英語聽力：自然百科 鴨嘴獸

They are extremely awkward on land, and not exactly graceful in the water. But there's something endearing about these egg-laying mammals. Platypuses can only be found in the rivers, streams and lakes along the east coast of Australia. But they range as far north as northern Queensland, all the way down to the southern Island of Tasmania. That's quite a range for these little creatures. But there are gaps between populations. Large tracks of land between the rivers and lakes make it difficult for the platypuses to migrate from one area to another. Researchers believe it's possible that isolated pockets of animals could have evolved differently, could even be separate subspecies.

"The interesting things about platypuses are that as you come up to the coast in Tasmania, they get smaller, as well as that the total body size is actually less than some of the northern ones. So the maximum weight for one in this area is somewhere in the region of a kilogram, about 2.5 pounds, whereas, they're round about 3 times that weight in Tasmania."

Stephen Kolymyjec from James Cook University is using genetic material to determinegene flow from one population to another. He examines the size and health of the population as well. What fascinates him the most are the differences between the northern and southern platypuses.

"The platypuses up here in north Queensland are about a 3rd the size of the ones down south, which is a pretty big size difference. It may be because of climate, but may be because of actual differences in the species itself. "

"Populations here are isolated from the populations in the south. So we're interested in looking at the effect of the gaps and the ranges, and especially this far north. And one of the tools that we're using to do that is the population genetics. "

Stephen and his colleague David Blair are working in some of the oldest rainforest in the world.

"This is Dirran Creek. It's a tributary of the North Johnstone River Catchment. It's one of the many upland freshwater streams in northern Queensland and it's abundant in platypuses."

Collecting genetic samples from a platypus can be rather challenging. Special nets are carefully placed in the streams. They are not weighted down. So platypuses can swim up to the surface once they become entangled to prevent drowning. With the nets in place, the team awaits until nightfall when platypuses are more active. Then it's time to collect their subjects. Here’s something most people might not be aware of—a platypus should always be held by its tail, especially if it's a male. They are one of the few venomous mammals with a spur on the hind foot, capable of injecting some rather potent and painful venom. So gripping the fatty tail is best for the platypus and the hanger. Now it's time to collect the necessary data. The platypus is weighed (200) and measured, both the body (43) and the sizeable bill (53). The scientists extract samples ofDNA.

"The principal samples we are collecting, for that is a small piece of skin from the toe web on the edge of the foot. That gives us enough DNA when /we take that back to the laboratory to be able to do quite a lot of genetic analysis. In addition to that, we are collecting a little bit of toe skin to go to a laboratory in Adelaide, where researchers are making cell cultures for further genetic work, that interested in chromosome studies, that interested in studies on the other strange sex chromosome that platypuses have. Well, most mammals have an XY sex determining system. Well, the platypus has gone a rather long way further than that. The Platypus has 5 Xchromosomes and 5 Y chromosomes. You can ask the question why? I can't give you an answer. "

Once the platypus is microchipped, it's released back into the water.

"Just let him go, darling. "

"We ought to learn how much difference there is between northern populations from southern populations. Up here in the north there are a few gaps where they just do not occur, and there're no historical records of them ever occurring in those areas. And so we're looking at what kind of effect these gaps had on their genetic health. The actual species, they might be very different, they might be not different. It depends on when the last platypus is able to cross these gaps. "

If the smaller northern platypuses are found to be genetically different from the southern platypuses, they may be recognized as a newly identified subspecies, making them an even more unique version of one of the most unique animals on the planet.