Koala Development

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Adult Koala

The koala (Phascolarctos cinereus) is an arboreal herbivorous marsupial native to Australia, and the only extant representative of the family Phascolarctidae.

(Greek, phaskolos = "pouch" and arktos = "bear"; Latin, cinereus = "ash-coloured")

Koala comes from the Dharuk gula, the word is erroneously said to mean "doesn't drink"

Australian Animal: echidna | kangaroo | koala | platypus | possum | Category:Echidna | Category:Kangaroo | Category:Koala | Category:Platypus | Category:Possum | Category:Marsupial | Category:Monotreme | Development Timetable | K12
Historic Australian Animal  
Historic Embryology: 1880 Platypus Cochlea | 1887 Monotremata and Marsupialia | 1910 Eastern Quoll | 1915 The Monotreme Skull | 1939 Early Echidna

The Hill Collection contains much histology of echidna and platypus embryonic development.

Embryology History | Historic Disclaimer

Other Marsupials  
Monito del Monte Development | Opossum Development

Some Recent Findings

  • Characterisation of the immune compounds in koala milk using a combined transcriptomic and proteomic approach[1] "Production of milk is a key characteristic of mammals, but the features of lactation vary greatly between monotreme, marsupial and eutherian mammals. Marsupials have a short gestation followed by a long lactation period, and milk constituents vary greatly across lactation. Marsupials are born immunologically naïve and rely on their mother's milk for immunological protection. Koalas (Phascolarctos cinereus) are an iconic Australian species that are increasingly threatened by disease. Here we use a mammary transcriptome, two milk proteomes and the koala genome to comprehensively characterise the protein components of koala milk across lactation, with a focus on immune constituents. The most abundant proteins were well-characterised milk proteins, including β-lactoglobulin and lactotransferrin. In the mammary transcriptome, 851 immune transcripts were expressed, including immunoglobulins and complement components. We identified many abundant antimicrobial peptides, as well as novel proteins with potential antimicrobial roles. We discovered that marsupial VELP is an ortholog of eutherian Glycam1, and likely has an antimicrobial function in milk. We also identified highly-abundant koala endogenous-retrovirus sequences, identifying a potential transmission route from mother to young."
  • Developmental origins of precocial forelimbs in marsupial neonates[2] "Marsupial mammals are born in an embryonic state, as compared with their eutherian counterparts, yet certain features are accelerated. The most conspicuous of these features are the precocial forelimbs, which the newborns use to climb unaided from the opening of the birth canal to the teat. The developmental mechanisms that produce this acceleration are unknown. Here we show that heterochronic and heterotopic changes early in limb development contribute to forelimb acceleration. Using Tbx5 and Tbx4 as fore- and hindlimb field markers, respectively, we have found that, compared with mouse, both limb fields arise notably early during opossum development."
  • Levonorgestrel, not etonogestrel, provides contraception in free-ranging koalas[3] "Management of high-density koala (Phascolarctos cinereus) populations is essential because of the browsing damage they inflict on their habitat. We have tested two types of gestagen implant, namely levonorgestrel and etonogestrel, as contraceptives for koalas. Free-ranging female koalas were given either a control, levonorgestrel (70 mg) or etonogestrel (34 or 68 mg) implant before the breeding season. ...Plasma progesterone in levonorgestrel-treated females remained low all year, but rose in controls concurrent with the onset of the breeding season. This suggests that levonorgestrel prevents pregnancy by blocking ovulation. Etonogestrel had absolutely no contraceptive effect at the two doses delivered and so is not suitable for controlling koala populations. In contrast, levonorgestrel was effective as a long-term, reversible contraceptive in wild koalas."
  • Artificial insemination in marsupials[4] "Artificial insemination has been used to produce viable young in two marsupial species, the koala and tammar wallaby. However, in these species the timing of ovulation can be predicted with considerably more confidence than in any other marsupial. In a limited number of other marsupials, such precise timing of ovulation has only been achieved using hormonal treatment leading to conception but not live young. A unique marsupial ART strategy which has been shown to have promise is cross-fostering; the transfer of pouch young of a threatened species to the pouches of foster mothers of a common related species as a means to increase productivity. For the foreseeable future, except for a few highly iconic or well studied species, there is unlikely to be sufficient reproductive information on which to base AI. However, if more generic approaches can be developed; such as ICSI (to generate embryos) and female synchronization (to provide oocyte donors or embryo recipients), then the prospects for broader application of AI/ART to marsupials are promising."
More recent papers  
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This table shows an automated computer PubMed search using the listed sub-heading term.

