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Biology

Post-coital LH surge in the koala (Phascolarctos cinereus)

Johnston, SD, O’Callaghan, P, Nilsson, K & Curlewis, JD 2001, Proceedings of the 32nd Annual Conference of the Society for Reproductive Biology, 9 - 12 September, Gold Coast, p. 59.

This study puts forward initial evidence of a surge of luteinising hormone (LH) in female koalas. Occurring 24 hours after mating, the observed LH surge is considered to be induced by the act of copulation, though this is yet to be confirmed.

  Previous research has suggested that the luteal phase of the oestrous cycle in female koalas is induced by the act of mating; specifically, the thrusting of the penis into the urogenital sinus. The post-coital luteal phase has previously been confirmed by association with a rise in progestogen. The purpose of this study was to build upon previous findings by measuring plasma LH concentrations to identify a post-coital LH surge. During the breeding season, sexually mature female koalas in a captive population were exposed to one of three stimulus types: a complete act of natural copulation with a male, being mounted by a male but with no penile penetration of the urogenital sinus, or the presence of a nearby male with no physical contact. Blood samples were taken from the koalas before and at several stages after receiving the stimulus, and plasma concentrations of LH measured. This experiment revealed no significant LH surge in any of the koalas within the 12-hour period following stimulation, although one koala that was naturally mated exhibited an increased LH secretion after 24 hours. Following this finding, a second experiment was conducted in which an additional three female koalas were naturally mated and blood samples analysed for LH plasma concentrations over a greater time period post-coitus. This latter group of females all demonstrated a surge of LH between 24 and 32 hours after mating. Given the delay between mating and the commencement of the luteal phase, it may be 48 to 60 hours after mating that ovulation occurs. During this period, the female may be able to store sperm in the reproductive tract for delayed fertilisation.

  Given initial suggestions of a ‘copuloceptive reflex’ in koalas by which the luteal phase and hence ovulation are induced by the act of mating, this study adds weight to previous findings by documenting a phenomenon that was previously only assumed to occur. This finding contributes to understandings of reproduction in the koala and is informative for the reproductive management of captive koala populations.

 

Summarised by Joanna Horsfall

 

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