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

CONTEXT: 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. AIMS: The aim of the current study was to determine the sperm morphology of an individual Palawan spiny rat, M. panglima . METHODS: Light and transmission electron microscopy were carried out. KEY RESULTS: 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. CONCLUSIONS: 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. IMPLICATIONS: These findings suggest markedly different selective pressures may have resulted in this unique sperm morphology, the functional significance of which remains to be determined.

Unusual germ cell organization in the seminiferous epithelium of a murid rodent from southern Asia, the greater bandicoot rat, Bandicota Indica.

In the greater bandicoot rat, Bandicota indica, of south-east Asia, nine cell associations were documented in the testicular seminiferous epithelium. In about 10% of the tubule cross sections two or more cell associations occurred and, furthermore, some of the generations of germ cells within the cell associations were sometimes either out of phase, or missing, in the tubule cross sections. These features, together with the fact that this species has a highly pleiomorphic sperm head shape, are somewhat reminiscent of those of the seminiferous epithelium in humans and some other primates but not of common laboratory rodents. This species could thus be a good model for investigating irregular patterns of spermatogenesis in naturally occurring wild species of rodent.

Studies on sperm storage in the vas deferens of the spinifex hopping mouse (Notomys alexis).

The cauda epididymidis, with its relatively cool temperature (32-35 degrees C), is considered to be the main site of sperm storage in male mammals. However, in the adult male spinifex hopping mouse, Notomys alexis, similar numbers of spermatozoa are found in the vas deferens to those in the cauda epididymidis. The present study shows that, unlike in the laboratory mouse in which spermatozoa of the vas deferens are found mainly in the epididymal region of the duct, spermatozoa in the hopping mouse are localized mainly to the middle and urethral regions of the vas deferens which lies in the inguinal and lower abdominal region of the body cavity. After ligation of the vas deferens close to its connection with the epididymis, many spermatozoa in the vas deferens retain the potential for motility for up to 2 weeks, indicating that the viability of spermatozoa is not compromised by being restricted to core body temperature. This urethral region of the vas deferens, in which spermatozoa reside, has a highly divergent structural organization compared with that of common laboratory rodents in which there is an expanded lumen with a network of epithelial folds. Ultrastructural observations of the cells lining the duct indicate that there are not any marked differences in morphology compared with the cells lining the duct in common laboratory murids, but the infoldings of the vas deferens of the hopping mouse are highly vascular which might facilitate supply of oxygen and nutrients to the spermatozoa residing in the lumen.

A comparative study of sperm production in two species of Australian arid zone rodents (Pseudomys australis, Notomys alexis) with marked differences in testis size.

The plains rat, Pseudomys australis, and the spinifex hopping mouse, Notomys alexis, show marked differences in the size of their testes and in the number of spermatozoa within the epididymides. In the present study, the dynamics of sperm production and the duration of sperm transit along the male excurrent ducts were compared between these two species. The durations of the cycle of the seminiferous epithelium, spermatogenesis and sperm transit were determined by tracking cells using autoradiography after [(3)H]thymidine incorporation. Daily sperm production was determined from counts of testicular spermatids after homogenization and further estimates of sperm transit were obtained by dividing sperm reserves within the various regions of the extratesticular ducts by the daily sperm production of the attached testis. In the plains rat, the mean duration of the cycle of the seminiferous epithelium was 11.2 days, the duration of spermatogenesis was 45 days, daily sperm production was 2.6 x 10(7) spermatozoa per gram of testis and epididymal transit of spermatozoa took approximately 9 days (caput 0.8 days; corpus 1.5 days; cauda 6.5 days). In contrast, in the hopping mouse, the mean duration of the cycle of the seminiferous epithelium was 14 days, the duration of spermatogenesis was 56 days and daily sperm production per gram of testis was < 1.0 x 10(7). Epididymal transit of spermatozoa was completed in about 4 days (caput + corpus < 1 day; cauda 3 days); however, spermatozoa may be stored for an additional 1.5-2.0 days in the vas deferens. These results indicate that, in addition to small testes, the hopping mouse shows a low efficiency of sperm production, a relatively long duration of spermatogenesis and rapid passage of spermatozoa through the epididymis, all of which contribute to low epididymal sperm counts. These data are considered in relation to interspecific differences in sperm competition.

