The Venom Chronicles: Platypus Tales

Imagine yourself standing on the shore of a river in eastern Australia, arms outstretched to avoid being nipped by the flailing, angry platypus you have suspended upside down by its tail. The scene is strange enough without considering the oddities of the animal you have captured: It has the fur of a mammal, the bill of a duck, and the tail of a beaver, and it lays eggs like a reptile. And it's venomous. The platypus is one of a very select group of mammals that produces venom, and it is giving scientists clues into how and why venom evolved across species.

Catch me if you can! By Stefan Kraft (GFDL or CC-BY-SA-3.0) via Wikimedia Commons.
Right now, not much is known about the contents of platypus venom. Part of the reason for this is that platypuses are somewhat tough to come by. They don't breed well in captivity, and concerns about disturbing them during mating season make them difficult to track down in the wild. Fortunately for us, field scientists like Tom Grant of the University of New South Wales regularly put themselves in the aforementioned strange scenarios on eastern Australian rivers. Grant and his colleagues lay nets in the water in hopes of trapping an animal, and when they have one, they grab it by its long tail and hold it upside down. Platypus venom spurs are located on the hind legs, so while one scientist holds the angry, dangling platypus by the tail as far away from himself as possible to avoid being stung, another holds a small pipette up to the spurs in hopes of extracting a little venom that can be stored and studied. The venom is strong enough to kill a dog and cause debilitating pain to a human. Just another day at the office.
The scientists' troubles don't end there. Only the male platypus produces venom, and only during mating season. (Scientists are not yet sure why, but most believe it's because the venom is used for territorial defense while mating.) Unfortunately, this narrows both the window of time and number of subjects the scientists can study. And unlike more widely studied animals like spiders and snakes, platypuses can't be electrically stimulated to release venom, so researchers have to rely on the trace amounts secreted through the spurs of captured platypuses. Reliably separating all the components of the venom takes a sample much larger than the mere 100 microliters field researchers are usually able to get. 

Still, researchers have been able to investigate some fascinating questions about how venom evolved in animals like the platypus. Camilla Whittington at the University of Sydney is curious about why platypus venom has such a strikingly similar toxin profile to reptile venom, despite the fact that it evolved independently. She thinks the toxins in platypuses originally arose when a gene that coded for part of the immune system was accidentally duplicated. Accidental copies like this are often important tools in evolution, since the first intact version of the gene can perform its normal function while the second can try out new combinations without threatening the survival of the animal. In this case, the gene seems to have been one involved in breaking open the cell walls of invasive microbes that could have made the platypus sick. With a little evolutionary tinkering, the gene morphed into one that could break open the cells of predators and cause extreme pain and sometimes death.

Whittington says this kind of evolutionary development of venom from the immune system is fairly common, and is part of why we see the same kinds of venom cropping up in many different animals. She describes this phenomenon as a "venom motif" that nature selects for again and again. The reason? It works. Nature seems to have found a useful template for venom, and as long as it remains effective, anything that evolves to be venomous will very likely follow a venom motif, whether it's mammalian, reptile, amphibian, or anything else.

There is still a great deal of work to be done on platypus venom, both on what's in it and how it's used. Who knows what other evolutionary secrets this anomalous Australian mammal will help uncover?

This is the final installment of The Venom Chronicles, a blog series by Hannah Krakauer, a research intern at NOVA and a student at Stanford University. From more on the science of venom, watch Venom: Nature's Killer streaming online, or check your local listings to find out when it will air near you. 

User Comments:

This is neat stuff. look forward to more.

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