Cross-fostering is the rearing of young by a surrogate mother of a different taxon. In marsupials this technique has been used to study lactation as well as pouch young growth and development. Recently, cross-fostering and short-term pouch young isolation have been used by wildlife agencies and zoos to increase female reproductive rates and fecundity, and to manage the genetics of captive and wild animals as part of wider conservation and management strategies for macropodoid marsupials. Data on cross-fostering are now available for six potoroid and 13 macropodid species. Success of cross-fostering studies between donor and foster species varies widely from complete failure to an eight-fold increase in the production of pouch young annually. Factors implicated in successful cross-fostering include relative size of donor and surrogate females, size of pouch young at weaning, differences in length of pouch life between species and size differences between donor young and those of the surrogate species at transfer. Studies have shown that females regulate milk composition and production irrespective of pouch young age, and that transfer of donor young to species with more immature or advanced mammary glands will result in a slowing or an acceleration of pouch young growth and development, and affect the duration of pouch life. Small pouch young tolerate short-term isolation from the pouch at a range of temperatures, provided high humidity is maintained throughout the period of isolation. Maintenance of pouch young at temperatures lower than those that occur in the pouch (23 degrees C compared with 37 degrees C) during isolation reduces the pouch young's basal metabolic rate, oxygen consumption and evaporative water loss and thus improves survival rates of very small pouch young. The success of these techniques in managing population genetics and accelerating breeding in donor species within the Macropodoidea are enhanced by post-partum oestrus and mating after the removal of pouch young, and the reactivation and birth of the diapausing embryo. This chapter reviews the available data on cross-fostering and pouch young isolation in macropodoid marsupials, and examines use of these techniques in the conservation and management of species in this group.

Mammalian dispersal tends to be male-biased although female-biased dispersal has also been reported in a range of taxa. Most of our knowledge on mammalian sex-biased dispersal is based on studies of eutherians and less work has been done on the direction and causes of sex-biased dispersal in marsupials. This study investigated dispersal of swamp wallabies between two habitat patches in South Gippsland, Victoria, using genetic methods. A Bayesian clustering test showed a high level of genetic exchange between the two habitat patches despite their separation by 10–17 km of cleared land, a creek and a highway. Females in the overall sample were more closely related to each other than males were to each other and females within habitat patches were more closely related than females between habitat patches whereas the converse was true for males. Bayesian inference showed that more males were migrating from the east to the west habitat patch whereas the converse was true for females and the male migration rate was higher than the female migration rate. The differential migration rate did not cause a significant difference in relatedness between patches in females but it did in males. These relatedness and migration patterns indicate that dispersal in the swamp wallaby is male-biased.

The swamp wallaby (Wallabia bicolor) is a common, medium-sized, browsing macropodid marsupial that is unique in many ways. Relatively little is known about the reproductive biology of this species. Previous studies have proposed that the swamp wallaby has a pre-partum oestrus because the gestation period (x = 35.5 days, n = 4) is on average longer than the oestrus period (x = 31.0 days, n = 5) and the period from the removal of pouch young (RPY) to mating (x = 26.0 days, n = 3). In the current study, the period from RPY to birth was confirmed at x = 31.25 days (n = 4) in captive animals, consistent with a pre-partum oestrus. A growth curve for swamp wallaby pouch young was constructed from the progeny of captive animals to estimate the age and date of birth of young in a wild, culled population in South Gippsland, Victoria, and the reproduction of females in the wild throughout the year was examined. Young were born in every month of the year, with no statistically significant variation in the number of young born in each month. Females did not have a period of seasonal anoestrus and conceived throughout the year. Female swamp wallabies in South Gippsland bred continuously throughout the period of this study.

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.