INTERSPECIFIC VARIATION IN STRUCTURAL ORGANIZATION OF THE SPERMATOZOON IN THE ASIAN BANDICOOT RATS, BANDICOTA SPECIES (FAMILY MURIDAE)

The structural organisation of the spermatozoon from two species of ba ndicoot rats Bandicota bengalensis and Bandicota indica was investigat ed by light and electron microscopy together with the effect of incuba tion in Triton-X 100 and sodium dodecyl sulphate. The sperm head of B. bengalensis is invariably falciform, has a uniform electron-dense nuc leus capped by an acrosome with a posteriolateral equatorial segment, a subacrosomal cytoskeleton with a large rostral perforatorium, and a sperm tail, attached to the lower concave surface of the sperm head, w ith typical coarse fibres and fibrous sheath. By contrast, the sperm b ead shapes of B. indica are generally conical or bulbous, the nucleus contains a few large vacuoles, the acrosome lacks an equatorial segmen t, no recognisable perforatorium occurs, and the sperm tail, which is attached basally, is very short with only modest development of coarse fibres and fibrous sheath. These results indicate that, within the ge nus Bandicota, huge interspecific differences in morphology of the spe rmatozoon have evolved. The spermatozoa of B. bengalensis are similar to those of Rattus and many other murids and thus presumably represent the ancestral condition, whereas those of B. indica (and B. savilei) are unlike spermatozoa from any other eutherian mammal so far describe d. (C) 1998 The Royal Swedish Academy of Sciences. Published by Elsevi er Science Ltd. All rights reserved.