March 31, 2009
Strange BiologyThe Curious Case of the Platypus
The platypus is native to Australia. (Photo Credit: Peter Scoones/Photo Researchers, Inc.)
The platypus is a curious animal. It has a bill like a duck, it produces milk and has fur like a mammal, and it lays eggs like a reptile. Scientists recently sequenced the entire genome of a platypus and discovered that its odd appearance is in fact a testament to its bird, reptile, and mammal ancestors.
Natural History
A platypus (scientific name Ornithorhynchus anatinus) is an animal like no other. It is classified as a monotreme. Animals that are classified as monotremes are mammals that lay eggs. In addition to the platypus, there are two kinds of echidna that are also classified as monotremes. Platypuses and echidnas are endemic to the South Pacific and are only found in Australia, Tasmania, and New Guinea.
Platypuses live in lakes, rivers, and streams in eastern Australia. Characteristics of a platypus body include waterproof fur, webbed feet, and a horizontally-flattened tail to aid in movement underwater. The platypus has extremely sensitive senses of sight, smell, and hearing. When underwater, the platypus closes its eyes and ears.
Unusual Characteristics
A male platypus has a sharp spur on its hind foot that packs a venomous punch. (Photo Credit: ANT Photo Library/Photo Researchers, Inc.)
Both male and female platypuses are born with a spur on each hind leg. While females lose their spur within the first year of their life, males retain their leg spurs over their entire lifetime. The spur is a claw-shaped growth that is connected to a venom gland. Males use the spurs to defend themselves against predators and competing male platypuses during mating season. The spur is very sharp and can inflict a very serious wound. While strong enough to kill a large dog, the venom does not appear to cause life-threatening injuries to humans.
When underwater, the platypus uses its super-sensitive bill to detect prey. Unlike a duck's hard bill, a platypus's bill is soft and flexible. The surface of the platypus bill is packed with 40,000 electroreceptor which are arranged in rows along the length of the bill. Like the name suggests, electroreceptors are used to detect tiny bursts of electricity. In addition to electroreceptors, a platypus bill also has 60,000 mechanoreceptors. These are nerve endings that can detect small changes in pressure. When underwater, the platypus uses the electroreceptors to determine the location of prey by detecting the electricity produced when prey items contract their muscles. The mechanoreceptors are used to detect where their prey is moving underwater. Together, the electroreceptors and mechanoreceptors in the platypus bill help the platypus locate and zero in on its prey.
Genome Sequencing
In May 2008, a group of scientists announced that they had completed the genome sequencing for the platypus. The research, sponsored in part by the National Human Genome Research Institute associated with the National Institutes of Health, was led by scientists at the Washington University School of Medicine and included researchers from the United States, Australia, England, Germany, Israel, Japan, New Zealand, and Spain. The scientists studied the genome of a female platypus nicknamed "Glennie" from Glenrock Station, New South Wales, Australia. The results of the scientists' research was published in the May 8, 2008 edition of the journal Nature.
Studying the platypus genome may help scientists determine when certain genes and traits specific to mammals may have emerged over time. (Photo Credit: ARCO/Mosebach K/age fotostock)
Evolutionary Ancestors
In the study, the scientists compared the platypus genome with human, mouse, opossum, dog, and chicken genomes, as well as the draft green anole genome. They discovered that the platypus shares 82 percent of its genes with these animals. The scientists also found that platypuses share the same total amount of genes—approximately 18,500—that other mammals have.
Characteristics such as egg-laying (females) and venomous spurs (males) were found to have origins in reptilian ancestors, although egg fertilization was found to have both reptilian and mammalian origins. Characteristics including fur, milk production (females), and a strong sense of smell were found to all be consistent with mammalian ancestors.
Implications
Researchers hope that by studying the platypus's genome, they can determine when certain genes and traits specific to mammals, the class that includes humans, originated during evolutionary history. By comparing the platypus genome to the genomes of other mammals, scientists may be able to determine when certain traits were gained or lost over time.
Comments
Comment from: Ashlyn
October 11, 2011 11:53 AM [#]
Very interesting article. I learned some new things about platypuses!(: