83.6 Friday, Jan. 6 Functional morphology of penile erection in the American alligator (Alligator mississippiensis): indirect eversion and elastic retraction KELLY, D.A.; University of Massachusetts, Amherst firstname.lastname@example.org
The intromittent organs of mammals, turtles, snakes and lizards contain variable-volume hydrostatic skeletons that are stored in a flexible state and inflate with fluid before males attempt copulation. Here I present data that suggest crocodilians have evolved a mechanism for penile erection that does not require inflation and detumescence. Dissections of the cloaca in sexually mature male American alligators (Alligator mississippiensis) show that although the cross section of the proximal shaft of the alligator penis superficially resembles the inflatable mammalian corpus cavernosum, it contains dense collagenous tissues that do not significantly change shape when fluid is added to the central vascular space. The large proportion of collagen in the wall and central space of the alligator penis stiffens the structure so it can be simply everted for copulation and rapidly retracted at its completion. Because there are no muscles connecting the penis to the wall of the cloaca, I hypothesize that eversion and retraction are effected indirectly. The contraction of paired levator cloacae muscles around the anterior end of the cloaca rotates the penis out of the cloacal opening and strains tendons that connect the base of the penis to the ischium. When the cloacal muscles relax, the elastic recoil of these tendons returns the penis to its original position inside the cloaca.