Koala Development

Embryology - 2 Dec 2023        Expand to Translate
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Introduction

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")

Some Recent Findings

Composition of marsupial zona pellucida "In eutherians the zona pellucida is formed from three or four proteins (ZP1, ZP2, ZP3, ZP4). In the few marsupials that have been studied, however, only three of these have been characterised (ZP2, ZP3, ZP4). Nevertheless, the composition in marsupials may be more complex, since a duplication of the ZP3 gene was recently described in one species. The aim of this work was to elucidate the ZP composition in marsupials and relate it to the evolution of the ZP gene family. For that, an in silico and molecular analysis was undertaken, focusing on two South American species (gray short-tailed opossum and common opossum) and five Australian species (brushtail possum, koala, Bennett's wallaby, Tammar wallaby and Tasmanian devil). This analysis identified the presence of ZP1 mRNA and mRNA from two or three paralogues of ZP3 in marsupials. Furthermore, evidence for ZP1 and ZP4 pseudogenes in the South American subfamily Didelphinae and for ZP3 pseudogenes in two marsupials is provided. In conclusion, two different composition models are proposed for marsupials: a model with four proteins (ZP1, ZP2 and ZP3 (two copies)) for the South American species and a model with six proteins (ZP1, ZP2, ZP3 (three copies) and ZP4) for the Australasian species." zona pellucida Characterisation of the immune compounds in koala milk using a combined transcriptomic and proteomic approach "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." milk The koala (Phascolarctos cinereus): a case study in the development of reproductive technology in a marsupial "The successful development and application of an assisted breeding program in any animal relies primarily on a thorough understanding of the fundamental reproductive biology (anatomy, physiology and behaviour) of the species in question. Surely, the ultimate goal and greatest hallmark of such a program is the efficacious establishment of a series of reliable techniques that facilitate the reproductive and genetic management of fragmented populations, both in captivity and in the wild. Such an achievement is all the more challenging when the reproductive biology of that species is essentially rudimentary and without adequate reproductive models to compare to. Using the koala (Phascolarctos cinereus) as a case study, this chapter provides some personal insights into the evolution of a concept that began as a small undergraduate student project but that subsequently evolved into the first-ever successful artificial insemination of a marsupial. Apart from this historical perspective, we also provide a brief review of the current reproductive biology of the koala, discuss technical elements of current assisted breeding technology of this species, its potential application to the wombat, and the future role it might play in helping to conserve wild koala populations. There is little doubt that the unique reproductive biology and tractability of the koala has in this case been a benefit rather than a hindrance to the success of artificial breeding in this species."

More recent papers

This table allows an automated computer search of the external PubMed database using the listed "Search term" text link. This search now requires a manual link as the original PubMed extension has been disabled. The displayed list of references do not reflect any editorial selection of material based on content or relevance. References also appear on 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. More? References | Discussion Page | Journal Searches | 2019 References | 2020 References Search term: Koala Embryology | Koala Development

Older papers

These papers originally appeared in the Some Recent Findings table, but as that list grew in length have now been shuffled down to this collapsible table. See also the Discussion Page for other references listed by year and References on this current page. Developmental origins of precocial forelimbs in marsupial neonates "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." limb Levonorgestrel, not etonogestrel, provides contraception in free-ranging koalas "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 "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." fertilisation

Taxon

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.
• 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.
• 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.

• 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.

Oocyte

Ovarian Follicle Development

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

• 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:

• 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 | zona pellucida

Spermatozoa

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.

Links: spermatozoa

References

Reviews

Johnston SD & Holt WV. (2014). The koala (Phascolarctos cinereus): a case study in the development of reproductive technology in a marsupial. Adv. Exp. Med. Biol. , 753, 171-203. PMID: 25091911 DOI.

Renfree MB. (1993). Diapause, pregnancy, and parturition in Australian marsupials. J. Exp. Zool. , 266, 450-62. PMID: 8371091 DOI.

Articles

Chapman JA, Leigh CM & Breed WG. (2006). The zona pellucida of the koala (Phascolarctos cinereus): its morphogenesis and thickness. J. Anat. , 209, 393-400. PMID: 16928207 DOI.

Gifford A, Fry G, Houlden BA, Fletcher TP & Deane EM. (2002). Gestational length in the koala, Phascolarctos cinereus. Anim. Reprod. Sci. , 70, 261-6. PMID: 11943495

Grand TI & Barboza PS. (2001). Anatomy and development of the koala, Phascolarctos cinereus: an evolutionary perspective on the superfamily Vombatoidea. Anat. Embryol. , 203, 211-23. PMID: 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

External Links

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• NSW Government Information
• Information on Koalas
• Lone Pine Koala Sanctuary

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Cite this page: Hill, M.A. (2023, December 2) Embryology Koala Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Koala_Development

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© Dr Mark Hill 2023, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G