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PubMed2001

Maintenance nitrogen requirement of an obligate nectarivore, the honey possum, Tarsipes rostratus.

A nitrogen balance feeding trial was carried out with the marsupial honey possum, Tarsipes rostratus, using four pollen-honey diets varying in nitrogen content from 9.4 mg.g(-1) to 2.3 mg.g(-1) dry matter. The dietary maintenance nitrogen requirement (MNR) was determined by regression analysis as 89 +/- 21 mg N.kg(-0.75).day(-1) and the truly digestible MNR was 79 mg N.kg(-0.75).day(-1). Regressing nitrogen balance on daily nitrogen intake separately for ten males and seven females revealed that the slopes of the fitted lines did not vary significantly, but the difference in the intercepts approached significance. This suggests that the MNR for females may be lower than that of males. The nitrogen digestibility of the diet was 76% and the biological value (BV) was 58%. A comparison of the MNR of the honey possum with that of other marsupials shows that it is indeed much lower than that of herbivorous macropodid marsupials and is close to that of the sap- and gum-feeding sugar glider, Petarurus breviceps. The endogenous urinary nitrogen excretion (EUN) of the honey possum was 42 mg N.kg(-0.75.day(-1) and a regression analysis with other published data showed that the EUN per unit basal heat production is significantly lower than that of eutherian mammals. Measurements of the actual feeding rates of animals in the field, taken together with the low MNR, do not lend support to the hypothesis that the honey possum exhibits a reduced rate of reproduction due to a deficiency in dietary nitrogen. It is possible that the quality of nitrogen provided by pollen, as reflected in its composition of essential amino acids, may be a limiting factor.

Animals↗
PubMed2001

Neurochemical and thermal control of surfactant secretion by alveolar type II cells isolated from the marsupial, Sminthopsis crassicaudata.

Pulmonary surfactant is synthesised in alveolar type II cells and secreted into the lining of the lung in response to ventilation, temperature changes and autonomic neurotransmitters. Type II cells were isolated from the heterothermic marsupial, Sminthopsis crassicaudata. The neurotransmitters, isoproterenol and carbamylcholine chloride significantly increased phosphatidylcholine secretion at 37 degrees C (basal: 14.2%, isoproterenol: 20.1%, carbamylcholine: 17.0%). Temperature reduced the rate of secretion from dunnart type II cells (e.g. basal: 14.2% at 37 degrees C; 7.2% at 18 degrees C). However, the change in secretory rate between 37 degrees C and 18 degrees C was less than expected if due to temperature alone (Q10= 1.4). The surfactant secretory pathway is therefore modulated by factors other than and in addition to, temperature. The response of dunnart type II cells to the agonists remained the same at both temperatures. Basal secretion was higher in dunnart type II cells (14.2% in 4 h) than has been reported in rat type II cells (1.9% in 3 h) and consequently, the agonist-stimulated increases in secretion from dunnart type II cells (41% above basal in 4 h) were much lower than observed for rat type II cells (200% above basal in 1.5 h).

Animals↗
PubMed1998

Development of endothermy in a Tasmanian marsupial, Bettongia gaimardi and its response to cold and noradrenaline.

Marsupials at birth are ectothermic and gradually attain the ability to change their metabolic heat production during pouch life. How this process occurs in the bettong has been measured on 13 pouch young from week 1 until 3 weeks after pouch vacation (week 18). Oxygen consumption was measured at 35 degrees C (pouch temperature) and at 22 degrees C. The results at 35 degrees C showed an increase in metabolic rate from week 1 until week 12 when there was a decrease to near adult levels after pouch vacation. At 22 degrees C young bettongs had a lower metabolic rate (compared with measurements made at 35 degrees C) until week 9 after which there was an increase above measurements made at 35 degrees C. Noradrenaline had little effect until week 10 after which the metabolic rate (although measured at 35 degrees C) paralleled the levels measured at 22 degrees C. The free thyroxine level was low in early pouch life, increased to a peak at week 12 then decreased. Thermal conductance increased until week 10 after which it decreased, reaching values similar to those of adult bettongs by week 20. The results indicate that non-shivering thermogenesis occurs in this macropodoid marsupial. This phenomenon may be a phylogenetic difference between macropodid and non-macropodid marsupials as also suggested by Nicol et al. (1997).

Age Factors↗
PubMed1999

The energetic cost of arousal from torpor in the marsupial Sminthopsis macroura: benefits of summer ambient temperature cycles.

