Spermiogenesis in the brush-tailed possum,Trichosurus vulpecula (Marsupialia)

Summary Acrosome development in the Australian Brush-tailed possum, Trichosurus vulpecula, displays a number of extraordinary features. This is particularly evident in the later stages of spermiogenesis, when the area of the nuclear surface bounded by the nuclear ring, and covered by the acrosome, is reduced considerable. As a result, the acrosomal material becomes located over its definitive position on the anterior third of the dorsal nuclear surface; in this process it is thrown into a series of folds, and a wide subacrosomal space is formed.Further changes around the time of spermiation result in the release of a spermatozoon in which a thin layer of acrosomal material is closely applied to the nucleus over the area of the definitive location of the acrosome, whilst its margins are greatly extended and project freely away from the nucleus. The latter feature does not appear to have been reported for the sperm of other mammals.The authors would like to thank Dr. D.J.H. Cockayne, Director of the Electron Microscope Unit, University of Sydney, for the generous provision of transmission electron microscope facilities, and Dr. M.R. Dickson, Electron Microscopist in charge, Biomedical Electron Microscope Unit, University of New South Wales, for the use of other facilities. Also, thanks are due to Miss Robin Arnold and Mrs. Eva Vassak of the Department of Histology and Embryology, University of Sydney, for their expert assistance. The assistance of the N.S.W. National Parks and Wildlife Service in the provision of permits to work on these native mammals is acknowledged     

Putative osmolytes in the kidney of the Australian brush-tailed possum,Trichosurus vulpecula

The Australian brush-tailed possum, Trichosurus vulpecula, is capable of producing a moderately concentrated urine, at least up to 1300 mOsm l(-1). Kidneys of adult animals fed in captivity on a normal diet with ready access to water were analysed. The inner medullary regions were found to have moderately high concentrations of sodium (outer medulla, 367+/-37; inner medulla 975+/-93 mmol kg(-1) dry wt.), chloride (outer medulla 240+/-21; inner medulla 701+/-23 mmol kg(-1) dry wt.) and urea (outer medulla, 252+/-62; inner medulla, 714+/-69 mmol kg(-1) protein). When the animals were fed on a 'wet diet', amounts of these substances in the outer medulla and cortex were reduced, although with the exception of urea these changes were not significant. There were highly significant changes in amounts of Na(+), Cl(-) and urea in the inner medulla (Na(+), 566+/-7; Cl(-), 422+/-9 mmol kg(-1) dry wt.; urea 393+/-84 mmol kg(-1) protein). Likewise, the inner medulla of animals fed a 'dry diet' with limited access to water showed highly significant increases in the same substances (Na(+), 1213+/-167; Cl(-), 974+/-137 mmol kg(-1) dry wt.; urea, 1672+/-98 mmol kg(-1) protein). Inositol was found in the outer medulla (224+/-90 mmol kg(-1) protein) and inner medulla (282 mmol kg(-1) protein) as was sorbitol (outer medulla, 62+/-20; inner medulla, 274+/-72 mmol kg(-1) protein). Both these polyols were reduced in amount in renal tissue from 'wet diet' animals, and increased in 'dry diet' animals, but the changes were not statistically significant. The methylamines, betaine and glycerophosphorylcholine (GPC), showed a similar pattern, but both were significantly elevated in the inner medulla of 'dry diet' animals (betaine 154+/-57 to 315+/-29 mmol kg(-1) protein; GPC 35+/-7 to 47+/-10 mmol kg(-1) protein). It was concluded that in this marsupial the concentrating mechanism probably functions in a similar way to that in higher mammals, and that the mechanism of osmoprotection of the medulla of the kidney involves the same osmolytes. However, the high ratio of betaine to GPC in the inner medulla resembles the situation in the avian kidney.     

Morphological trends in the Common brushtail possum, Trichosurus vulpecula, in New Zealand

Over 300 specimens of the Australian introduced Common brushtail possum, taken from throughout its range in New Zealand, were measured. A north-south trend in skull size was found, which conforms with Bergmann's rule. This trend probably evolved during less than 50 years (30-35 generations), and is not significantly different from the present Australian trend for skull size in this species. Males are slightly larger (1.8% in skull length) than females.     