Organization of testicular interstitial tissue of an Australian rodent, the spinifex hopping mouse, Notomys alexis.

The organization of testicular interstitial tissue of the spinifex hopping mouse, Notomys alexis differs from that of other rodents. It comprises between 10.3% and 17.3% (average 15.0%) of the total testicular volume, and is variable in its organization both at different locations within the testis of the one animal and among different individuals. Abundant, closely packed Leydig cells are usually present; however, in some regions large, thick-walled blood vessels and extensive peritubular lymphatic spaces, often lacking an endothelium adjacent to the Leydig cells, are also prominent. The Leydig cells in contact with the large blood vessels and lymphatics, unlike those in regions where lymph is sparse, are not densely packed and sometimes contain numerous lipid droplets. Ultrastructure of Leydig cells is typical of steroid-producing cells; however, mitochondria are often extremely large, unusual in shape or bizarrely arranged in relation to one another. Also electron-dense bodies displaying a paracrystalline-like internal structure of parallel, electron-dense filaments arranged in a lattice pattern occur in the cytoplasm of many cells. The significance of these unusual ultrastructural features and the organization of the interstitial tissue remain to be determined conclusively, but may relate to steroid synthesis, secretion and uptake.

Light microscopical structure of the excurrent ducts and distribution of spermatozoa in the Australian rodents Pseudomys australis and Notomys alexis.

The light microscopical structure of the male excurrent ducts and the distribution of spermatozoa were examined in two species of Australian rodents, the plains rat, Pseudomys australis, and the hopping mouse, Notomys alexis. In plains rats the microstructure of the ductus epididymidis and ductus deferens was similar to that of the common laboratory rodents, with the majority of the spermatozoa being found in the cauda epididymides. By contrast, in the hopping mouse, the structure of the cauda epididymidis differed significantly as the height of the epithelium and stereocilia did not decrease from the distal caput to the cauda region, and luminal diameter did not increase markedly along its length. In addition, few spermatozoa were stored in the cauda region of the tract, and as many as 60% were located in the ductus deferens, the distal portion of which displayed a highly infolded epithelium and underlying lamina propria. These differences in histological structure of the hopping mouse excurrent ducts presumably reflect divergence in function of the various regions of the tract. Although the functional implications of the present findings remain to be determined, this study demonstrates the considerable plasticity in the male excurrent ducts amongst the hydromyine rodents of Australia.

Cytological organization of the seminiferous epithelium in the Australian rodents Pseudomys australis and Notomys alexis.

Absolute and relative testis mass of two species of conilurine rodents, the plains rat (Pseudomys australis) and the hopping mouse (Notomys alexis), were markedly different. In plains rats the testis comprised approximately 3% of body mass while in hopping mice they rarely accounted for more than 0.2%. In both species, 8 cellular associations, or cycle stages, were recognized in the seminiferous epithelium. The relative frequencies, and hence durations, of Stages I to VIII were 5.1, 7.0, 12.5, 10.5, 5.4, 25.9, 4.4 and 29.0% of one cycle for plains rats (N = 14), and 20.4, 10.9, 9.6, 8.1, 5.1, 20.4, 14.7 and 10.8% for laboratory-bred hopping mice (N = 35). Generally, the relative durations of the cycle stages were very similar between plains rat individuals, but were variable between hopping mice. Also, organization of the seminiferous epithelium was less rigid in hopping mouse testes, and several anomalies were observed. These included: the occurrence of 2-4 cellular associations in about 20% (range 11.3-33.9%) of tubular cross-sections, deviations in cellular composition in certain cycle stages from that usually observed, and an increased incidence of degenerating cells, together with the presence of multinucleated "giant' cells, within the seminiferous epithelium.