Sperm morphology of the dipodid rodents (jerboas) common in Egypt

Sperm morphology of the jerboas Allactaga and Jaculus species common in Egypt was described by light and transmission electron microscopy. Two morphs of spermatozoa were observed among these dipodids. One type observed in the smaller jerboa, A. tetradactyla, has a paddle-shaped long head, long tail, and the connecting piece of tail inserts off-centre at the base of the sperm head. The other form found in both lesser jerboas, Jaculus jaculus subspecies and large jerboa, Jaculus orientalis orientalis, has a pear-shaped short head, relatively short tail, and the connecting piece of the tail attaches midbasally to the lower concave surface of the sperm head. In both types, the sperm has nearly the same internal organization and the head is symmetrical, bilaterally flattened, lacks any traces of hooks or processes, and is capped by a massive symmetrical apical acrosomal segment. Accordingly, it was concluded that they are part of one evolutionary radiation and the the << symmetrical head-short tail >> sperm type represents the ancestral type for dipodid rodents. Moreover, it was shown that the dipodids share many of their sperm features with muroids. Hence, it was suggested that the dipodids during their evolution have formed a clade that has been branched off either from Muroidea or Myomorpha. Of course this association needs more further studies which are under consideration.