An investigation into the unique anatomy, physiology, natural history and management of Australian marsupials and monotremes. The University of Queensland my. Search this site Search UQ. Home Biology of Australian Marsupials and Monotremes. Print Feedback. Course level Undergraduate Faculties are the major organisational units with responsibility for academic programs. In some species the marsupium is present and in others it is simply reduced to folds of skin that cover the nipples.
Opossums generally have long tails that are often capable of holding or grasping objects such as tree branches. Most species live primarily within trees on a diet of leaves and insects. Some species also feed on birds and their eggs. The lutrine opossum from the genus Lutreolina lives a semi-aquatic life and has a carnivorous diet feeding primarily on insects. Within Australia, possums are familiar animals in many settings as they are very opportunisitc and find ways to take advantage from many human activities.
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The brush-tail possum is a nocturnal marsupial that feeds primarily on plant material but also eats insects, small birds and eggs. It has a long dark black tail and grows to around 6 kg. Kangaroos and wallabies belong to the family Macropodidae which also includes euros. The smallest wallaby, the rock wallaby Petrogale burbidgei , weighs up to 1.
Both animals are specialized jumpers and kangaroos are the only large mammals that move by hopping on two legs. Ecologically, kangaroos fill a similar niche to the jumping ungulates in other continents such as antelopes and spring boks in Africa. Found only in eastern Australia, the koala is the only member of the family Phascolarctidae. Koalas are rather large marsupials and weigh up to 12 kg. Due to the fact that koalas feed only on the toxic and energy poor leaves of Eucalyptus trees, they are very inactive and move slowly which helps to reduce their energy expenditure.
Koalas live solitary lives and have home ranges that can sometimes overlap. Relative to other marsupials, the koala require a long time to reach maturity. The three species of wombats come from a single family known as Vombatidae. Many of their structural features, such as their skull, teeth and faces, are very similar to those of rodents. They have short and powerful limbs and an almost absent tail.
Mikkelsen et al. This could potentially explain the substantial conservation of X-chromosome synteny in eutherians.
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It will be interesting to see how stable the X chromosome is within marsupials. On a different note, Mikkelsen et al. This is interpreted to result from a reduced ability of GC-biased gene conversion to counterbalance AT-biased mutation rate in the opossum [ 15 ].
The plausibility of this interpretation arises from linkage data showing that recombination within opossum autosomes is substantially lower than that observed in other amniotes, as well as observations that the opossum has lower rates of gene and segmental duplication [ 6 ]. Hence, lowered recombination rates in opossum are interpreted to result in less gene conversion and, consequently, in a shift in nucleotide base composition towards AT.
Further evidence for this hypothesis is provided by the X chromosome, in which the recombination rate is most similar to that observed in placentals and the GC content is almost twice that in opossum autosomes and well within the GC range observed in placental X chromosomes. One temptation when interpreting marsupial-placental dichotomies is to take the marsupial state as ancestral or somehow more primitive.
Difficulties in the cloning of opossum homologs of human immunity-related genes, such as those in the major histocompatibility complex MHC , led to early suggestions that marsupials possessed a primitive immune system, with a level of complexity matching that of fish and birds.
This notion has surely been dispelled by the publication of the opossum genome [ 6 ] and some of its companion papers [ 16 , 17 ], which find that the complexity of the opossum immune system matches that of placental mammals. The difficulties in identifying and cloning marsupial MHC genes were possibly due to a high rate of innovation and divergence in genes of the immune system. Finally, it is worth remembering that, as in many other eukaryotic genomes [ 18 ], large heterochromatic regions remain unsequenced in the opossum genome.
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These segments defy conventional methods of sequencing and assembly and understandably lag behind the determination of euchromatic segments. They include, for example, Y-chromosome sequences that remain an enormous challenge to sequence analyses in many species, including mammals [ 19 ] and flies [ 20 ].
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A similar situation also occurs within other heterochromatic regions, such as those found within centromeres. Thus, it is fair to say that the physical gap represented by all heterochromatic regions of all genomes is matched by a knowledge gap of the genes and functional regions within them.
Eventual elucidation of these segments will help further our understanding of the role of heterochromatin in eukaryotic genomic structure and regulation. The opossum genome [ 6 ] highlights two central themes in eukaryotic genome evolution. First, it stresses the similarity of the complement of protein-coding genes across a large number of eukaryotic genomes.
Second, it emphasizes the prominent role that differential expression of this protein set has on shaping physiological, morphological and behavioral differences across taxa. Hence, differences in the timing, location and expression level of a common set of genes appear to have led marsupials and placentals to take distinct paths towards developing a mammal, radically different in many aspects of gestation, embryogenesis and lactation.
What is most intriguing, however, is that many marsupials have evolved life histories and morphological adaptations that are strikingly similar to those evolved independently by placental mammals.
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Uncovering the regulatory changes underlying these major differences, together with those instances of striking convergence, promises to be fascinating. It can only be made more interesting and potentially informative with the addition of new genomes, some of which are already on their way, including those of a monotreme the platypus Ornithorhynchus anatinus and another marsupial the tammar wallaby Macropus eugenii.
In particular, M. This makes these two pairs ideally suited for providing valuable insights into the patterns of structural and regulatory genome evolution within and between each of these groups. Eventually, the integration of sequence data with phenotypic information will be crucial to interpreting the findings from comparative genome analyses. Relevant phenotypic information includes, for instance, genome-wide chromatin and gene-expression data with anatomical and developmental resolution that will inform both the biology and radiation of opossums as well as our own.
Mol Phylogenet Evol. Kirsch JAW: The classification of marsupials with special reference to karyotypes and serum proteins. The Biology of Marsupials. Edited by: Hunsaker D.
Samollow PB: Status and applications of genomic resources for the gray, short-tailed opossum, Monodelphis domestica , an American marsupial model for comparative biology. Aust J Zool. Tyndale-Biscoe H: Life of Marsupials. Evol Dev.
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