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Anatomy & physiology

Age-dependent changes in gross and histological morphology of the thyroid gland in South Australian koalas (Phascolarctos cinereus)

Graham, C, Woolford, L, Johnson, L & Speight, KN 2014, Australian Journal of Zoology, vol. 62, pp. 360-365.

This study investigated the morphological changes of the koala thyroid gland, which were determined to be linked to the age of the koala, rather than health status or sex. Juvenile koalas were mostly observed to exhibit typical thyroid gland morphology, while most adult koalas presented with colloidal goitre. The authors suggest an association of the findings with the low metabolism of koalas or dietary goitrogen exposure.

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Assessment of the hemorheological profile of koala and echidna

Baskurt, OK, Marshall-Gradisnik, S, Pyne, M, Simmonds, M, Brenu, E, Christy, R & Meiselman, J 2010, Zoology, vol. 113, no. 2, pp. 110-117.

Blood samples from six echidnas and six koalas were analysed and compared to human blood for the following parameters: red blood cell (RBC) deformability, RBC aggregation, surface charge and aggregability, blood viscosity (62.5-1250 s -1) and hematological characteristics. The koalas had the highest average RBC volume (107.7 ± 2.6 fl) out of humans (88.4 ± 1.2 fl) and echidnas (81.3 ± 2.6 fl). RBC deformability of the koala was significantly greater than that of both human and echidna. RBCs of the echidna had less aggregability than human or koala RBCs, whilst aggregation was comparable for all three species in autologous plasma. RBC surface charge was similar between echidnas and humans, but 40% less in koalas by comparison.

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Bony Orbital Anatomy of the Koala (Phascolarctos cinereus)

Kempster, RC & Hirst, LW 2002, The Anatomical Record, vol. 267, pp. 288-291.

This study was the first to document anatomical details of the normal koala orbit, which showed consistencies in the overall orbital structure compared with other marsupials. This information can be used to improve understandings of the koala’s anatomy and aid research efforts to find treatments for ocular disease in the koala.

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Broad-scale phylogenomics provides insights into retrovirushost evolution

Alexander Hayward1, Manfred Grabherr, and Patric Jern1

Science for Life Laboratory, Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala Biomedical Centre, SE-75123 Uppsala, Sweden

Edited by Stephen P. Goff, Columbia University College of Physicians and Surgeons, New York, NY, and approved November 1, 2013 (received for review August 14, 2013)


Genomic data provide an excellent resource to improve understanding of retrovirus evolution and the complex relationships among viruses and their hosts. In conjunction with broad-scale in silico screening of vertebrate genomes, this resource offers an opportunity to complement data on the evolution and frequency of past retroviral spread and so evaluate future risks and limitations for horizontal transmission between different host species. Here, we develop a methodology for extracting phylogenetic signal from large endogenous retrovirus (ERV) datasets by collapsing information to facilitate broad-scale phylogenomics across a wide sample of hosts. Starting with nearly 90,000 ERVs from 60 vertebrate host genomes, we construct phylogenetic hypotheses and draw inferences regarding the designation, host distribution, origin, and transmission of the Gammaretrovirus genus and associated class I ERVs. Our results uncover remarkable depths in retroviral sequence diversity, supported within a phylogenetic context. This finding suggests that current infectious exogenous retrovirus diversity may be underestimated, adding credence to the possibility that many additional exogenous retroviruses may remain to be discovered in vertebrate taxa. We demonstrate a history of frequent horizontal interorder transmissions from a rodent reservoir and suggest that rats may have acted as important overlooked facilitators of gammaretrovirus spread across diverse mammalian hosts. Together, these results demonstrate the promise of the methodology used here to analyze large ERV datasets and improve understanding of retroviral evolution and diversity for utilization in wider applications.

Characteristics of koala (Phascolarctos cinereus adustus) semen collected by artificial vagina

Johnston, SD, O’Callaghan, P, McGowan, MR & Phillips, NJ 1997, Journal of Reproduction and Fertility, vol. 109, no. 1, pp. 319-323.

An artificial vagina is recommended as a simple, reliable and non-invasive method of semen collection from koalas in captivity. Out of 90 attempts, 40% resulted in collection of a complete ejaculate comprising a rubbery copulatory plug fraction and a sperm fraction with high motile spermatozoa content. No semen was collected in 38% of trials, while only partial ejaculates were collected in 14.5% of trials. Urine was detected in 4.5% of samples, and 3% of semen samples were collected after the koala’s ejaculation behaviour had ended.

