Morphological diversity and evolution of the spermatozoon in the mouse‐related clade of rodents

Most species in the three highly speciose families of the mouse‐related clade of rodents, the Muridae, Cricetidae, and Nesomyidae (superfamily Muroidea), have a highly complex sperm head in which there is an apical hook but there are few data available for the other related families of these rodents. In the current study, using light and electron microscopies, we investigated the structure of the spermatozoon in representative species of four other families within the mouse‐related clade, the Dipodidae, Spalacidae, Pedetidae, and Heteromyidae, that diverged at or near the base of the muroid lineage. Our results indicate that a diverse array of sperm head shapes and tail lengths occurs but none of the species in the families Spalacidae, Dipodidae, or Pedetidae has a sperm head with an apical hook. By contrast, a rostrally extending apical hook is present in spermatozoa of members of the Family Heteromyidae which also invariably have comparatively long sperm tails. These findings suggest that the hook‐shaped sperm head in the murid, cricetid, and nesomyid rodents evolved after divergence of this lineage from its common ancestor with the other families of the mouse‐related clade, and that separate, and independent, convergent evolution of a similar sperm head form, and long sperm tail, occurred in the Heteromyidae. J. Morphol. 275:540–547, 2014. © 2013 Wiley Periodicals, Inc.     

A study in hystricomorph rodent relationships: the karyotypes of Thryonomys gregorianns, Pedetes capensis and Hystrix cristata

Karyotypes and G band patterns of Thryonomys gregorianus, Pedetes capensis and Hystrix cristata from Kenya are reported. Both Thryonomys and Pedetes have a diploid number of 40 but differ in the overall pattern of their karyotypes and by the presence of a marker chromosome in Thryonomys. The marker chromosome unites Thryonomys with the ctenodactylids. The karyotype of Hystrix cristata , with a diploid number of 60, bears some resemblance to the African bathyergids and Petromus but none to the erethizontids. The African hystricomorph-hystricognath rodents, with the exception of Pedetes , bear more resemblance to the South American caviomorphs than to any other group of rodents.