The phylogenetic distribution of the ampulla ureter and ampulla urogenital/uriniferous papilla in the Serpentes

Abstract

The ampulla ureter and ampulla urogenital ⁄ uriniferous papilla represent differing morphologies of the caudal urogenital ducts in snakes. The ampulla ureter is an enlarged portion of the caudal extremity of the ureter that communicates the cranial regions of the ureter and the ductus deferens ⁄ Wolffian duct to the urodaeum. The ampulla urogenital ⁄ uriniferous papilla is an enlarged pouch, distinct from the ureter, which communicates the ureter and ductus deferens ⁄ Wolffian duct to the urodaeum. Although functional differences of these two structures are unknown, the ampulla urogenital ⁄ uriniferous papilla may have evolved for urine storage in males and females, and secondarily evolved a reproductive function in males. The most parsimonious optimization of the ampulla ureter and ampulla urogenital ⁄ uriniferous papilla indicates that the ampulla ureter is the ancestral state in snakes. Examining the presence or absence of the ampulla ureter and ampulla urogenital ⁄ uriniferous papilla in snakes on conflicting caenophidian phylogenies results in two hypotheses for the evolution of these variant morphologies: (1) The ampulla urogenital ⁄ uriniferous papilla evolved from the ampulla ureter independently in the Colubroidea and Elapoidea with subsequent losses of the ampulla urogenital ⁄ uriniferous papilla in the Elapoidea and (2) a single transition from the ampulla ureter to the ampulla urogenital ⁄ uriniferous papilla on the branch leading to the Colubroidea + Elapoidea with subsequent losses of the ampulla urogenital ⁄ uriniferous papilla in the Elapoidea and Colubroidea. The presence of the ampullae urogenital ⁄ uriniferous papilla in only the Colubroidea and Elapoidea highlights the affinity of these two taxonomic groups, a relationship that is strongly supported in published cladograms produced with molecular datasets.