Often regarded as the strangest mammal in the world, the Australian beaver-like duck lip platypus exhibits a number of strange features: it lays eggs instead of laying live babies, suckling milk, it has toxic spores and even contains 10 sex chromosomes. Now, an international team of researchers led by the University of Copenhagen has conducted a unique mapping of the platypus genome and found answers as to where some of its alien traits came from.
It lays eggs, but has nurses, is toothless, has a poisonous spur, has woven legs, shining fur and has 10 sex chromosomes. Ever since Europeans discovered the platypus in Australia in the late 1700s, the strange creature, duck, semiaquatic lips has bothered scientific researchers.
Today’s researchers are still trying to understand why the platypus – often considered the strangest mammal in the world – needed to be so special. The understanding has now improved, for the most part. For the first time, an international team of researchers, led by biologists from the University of Copenhagen, has mapped the entire platypus genome. The study is published in the scientific journal, Nature.
“The whole genome has given us answers to how some of the strange features of platypus have emerged. At the same time, encoding the genome for platypus is important for our understanding of how other mammals evolved – we holds the key to why we and other eutheria mammals became young live – laying animals instead of egg – laying animals, “explained Dr Guojie Zhang from the Department of the Eutheria. Biology.
The platypus belongs to an ancient group of mammals – monotremes – that existed millions of years before any modern mammal appeared.
“Of course, the platypus belongs to the class Mammalia. But genetically, it is a mixture of mammals, birds and reptiles. It retained many of the original features of its ancestors – which may contribute to its success in breeding. change to the environment in which they live, “says Dr Zhang.
Losing eggs, skimming milk and toothless
One of the most unusual features of platypus is that, although it lays eggs, it also contains raspberry glands that are used to feed its babies, not through nipples, but with milk – sweat from his body.
During our own evolution, humans lost all three so-called vitellogenin genes, each of which is important for the production of egg yolks. On the other hand, all three are still there. The study shows that platypuses still carry one of these three vitellogenin genes, despite losing the other two about 130 million years ago. The platypus continues to lay eggs as a result of the only remaining gene. This may be because it is not as dependent on the formation of yolk proteins as birds and reptiles, as platypuses produce milk for their offspring.
In all other mammals, casein genes have been replaced by vitellogenin genes, which are responsible for our ability to produce casein protein, a key component in mammalian milk. The new research shows that platypus also carry casein genes, so their milk combination is very similar to that of cattle, humans and other mammals.
“It tells us that milk production in all developed mammal species was developed through the same set of genes derived from a common ancestor who lived more than 170 million years ago – along with the dinosaurs. early Jurassic, “says Guojie Zhang.
Another feature that makes the platypus so special is that, unlike most mammals, it is toothless. Although teeth were given to the ancestors closest to these monotremes, the modern platypus is equipped with two horn plates that are used for shredding food. The study states that platypus lost its teeth about 120 million years ago, when four of the eight genes responsible for tooth development disappeared.
The same animal with 10 sex chromosomes
But another strange thing the researchers did is examine how their gender is determined. Humans and all other mammals on Earth have two sex-determining chromosomes – the X and Y chromosome system in which XX are female and XY male. The monotremes, however, include our duck-billed friends from Down Under, with 10 sex chromosomes, with five Y chromosomes and five X.
Thanks to the almost complete chromosomal stage genomes, researchers can now say that these 10 sex chromosomes in the ancestors of the monotremes were organized in the form of a ring that was subsequently broken down into many small fragments of X and Y chromosomes. At the same time, genome mapping reveals that most monotreme sex chromosomes are more common with hens than they are with humans. But what it does show is that mammals and birds are evolved.
PLATYPUS INFORMATION
- The platypus is endemic to eastern Australia and Tasmania. It is a protected species and classified by the IUCN as near-threatened.
- Reasons why platypuses are considered mammals include: they have raspberry glands, they grow hair and they have three bones in their middle ears. Each draw helps define a mammal.
- The platypus belongs to the monotreme mammal order, so named because monotremes use a single opening for urination, defecation and sexual reproduction.
- The animal is a good swimmer and spends much of its time hunting for insects and shellfish in rivers.
- Its distinctive beak is filled with electric sensors that are used to detect prey in muddy river beds.
- The male platypus has a poisonous spur on the back of each leg. The poison is poisonous enough to kill a dog and is applied when males fight for land.
- Another study in 2020 showed that platypus fur is fluorescent. The brown fur of the animal shows a blue-green color when exposed to UV light. (source: https: /
/ )doi. org / 10. 1515 / mammalia-2020-0027
FINALLY THE INSPECTION
- Advanced gene technology that combines several advanced techniques has allowed the near-complete genome research team at the chromosomal level both from the platypus and its cousin, the echidna– the same two types of animals monotreme is currently live. The gene data fills 90 percent of the gaps in previous genetic mapping. More than 96% of genome sequences are now embedded in chromosomes.
- The researchers have compared the genes and monotreme genomes from chickens, humans, rats, Tasmanian devils and lizards.
- In addition to Yang Zhou (lead author) and Guojie Zhang from the University of Copenhagen, the research was conducted by, among others: Linda Shearwin-Whyatt from the University of Adelaide (Australia) and Jing Li from Zhejiang University (China). A full list of authors can be found in the research article.
- The study was published in the prestigious scientific journal, Nature.
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