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Coprophagy in leporids and other mammalian herbivores


Forestry and Forest Products Research Institute, Hitsujigaoka 7, Toyohira, Sapporo 


Leporids have long been known to reingest soft faeces. However, it was recently found that they regularly reingest hard faeces, too. During the daytime, both soft and hard faeces are defecated and all of the faeces are reingested. Excreted at night are the hard faeces, which are normally discarded but reingested in starvation. The separation mechanism in the proximal colon, which diverts fine particles into the caecum and thus only passes large food particles, produces hard faeces. When the mechanism ceases acting, fermented caecal materials are excreted as soft faeces. The reingestion of soft faeces, rich in vitamins and microbial proteins, is physiologically imperative. Hard faeces are basically a refuse, but their thorough mastication at reingestion reduces poorly digestible large particles to fine ones good for fermentation. The regular reingestion of daytime hard faeces thus promotes food digestibility. The temporary use of night-time hard faeces allows leporids to do without food for some time. It thus gives leporids behavioural flexibility and thereby an ecological advantage. Reingestion is also known in other small- to medium-sized herbivores, which are all caecal fermenters. Morphological differentiation between faeces is reported only in larger species, but all ingested faeces are found to be richer in nutrients than discarded ones. Thus a separation mechanism is probably present in all reingesting species. Reingestion activity is deeply related to other behavioural and physiological traits of small mammalian herbivores, hence its study is important to understanding of their ecology and biology. Leporids are the largest of the reingesting species except for the semi-aquatic Coypu, and reingestion by leporids is certainly the most sophisticated. This development of a reingestion-involved digestive system has probably brought them to their present niche,as terrestrial medium-sized generalist mammalian herbivores, and consequently made their characteristic hide-and-run lifeforms by exposing them to a strong predation pressure.

Histopathological examination of the pancreas of the koala (Phascolarctos cinereus)

Higgins, DP & Canfield, PJ 2009, Journal of Comparative Pathology, vol. 140, no. 1, pp. 217-224.

Autolysis of pancreatic tissue from koalas was previously thought to make these samples unsuitable for histopathological examination; however, this study demonstrates that many abnormalities of the pancreas can be detected using established criteria for the stages of autolysis up to 72 hours post mortem.

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Influence of flow rate and aldosterone administration on mandibular salivary composition in the koala (Phascolarctos cinereus)


School of Biological Science, University of N.S.W., P.O. Box I , Kensington, N.S.W., Australia, 2033

The possibility of adaptations of mandibular salivary function to a diet of eucalypt leaves and for evaporative cooling was investigated in anaesthetized koalas. Salivary composition, at a range of flow rates up to maximum and during aldosterone administration, was measured in saliva evoked by intravenous infusion of carbamylcholine chloride. Maximum fluid secretion rates per gram tissue (230 + 18.2 μl/min/g gland) were similar to mandibular glands of other species and about four times the rates/g gland reported for the parotid gland of koalas. Salivary concentrations of Na (6.1 ± 0.91 to 67.7 ± 3.51 mmol·1-1), Cl (7.2 ± 0.71 to 53.0 ± 2.82 mmol·1-1), HCO3 (8.6 ± 0.81 to 19.4 ± 2.13 mmol·1-1) and the osmolality (26.7 ± 2.34 to 132.9 ± 5.47 mosmol·kg-1) were positively correlated with salivary flow rate. The concentrations of urea (1.87 ± 0.034 to 0.71 ± 0.099 mmol·1-1), K (13.0 ± 0.90 to 6.25 ± 0.482 mmol·1-1), Mg (33.6 ± 2.53 to 10.1 ± 4.68 μmol·1-1), H+ (246.2 ± 55.78 to 62.1 ± 8.01 ηmol·1-1) and PO4 (3.46 ± 0.350 to 1.13 ± 0.044 mmol·1-1) were negatively related to flow rate. Total protein (411 ± 44.4 to 656 ± 146.4 mg·1-1) and total Ca (356 ± 45.2 to 467 ± 61.6 μmol·1-1) concentrations were not correlated with flow but were highly correlated with one another. With salivary amylase activity being absent and plasma amylase activity being very low indicating low production rates by other tissues, the koala is likely to have limited ability to digest starch. Intravenous infusion of aldosterone at 5 μg·h-1 for 90 min followed by 50 μg·h-1 for 105 min demonstrated that the gland responded rapidly to changes in endogenous mineralocorticoid levels. Mean salivary Na/K ratio before aldosterone administration was 6.9 ± 2.01, the ratio had fallen significantly (P<0.05) after 75-90 min infusion and had fallen to 0.71 ± 0.172 by the last 30 min of infusion.