  • Therefore the list of references do not reflect any editorial selection of material based on content or relevance.
  • References appear in this list based upon the date of the actual page viewing.

References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability.

Links: References | Discussion Page | Pubmed Most Recent | Journal Searches

Search term: Koala Embryology

Elleke Cremers, Carel Thijs, John Penders, Eugene Jansen, Monique Mommers Maternal and child's vitamin D supplement use and vitamin D level in relation to childhood lung function: the KOALA Birth Cohort Study. Thorax: 2011, 66(6);474-80 PubMed 21422038

Kentaro Katayama, Sayaka Miyamoto, Aki Furuno, Kouyou Akiyama, Sakino Takahashi, Hiroetsu Suzuki, Takehito Tsuji, Tetsuo Kunieda Characterization of the chromosomal inversion associated with the Koa mutation in the mouse revealed the cause of skeletal abnormalities. BMC Genet.: 2009, 10;60 PubMed 19772620

Geoffrey W Pye Shoulder dysplasia in koalas (Phascolarctos cinereus) at San Diego Zoo. J. Zoo Wildl. Med.: 2009, 40(3);453-7 PubMed 19746859

Katherine A Fantauzzo, Marija Tadin-Strapps, Yun You, Sarah E Mentzer, Friedrich A M Baumeister, Stefano Cianfarani, Lionel Van Maldergem, Dorothy Warburton, John P Sundberg, Angela M Christiano A position effect on TRPS1 is associated with Ambras syndrome in humans and the Koala phenotype in mice. Hum. Mol. Genet.: 2008, 17(22);3539-51 PubMed 18713754

A Gifford, G Fry, B A Houlden, T P Fletcher, E M Deane Gestational length in the koala, Phascolarctos cinereus. Anim. Reprod. Sci.: 2002, 70(3-4);261-6 PubMed 11943495


Taxonomy ID: 38626

Genbank common name: koala Inherited blast name: marsupials

Rank: species

Genetic code: Translation table 1 (Standard)

Mitochondrial genetic code: Translation table 2 (Vertebrate Mitochondrial)

Lineage ( full ) cellular organisms; Eukaryota; Fungi/Metazoa group; Metazoa; Eumetazoa; Bilateria; Coelomata; Deuterostomia; Chordata; Craniata; Vertebrata; Gnathostomata; Teleostomi; Euteleostomi; Sarcopterygii; Tetrapoda; Amniota; Mammalia; Theria; Metatheria; Diprotodontia; Phascolarctidae; Phascolarctos

Links: Taxonomy Browser Phascolarctos cinereus

Development Overview

Koala fetus near birth.
  • Adults - females reach maturity at 2 to 3 years of age, males at about 3 years of age.[5]
  • Joey - a single young produced each year for about 12 years.
  • Gestation - approximately 35 days, born under-developed (hairless, blind, and earless). There is a report of extended gestation.[6]
  • Birth - joey about 6 mm long crawls into the the mother's downward-facing pouch.
  • Pouch Development - joey remain in the pouch for about 6 months attached to one of the two available teats and feeding on milk, complete development.
  • Outside of the pouch - joey then begins to explore and to consume small quantities of the mother’s "pap" (thought to come from the mother's cecum) in order to inoculate its gut with the microbes necessary to digest eucalypt leaves.
  • Joey will remain with its mother for about another 6 months, riding on her back, and feeding on both milk and eucalypt leaves until weaning is complete at about 12 months of age.

System Development

The marsupial neonate at birth has a variation between the degree of development of different systems.[7]

  • well-developed - digestive, respiratory and circulatory system.
  • not well-developed - retains fetal excretory system with a fully functional mesonephric kidney and undifferentiated gonads and genitalia.


Ovarian Follicle Development

The following data is from a histological study of ovaries from adult female koalas.[8]

  • primordial follicles - have a small primary oocyte surrounded by a few squamous epithelial cells
  • primary follicles - have a single layer of cuboidal granulosa cells around the oocyte.
  • secondary follicles - have two or more layers of granulosa cells but no antrum
  • tertiary follicles (Graafian) - have many layers of granulosa cells surrounding a follicular fluid-filled antrum of variable size.
    • oocytes about 140 µm in diameter (range 110–162 µm: n = 5 individuals) surrounded by a zona pellucida (ZP) about 8 µm thick, which is twice as thick as most other marsupial species.