The costs of arousal from induced torpor were measured in the striped-faced dunnart (Sminthopsis macroura, ca. 25 g) under two experimental ambient temperature cycles. The sinusoidal-type temperature cycles were designed to evaluate the effects of passive, ambient temperature heating during arousal from torpor in these insectivorous marsupials. It was hypothesised that diel ambient temperature cycles may offer significant energy savings during arousal in animals that employ daily torpor in summer as a response to unpredictable food availability. The cost of arousal in animal in which passive, exogenous heating occurred was significantly lower than that in animals not exposed to an ambient temperature cycle. The total cost of all three phases of torpor (entry maintenance and arousal) was almost halved when animals were exposed to an ambient heating cycle from 15 degrees C to 25 degrees C over a 24-h period. In all animals, irrespective of the experimental ambient temperature cycle employed, the minimum torpor body temperature was 17-18 degrees C. The body temperature (Tb) of animals exposed to exogenous heating increased from the torpor Tb minimum to a mean value of 22.59 degrees C before endogenous heat production commenced. This relatively small increase in Tb of ca. 5 degrees C through 'free' passive heating was sufficient to account for the significant ca. three-fold decrease in the cost of arousal and may represent an important energetic aid to free-ranging animals.

Adaptation, Physiological↗
PubMed1999

Field energetics and the estimation of pollen and nectar intake in the marsupial honey possum, Tarsipes rostratus, in heathland habitats of south-western Australia.

A method is described, based on the simultaneous turnover of both stable (18O) and radioactive isotopes (3H and 22Na), whereby the daily nectar and pollen intake of free-ranging marsupial honey possums (Tarsipes rostratus) may be estimated. The field metabolic rate is measured using doubly labelled water and nectar intake is estimated independently from the measured water and sodium fluxes. The method assumes that free-water intake is negligible (but may be accounted for if not the case), that virtually all dietary sodium is derived from nectar rather than from pollen, and that the animals are in energetic balance over the period of measurement. These assumptions have been tested and found to be robust, except during periods of heavy rain when significant intakes of free-water were recorded. Leaching experiments with pollen grains suggest that less than 10% of the sodium ingested by honey possums is derived from pollen and calculations thus assumed a 90%:10% split between nectar and pollen. Nectar intake averaged 5.9 +/- 0.6 ml.day-1 and regressing nectar intake on daily change in body mass predicts an intake of approximately 7 ml.day-1 nectar to maintain balance for a 9 g honey possum. Estimates of pollen intake averaged 660 +/- 156 mg.day-1 and a similar regression analysis of the data predicts that a daily intake of approximately 1 g pollen would be needed to maintain mass balance of honey possums. Estimated nectar and pollen intakes did not differ significantly between males and females, but nectar intake was higher in winter compared with dry periods of the year. The sugar content of nectar falls during winter, however, and the overall energy derived from nectar thus remains roughly constant. Estimates of pollen and nectar intake for individual animals were not significantly correlated, suggesting that honey possums forage selectively for these two food items.

Animals↗
PubMed2001

Intraspecific differences in behaviour and physiology: effects of captive breeding on patterns of torpor in feathertail gliders.

Studies on the physiology of mammals and birds are often conducted using captive-bred individuals and it is commonly assumed that the resulting data are representative of individuals living in the field. To investigate whether these assumptions are justified, we quantified morphological, behavioural, and physiological variables of the small marsupial feathertail glider (Acrobates pygmaeus). We compared three populations: (i) individuals from a cool-temperate, montane area, (ii) individuals form a subtropical, coastal area, and (iii) captive-bred individuals. Captive-bred gliders differed from the montane field gliders in morphology (longer tails and snouts), behaviour (longer activity periods) and physiology (less frequent torpor, shorter torpor, shallower torpor, higher metabolic rates during rest and torpor, and slower rates of rewarming). Most of these differences were also apparent between the captive-bred and the coastal field gliders. Unlike both field populations, captive-bred gliders often became hypothermic and were unable to rewarm. In contrast to the other physiological variables, the minimum body temperatures defended during torpor and the corresponding air temperatures differed between the montane and coastal field gliders, but were similar in coastal field and captive-bred gliders. Our study shows that morphology, behaviour and physiology can be strongly affected by breeding in or acclimation to captivity. The poor expression of torpor and thermal performance of the captive-bred gliders raises the question of whether they possess the physiological capability for survival in the wild. Even though captive breeding appears to have only minor effects on some physiological variables, data from captive-bred individuals should only be extrapolated to the field with caution.

