The highly divergent spermatozoon of the Palawan spiny rat, Maxomys panglima has an extremely long tail

Sperm morphology varies greatly across mammalian species and this variability is especially evident in murid rodents with both sperm head shape and tail length being sexually selected traits. The Palawan spiny rat, Maxomys panglima has a longer sperm tail than that currently recorded for any other mammalian species. The aim of the current study was to determine the sperm morphology of an individual Palawan spiny rat, M. panglima . Light and transmission electron microscopy were carried out. We found that the sperm tail of M. panglima has an average length of 380μm with the midpiece being approximately 185μm in length with comparatively small mitochondria but very large coarse fibres. Furthermore, the sperm head has a less acutely flexed apical hook than that of most other murid rodents including those of several other Maxomys species. The Palawan spiny rat has a highly divergent sperm morphology with an extremely long tail. It may turn out to be an important species for testing various hypotheses of sperm form and function in mammals. These findings suggest markedly different selective pressures may have resulted in this unique sperm morphology, the functional significance of which remains to be determined.