Koala Development

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

• 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. Koalas were monitored every 4-12 weeks for births. Plasma progesterone was measured and a cytological smear of the urogenital sinus was taken. Fertility was high in the control group and the two etonogestrel-treated groups, with approximately 90% of females giving birth. In contrast, no levonorgestrel-treated female produced young during the study. Removal of levonorgestrel implants from six females reversed the contraceptive effect in the next breeding season, whereas the eight females in which the levonorgestrel implants were left in remained infertile for six breeding seasons. Vaginal cytology showed evidence of oestrous cycles during the breeding season in all females from all groups and there was no difference seen in the prevalence of cornified epithelial cells in the oestrous smears. This indirectly suggests that levonorgestrel does not prevent follicular development and oestrous cycling. 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."

Development Overview

• 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

Reviews

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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: Koala development | marsupial development

External Links

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