The Platypus
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The Platypus (Ornithorhynchus anatinus) is a semi - aquatic animal endemic to eastern australia, including Tazmania. Together with the four species of echidna, it is one of the five extant species of menotremes, the only mammals that lat eggs instead of giving birth to live young. It is the sole living representative of its family (Ornithorhynchidae) and genus (Ornithorhynchus), though a number of relates animal have been found in the fossil record.The bizarre appearance of this egg-laying, venomous, ducks-billed, beaver-tailed,otter-footed mammal baffled European naturalists when they first encountered it, with some considering it an elaborate fraud. It is one of the few venomous mammals ; the male Platypus has a spur on the hind foot that delivers a venom capable of causing severe pain to humans. The unique features of the Platypus make it an important subject in the study of evolutionary biology and a recognisable and iconic symbol of Australia; it has appeared as a mascot at national events and is featured on the reverse of the Austtralian 20 cent coin.The platypus (Ornithorhynchus anatinus) is an Australian icon. It is an integral part of the biodiversity of many eastern Australian freshwater ecosystems and is protected by legislation in all States in which it occurs. Its conservation is of considerable importance not only because of its unique features, status and niche but also because it is the only living representative of a significant lineage of platypus-like animals with a 60 million year fossil history. As a result of its specific habitat requirements it is affected by many of the widely recognised threatening processes operating in Australian limnological systems. In spite of these threatening processes, the species has continued to inhabit and reproduce in considerably degraded environments. The present overall distribution of the platypus appears to be little different from pre-European times. There are, however, now almost certainly no naturally occurring populations in South Australia, where it once occurred, and its distribution has apparently shrunk in the lower reaches of the Murray and Murrumbidgee River systems in Victoria and New South Wales. Despite being considered common throughout its current distribution its abundance is not readily measured and therefore its future conservation status is not easily predicted. Several studies have reported fragmentation of platypus distribution within individual river systems. This has been attributed to poor land management practices associated with stream bank erosion, loss of riparian vegetation and channel sedimentation. There is currently also evidence for adverse effects of river regulation and impoundments, introduced species, poor water quality, fisheries by-catch mortality and disease on platypus populations, but none of these has been well studied. Investigations of these aspects of the species' biology and interaction with human activities are research priorities, while management priorities include the development and implementation of strategies aimed at reducing the effects of these human activities on the platypus and its habitat.
An international consortium of scientists, led by Washington University School of Medicine in St. Louis, has decoded the genome of the platypus, showing that the animal's peculiar mix of features is reflected in its DNA. An analysis of the genome, published today in the journal Nature, can help scientists piece together a more complete picture of the evolution of all mammals, including humans.
The platypus, classified as a mammal because it produces milk and is covered in a coat of fur, also possesses features of reptiles, birds and their common ancestors, along with some curious attributes of its own. One of only two mammals that lays eggs, the platypus also sports a duck-like bill that holds a sophisticated electrosensory system used to forage for food underwater. Males possess hind leg spurs that can deliver pain-inducing venom to its foes competing for a mate or territory during the breeding season.
"The fascinating mix of features in the platypus genome provides many clues to the function and evolution of all mammalian genomes," says Richard K. Wilson, Ph.D., director of the The Genome Center at Washington University and the paper's senior author. "By comparing the platypus genome to other mammalian genomes, we'll be able to study genes that have been conserved throughout evolution."
The platypus represents the earliest offshoot of the mammalian lineage some 166 million years ago from primitive ancestors that had features of both mammals and reptiles. "What is unique about the platypus is that it has retained a large overlap between two very different classifications, while later mammals lost the features of reptiles," says Wes Warren, Ph.D., an assistant professor of genetics, who led the project.
Comparison of the platypus genome with the DNA of humans and other mammals, which diverged later, and the genomes of birds, whose ancestors branched off an estimated 315 million years ago, can help scientists fill gaps in their understanding of mammalian evolution. The comparison also will allow scientists to date the emergence of genes and traits specific to mammals.
The Nature paper analyzes the genome sequence of a female platypus named Glennie from New South Wales, Australia. The project was largely funded by the National Human Genome Research Institute, part of the National Institutes of Health, and includes scientists from the United States, Australia, England, Germany, Israel, Japan, New Zealand and Spain.
At first glance, the platypus appears as if it was the result of an evolutionary accident," says Francis S. Collins, M.D., Ph.D., director of NHGRI. "But as weird as this animal looks, its genome sequence is priceless for understanding how mammalian biological processes evolved.
While we've always been able to compare and consider all of these creatures on the basis of their physical characteristics, internal anatomy and behavior, it's truly amazing to be able to compare their genetic blueprints and begin to get a close-up look at how evolution brings about change," Wilson says.
As part of their analysis, the researchers compared the platypus genome with genomes of the human, mouse, dog, opossum and chicken. They found that the platypus shares 82 percent of its genes with these animals. The chicken genome was chosen because it represents a group of egg-laying animals, including extinct reptiles, which passed on much of their DNA to the platypus and other mammals over the course of evolution.
The researchers also found genes that support egg laying - a feature of reptiles - as well as lactation - a characteristic of all mammals. Interestingly, the platypus lack nipples, so its young nurse through the abdominal skin.
The researchers also attempted to determine which characteristics of the platypus were linked to reptiles at the DNA level. When they analyzed the genetic sequences responsible for venom production in the male platypus, they found it arose from duplications in a group of genes that evolved from ancestral reptile genomes. Amazingly, duplications in the same genes appear to have evolved independently in venomous reptiles.
The platypus swims with its eyes, ears and nostrils closed, relying on electrosensory receptors in its bill to detect faint electric fields emitted by underwater prey. Surprisingly, the researchers found the genome contains an expansion of genes that code for a particular type of odor receptor. "We were expecting very few of these odor receptor genes because the animals spend the majority of their life in the water," Warren says.
Similar genes are found in animals that rely on a sense of smell, such as rodents and dogs, and the scientists suspect that their addition in the platypus allows the animals to detect odors while foraging underwater.
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