Koala Development
Introduction
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
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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
Development Overview
- 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)
- mucoid coat
- outer shell coat.
- an additional extracellular matrix coat that lines the zona pellucida also occurs in some species.
- 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
Reviews
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Articles
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Books
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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: Phascolarctos cinereus | Koala development | marsupial development