Uterine oxytocin receptors in an Australian marsupial, the brushtail possum, Trichosurus vulpecula

1. Oxytocin receptors in the uterus of the brushtail possum (T. vulpecula) were characterized by radioreceptor assay and compared with those of the sheep and rat uterus. 2. A single oxytocin binding site was found with an affinity (Kd) and receptor concentration (Ro) of 3.0 +/- 0.8 nmol/l and 200 +/- 60 fmol/mg protein, respectively (SEM; n = 5). The receptor was stable at -20 degrees C; divalent ions were required for optimum binding. 3. Competitive displacement curves with related peptides showed the following order of specificity: vasotocin greater than oxytocin greater than mesotocin = arginine-vasopressin = [Thr4, Gly7]-oxytocin greater than lysine-vasopressin = isotocin much greater than [d(CH2)5, D-Phe2, Ile4, Ala9-NH2]-AVP. 4. It was concluded that oxytocin receptors in the possum have similar characteristics to those of placental mammals.     

Organic osmolytes in the developing kidney of the Australian brush-tailed possum, Trichosurus vulpecula

Developmental changes in the plasma and urine composition of 120 immature possums, Trichosurus vulpecula, were investigated and correlated with changes in the osmolyte composition of the kidneys. In early life, when the animal is confined in the pouch, the urine is more or less isosmotic with the plasma (300+/-70 mOsm kg(-1)), but rises steeply in animals more than 90 days old, up to 667+/-53 mOsm kg(-1) in the oldest age group. In parallel with this change there are corresponding increases in medullary osmolytes. Measured as mmol kg(-1) wet weight, sorbitol was found to increase from 2.1+/-0.8 to 9.7+/-2.2, myo-inositol from 10.9+/-6.2 to 33.6+/-11.7, while the methylamines glycerophosphorylcholine and betaine rose from 6.2+/-0.5 to 15.3+/-3.1 and 3.9+/-2.2 to 9.4+/-2.5 mmol kg(-1) wet weight respectively. Medullary taurine showed no significant changes with age in young possums, while urea increased from 11+/-4.6 to 49+/-7.1 mmol kg(-1) wet weight. These values are similar to, but less than, those found in adult kidneys, but probably further refinement of the concentrating ability of the kidney occurs after the young animal becomes independent.     

The development of thermoregulation in the marsupial brushtail possum Trichosurus vulpecula

• 1.1. The adult possums showed a circadian rhythm of body temperature with a peak in temperature around midnight and a nadir at noon.
• 2.2. The young possum within the pouch displayed a circadian rhythm with the highest temperatures during the day and the lowest in the early evening.
• 3.3. Although the body temperature of the young possum exceeded that of the mother occasionally, for the major part of the 24 hr the body temperature of the young was lower than that of the mother.
• 4.4. The young possum could maintain a steady body temperature between 140 and 167 days post partum. A circadian rhythm of temperature was observed between 157–190 days post partum.
• 5.5. All adipose tissue examined with the light and electron microscope had the morphology of white adipose tissue.

     

Mapping human X-linked genes in the phalangerid marsupial Trichosurus vulpecula.

We mapped 15 human X-chromosome markers in the common brush-tailed possum, Trichosurus vulpecula (Kerr), which represents the Australian marsupial family Phalangeridae. In situ hybridization was used to localize highly conserved human X-linked genes to chromosomes of T. vulpecula diploid lines. Ten genes located on the long arm of the human X (human Xq genes) all mapped to the possum X chromosome. However, all five genes located on the short arm of the human X (human Xp genes) mapped to autosomes. These findings confirm our previous work, which showed that the X chromosome in macropodid and dasyurid marsupials bears all the human Xq genes but none of the human Xp genes studied. This suggests that the marsupial X is highly conserved, but its gene content reflects that of only part of the eutherian X, a result consistent with our hypothesis that an autosomal region was added to the X early in eutherian divergence.     

Analysis of the characteristics of fruit eaten by possums,Trichosurus vulpecula,in New Zealand

Abstract

The colours and sizes of the fleshy fruits of native trees and shrubs in the New Zealand flora and in the flora of the Orongorongo Valley, southern Rimutaka Range, were compared with those known to be eaten by possums to assess the degree of food selection by possums. Colour and diameter of fruits had little effect on whether they were selected by possums, but the size of the enclosed seed affected feeding behaviour. Fruits with seeds < 10 mm were eaten whole, whereas usually only the skin and flesh were eaten from fruits with larger seeds. An analysis of the wet and dry weights of the flesh and seeds of fruits growing in the Orongorongo Valley suggested that possums could maximise their dry matter intake from fruits by feeding preferentially on the larger fruits. Although this suggestion was supported in general by field observations, other studies suggest that annual variations in the abundance of fruits of the various species and their accessibility are also important in determining the contribution of fruits to the diet of possums.