COPULATORY ORGAN, MATING POSTURE AND LOCO MOTION - THEIR INTERRELATIONSHIP IN NONMAMMALIAN VERTEBRATES

Copulatory organ, mating posture and locomotion: their interrelationsh ip in non-mammalian vertebrates. This paper demonstrates, for the vert ebrate groups discussed, a relationship between mating posture, the le ngth of the copulatory organ, and the respective modes of locomotion. The modes of locomotion in the majority of non-mammalian vertebrate gr oups presuppose a massive, heavily muscularized, and relatively long t ail, which may either reinforce lateral flexions of the trunk or (in a nimals with rigid trunk) act as the only means of propulsion (e.g. in Chondrichthyes, Teleostei, Lepidosauria, and Crocodylia). Such a massi ve tail with gradual transition to the trunk necessitates a lateral ma ting position (regardless of whether the copulatory organ is paired or unpaired). Animals with a flexible trunk will, therefore, generate st rongly pronounced laterotruncal flexions ('dynamic lateral bending'). A long copulatory organ is not necessary (e.g. the short hemipenes of Lepidosauria). Animals with a rigid trunk, on the other hand, will not be capable of copulating unless by means of a relatively long penis o r a modified mating posture (e.g. Crocodylia). In the course of phylog eny, whenever a change in the mode of locomotion allows a reduction in tail length, this will lead to a corresponding change in mating postu re, with mating then being possible from a posterior position (e.g. Ch elonia, Aves, as well as Ascaphus among the Anura). The locomotion of the latter taxa is characterized by a completely or almost completely rigid trunk. Thus, contact between male and female cloaca cannot be as sisted by bending movements in the trunk. To compensate for truncal ri gidity, there is a trend towards linear extension of the penis, or oth er male copulatory organs (such as mixopterygia or gonopodia), e.g. in the pelagic Selachians, in Chelonia, and in the flightless ratites. F or those birds lacking a penis, the only methods of overcoming truncal rigidity are stationary locomotion (fluttering without forward moveme nt), having a mobile, swivelling cloacal region (uropygium), and simul taneous evagination of the proctodeum of both the male and female. Pen guins, being unable to perform stationary fluttering, resort to a some what modified mating posture.