Adaptation, Physiological↗
PubMed2001

Seasonal changes in the thermoenergetics of the marsupial sugar glider, Petaurus breviceps.

Little information is available on seasonal changes in thermal physiology and energy expenditure in marsupials. To provide new information on the subject, we quantified how body mass, body composition, metabolic rate, maximum heat production, body temperature and thermal conductance change with season in sugar gliders (Petaurus breviceps) held in outdoor aviaries. Sugar gliders increased body mass in autumn to a peak in May/June, which was caused to a large extent by an increase in body fat content. Body mass then declined to minimum values in August/September. Resting metabolic rate both below and above the thermoneutral zone (TNZ) was higher in summer than in winter and the lower critical temperature of the TNZ occurred at a higher ambient temperature (Ta) in summer. The basal metabolic rate was as much as 45% below that predicted from allometric equations for placental mammals and was about 15% lower in winter than in summer. In contrast, maximum heat production was raised significantly by about 20% in winter. This, together with an approximately 20% decrease in thermal conductance, resulted in a 13 degrees C reduction of the minimum effective Ta gliders were able to withstand. Our study provides the first evidence that, despite the apparent lack of functional brown adipose tissue, sugar gliders are able to significantly increase heat production in winter. Moreover, the lower thermoregulatory heat production at most TaS in winter, when food in the wild is scarce, should allow them to reduce energy expenditure.

Animals↗
PubMed1998

A new look at kinetochore structure in vertebrate somatic cells using high-pressure freezing and freeze substitution.

Three decades of structural analysis have produced the view that the kinetochore in vertebrate cells is a disk-shaped structure composed of three distinct structural domains. The most prominent of these consists of a conspicuous electron opaque outer plate that is separated by a light-staining electron-translucent middle plate from an inner plate associated with the surface of the pericentric heterochromatin. Spindle microtubules terminate in the outer plate and, in their absence, a conspicuous corona of fine filaments radiates from the cytoplasmic surface of this plate. Here we report for the first time the ultrastructure of kinetochores in untreated and Colcemid-treated vertebrate somatic (PtK1) cells prepared for optimal structural preservation using high-pressure freezing and freeze substitution. In serial thin sections, and electron tomographic reconstructions, the kinetochore appears as a 50-75 nm thick mat of light-staining fibrous material that is directly connected with the more electron-opaque surface of the centromeric heterochromatin. This mat corresponds to the outer plate in conventional preparations, and is surrounded on its cytoplasmic surface by a conspicuous 100-150 nm wide zone that excludes ribosomes and other cytoplasmic components. High magnification views of this zone reveal that it contains a loose network of light-staining, thin (<9 nm diameter) fibers that are analogous to the corona fibers in conventional preparations. Unlike the chromosome arms, which appear uniformly electron opaque, the chromatin in the primary constriction appears mottled. Since the middle plate is not visible in these kinetochore preparations this feature is likely an artifact produced by extraction and coagulation during conventional fixation and/or dehydration procedures.

Animals↗
PubMed2003

Comparative morphological study of the lingual papillae and their connective tissue cores of the koala.

The stereo structure of each lingual papilla of the koala has a similar structure to that of various other animal species: the koala has a lingual prominence (intermolar prominence) with larger filiform papillae. (A lingual prominence is a characteristic in herbivorous animals.) The external form and connective tissue core (CTC) of the filiform papillae of koalas consist of one large main process and several smaller accessory processes. (These are similar to carnivorous animals.) Fungiform CTC have a thick dome-like structure, with several taste buds on the top. There are three vallate papillae: one central midline and two laterally located vallate papillae. The central vallate papilla has a posterior pouch lined with ciliated and non-ciliated epithelial cells. Long conical papillae are distributed in the posterior lateral area where foliate papillae are distributed in many other animal species. (Finger-like papillae are seen in dog and cat instead of foliate papillae.) It may be suggested that the tongue of the koala evolved in a special environment in Australia. Even though it has still retained special features similar to those of carnivorous cats and dogs it has evolved to resemble the tongues of herbivorous animals.

Animals↗
PubMed2001

Anatomy and development of the koala, Phascolarctos cinereus: an evolutionary perspective on the superfamily Vombatoidea.

