Australia: The Land Where Time Began

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Marsupial Reproduction Patterns - Classification

Sharman et al. (1966) was the first to classify the reproductive patterns of marsupials, recognising 4 groups. With the accumulation of more information it was concluded that Group 1, that is exemplified by Trichosurus vulpecula, of their classification represents the basic reproduction pattern of marsupials (Tyndale-Biscoe, 1984). It was also concluded that Group 2, exemplified by Setonix brachyurus, represented the only departure from the basic pattern that was significant (Tyndale-Biscoe, 1984). The authors¹ suggest that the pattern of the peramelids is distinct enough from the basic marsupial pattern to indicate they should have a separate classification, and results from new information on the Burramyidae and Tarsipes suggests they also should also be classified separately. The authors¹ suggest the patterns of the peramelids, Burramyidae and Tarsipes can all be derived from the basic marsupial pattern. They have defined the 4 groups that follow.

Group 1 Marsupials that are polyoestrous and polyovular in which gestation lasts less than the oestrous cycle and coincides with the luteal phase. In Antechinus monoestry is an adaptation derived from this to suit it to special ecological constraints. In the folivorous species the monovular condition is derived. Didelphidae, Dasyuridae, Petauridae and Phalangeridae.

Group 2 Marsupials that are polyoestrous and polyovular in which gestation is shorter than the luteal phase, which is prolonged into lactation. There is also a well-developed chorioallantoic placenta. Peramelidae and Thylacomyidae.

Group 3 Marsupials that are polyoestrous and polyovular in which gestation extends into the follicular phase and occupies 94-109 % of the oestrous cycle. Ovulation is post partum, rarely pre-partum, with subsequent inhibition of the corpus luteum and embryonic diapause. 3i is an intermediate group that have an extended gestation but within a luteal phase that is extended, gestation is 80-88 % of the long oestrous cycle. There is rarely postpartum ovulation, and when it does occur there is inhibition of the corpus luteum and embryonic diapause occurs. Macropodidae and Potoroidae.

Group 4 Marsupials that are polyoestrous and polytocous, and have a pre-luteal phase and gestation that is very prolonged, including a long period of embryonic diapause. The authors¹ say it is not clear whether diapause is obligatory or is associated with concurrent lactation. Burramyidae, except Burramys that has the Group 1 pattern, and Tarsipedidae.

 

Sources & Further reading

  1. Tyndale-Biscoe, Hugh & Renfree, Marilyn, 1987, Reproductive Physiology of Marsupials, Cambridge University Press.
Author: M. H. Monroe
Email:  admin@austhrutime.com
Last Updated 26/05/2012

 

 

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading