The Evolution of the Sperm Transport Complex in Male Plethodontid Salamanders (Amphibia, Urodela, Plethodontidae)

Based on previous literature, male salamanders of the genus Eurycea possess sperm transport ducts that are homogenous (in terms of histology) along their entire length; i.e., a transverse tubule. Considering this structural homogeneity is unique among salamanders, this feature could potentially be a synapomorphy for Spelerpinae. We tested this hypothesis by re-evaluating the histology of the sperm transport ducts of multiple members of Spelerpinae (Eurycea longicauda, E. lucifuga, and E. multiplicata) and compared our results with representatives from all subfamilies of Plethodontidae (Bolitoglossinae, Hemidactylinae, and Plethodontinae). We reject the findings of previous work that spelerpine salamanders possess homogenous sperm transport ducts along their entire length. Discrete regions are present along the sperm transport ducts of Spelerpinae that include, from proximal to distal, a vas efferens, genital kidney proximal tubule, genital kidney distal tubule, and genital kidney collecting tubule. A distinct renal corpuscle often exists between the communication of the vas efferens and genital kidney proximal tubule. This regionality is not only stereotypical for the sperm transport ducts in all plethodontid salamanders, but also for salamanders in general. Similar to other lineages of salamanders (i.e., Rhyacotritonidae and Sirenidae), all plethodontid salamanders examined lack a longitudinal collecting duct and distinct neck and intermediate segments. We found no characteristic that could potentially serve as a non-ambiguous synapomorphy for Spelerpinae or Plethodontidae with use of sperm transport duct histology. However, it appears that the Bolitoglossinae, Hemidactylinae, and Spelerpinae often lack arteriole connection to their glomeruli within the genital kidney renal corpuscles, yet this trait is ambiguous within taxa of these subfamilies.