SPERMATOZOA OF MURID RODENTS FROM AFRICA - MORPHOLOGICAL DIVERSITY AND EVOLUTIONARY TRENDS

The diversity of the structural organization of the spermatozoa of Afr ican murid rodents is described at the light and transmission electron microscopical level of resolution. In most species the sperm head is falciform in shape but it varies somewhat in overall breadth, width, a nd length. A typical perforatorium is present and the acrosome splits into a large head cap over the convex surface and a smaller ventral se gment similar to the sperm head of most Asian and Australasian murids. In a few species, however, the morphology is very different. In Acomy s and Uranomys spermatozoa, the apical hook is more bilaterally flatte ned, has a large apical acrosomal region, and no separate ventral segm ent. Two species of Aethomys have, in addition to an apical hook, a 4 mu m long extension of the cytoskeletal material that projects from th e concave surface of the sperm head, whereas in Dasymys two large vent ral processes extend from the upper concave region which contain nucle ar material basally and a huge extension of cytoskeleton apically. In Aethomys chrysophilus type B, the sperm nucleus is unique in form and often has a central region in which threads of chromatin can be seen; it is capped by a massive acrosome whose apical segment is complex and convoluted in structure. Stochomys longicaudatus appears to have a co nical sperm head, and in all three Lophuromys species the sperm head i s spatulate in shape with the flat, plate-like nucleus capped by a thi n acrosome. The evolutionary trends in changes of sperm head shape and design of these rodents are discussed. It is suggested that some of t he differences in morphology may relate to the variation in structural organization of the coats around the egg through which the spermatozo on has to pass in order for fertilization to occur.