Marsupials such as the kangaroo and koala began to diversify in Australia millions of years ago, from species in the same group that lived in South America, according to a recent hypothesis that has gained momentum. This approach argues that the Brazilian marsupials - the best known are the skunk, the opossum, and the shorttail - form the oldest branch of this group of animals that still have living representatives. The lineages that lived in Europe or Asia have become extinct (only one species lives in the United States and Canada), and only those from South America and Australia remain.
This view, reinforced by a study by researchers from the German University of Münster, published in July 2010 in the journal PLoS Biology, indicates that the branch of marsupials that encompasses Brazilian species gave rise to another, which currently has only a living species, which is the mountain monkey (Dromiciops glories), an animal of up to 25 grams from the mountains of Chile and Argentina. This small animal may be the most distant living relative of the nearly 200 species of Australian marsupials, including the larger varieties of
s, which can weigh 70 kilograms.
Genetically, says Ariovaldo Cruz Neto, a kangaroo researcher at the São Paulo State University (Unesp) of Rio Claro who studies these animals in collaboration with Australian colleagues, the monkey exhibits a greater degree of kinship with Australian species than with those of South America. South. The Brazilian marsupials, although they are older, are not more closely related to any of those living in Australia. According to another hypothesis, presented in 2008 in PLoS One by a group from the Australian University of New South Wales, the species that originated the Australian marsupials would have been another, Djarthia murgonensis, which lived 30 million years ago in the east of a supercontinent that included present-day South America and Australia.
Despite the distance, American and Australian marsupials bear other similarities besides the fact that their young are born incomplete, hairless and blind, after a gestation of one or two weeks, and they go towards the mother's teats, normally protected by a bag called a pouch, where they grow for another two to three months before seeing the light. Cruz Neto and his collaborators from Australia verified that the organism of the South American and Australian marsupials works in a very similar way to produce and burn energy, regardless of the size or type of environment in which they live.
Most of the nearly 90 species of marsupials in America weigh between 10 grams and 1 kg, generally live in forests, and feed primarily on insects. Meanwhile, a kangaroo can have the bearing of an adult male, although the smallest of the 21 species in this group weighs 400 grams. In Australia, marsupials live in tunnels, in the desert or in rainforests, and, like the Americans, they feed mainly on invertebrates and small fruits, although one species prefers nectar and the other is carnivorous.
Similar organisms
The researchers examined the metabolism of representatives of two species of South American possums, Gracilinanus agilis and Micoureus Paraguayans. The first exhibited an average body temperature of 33.5 ° Celsius, and the other, 33.3 ° Celsius, at least two degrees below the average temperature of placental mammals, the group to which we belong. Another measure was the basal metabolic rate, which indicates the minimum level of energy that the animal needs to maintain the vital functions of the body. To maintain this index, each of both species spends, respectively, 4.8 kilocalories (kcal) and 5.5 kcal per day.
The body temperature and metabolic rate of the two Brazilian marsupials were very close to those of other Australian marsupials that had already been tested. From a physiological point of view, says Cruz Neto, once a marsupial, always a marsupial, despite millions of years of independent evolution and the differences in diet and habitat of the species that live in South America and Australia.. According to him, apparently, there has been no selective pressure that resulted in the modification of the physiological plane, which was enough for these animals to colonize Australia. It's as if marsupials have suitcases with clothes that allow them to live in different environments.
South American marsupials, although less different from other than Australians, exhibit subtle and relevant distinctions in size and shape of the skull, jaw, scapula, and pelvis, which express their eating habits and the environments in which they live. . Diego Astúa, a professor at the Federal University of Pernambuco, compared the measurements of the skulls of 2,932 animals of the didélfidos family, which includes most of the Brazilian marsupials, those that live in the Andes and the little monkey of the mountain. In a work published in 2010, he showed that half of the dolphin's exhibit differences in size and in the shape of the skull. In all cases, the males were more stubborn than the females.
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