Koala Development: Difference between revisions

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== Development Overview ==
== Development Overview ==
[[Koala fetus.jpg|thumb|Koala fetus near birth.
[[Koala fetus.jpg|thumb|Koala fetus near birth.]]


* Females reach maturity at 2 to 3 years of age, males at 3 to 4 years, producing a single young (joey) each year for about 12 years.  
* Females reach maturity at 2 to 3 years of age, males at 3 to 4 years, producing a single young (joey) each year for about 12 years.  

Revision as of 17:32, 1 December 2010

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"

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. Patterning of the forelimb buds is also accelerated, as Shh expression appears early relative to the outgrowth of the bud itself. In addition, the forelimb fields and forelimb myocyte allocation are increased in size and number, respectively, and migration of the spinal nerves into the forelimb bud has been modified. This shift in the extent of the forelimb field is accompanied by shifts in Hox gene expression along the anterior-posterior axis. Furthermore, we found that both fore- and hindlimb fields arise gradually during gastrulation and extension of the embryonic axis, in contrast to the appearance of the limb fields in their entirety in all other known cases. Our results show a surprising evolutionary flexibility in the early limb development program of amniotes and rule out the induction of the limb fields by mature structures such as the somites or mesonephros."
  • 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

thumb|Koala fetus near birth.

  • Females reach maturity at 2 to 3 years of age, males at 3 to 4 years, producing a single young (joey) each year for about 12 years.
  • Gestation is 35 days.
  • Born hairless, blind, and earless. At birth the joey, only a quarter of an inch long, crawls into the downward-facing pouch on the mother's belly (which is closed by a drawstring-like muscle that the mother can tighten at will) and attaches itself to one of the two teats.
  • Young remain hidden in the pouch for about six months, only feeding on milk. During this time they grow ears, eyes, and fur.
  • The joey then begins to explore outside of the pouch. At about this stage it begins 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.
  • The joey will remain with its mother for another six months or so, riding on her back, and feeding on both milk and eucalypt leaves until weaning is complete at about 12 months of age.

References

  1. <pubmed>21098569</pubmed>
  2. <pubmed>20591325</pubmed>
  3. <pubmed>18950846</pubmed>

Reviews

<pubmed></pubmed>


Articles

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