Koala Development: Difference between revisions

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[[Category:Australia]]
[[Category:Australia]]
[[Category:Koala]]

Revision as of 06:53, 5 November 2011

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")

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


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Some Recent Findings

  • Developmental origins of precocial forelimbs in marsupial neonates[1] "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[2] "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[3] "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."

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.[4]
  • 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.[5]
  • 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.[6]

  • 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.[7]

  • 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:[8]

  • 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

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.[9]


Links: Spermatozoa Development

References

  1. <pubmed>21098569</pubmed>
  2. <pubmed>20591325</pubmed>
  3. <pubmed>18950846</pubmed>
  4. <pubmed>9543340</pubmed>
  5. <pubmed>11943495</pubmed>
  6. <pubmed>11999321</pubmed>
  7. <pubmed>16928207</pubmed>
  8. <pubmed>10729728</pubmed>
  9. <pubmed>17609294</pubmed>

Reviews

<pubmed></pubmed>


Articles

<pubmed>16928207</pubmed> <pubmed>11303907</pubmed>

Books

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 Nov 2010 "Koala development" 41 reference articles of which 0 were reviews.


Search PubMed: Phascolarctos cinereus | Koala development | marsupial development

External Links