Marsupial eggs are enclosed by a series of layers:[9]

  • zona pellucida, three zona proteins (ZPA, ZPB, ZPC)
      • an additional extracellular matrix coat that lines the zona pellucida also occurs in some species.
  • mucoid coat
  • outer shell coat.

Links: Oocyte Development


The spermatozoa head is hook-shaped with the most of the acrosomal contents lying within a nuclear concavity. Spermatozoa nuclei show a range of morphologies and a tendency to swell after cryopreservation procedures.[10]

Links: Spermatozoa Development


  1. Katrina M Morris, Denis O'Meally, Thiri Zaw, Xiaomin Song, Amber Gillett, Mark P Molloy, Adam Polkinghorne, Katherine Belov Characterisation of the immune compounds in koala milk using a combined transcriptomic and proteomic approach. Sci Rep: 2016, 6;35011 PubMed 27713568
  2. Anna L Keyte, Kathleen K Smith Developmental origins of precocial forelimbs in marsupial neonates. Development: 2010, 137(24);4283-94 PubMed 21098569
  3. E F Hynes, K A Handasyde, Geoff Shaw, Marilyn B Renfree Levonorgestrel, not etonogestrel, provides contraception in free-ranging koalas. Reprod. Fertil. Dev.: 2010, 22(6);913-9 PubMed 20591325
  4. John C Rodger, Damien B B P Paris, Natasha A Czarny, Merrilee S Harris, Frank C Molinia, David A Taggart, Camryn D Allen, Stephen D Johnston Artificial insemination in marsupials. Theriogenology: 2009, 71(1);176-89 PubMed 18950846
  5. C Esson, P J Armati Development of the male urogenital system of the koala phascolarctos cinereus. Anat. Embryol.: 1998, 197(3);217-27 PubMed 9543340
  6. A Gifford, G Fry, B A Houlden, T P Fletcher, E M Deane Gestational length in the koala, Phascolarctos cinereus. Anim. Reprod. Sci.: 2002, 70(3-4);261-6 PubMed 11943495
  7. M B Renfree, A J Pask, G Shaw Sex down under: the differentiation of sexual dimorphisms during marsupial development. Reprod. Fertil. Dev.: 2001, 13(7-8);679-90 PubMed 11999321
  8. Jamie A Chapman, Christopher M Leigh, William G Breed The zona pellucida of the koala (Phascolarctos cinereus): its morphogenesis and thickness. J. Anat.: 2006, 209(3);393-400 PubMed 16928207
  9. L Selwood Marsupial egg and embryo coats. Cells Tissues Organs (Print): 2000, 166(2);208-19 PubMed 10729728
  10. Stephen D Johnston, Carmen López-Fernández, Altea Gosálbez, Yengpeng Zee, William V Holt, Camryn Allen, Jaime Gosálvez The relationship between sperm morphology and chromatin integrity in the koala (Phascolarctos cinereus) as assessed by the Sperm Chromatin Dispersion test (SCDt). J. Androl.: 2007, 28(6);891-9 PubMed 17609294


Stephen D Johnston, William V Holt The Koala (Phascolarctos cinereus): A Case Study in the Development of Reproductive Technology in a Marsupial. Adv. Exp. Med. Biol.: 2014, 753;171-203 PubMed 25091911

M B Renfree Diapause, pregnancy, and parturition in Australian marsupials. J. Exp. Zool.: 1993, 266(5);450-62 PubMed 8371091


Jamie A Chapman, Christopher M Leigh, William G Breed The zona pellucida of the koala (Phascolarctos cinereus): its morphogenesis and thickness. J. Anat.: 2006, 209(3);393-400 PubMed 16928207

T I Grand, P S Barboza Anatomy and development of the koala, Phascolarctos cinereus: an evolutionary perspective on the superfamily Vombatoidea. Anat. Embryol.: 2001, 203(3);211-23 PubMed 11303907


Search PubMed

Note searches using the term "Koala" will also find papers that refer to the KOALA Birth Cohort Study, a European study not related to the Australian animal.

Search PubMed: Phascolarctos cinereus | Koala development | marsupial development

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Cite this page: Hill, M.A. (2018, April 25) Embryology Koala Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Koala_Development

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