Fifteen koalas (Phascolarctos cinereus)--5 pouched young from 4 to 6.5 months and 10 adults from 5 to 16.5 years--were analyzed for functional parameters (body composition, limb segment and muscle mass, post-cranial skeletal characters) and developmental expressions (growth of body, brain, musculature). These data were compared with a convergent eutherian, the three-toed sloth, Bradypus infuscatus, and with the koala's distant (Macropodid; wallabies) and proximate (Vombatid; wombats) marsupial relatives. Musculoskeletal structures correlated with sitting and climbing; the growth of the young and the physiological demands of adulthood correlated with the low-quality diet of Eucalyptus foliage. The gestalt of the ancestral Vombatoids (pronograde quadrupeds, generalist browsers and social conservatives with low basal metabolism and attenuated development) provided the baseline essential for their locomotor and nutritional divergence into arboreal browsers, the koalas, and fossorial grazers, the wombats.

Animals↗
PubMed1998

Development of the male urogenital system of the koala phascolarctos cinereus.

This paper described several developmental stages of the male urogenital system in the koala Phascolarctos cinereus, employing both light and scanning electron microscopy. There are few studies of the development of the urogenital system in male marsupials. Findings by White and Timms (1994) that male koalas can be infected with Chlamydia psittaci emphasise the importance of studies on male animals and in particular their reproductive system. Specimens in our study ranged in age from 15 days postnatal to adults. Due to the rarity of such specimens, details of each specimen are linked to the changes of the structures at each available stage. Light microscopy revealed that differentiation of the gonads had commenced by 15 days postnatal and that the cytological arrangements of the urogenital system are essentially the same as those of other mammals. Scanning electron microscopy revealed stereocilia and microvilli along the lumen of each ductus epididymis and cilia and microvilli along the lumina of the vasa deferentia and urethra. The development of these structures coincided with the onset of sexual maturation, sperm production and differentiation at about three years of age.

Age Factors↗
PubMed1999

Development of the thymus, spleen, lymph nodes and liver in the marsupial, Isoodon macrourus (Northern brown bandicoot, Peramelidae).

We report for the first time the development and morphological characteristics of the spleen thymus, lymph nodes and liver of the northern brown bandicoot, Isoodon macrourus. To date few marsupial species have been studied. The development and morphological characteristics of the organs shared the typical features of those few other marsupials studied as well as those of eutherians. These suggest comparative functional properties with the eutherian immune system. The thymus differentiated within the first week of pouch life and showed evidence of immunolymphopoiesis up to juvenile stages. The spleen, though seeded by lymphocytes within the first week of pouch life, was slower to mature, but differentiated and showed signs of immunocompetency by the time young left the pouch. The mature spleen displayed the same anatomical blood filtering and immunosurveillance properties as that of the eutherian spleen, with evidence of erythrocyte destruction, thrombopoietic activity, activation and differentiation of immunocompetent lymphocytes. However, the absence of sheathed capillary structures in the spleen may indicate differences in the humoral response to circulating antigens. Similarly, lymph nodes also mature by this stage with anterior nodes appearing before posterior nodes. The mature lymph nodes displayed structural features of secondary immuno-lymphoid organs consistent with production of immune responses. Finally, the liver displayed haemopoietic activity for the first four weeks of pouch life. The pattern of development in the bandicoot appears to parallel the pattern reported for other marsupials, yet the thymus matures considerably earlier than previously reported and may be of significance in the development and onset of cell-mediated immunity. Current studies to characterise cellular components, such as T/B lymphocyes and accessory cells of these organs will help to define the mechanisms of immune recognition, activation and hence outline the basis of the marsupial humoral and cellular immunity.

Age Factors↗
PubMed2002

The mitochondrial 12S gene is a suitable marker of populations of Sarcoptes scabiei from wombats, dogs and humans in Australia.

We sequenced part of the mitochondrial 12S ribosomal RNA gene of 23 specimens of Sarcoptes scabiei from eight wombats, one dog and three humans. Twelve of the 326 nucleotide positions varied among these mites and there were nine haplotypes (sequences) that differed by 1-8 nucleotides. Phylogenetic analyses indicated that these mites were from two lineages: (1) mites from wombats from Victoria, Australia, and mites from the humans and dog from the Northern Territory, Australia (haplotypes 1-4, 9); and (2) mites from the humans and dog from the Northern Territory (haplotypes 5-8). Mites from the three different hosts (wombats, a dog and humans) had not diverged phylogenetically; rather, these mites had similar 12S sequences. Thus, we conclude that these mites from wombats, humans and a dog are closely related, and that they diverged from a common ancestor relatively recently. This conclusion is consistent with the argument that people and/or their dogs introduced to Australia the S. scabiei mites that infect wombats in Australia . So, S. scabiei, which has been blamed for the extinction of populations of wombats in Australia, may be a parasitic mite that was introduced to Australia with people and/or their dogs. These data show that the mitochondrial 12S rRNA gene may be a suitable population marker of S. scabiei from wombats, dogs and humans in Australia.

