Ultrastructure and motility of spermatozoa in Macropodid and Potoroidid marsupials

Abstract

In order to gain some understanding of the significance of the morphological features of spermatozoa within the Macropodoidea, the motility of spermatozoa from two macropodids (Petrogale xanthopus and Dendrolagus matschiei) and the motility, number and distribution of spermatozoa from three potoroidids (Aepyprymnus rufescens, Bettongia penicillata and Potorous tridactylus) were examined. Sperm were collected by electro-ejaculation or from the cauda epididymides. Epididymides from the potoroidids were divided into 12 regions. One epididymidis per animal was fixed for light and transmission electron microscopy and, on the contralateral side, the number of sperm, their distribution and motility were determined. In general, spermatozoa of all five species differed markedly from one another in head and flagella dimensions. Spermatozoa from B. penicillata and P. tridactylus were significantly longer and broader and had a smaller acrosome relative to head length, and there was a radial displacement of dense fibres. They also progressed more rapidly in standard culture media. Spermatozoa from at least three species were able to alter their motility pattern in vitro as media viscosity increased. Sperm movement in all species appeared to be restricted to one plane and showed no evidence of rotation, whereas lateral head displacement was often pronounced; there was no evidence of a sinusoidal mode of progressive motility. Testicular and epididymal sperm numbers in A. rufescens and P. tridactylus were relatively high (approximately 17.5-50 x 10(6)). In A. rufescens, approximately 69% of all epididymal sperm were located in the cauda epididymidis compared with approximately 40% in P. tridactylus. This study demonstrated that marked radial displacement of the dense fibres is probably closely associated with the ability to develop a sinusoidal mode of progressive movement, and that this feature of the sperm tail structure is not just linked with sperm size. Sperm size, however, is associated with sperm velocity.