It was concluded that the mandibular gland of the koala, with its relatively high secretory capacity and its sensitivity to stimulation, would have the major influence on the composition of mixed saliva during low-flow reflex secretion. Additionally, because the gland is responsive to acute changes in mineralocorticoids and produces a markedly hypotonic saliva, the mandibular is better adapted than the parotid gland to be the primary source of saliva for evaporative cooling.

Intraorbital anatomy of the koala (Phascolarctos cinereus)

Kempster, RC, Bancroft, BJ & Hirst, LW 2002, The Anatomical Record, vol. 267, pp. 277-287.

Detailed descriptions of the koala anatomy generate baseline information for understanding and treating diseases in the koala. This study provides baseline anatomical details of the normal koala orbit, excluding the bulbus oculi.

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Koala and Possum Populations in Queensland during the Harvest Period, 1906-1936 

Greg Gordon1,3 and Frances Hrdina


1Queensland Parks and Wildlife Service. PO Box 155, Brisbane Albert St Qld 4002.

230/38 Dundee Rd, North Maclean Qld 4280

3Address for corresponding author: PO Box 636, Paddington Qld 4064;


The Queensland Koala Phascolaretos cinereus and possum harvests were regulated from 1906·1927 and 1906·1936. respectively. Before that, there was an uncontrolled harvest. Historical data from the harvest period were analysed to gain information on P. cinereus and possum (mainly Trichosurus vulpecula) population ecology and status. P. cinereus numbers peaked in southern Queensland around the turn of the century or in the first decade of the 20th century. In central Queensland, they peaked later, probably in the 1920s, and in north Queensland there does not appear to have been any pronounced fluctuation in numbers. P. cinereus populations experienced diseases similar to those occurring today. Chlamydial diseases were common and occurred in most parts of the State, with cystitis being more common. Some diseases were not clearly identified. In contrast to current populations, P. cinereus populations then had many more episodes of high mortality, population size appears markedly more volatile and overall abundance was much higher. Southern Queensland populations declined greatly at the time of the harvests, but the central Queensland population expanded after the last harvest and harvest mortaiity does not provide an adequate explanation of population decline. Although it is sometimes said, particularly with regard to island populations, that Queensland (and New South Wales) P. cinereus populations differ from those of Victoria in that they do not exhibit local irruptions and excessively high abundance, the population phenomena appear similar to those occurring in Victorian populations. Queensland populations achieved very high growth rates that resulted in unsustainable population densities and, eventually, mass mortality. Possum populations were subject to very high harvests that were apparently sustainable,at least in the short term,and showed fluctuations that were partly similar to those of P. cinereus. The P. cinereus, and probably also the possum population fluctuations, are mostly consistent with models of herbivore irruptions. The koala population fluctuations are interpreted in terms of herbivore irruption theory.We suggest that koala population expansion was a response to an increase in food availability (possibly due to the development of regrowth vegetation and/or waves of die back) resulting from land development patterns. A subsequent decline in food availability, accompanied by severe outbreaks of chlamydial disease (probably due to poor nutrition), led to severe declines in koala population size, often to levels well below the apparent carrying capacity. Populations of at least some possum species (T. vulpecula and possibly P. peregrinus) also appear to have experienced irruptions and declines, but the fluctuations do not correlate as closely with major aspects ofthe development of land for pastoralism and agriculture as do the changes in P. cinereus populations. Specific factors responsible for the expansion and decline of T. vulpecula and P. peregrinus populations were not identified.Very high harvests in 1919 and 1920 also seemed to affect possum numbers.

Locomotion and basicranial anatomy in primates and marsupials

Catalina I. Villamil a, b, c

a Department of Anthropology, Dickinson College, PO Box 1773, Carlisle, PA 17013, USA
b Center for the Study of Human Origins, Department of Anthropology, New York University, 25 Waverly Place, New York, NY 10003, USA
c New York Consortium in Evolutionary Primatology, New York, NY 10024, USA


There is ongoing debate in paleoanthropology about whether and how the anatomy of the cranium, and
especially the cranial base, is evolving in response to locomotor and postural changes. However, the majority of studies focus on two-dimensional data, which fails to capture the complexity of cranial anatomy. This study tests whether three-dimensional cranial base anatomy is linked to locomotion or to other factors in primates (n = 473) and marsupials (n = 231). Results indicate that although there is a small effect of locomotion on cranial base anatomy in primates, this is not the case in marsupials. Instead, facial anatomy likely drives variation in cranial base anatomy in both primates and marsupials, with additional roles for body size and brain size. Although some changes to foramen magnum position and orientation are phylogenetically useful among the hominoids, they do not necessarily reflect locomotion or positional behavior. The interplay between locomotion, posture, and facial anatomy in primates requires further investigation.

