(29) Comparing American Alligator and Nile Crocodile Phallic Collagen Architecture using Picrosirius Red Staining & Polarized Light Microscopy

     Collagen fiber architecture plays important roles in maintaining tissue structure and influencing function. In many male copulatory structures, collagen fiber bundles contribute to the production of rigidity that... [ view full abstract ]

     Collagen fiber architecture plays important roles in maintaining tissue structure and influencing function. In many male copulatory structures, collagen fiber bundles contribute to the production of rigidity that allows intromission. Picrosirius red staining of histological tissues sections causes collagen fibers to emit birefringent light when viewed under a circularly polarized light microscope. We employed this simple and sensitive method to identify and compare the collagen fiber architectures in American alligator (Alligator mississippiensis) and Nile crocodile (Crocodylus niloticus) histological tissue sections. The overall structure and function the American alligator and the Nile crocodile phalli are similar.  For example, with increased blood pressure into the copulatory structure the distal glans expands. However, the shape of the phallic glans upon inflation markedly differs between the two species. The picrosirius red staining and polarized light microscopy revealed overall similarities but also differences in collagen bundle fiber thicknesses and orientation associated with the species-specific glans shapes. Examining the collagen fiber bundle architectures that underlie the phallic glans adds insight to understanding the biomechanical properties of the alligator and crocodile phalli and allows us to posit how the extracellular matrix architecture translates into biological functions during copulation.