Marsupial and monotreme milk-a review of its nutrient and immune properties

All mammals are characterized by the ability of females to produce milk. Marsupial (metatherian) and monotreme (prototherian) young are born in a highly altricial state and rely on their mother’s milk for the first part of their life. Here we review the role and importance of milk in marsupial and monotreme development. Milk is the primary source of sustenance for young marsupials and monotremes and its composition varies at different stages of development. We applied nutritional geometry techniques to a limited number of species with values available to analyze changes in macronutrient composition of milk at different stages. Macronutrient energy composition of marsupial milk varies between species and changes concentration during the course of lactation. As well as nourishment, marsupial and monotreme milk supplies growth and immune factors. Neonates are unable to mount a specific immune response shortly after birth and therefore rely on immunoglobulins, immunological cells and other immunologically important molecules transferred through milk. Milk is also essential to the development of the maternal-young bond and is achieved through feedback systems and odor preferences in eutherian mammals. However, we have much to learn about the role of milk in marsupial and monotreme mother-young bonding. Further research is warranted in gaining a better understanding of the role of milk as a source of nutrition, developmental factors and immunity, in a broader range of marsupial species, and monotremes.

Habitats modified for tourism affect the movement patterns of an endemic marsupial, the Rottnest Island quokka (Setonix brachyurus)

The quokka (Setonix brachyurus), an iconic marsupial endemic to Western Australia, is listed as vulnerable. It is found at its greatest abundance on Rottnest Island, where little is known about its home range and movement patterns. We estimated the home ranges of 22 male and 23 female quokkas within each season in four habitat types on Rottnest Island: coastal dune, grass/heath, woodland and settlement areas developed for tourism. We also tested for factors affecting home range and space use. The mean seasonal home-range size of quokkas was 1.91 ± 0.23 ha, and there was no effect of sex or weight, habitat type or wet or dry periods on the size of the home ranges. Home-range overlap during both night and day was significantly lower in the settlement (25.9%), compared with costal dunes (78.5%), woodlands (70.3%) and grass/heath (66.6%). This was due to feeding and resting sites being spatially separated, with quokkas resting outside of the settled areas during the day and travelling back to these areas to feed at night. This research demonstrates how tourism development can impact on the behaviour and movement patterns of local species and will inform future management of the quokka on Rottnest Island.

Spatial ecology of the quokka (Setonix brachyurus) in the southern forests of Western Australia: implications for the maintenance, or restoration, of functional metapopulations

We used radio-telemetry to investigate the home-range size and movement patterns of the quokka (Setonix brachyurus) in the southern forests of Western Australia to assess the ability of animals to move between increasingly segregated habitat patches and to identify implications for metapopulation function. We found that quokkas in this region have a much larger home range (71 ± 5.8 ha) and move larger distances (up to 10 km per night) than previously reported for this species in other regions. Temporal and sex variations in home-range size, overlap and movement patterns provided insights into the social structure, reproductive strategies and resource availability for the species in this part of its range. Quokkas moved up to 14 km between habitat patches, where these patches were connected by dense riparian vegetation. While riparian vegetation was used exclusively for movement between habitat patches, quokkas spent only 40% of their time in this ecotype. The current management paradigm of protecting linear riparian vegetation as habitat for quokkas is important for maintaining habitat connectivity, but is unlikely to meet broader habitat and spatial requirements. Management of preferred habitat as well as riparian corridors is necessary for the maintenance of a functional metapopulation.

The tammar wallaby: a non-traditional animal model to study growth axis maturation

Maturation of the growth hormone (GH)/insulin-like growth factor 1 (IGF1) axis is a critical developmental event that becomes functional over the peripartum period in precocial eutherian mammals such as sheep. In mice and marsupials that give birth to altricial young, the GH/IGF1 axis matures well after birth, suggesting that functional maturation is associated with developmental stage, not parturition. Recent foster-forward studies in one marsupial, the tammar wallaby (Macropus eugenii), have corroborated this hypothesis. 'Fostering' tammar young not only markedly accelerates their development and growth rates, but also affects the timing of maturation of the growth axis compared with normal growing young, providing a novel non-traditional animal model for nutritional manipulation. This review discusses how nutrition affects the maturation of the growth axis in marsupials compared with traditional eutherian animal models.

Effects of nutritional manipulation on body composition in the developing marsupial, Macropus eugenii

When 60-day-old tammar wallaby pouch young (Macropus eugenii) are fostered to mothers at 120 days of lactation, their growth, developmental rate and maturation of their GH/IGF axes are markedly accelerated. To determine the effect of fostering on energy intake, body composition and fat accretion, we first measured total body fat and lean mass in these young. Next, we mimicked the triglyceride oleic and palmitic acid composition of 120-day milk by supplementing 60 day young with these fatty acids and comparing their growth with that of growth accelerated young. There was no difference in the weight or growth axis maturation of supplemented young but there was significantly more body fat in these and in the growth-accelerated fostered young than in controls. We conclude that the accelerated growth and GH/IGF axis maturation observed previously in fostered young is most likely due to increased milk consumption and earlier access to specific nutrients.

Consumption of milk by quokka (Setonix brachyurus) young

We investigated the consumption of milk by the young quokka using the stable isotope deuterium oxide. The volume of milk consumed increased from 1.6 mL day–1 at 55 days post partum to 32.5 mL day–1 at 165 days. The daily energy intake ranged from ~22 to 151 kJ day–1 during pouch life. The crude growth efficiency (grams of growth per millilitre of milk consumed) increased from an average of 0.35 to 0.46 g mL–1 in the early stages of pouch life, and then decreased to 0.24 g mL–1 during Phase 2b of lactation. The crude growth efficiency measured in our study indicates that quokkas are equally efficient in converting milk energy to body mass as other marsupials reported in the literature. Measuring milk intake with this method offers a non-toxic, minimally invasive alternative to other techniques for measuring milk consumption in marsupials, when milk is the only source of water intake.