Microflora of the pouch of the koala (Phascolarctos cinereus)

Osawa, R, Blanshard, WH & O’Callaghan, P 1992, Journal of Wildlife Diseases, vol. 28, no. 2, pp. 276-280.

The pouches of female koalas are resistant to microbial colonisation, with a majority of pouch swabs revealing no microbial growth. Of 17 female koalas, only four (24%) were observed to have bacterial or yeast growths in the pouch.

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Ophthalmologic examination of the normal eye of the koala  

Hirst, LW, Brown, AS, Kempster, R & Winney, N 1992, Journal of Wildlife Diseases, vol. 28, no. 3, pp. 419 -423.  

  Examination of the eyes of 28 koalas (Phascolarctos cinereus) was performed to document the typical in vivo formation. 22 of the 28 investigated koalas had eyes that were normal. Upon examination using slit-lamps, the cornea was found to have atypical lamellae with average keratometric measurements at 59.3 ±  3 diopters. The measurement of the endothelial cell area of the cornea was 381.4 ± m2  ± 46.8 ± m2. No identifiable features that would explain the ocular infection susceptibility of this species by Chlamydia psittaci infection were noted.  

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Post-coital LH surge in the koala (Phascolarctos cinereus)

Johnston, SD, O’Callaghan, P, Nilsson, K & Curlewis, JD 2001, Proceedings of the 32nd Annual Conference of the Society for Reproductive Biology, 9 - 12 September, Gold Coast, p. 59.

This study puts forward initial evidence of a surge of luteinising hormone (LH) in female koalas. Occurring 24 hours after mating, the observed LH surge is considered to be induced by the act of copulation, though this is yet to be confirmed.

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Seasonal changes in haematocrit in captive koalas (Phascolarctos cinereus)

Cleva, GM, Stone, GM & Dickens, RK 1994, Australian Journal of Zoology, vol. 42, no. 2, pp. 233-236.

Distinct changes in microhaematocrit (ratio of red blood cell volume to the total blood volume) with season were observed in captive koalas, with raised levels in the winter and reduced values during the summer. Additionally, microhaematocrit was negatively correlated with the lowest and highest temperatures in the day. No associations of the differences in haematocrit with variations in body weight, plasma osmolarity or the concentration of plasma protein were discovered.

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Seasonal reproduction in wild and captive male koala (Phascolarctos cinereus) populations in south-east Queensland


Camryn D. AllenA,H, Deidré L. de VilliersB, Brett D. ManningB, David S. DiqueB, Michelle BurridgeC, Mandy L. ChaferC, Vere N. NicolsonC, Sophia C. JagoC, Allan J. McKinnonB, Rosemary J. BoothB, Jeff J. McKeeD, Michael J. PyneE, Yeng Peng ZeeA, Geoff Lundie-JenkinsB, Peter TheilemannB, Richard J. WilsonF, Frank N. CarrickG and Stephen D. JohnstonA

School of Animal Studies,The University of Queensland, Gatton, Qld 4343, Australia

Environmental Protection Agency, Brisbane, Qld 4000, Australia.

Dreamworld, Coomera, Qld 4209, Australia.

Mobile Disease Ecology Unit, Ecosure, West Burleigh, Qld 4219, Australia.

Currumbin Wildlife Sanctuary, Currumbin, Qld 4223, Australia.

Department of Mathematics, The University of Queensland, St Lucia, Qld 4072, Australia.

Centre for Mined Land Rehabilitation,The University of Queensland, St Lucia, Qld 4072, Australia.

