Comparative Histomorphology of Oviducts from Metamorphic and Paedomorphic Ambystoma talpoideum (Caudata: Ambystomatidae)

Oviducts of paedomorphic and metamorphic Ambystoma talpoideum were examined to determine if previously observed differences in egg mass characteristics between the two morphs originated from differences in oviductal histomorphology/histochemistry. We found no evidence to support this hypothesis. At least seven oviductal regions were easily identified in the oviducts of both paedomorphic and metamorphic individuals; these were as follows (from cranial to caudal): 1) pars recta (termed Region A), 2) pars convoluta (termed Regions B through F), and 3) the uterine region (termed Region G). While slight structure and staining differences were evident in Region D of the pars convoluta when paedomorphic A. talpoideum from South Carolina were compared with metamorphic A. talpoideum from Arkansas, there were no differences observed between paedomorphic and metamorphic individuals of A. talpoideum from Arkansas. Thus, any observed oviductal variation was most likely the result of geographic variation and not from differences involving metamorphosis between paedomorphic and metamorphic A. talpoideum. The number of oviductal regions of A. talpoideum was comparable with previous studies on plethodontids and salamandrids, and this study represents the first treatise of oviductal anatomy of an ambystomatid using a histochemical approach beyond general staining with hematoxylin and eosin.