ULTRASTRUCTURE AND MOTILITY OF SPERMATOZOA IN THE MALE REPRODUCTIVE-TRACT OF PERAMELOID MARSUPIALS

The number, distribution, maturation, motility and ultrastructure of s permatozoa from both northern (Isoodon macrourus) and southern (Isoodo n obesulus) brown bandicoots were examined. One epididymidis per anima l was fixed for light microscopy and transmission electron microscopy, and the contralateral side was used for the determination of sperm nu mber, distribution and motility. Sperm form was similar between the tw o species. Approximately 56 x 10(6) testicular sperm and 100 x 10(6) e pididymal sperm per side were present in I. macrourus, about 60% of wh ich were in the caudal region. Initiation of sperm nuclear rotation an d loss of the cytoplasmic droplet was first observed in distal caput o r proximal corpus segments along with slow progressive motility. In th ese sperm, dislocation and anterior movement of the sperm neck from th e implantation fossa and the modification of the distal margins of the sperm acrosome were evident. Motility of cauda epididymidal spermatoz oa was rapid and coordinated, movement was restricted to one plane, an d lateral head displacement was marked. As media viscosity increased, sperm velocity decreased, as did the amplitude of the tail beat, its f requency, and lateral head displacement but, in viscous mineral oil an d mixtures of media and prostatic exudate, extremely rapid sinusoidal motility occurred. This study has detailed unusual morphological chang es in bandicoot sperm during epididymal maturation and has shown that, although bandicoot sperm differ morphologically from those of the das yurids, particularly in relation to head-tail orientation and tail ult rastructure, they exhibit similar motility.