged surfaces. Surface morphology (assessed via scanning electron microscopy) varies between species at a gross level concerning the shape and overall orientation of the enlarged surface. Surface morphologies include a well-developed circular pad (D. fuscus), a well-developed oval pad (P. cinereus), and a poorly developed circular pad (E. cirrigera). Furthermore, surface morphology appears to vary at the cellular level as well, with Desmognathus having polygonal squamous cells with microprojections and Eurycea having polygonal cells with nanopillars in a honeycomb arrangement. These differences may be attributed to differences in habitat preference as the three species tested include a terrestrial, semi-aquatic, and aquatic dwelling species. However, further investigation including light microscopy and enhanced scanning electron microscopy are needed. Further understanding of the morphological variation will aid in our understanding of ecomorphology and understanding of morphological evolution in amphibians.