Cross-fostering for the conservation of rat-kangaroos (Marsupialia: Potoroidae)

Cross-fostering is an assisted reproductive method that has been used to improve the_ productivity of endangered marsupial fauna. Pouch young from endangered species are transferred to the pouch of related common species, allowing the donor female to produce further offspring without going through the entire lactation cycle. In this project I tested the applicability of cross-fostering in rat-kangaroos (family Potoroidae) using the Tasmanian bettong (Bettongia gaimardt) and the Longnosed potoroo (Potorous tridacty/us) as model species. The effect of a 'transfer age difference' (TAD) between transferred young was investigated to determine the most beneficial time for pouch young transfer: optimising both the mother's reproductive rate and young's survival to independence. Thirty two young were transferred, 18 intra-species and 14 inter-species. The transfers were carried out at various stages of pouch life (1 to 11 weeks) with TADs ranging from 0 to 3 weeks. Nutritional analyses were undertaken on 460 milk samples. Growth measurements and development data were obtained for 110 bettong and 46 potoroo young. The effect of cross-fostering on species specific behaviour patterns was investigated using both video-recordings and direct observations. Twenty one young survived and 19 subsequently bred successfully. Milk composition and production rates did not appear to be affected by transfers. Comparisons of growth rates between cross-fostered and either fostered or untransferred young showed an advantage for cross-fostered potoroos and a disadvantage for cross-fostered bettong. These were most pronounced during the period between pouch vacation and weaning. During asynchronous intraspecies transfers the younger of the two transferees grew faster than untransferred bettong young. The magnitude of both these effects increased with TAD up to an age difference of three weeks when growth related problems appeared. Although cross-fostered young were influenced by transfer mothers' behaviour, they developed normal pecies-specific behaviour. Difficulties in reuniting cross-fostered young with their own species were probably a consequence of different levels of sociability in the two species. At maturity, all surviving transfer young were successful in both mate recognition and production of offspring. Growth and development of the transfer young are affected by the design of the fransfer procedure. The combination of species, temperament and experience of the transfer mother; the age of young at transfer arid the TAD all affect the outcome. The accessibility of the young in the pouch enables progress monitoring and, where required, early intervention for repeated transfers and/or hand-rearing. Recommendations for the management of transfer animals in captivity are provided.