Sperm morphology and storage in the female reproductive tract of the fat-tailed dunnart,Sminthopsis crassicaudata (Marsupialia: Dasyuridae)

A study of spermatozoa in the isthmus of the oviduct and of the surrounding epithelial cells in the dasyurid marsupial, Sminthopsis crassicaudata, was carried out. At least 10% of the ejaculated spermatozoa probably populate the isthmus region, where many come to reside in crypts until around the time of ovulation. Ultrastructural observations of spermatozoa in this region indicated that they had intact acrosomes and were identical in their morphology with those in the cauda epididymidis. After ovulation spermatozoa rapidly disappeared, some of which may be phagocytosed by the cells lining the crypts. These epithelial cells were also found to have many large, electron-dense granules at the time of sperm storage, but the contents did not appear to be released until the zygotes passed along the tract. The secretory activity of these cells may thus relate more to the production of the shell membrane that comes to surround the zygote than to the cells performing a nutritive or protective function for the spermatozoa during their period of storage within the female reproductive tract.     

Molecular Relationships of New Guinean Three-Striped Dasyures, (Myoictis, Marsupialia: Dasyuridae)

Complete nucleotide sequences of the cytochrome b and 12S rRNA genes and partial sequences of the mitochondrial 16S rRNA gene and the nuclear ɛ-globin gene were obtained from multiple exemplars of the New Guinean dasyurid, Myoictis. Allozyme data were also obtained from most of the same animals. The molecular data show that the genus comprises a number of genetically distinct lineages which correspond with groups proposed by Woolley (2005) on the basis of a number of morphological traits, including the form of the tail i.e. Myoictis leucura (sp. nov.), M. melas, M. wallacei and M. wavicus (new status). Divergence dates estimated from the weighted-average distances for the combined cytochrome b and 12S rRNA data, calibrated with a dasyurid-thylacine divergence 25 million years ago, suggest that the early cladogenic events separating Myoictis took place in the late Miocene. Subsequent separation of M. wavicus and M. leucura from a common ancestor as well as some genetic differentiation within M. melas, took place in the medial Pliocene.     

Habitat of the white-footed dunnart Sminthopsis leucopus (Gray) (Dasyuridae: Marsupialia) in a logged,burnt forest near Bega,New South Wales

In the winter of 1981, 9 months after an intense fire in November 1980 in the recently logged Mumbulla State Forest, the numbers of a small population of Sminthopsis leucopus had slightly increased, while the common species of small mammals had declined sharply from the previous winter. The study reported in this paper aimed to identify the habitat of S. leucopus. Ninety study plots were divided equally among three classes of forest (unlogged forest, and forest logged in 1979 and 1980), between two aspects (north- and south-facing slopes), and among three topographic positions (ridge, midslope and gully). Plots were assessed on the basis of both floristic data and the structural components of ground, shrub and tree cover. The primary finding was that the habitat of S. leucopus was the treeless ridges and mid-slopes with less than 51% ground cover in the logged areas of burnt forest. The floristic analysis showed that the vegetation subcommunities restricted to gullies, or carrying a ferny ground layer of vegetation, were not selected by S. leucopus. An analysis of movements of male S. leucopus identified two classes. ‘Resident’ males occurred on logged ridges and midslopes characterized by a floristic subcommunity of open forest with a grassy understorey.‘Explorer’ males moved through a variety of ridge habitats, including unlogged forest, and were spread more widely through the floristic communities. The pattern of habitat selection identified in this study shows S. leucopus to be ecologically distinct from the other species of small mammals in the forest and thus in need of special consideration in management programmes if it is to be conserved. Under the current regime, the uniform treatment of the forest leads to widespread stands of dense regrowth to the exclusion of the species and is inimical to its survival.     

Seasonal changes in glomerular filtration rate in Antechinus stuartii (Marsupialia: Dasyuridae)

The small marsupial Antechinus stuartii experiences a synchronised life cycle that culminates in complete male mortality (within 3 weeks) following the 1 week mating period in mid-August (late winter). There are pronounced physiological changes in male A. stuartii over the life cycle and renal function was assessed for correlation with these changes. Glomerular filtration rate and urine and plasma electrolytes were determined in male and female A. stuartii in February, May, July and August. Females showed little change in glomerular filtration rate, except for pre-mating values in August which decreased. In contrast, glomerular filtration rate of males decreased significantly in July and August. Plasma sodium and chloride levels were higher in males than females and were higher in animals in July and August than in February and May. Plasma potassium levels dropped in both males and females in July and August. Plasma osmolality was higher in animals in February compared to animals from May and August. However, there were no significant sex or seasonal differences in urine electrolytes, although urea concentration was higher in females than males. Urine osmolality was higher in both sexes in July and August. There were no significant differences in total excretory rates of sodium, potassium or chloride between sexes or between seasons. Many of the alterations in renal function are correlated with known physiological and hormonal profiles in A. stuartii. This is the first observation of seasonal changes in glomerular filtration rate that are unrelated to dietary and water stresses. Accepted: 8 September 1997     

A timetable of embryonic development, and ovarian and uterine changes during pregnancy, in the stripe-faced dunnart, Sminthopsis macroura (Marsupialia: Dasyuridae)

