Uncertain breeding: a short history of reproduction in monotremes.

Although much is known about the biology of monotremes, many important aspects of their reproduction remain unclear. Studies over the last century have provided valuable information on various aspects of monotreme reproduction including the structure and function of their reproductive system, breeding behaviour, sex determination and seasonality. All three living genera of monotremes have been successfully maintained in captivity, often for long periods, yet breeding has been rare and unpredictable. When breeding has occurred, however, significant gains in knowledge have ensued; for example a more accurate estimate of the gestation period of the platypus and the incubation period for the Tachyglossus egg. One of the great challenges for zoos has been to understand why breeding of monotremes is difficult to achieve. Analysis of breeding successes of platypuses and short-beaked echidnas provides some insights. The evidence suggests that although annual breeding seasons are regionally predictable, individual adult females breed unpredictably, with some showing breeding intervals of many years. The reason for this variation in individual breeding intervals may be resource-dependant, influenced by social factors or may even be genetically induced. Better knowledge of factors that influence breeding intervals may improve the success of monotreme captive breeding programmes. More certainty in captive breeding is also an important issue for enterprises wishing to trade in Australian wildlife since current legislation limits export of Australian fauna for display to at least second-generation captive-bred individuals. Given their unique evolutionary position, knowledge of reproduction in monotremes needs to be gained in advance of any future population declines so that appropriate strategies can be developed to ensure their survival.