Morphology of gustatory organs of a crocodile newt (genus Tylototriton)

Abstract

The evolutionary causes behind the development of taste discs (TDs), recognized as the only gustatory organs in metamorphosed Batrachia (Caudata and Anura), have yet to be determined. Taste buds (TBs) serve as the gustatory organs in aquatic batrachian larvae, as well as in both larval and adult caecilians (Gymnophiona) inhabiting either aquatic environments or moist terrestrial habitats. We describe the morphology of gustatory organs of adult crocodile newts (Tylototriton cf. verrucosus, Salamandridae, Caudata). Crocodile newts are semi-aquatic and exhibit increased specialization towards an aquatic feeding, distinguishing it from most members of the subfamily Pleurodelinae. Our findings confirm that TDs serve as the gustatory organs in adult T. cf. verrucosus, similarly to many batrachians. We also determined the density and sizes of TDs’ sensory zones on the tongue and palate of T. cf. verrucosus, which differs from Batrachia. In terms of micro-morphology, two types of gustatory cells (GCs) were identified in the gustatory epithelium of T. cf. verrucosus. Our literature analysis suggests that TDs were larger in anurans compared to caudate amphibians, but were also larger in aquatic/semi-aquatic than in terrestrial anurans.