Aged stages (63) were available for establishment of a timetable of embryonic development of the stripe-faced dunnart. On Day 0 oocytes reaching maturity were found in the ovary. Within +/- 24 h of time 0 (time of minimum morning weight) polymorphonuclear leucocytes appeared and spermatozoa were last detected in the urine of 70% of females. Embryos were collected at intervals during pregnancy by hemihysterectomy and the embryos in the contralateral uterus either were examined at a later stage of pregnancy or allowed to develop to term. Cleavage to the unilaminar blastocyst stage with around 32 cells took 3 days with a cleavage arrest of 24 h at the 4-cell stage. Expansion of the unilaminar blastocyst occurred over the next 3 days. Primitive endoderm cells appeared on Day 6, fully bilaminar blastocysts by the end of Day 7 and trilaminar blastocysts on Day 8. Shell loss and implantation of 13-15-somite stage embryos occurred on Day 8 and organogenesis over the next 2-3 days. The gestation period was 9.5-12.0 days with most births occurring between 10.5 and 11.0 days. Major steps in embryonic development were correlated with stages in the development of the corpora lutea, which were maximal in size, and possibly in secretory activity, when the embryos were at the bilaminar blastocyst stage. Regression commenced when the embryos were at the primitive streak stage. At the time the corpora lutea were maximal the uterine epithelium reached its greatest height and the endometrium was thick and folded. Later in pregnancy villous-like projections of the epithelium formed, and the luminal epithelial cells became rounded. Two cell populations, a tier of 8 smaller cells above the yolk mass and a tier of 8 larger cells around the sides of the yolk mass appeared at the 16-cell stage. From the 16-cell stage to the blastocyst stage, with 150-200 cells, two cell populations distinguished by size, cell cycle time, cytoplasmic appearance and position relative to the yolk mass were present. The two populations were indistinguishable in blastocysts with greater than 200 and less than 2000 cells. They reappeared in blastocysts with greater than 2000 cells, as the darker cells of the embryoblast, and as the paler cells of the trophoblast. The darker cells lay in the yolky hemisphere and the paler cells in the non-yolky hemisphere.     

Milk composition in the eastern quoll, Dasyurus viverrinus (Marsupialia:Dasyuridae)

The milk constituents of Dasyurus viverrinus, a carnivorous marsupial, exhibited major quantitative and qualitative changes during the course of lactation. The milk produced in the early stages of lactation was dilute, about 13-16% (w/w) solids before 3 weeks with carbohydrate representing the major fraction. In the latter stages of lactation the milk was concentrated, around 30% solids, and lipid was the predominant fraction. Palmitic acid was the major fatty acid present in early-stage milk but oleic acid became predominant in milk after 10 weeks post-partum. The changes in milk composition in D. viverrinus were similar to those described for the milks of herbivorous marsupials which therefore suggests that this pattern may be uniform throughout the Marsupialia.     

Social and foraging components of the home range in Antechinus stuartii (Dasyuridae: Marsupialia)

The home range of Antechinus stuartii has two components. A small area (0.94 ha for males, 0.38 ha for females) is used for foraging, while a much greater social range (mean for males in a given year may exeed 5 ha; the mean for females never exceeded 3 ha) encompasses communal nests, which are used by both males and females. The foraging range of females is stable throughout the year. The foraging range may not coincide at all, or only partially coincide with her social range. By contrast, male foraging ranges drift through the year, and generally lie within their social range. Intersexual differences reflect the different selection pressures on the sexes. Females require access to resources to sustain a costly lactation, while males require a knowledge of many possible sites for mating and early resolution of agonistic interactions with other males with which they cohabit during mating.     

Body-temperatures and torpor in Sminthopsis crassicaudata and S. larapinta (Marsupialia–Dasyuridae)

Body-temperatures in two species of insectivorous marsupial mice (family Dasyuridae) were measured using a rectal thermistor. In Sminthopsis crassicaudata at 21°C, body-temperatures ranged from–5–31 - 1° C (432 measurements on 12 mice). A diurnal temperature cycle with a mean amplitude of 0.79°C was revealed, with temperatures at a maximum at 02.00 hours and a minimum at 10.00 hours. Mean body-temperatures of sibs showed significant differences; in one litter a difference of 2.7°C was demonstrated. In S. larapinta , the diurnal temperature cycle was greater with a mean amplitude of 4.24°C. Body-temperatures ranged from 38.8–22.9°C.
Changes in surface-temperature (Ts) in unrestrained animals during entry into and arousal from torpor, were measured using thermocouples fitted inside the nest-box and a recording potentiometer. S. larapinta had a daily torpor with or without food at room temperature, while in S. crassicaudata torpor could only be induced by lack of food. The lowest T_s reached were 18° and 17°C respectively. It is suggested that the torpor-mechanism may have evolved in these species to meet temporary or seasonal shortages of food.     

Linstowinema breve n. sp. (Nematoda: Seuratidae) a parasite of Antechinus agilis (Marsupialia: Dasyuridae) from Australia

A new echinonematine nematode, Linstowinema breve sp. n., from the small intestine of the dasyurid marsupial Anthechinus agilis is described. The species is distinguished from its congeners by the possession of the following suite of characters: small size; first and third row of cephalic hooks similar in size; second row larger; 13-15 rows of body hooks without undulating edges on the dilated cuticle of the oesophageal region; oesophagus terminating at the level of the 5th-7th row of body hooks; ten pairs of caudal papillae; a large pair of lateral ad-cloacal papillae extend into small lateral alae. Linstowinema larvae previously recorded from A. agilis may be the same species. A key to species of the genus linstowinema is provided.     

The von Bertalanffy growth model fitted to Planigale tenuirostris (Marsupialia: Dasyuridae) post-weaning data

Growth of head length in P. tenuirostris from the end of weaning throughout life was studied in the laboratory. The growth curves for males and females followed the von Bertalanffy model. Growth continued throughout life and in each age class males were larger than females, resulting in a range of head lengths among mature planigales. This range in sizes has potentially important implications with respect to population niche breadth, resource partitioning and species diversity in dasyurid communities.