Corresponding author. Email:



The effects of breeding season (late spring to early autumn) on south-east Queensland male koala fertility were examined to improve the efficacy of the AI procedure and to determine the practicality of using free-range animals as semen donors for a genome resource bank. Seasonal changes in male koala reproductive function were assessed in a wild free-range population (n=14; obtained every 6 weeks from January to November 2005), a necropsied healthy wild population (n=84; obtained monthly from September 2004 to August 2005) and a captive population (n=7; obtained monthly from October 2005 to October 2006). Reproductive parameters investigated included body weight, coat score, sternal gland area and activity, testosterone secretion, reproductive anatomy volume and semen quality (before and after cryopreservation).Collectively these findings show that reproduction in male koalas from south-eastQ ueensland changes seasonally and that winter appears to be the optimal season in which to collect semen samples by electroejaculation. While it was possible to repeatedly collect semen from free-range koalas for future genetic management via potential storage in a genome resource bank, the survival of these spermatozoa after cryopreservation was poor and will require further improvement.

Seasonal reproduction in wild and captive male koala (Phascolarctos cinereus) populations in south-east Queensland

Allen, CD, de Villiers, DL, Manning, BD, Dique, DS, Burridge, M, Chafer, ML, Nicolson, VN, Jago, SC, McKinnon, AJ, Booth, RJ, McKee, JJ, Pyne, MJ, Peng Zee, Y, Lundie-Jenkins, G, Theilemann, P, Wilson, RJ, Carrick, FN & Johnston, SD 2010, Reproduction, Fertility and Development, vol. 22, no. 1, pp. 695-709.

Male koalas exhibit seasonal changes in anatomical and physiological characteristics relating to fertility and reproduction. These seasonal variations have implications for artificial insemination (AI) programmes, as semen samples collected from wild koalas during winter appear to retain the highest quality after thawing from cryopreservation.

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Sperm membrane fatty acid composition in the Eastern grey kangaroo (Macropus giganteus), koala (Phascolarctos cinereus), and common wombat (Vombatus ursinus) and its relationship to cold shock injury and cryopreservation success

Miller, RR Jr, Sheffer, CJ, Cornett, CL, McClean, R, MacCallum, C & Johnston, SD 2004, Cryobiology, vol. 49, no. 1, pp. 137-148.

Koala cauda epididymidal spermatozoa have low membrane cholesterol levels and a high ratio of unsaturated/saturated membrane fatty acids compared to other studied species, including other marsupials. In particular, docosahexaenoic acid (DHA), a long-chain polyunsaturated fatty acid and the most predominant membrane fatty acid in the studied marsupial species, was found in high levels in koala spermatozoa and is thought to be related to its cryogenic tolerance.

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Surface enlargement in the large intestine of the koala (Phascolarctos cinereus): morphometric parameters

Snipes, RL, Snipes, H & Carrick, FN 1993, Australian Journal of Zoology, vol. 41, pp. 393-397.

Multiple parameters of the morphology of the koala’s large intestine were measured. A computer-aided planimeter was used to find the basal surface area of the caecum and colon, and the microscopically visible folds/plicae were measured to determine the surface enlargement of the mucosa. The basal surface areas were 890.6 cm2 for the caecum (32.0% of the entire intestine), 1434.8 cm2 for the colon (51.5%) and the entire intestine was 2785.0 cm2. An average of 8 and 12-14 longitudinal folds were found striping the caecum and proximal colon, respectively, which increased the surface area significantly. The surface areas for the caecum, colon and entire intestine, respectively, when including the extra surface from the folds were 3659.8 cm2 (45.9%), 3854.0 cm2 (48.3%) and 7973.4 cm2. Respective total surface areas were determined by multiplying the basal surface area by the surface enlargement factor. These were 10,979.5 cm2 (44.9%), 9808.5 cm2 (40.1%) and 24,464.7 cm2 for the caecum, colon and entire intestine, respectively.

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The structural organisation of sperm head components of the wombat and koala (suborder: Vombatiformes): an enigma amongst marsupials

Breed, WG, Leigh, CM & Ricci, M 2001, Journal of Anatomy, vol. 198, pp. 57-66.

Despite many similarities in sperm head morphology, the organisational structure of chromatin was found to differ between koala and wombat sperm; inferring that these structures are species-specific, a finding not previously described in any study.

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Variation in reproductive parameters in the captive male koala (Phascolarctos cinereus)

Cleva, GM, Stone, GM & Dickens, RK 1994, Reproduction, Fertility and Development, vol. 6, pp. 713-719.

The concentration of plasma androgens was measured in six male koalas of sexually mature age (3-10 years) over a period of 23 months. Four of these koalas were situated away from females, while two were housed with females. The concentration of androgens appeared to change seasonally, with the lowest levels observed mid-year, and increased steadily coming into the beginning of breeding season. Males living in female presence had higher androgen concentrations, even without females being in oestrus. These androgen concentration changes did not correlate with any changes in volume of the testicles.

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