Animals↗
PubMed1996

The marsupial shell membrane: an ultrastructural and immunogold localization study.

In the dasyurid marsupial, Sminthopsis crassicaudata, as the oocytes/embryos travel down the female reproductive tract two extracellular coats, the mucoid and shell membrane, come to surround them. Embryos recovered from the oviduct have a mucoid coat but no shell membrane which is only found surrounding uterine embryos. Initially, the shell membrane has a compact granular consistency but it later thins and becomes fibrous in texture with fibres oriented mainly in the plane of the membrane. Immunogold labelling with polyclonal antibodies raised against the extracellular coats was employed to determine the location and ultrastructural appearance of the secretory granules which contain mucoid and shell membrane precursors. Secretory granules in the luminal epithelium of the ampulla of the oviduct are of irregular electron density, while those in the isthmus are electron-dense and homogeneous. Both types give rise to the mucoid coat. Secretory granules in the epithelia of the utero-tubal junction and some endometrial glands are electron-lucent and contain some flocculent material which, after exocytosis, gives rise to the shell membrane.

Animals↗
PubMed1997

Ultrastructural localization of relaxin in the corpus luteum of the pregnant and early lactating tammar wallaby, Macropus eugenii.

Electron-microscope immunocytochemistry was used to determine the subcellular distribution and presence of immunoreactive relaxin throughout pregnancy and early lactation in the corpus luteum of a marsupial, the tammar wallaby. Membrane-bound, electron-dense granules were a prominent feature of the luteal cell cytoplasm. The highest numbers of granules were observed between days 20 and 24 of the 26-day gestation, with a rapid clearance immediately after birth. Relaxin immunogold particles were present only in small, electron-dense granules (200-350 nm in diameter), with no particles observed in larger granules (>400 nm diameter), nuclei or mitochondria. Relaxin immunoreactivity was low throughout early and mid pregnancy but increased markedly between days 21 and 22 and remained high over the last 4 days of pregnancy. The number of granules containing relaxin immunogold particles and the density of immunostaining were both reduced on the day of expected births (day 26). Our data demonstrate that electron-dense granules in the luteal cell cytoplasm of a pregnant marsupial contain relaxin. The peptide is produced in greatest amounts at the end of pregnancy, consistent with a role in parturition.

Animals↗
PubMed1999

Analysis of the thymidine kinase genes of macropodid herpesviruses 1 and 2.

The nucleotide sequences of the entire protein coding regions of the thymidine kinase (TK) genes of macropodid herpesvirus type 1 (MaHV-1) and type 2 (MaHV-2) were determined. The coding region of the MaHV-1 TK gene was 984 bp long and was predicted to encode a polypeptide of 327 amino acids. The coding region of the MaHV-2 TK gene was 1020 bp long and encoded a polypeptide of 340 amino acids. Comparisons of their deduced amino acid sequences with those of fifteen other herpesviruses revealed close homology to those of other alphaherpesviruses, particularly to human herpesvirus type 1 (HHV-1) and type 2 (HHV-2).

Alphaherpesvirinae↗
PubMed2005

Isolation, X location and activity of the marsupial homologue of SLC16A2, an XIST-flanking gene in eutherian mammals.

X chromosome inactivation (XCI) achieves dosage compensation between males and females for most X-linked genes in eutherian mammals. It is a whole-chromosome effect under the control of the XIST locus, although some genes escape inactivation. Marsupial XCI differs from the eutherian process, implying fundamental changes in the XCI mechanism during the evolution of the two lineages. There is no direct evidence for the existence of a marsupial XIST homologue. XCI has been studied for only a handful of genes in any marsupial, and none in the model kangaroo Macropus eugenii (the tammar wallaby). We have therefore studied the sequence, location and activity of a gene SLC16A2 (solute carrier, family 16, class A, member 2) that flanks XIST on the human and mouse X chromosomes. A BAC clone containing the marsupial SLC16A2 was mapped to the end of the long arm of the tammar X chromosome and used in RNA FISH experiments to determine whether one or both loci are transcribed in female cells. In male and female cells, only a single signal was found, indicating that the marsupial SLC16A2 gene is silenced on the inactivated X.

Amino Acid Sequence↗