Meeting Abstract
Animal phalluses use tissues with different material properties for a variety of functional roles, such as structural stiffness, tissue expansion, and gamete transport. These tissues can change shape and position relative to one another during reproductive function, and 3D modeling will improve our understanding of how they interact. Here, we present a model of the male adult American alligator (Alligator mississippiensis) phallus developed by combining 3D reconstructions of MRI image stacks with corresponding paraffin histological sections. Adult male alligator phalli collected at Lake Woodruff, Florida were fixative preserved, MRI-scanned intact after equilibrating in PBS, and then paraffin-sectioned and stained. Combining these techniques captured phallic anatomy with sufficient resolution to identify functional regions within the intact tissue: specifically the collagen-rich ridged shaft, the inflatable region of the distal glans, and the inflatable tissues defining the sperm-conducting ventral sulcus groove. MRI imaging also revealed collagen fiber bundle orientations, thus better explaining tissue-specific material properties associated with phallic function. These results demonstrate that this type of noninvasive imaging can facilitate investigation of tissue-specific material properties associated with phallic function by capturing internal morphology prior to histology or materials testing. It is applicable across the broad range of crocodylians. We hope to use this technique to understand phallic variation among crocodylians, identifying both conserved morphologies across species and species-specific phallic novelties, and to develop functional hypotheses incorporating the gross spatial relationships of reproductive tissues and their microanatomical and chemical characteristics.
