Sexual development and spermatozoon morphology in the male macropod marsupial Potorous tridactylus (Kerr.)

Abstract

A study of 24 male Tasmanian rat-kangaroos, Potorous tridactylus (Kerr), gave no evidence of either seasonal change in testis size or interruption to spermatogenesis during the 9 months when captures were made. One captive male (weight 1028 g) attained sexual maturity within a year and only a few epididymal sperm were found in a wild animal weighing 639 g. The spermatozoon head is of unusual shape. It is bluntly pointed anteriorly and broadens towards the centre. The posterior portion of the head is flattened dorsoventrally and a depression situated in its posterior ventral half gives it a forked appearance in the rear. The acrosome is almost entirely embedded in the anterior dorsal surface of the head. The nucleus possesses two basal granules and occupies most of the head volume. The flagellum is composed of a finely pointed neck, a middle piece with mitochondria1 helix, and a tail body which possesses no distinguishable end-piece. The flagellum is attached to the mid-ventral surface of the head by the extremely slender anterior portion of the neck. The axial filament complex passes throughout the entire length of the flagellum and is composed of at least four fibrils.