Spinifex Hopping Mouse Notomys Alexis Research Articles

Intra‐individual variation in sperm tail length in murine rodents

AbstractIn eutherian mammals, there are marked interspecific differences in sperm head shape and tail length. In a few species, sperm head variability occurs but intra‐individual variation in sperm tail length has rarely been investigated or commented upon. Here, we ask the question: Do murine rodent species that have variable sperm head shapes exhibit greater intra‐individual variation in sperm midpiece and total tail lengths than closely related species where little, or no, sperm head variability occurs? From three separate lineages, we selected three pairs of murine rodents, one of which has monomorphic, and the other variable, sperm head shape. These were from southern Asia the bandicoot rats Bandicota bengalensis and Bandicota indica, from southern Africa the veld rats, Aethomys chrysophilus and Aethomys ineptus and from Australia the fawn hopping mouse Notomys cervinus and the spinifex hopping mouse Notomys alexis. Cauda epididymal sperm smears were prepared and sperm midpiece and total tail lengths were determined. A linear mixed‐effects model was used to estimate intra‐individual variance. The results showed that in all three species where there are variable sperm head shapes (B. indica, A. ineptus and N. alexis), statistically significantly greater intra‐individual variability of sperm midpiece and total tail lengths occurs (P<0.0001 in all cases). These species all have relatively smaller testes mass compared with the closely related species with monomorphic sperm populations. This suggests that depressed levels of intermale sperm competition may result in the occurrence of variability in not only the divergent sperm head shape but also in the length of the midpiece as well as that of the total length of the sperm tail.

Comparative study of sperm chromatin condensation in the excurrent ducts of the laboratory mouse Mus musculus and spinifex hopping mouse Notomys alexis

In most mammals, post-testicular sperm maturation is completed in the caput and corpus epididymides, with storage occurring in the cauda epididymides. However, in the spinifex hopping mouse, Notomys alexis, epididymal sperm transit is rapid and some sperm storage occurs in the distal region of the vas deferens. The aim of the present study was to determine whether the rapid progression of sperm into the vas deferens in the hopping mouse results in late sperm maturation. To determine this, sperm nuclei from the epididymides and vasa deferentia of laboratory and hopping mice were compared for: (1) thiol content after staining with monobromobimane (mBBr); (2) chromatin resistance to acid denaturation following incubation with acetic alcohol and staining with acridine orange; and (3) chromatin resistance to in vitro decondensation after incubation with 1% sodium dodecyl sulfate (SDS). It was found that, whereas laboratory mouse sperm completed chromatin condensation by the time they reached the cauda epididymidis, hopping mouse sperm nuclei from the vas deferens showed significantly less mBBr fluorescence and a greater proportion of sperm were resistant to decondensation with SDS than those in the cauda epididymidis. Therefore, the results of the present study indicate that, unlike in the laboratory mouse, hopping mouse chromatin condensation of spermatozoa continues in the vas deferens and this may be due, at least in part, to rapid epididymal transit.

The effect of water deprivation on signalling molecules that utilise cGMP in the spinifex hopping mouse Notomys alexis.

In mammals the natriuretic and guanylin peptides influence renal and intestinal fluid content and electrolyte transport by binding to and activating guanylyl cyclase (GC) receptors that in turn stimulate production of the intracellular second messenger guanosine 3?:5?-cyclic monophospate (cGMP). However, the role of natriuretic and guanylin peptides in desert mammals is not understood. The spinifex hopping-mouse (Notomys alexis), has a suite of behavioural and physiological mechanisms that permits survival for extended periods without access to free water. Because signalling molecules that generate cGMP are known to promote water excretion, it was predicted that natriuretic and guanylin peptide synthesis would be down regulated in water-deprived N. alexis, and thus reduce the amount of water lost in the urine and faeces. However, in the kidney ANP and GC-A mRNA levels were increased in water-deprived mice, but CNP and GC-B mRNA levels were decreased. Water deprivation increased guanylin and uroguanylin mRNA expression in the distal colon, but it remained unchanged in the kidney and proximal colon. The expression of GC-C mRNA increased in the proximal colon but not in the distal colon. This study shows that water deprivation differentially affects the expression of regulatory molecules that stimulate cGMP production, and that a down-regulation associated with water conservation does not uniformly occur.

Factors affecting selection of native seeds in two species of Australian desert rodents

The preferences for different species of native seeds by two species of Australian desert rodents, the sandy inland mouse,Pseudomys hermannsburgensis, and the spinifex hopping-mouseNotomys alexis, were investigated. In two sets of cafeteria trials providing low and high numbers of different seed species, both rodent species showed discrimination, preferentially consuming certain seed species, while avoiding others. In one of the two trials,P. hermannsburgensisselected seeds with the highest free water content, whileN. alexisshowed no clear mechanism of seed choice in either trial. It is suggested that although both species of rodents are omnivorous,P. hermannsburgensisrelies more on seeds than doesN. alexis, and is thus the more efficient seed harvester.

Granivory and microhabitat use in Australian desert rodents: are seeds important?

The diet and microhabitat use of two species of native Australian desert rodents, the spinifex hoppingmouseNotomys alexis and sandy inland mousePseudomys hermannsburgensis, were studied in the Simpson Desert, south-western Queensland. Contrary to expectation, both species were confirmed from analyses of their stomach contents to be omnivorous. The diets of both species varied through time in a similar manner; seeds were important in summer and especially in winter, but in autumn invertebrates constituted nearly 50% and 60% of the diet ofN. alexis andP. hermannsburgensis, respectively. Other plant material (root, leaf, floral part, stem) was found in appreciable amounts in the stomach contents of both species, and fungi were identified from a small number of individuals. Both species showed a high degree of overlap in the broad types of food they ingested (seed, plant material, invertebrates); however, there was considerably less overlap in the species of seeds eaten. Analysis of microhabitat use suggested that this difference was due to differential foraging between the species; the larger, bipedalN. alexis forages in the open more than the smaller, quadrupedalP. hermannsburgensis, which is found more commonly in or under hummocks of spinifex grass. Although our findings parallel patterns of morphological specialisation and differential foraging on seeds that have been described within communities of North American heteromyid rodents, we found little evidence that the foraging economics ofN. alexis orP. hermannsburgensis should depend solely or primarily on the distribution patterns of seeds. In the absence of dietary information, we suggest that ecological studies of desert rodents which focus solely on granivory, and neglect other important aspects of rodent foraging, can lead to a misinterpretation of species coexistence and community structure.