Why have marsupials flourished in australia

It is currently believed that in marsupials the external reproductive organs, such as scrotum, mammary glands or pouch, are probably controlled directly by the sex chromosome constitution of the tissues involved, especially the X chromosome Cooper, In normal male marsupials, the X chromosome is involved in the development of scrotal bulges, as well as being involved in the production of the mammary glands and pouch in normal females Renfrew et al.

Tammars that are genetically abnormal, XO individuals, have internal female organs but no external female organs, mammary glands or pouch, though they posses a well-developed scrotum, that is empty.

XXY tammars have internal male reproductive organs and a well-developed penis, as a result of having a Y chromosome, but they have mammary glands and a small pouch in place of the scrotum, as they have 2 X chromosomes Sharman et al. Physiological Differences - marsupials vs other mammals. As with other mammals and birds, marsupials maintain a constant body temperature, the basal body temperature BBT , though at a different level than mammals and birds.

The BBTs of the different animal groups ranges from 30 o C in monotremes, Reptiles have a BBT of 30 o C that they maintain by moving between sunlight and shade. The reason for the different BBTs of the various groups is not known, though it appears to be genetically determined.

The BBT of marsupials has as great an effect on their lives as does their reproductive mode. The body temperature of an animal determines the speed of chemical reactions within the animal, the reaction speed approximately doubling for every 10 o C rise in temperature. The SMR of marsupials is , that of placentals is Brain anatomy - placentals vs marsupials. The relationship between marsupial groups, such as the Diprodontia and the Polyprotodontia, that appear similar can be distinguished by studying the links between the 2 halves of the forebrain.

In placentals there are 3 commissures in their brains, nerve tracts linking the 2 halves of the brain. The 2 linking the hemispheres of the forebrain are the larger anterior commissure, also linking the 2 olfactory lobes in the forebrain, and the smaller hippocampal commissure Johnson, The corpus callosum links the 2 halves of the cerebral cortex.

The corpus callosum is lacking in marsupials and monotremes. Among the marsupials, the Diprotodontia have a tract of nerve fibres, the faciculus aberrans, that extends the links of the anterior commissure to link the halves of the cerebral cortex. The Caenolestidae lack this tract, which supports the suggestion that their dentition, similar to that of the Diprotodonts, was probably a case of their dentition arising independently. At the time of writing the brain of Dromiciops had not been studied.

Sperm morphology and anatomy. Relationships among the marsupials can be indicated by the fine structure and morphology of their spermatozoa. The Didelphidae and the Caenolestidae, the 2 main families of American Marsupials, the sperm occur as conjoined pairs, the heads of the 2 spermatozoa being pressed closely together, remaining in this state until reaching the vicinity of the egg in the female's oviduct.

Such conjugation is unknown in any Australian marsupial, and is not known of in any placental. Unlike other American marsupials, Dromiciops also has sperm that is not conjugated, as is the case with Australian marsupials, adding further support to the notion that there were close links between the Australian and American marsupials.

In mammals, the sex chromosomes are a single pair of chromosomes carrying genes determining the sexual differentiation. The X chromosome, usually of normal size, also contains many genes not directly connected with sexual differentiation. The Y chromosome is usually very small and contains few genes not connected with sex determination. It has been suggested that the marsupial pattern is the original, primitive condition, additional sections of an autosome becoming attached to the X and Y chromosomes at some early stage in the evolution of placentals Jennifer Graves, The female potoroo Potorous tredactylus , has 10 autosomes and 2 large X chromosomes.

Males of this species have 10 autosomes, 1 large X chromosome, as well as 1 large Y and 1 small Y chromosome. The large Y chromosome is the remaining half of the autosome that fused with the original X chromosome, pairing at meiosis with 1 arm of the Large X chromosome, the small Y chromosome pairing with the other arm of the X chromosome. It is believed a similar process occurred in the swamp wallaby, with 8 autosomes, 1 large X chromosome, 1 large Y and 1 small Y chromosome.

The sequence of events involved has been determined by the use of chromosome painting , the addition of antibodies to the chromosomes of tammar wallabies.

The long arm of the X chromosome and the whole of the large Y chromosome are homologous with chromosomes 2 and 7 of the tammar, while only the short arm of the the X is homologous with the X chromosome of the tammar Toder et al.

In mammals the females have 2 X chromosomes, 1 from each parent, each of which has the same complement of genes, so the females get 2 of every gene, whereas the males have a single copy of each X chromosome gene, that invariably came from their mother. The last major drought in the mids reduced the kangaroo population to just seven million. Proponents of kangaroo hunting also note the benefits of kangaroo meat compared to more traditional beef or other livestock, reports BBC News, noting that it's low in fat and that kangaroos produce much less methane than farm animals.

Australia is no stranger to the perils of animal overpopulation. One menace is cane toads , a North American poisonous amphibian introduced to Australia in the s by farmers as pest control for sugar cane crops.

The populations have grown out of control and is now an infamous example of the perils of invasive species—even inspiring a cult classic documentary still shown to many biology students. Similarly, rabbits have had a devastating impact on the environment.

Introduced in for hunters to chase down, the fuzzy critters have been proliferating and munching on Australia's greens ever since. For instance, marsupials and their close relatives evolved into bear- and weasel-size carnivores, and one even evolved saber teeth. Others evolved to eat fruits and seeds. Many of these marsupials went extinct between then and now, but South America is still a marsupial hotspot today.

There are more than species of opossums, seven species of shrew opossums and the adorable monito del monte Dromiciops gliroides , whose Spanish name translates to "little monkey of the mountain. On a side note, within the last 1 million years, one of South America's opossums traveled north and now lives in North America. This is the Virginia opossum Didelphis virginiana , the only marsupial living north of Mexico, Beck said. Also, opossums belong to a different order than possums.

Possums are native to Australia and New Guinea, are closely related to kangaroos, and have a number of anatomical differences, such as enlarged lower incisors, that the South American opossum lacks, Beck said. So, how did marsupials get from South America to Australia? Up until about 40 million to 35 million years ago, both South America and Australia were connected to Antarctica, forming one giant land mass. At that time, Antarctica wasn't covered with ice, but instead with a temperate rainforest, and "it was not a bad place to live," Beck said.

It appears that marsupials and their relatives bounded down from South America, strode across Antarctica and wound up in Australia, Beck said. Scientists have long thought that when placental and marsupial mammals compete for resources, the placentals win. Before Tingamarra was found, it was thought that marsupials had done well in Australia because for many millions of years they had no placentals to compete with.

Discovery of Tingamarra surprised scientists, because it meant that placental mammals were indeed in Australia many millions of years ago, and the marsupials had flourished anyway. The Australian Museum respects and acknowledges the Gadigal people as the First Peoples and Traditional Custodians of the land and waterways on which the Museum stands. Image credit: gadigal yilimung shield made by Uncle Charles Chicka Madden.