(48) Understanding the 3D phallus of Alligator mississippiensis

     Phalli may combine tissues with differing material properties to impart structural stiffness, allow localized tissue expansion, and assist in gamete transport. Understanding these complex tissue morphologies... [ view full abstract ]

     Phalli may combine tissues with differing material properties to impart structural stiffness, allow localized tissue expansion, and assist in gamete transport. Understanding these complex tissue morphologies traditionally has relied on histological sectioning and staining. While these methods yield fine cellular-level details and valuable information about the tissues’ material composition, they also destroy many of their higher-level three-dimensional relationships by representing complex morphology in two dimensions. In contrast, magnetic resonance imaging (MRI) followed by reconstruction provides a rapid, nondestructive 3D imaging modality that makes it possible to study the spatial relationships of soft tissues before histological analysis. Here, we digitally reconstructed 321 transverse serial MRI images of an adult male American alligator (Alligator mississippiensis) phallus using BioVis 3D 3.1 and compared the structure of the resulting 3D model to representative histological tissue sections. We reconstructed the overall phallic form and internal structures including dense regions of collagen fiber bundles, spongiform inflatable tissues, tracts of smooth muscle fibers, and the semen-conducting sulcus. The final product better demonstrates the orientation and interactions of these functional tissue compartments. This imaging approach is broadly applicable across crocodylian species and can use to identify both conserved morphologies and species-specific phallic novelties associated with reproductive biology. We aim use this technique to understand phallic variation among crocodylians and relate these results to better understanding morphologies increase male copulatory success.