Der Zusammenhang zwischen Lokomotionsweise,Begattungsstellung und Penislänge bei Säugetieren1

Penis length, copulation and locomotion: Their relationship to each other in Mammals A relationship between the mode of locomotion, copulatory position and length of the male copulative organ has been found in all groups of Mammalia. In this paper particular emphasis is given to the orders of the Testiconda, while the Testiphaena receive only brief account (for explanation of terms see Frey 1991 a). Results from my previous antomical study are utilized that are essential for assessing the respective modes of locomotion (Frey 1991b). Information on penis length and copulatory position are taken from the literature and evaluated. Small and middle-sized Testiphaena, which represent the majority of mammals, are capable of a dynamic sagittal bending in the trunk, which is evidenced both in the galloping mode of locomotion and in the usual mammalian copulatory position (mounting). A sagittal bending of the trunk enables the male to bring his genital region into close proximity of the female's genital opening. In this case, a short penis is sufficient to ensure sperm transfer. The construction of the trunk in the Testiconda (excepting the Hyracoidea) entirely or nearly entirely prevents the sagittal bending. This is largely due to rigidity of the lumbar region or insufficient (dynamic) muscular control. The immobilization and/or the functional weakness of the lumbar region are derived from different anatomical conditions. 1. Shortening of the lumbar region, e.g., Tachyglossidae, Elephantidae, Sirenia; 2. Tightening of the lumbar region by tendons and muscles, e. g., Macroscelididae, Cetacea; 3. Xenarthry of the lumbar vertebrae and a double connection of the pelvis on the vertebral column, e. e., Bradypodidae, Myrmeco-phagidae; 4. The lumbar region may be flexible but the hypaxial muscles too short and weak, e. g., Tenrecinae, Soricidae, Erinaceidae. Lumbar rigidity or insufficient muscular control in the lumbar region, resulting from any of these conditions, makes copulation difficult by restricting close approximation of the male and female genitals. Most Testiconda compensate for this by having a long penis. The same also applies for large-sized Testiphaena. Although these animals have retained the ability to gallop, the flexibility of their trunk is restricted and mostly localized in a single joint due to the great body mass and the constructive constraints necessary for increased stability. A long penis is not the only way to compensate for the absence of sagittal flexion. A phylogenetic change in the copulatory posture also solves the problem as seen in the Myr-mecophagidae and Bradypodidae (both Testiconda) which are equipped with a secondarily short-enedpenis. The permanently aquatic testicondid mammals (Sirenia and Cetacea) cannot copulate in the usual mammalian mount position. This is largely due to the phylogenetic reduction and reconstruction of the extremities as well as the secondary evolution of a powerful tail. Sagittal movements of the heavily musculated tail act upon the more or less rigid trunk to provide for a “rear drive” locomotion. Both a change in the copulatory position and a long penis were necessary for these aquatic mammals. The only Testiconda in which a marked dynamic sagittal flexibility of the trunk is developed -the Hyracoidea - are characterized by a short penis. On the whole, the relationship between the mode of locomotion, copulatory position and penis length within the mammalia is confirmed. A rigid lumbar region as opposed to a sagittally flexible, presumably represents the primitive condition among mammals. All Testiconda have