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Black rats - brilliant adaptors -

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Black rats were responsible for the death of 75 million people in the 13th century during the Black
Plague. Today they cost the US grain industry $19 billion a year. But black rats also happen to be
brilliant at adaptation and survival. Feeling squirmish? Well the south Vietnamese aren't, with
their rat meat industry producing 10,000 tonnes of rat meat every year. They can be traced to
Southeast Asia they have spread throughout every continent and if you think they're not in your
house.... think again!

Robyn Williams: Rats changed the world, changed human history. They devour huge amounts of the food
we grow. The plagues they've brought killed millions and, in a way, helped create the modern world.
Dr Ken Aplin at CSIRO Wildlife in Canberra has been tracing their lifelines. He's just returned
from India.

Ken Aplin: Everywhere in the world is infested with black rats, and India in particular is
absolutely infested.

Robyn Williams: I remember from somebody who used to work here, Tony Barnett, professor of zoology
at the Australian National University in Canberra, he was consulted on the basis that the rats eat
vast amounts of the crops in India. Any idea how much? Way back, he said about 10% of the grain.

Ken Aplin: Yes, that's still pretty much the case in India, they still estimate around 10% to 15%
lost to rodents, not only black rats but a range of others as well. But in other parts of Southeast
Asia it's even higher. People growing crops in the uplands of Laos or Thailand, they lose 30% every
year, and in bad years they'll lose 70% or 80% of their crop.

Robyn Williams: That is a fantastic amount. What can be done about it?

Ken Aplin: At the CSIRO we've been working on trying to solve these problems for the last ten years
or so and with some success, particularly in lowland monoculture rice crops. The uplands are a much
more difficult problem and I don't know that there's a simple solution to it.

Robyn Williams: With that amount, to save even a small proportion would be a success, wouldn't it?

Ken Aplin: That's right and that's the way I think we have to approach this, just to try to reduce
the damage in areas where we think we can have success, and not try to beat these animals. They're
the greatest survivors, the greatest adaptors to disturbance, and of course humans are the greatest
disturbers of all, and we just have to live with rodents as our companions.

Robyn Williams: What about the rats in the United States or Australia? Any idea of the kind of loss
they sustain there?

Ken Aplin: I saw an estimate recently for the US, $19billion a year from the grain industry. If we
add loss to other sorts of food production then it would be much higher than that. And if you add
the health related cost of rodents then of course it goes even higher, and if we do that worldwide
I think we're looking at trillions of dollars of impact from just those household rats alone, let
alone other rodents that cause damage.

Robyn Williams: It's beyond belief. You've been tracing some of the archaeological history. I think
there are 56 species of this particular sort of rat. Did they all originate in one kind of ancient
mummy and daddy rat or were there several lines?

Ken Aplin: The rats we're most familiar with in Australia are the Norway rat, which is the one
that's been domesticated as the lab rat, and the black rat. As you say, there are about 60 species
of this Rattus group and they evolved in Southeast Asia. Some of them are relatively benign, some
of them are just harmless little forest rats that live on mountaintops and some are even
endangered, but a small number of them have teamed up with people over the last 4,000 or 5,000
years since we started to grow crops and clear forests. They moved in with us and they've travelled
throughout the world and now they occur absolutely everywhere.

Robyn Williams: How did you track their origins?

Ken Aplin: We've done it through using mitochondrial DNA sequencing that allows us to follow the
lineages, the evolutionary lineages of rats, and the key to that was collecting lots of specimens.
Since 2000 I've been working for about six months of each year in Southeast Asia through from India
to Papua New Guinea and north to Japan, and collected lots and lots of rats. So we've just started
to do the DNA work and extract the story.

Robyn Williams: Where do the five or six lines come from?

Ken Aplin: We think that within the black rat group that there are five or six distinct lineages.
They seem to come from distinct parts of that Southeast Asian region. One was probably found
originally on the Indian subcontinent, all the others in the Southeast Asian, southern China
region, but in slightly different areas. And as people have disturbed their habitats and started to
move around with sacks of grain and other goods they've carried these animals with them. And then
eventually, getting through to Europe, they've then hopped on ships and moved around the world
during the age of exploration. So by 1500, 1600 they were found on all continents.

Robyn Williams: But in our region in Melanesia, only about 3,500 years ago?

Ken Aplin: We think the earliest movements probably were out with the early Polynesian Austronesian
dispersals, through Taiwan probably and out into the Pacific down in Indonesia, but it's a very
complex pattern. We even have Indonesian rats turning up in the highlands of Sri Lanka, for
example, and in Madagascar, so there's a very, very complex pattern, we've only just started to
unravel it.

Robyn Williams: Ken, you talk with almost a glee or admiration of these creatures as if they're
unstoppable. Is there a way that we could take them on at all?

Ken Aplin: I don't believe there is. I think the only real hope is through some kind of
immuno-contraceptive approach, but even then I think evolution works against us because it's never
100% successful and the variants that survive then are going to expand and increase in numbers
again, so you're then back to square one, you start developing a new tool to try to combat them. I
really do think they're unstoppable. Recently having worked with these animals in a semi-captive
context, able to observe their behaviour really for the first time, I've realised how incredibly
intelligent they are, and also how incredibly shy and sensitive and how difficult to observe. We
just about all of us have these animals living in our house but very few would acknowledge that

Robyn Williams: I must say that having had my poor cat die a few weeks ago there are now telltale
signs in the food that you leave out. You can see those gnaw marks, but no other signs. Would that
be a black rat, do you think?

Ken Aplin: Almost certainly a black rat, yes. Black rats are the champion, and I think they're
actually much more intelligent than the lab rat. It's a species that we know very little about. For
example, Pest Animal CRC that's been operating in Australia for a number of years doesn't even have
the black rat on its list of target animals, even though it's probably one of our most widespread
and damaging pests at the household level.

Robyn Williams: And you say nearly every household in the whole country?

Ken Aplin: I would think so. I think I could find a black rat in just about every house, given a
small incentive.

Robyn Williams: What about turning a disadvantage into an advantage, my life's motto in fact. With
all those bodies, couldn't you turn it into some sort of industry? Has it been done?

Ken Aplin: It has been done on a huge scale but in limited areas. It depends on people's
willingness to handle the animals, and particularly to consume them. In the southern part of
Vietnam there's a rat meat industry where rats are harvested out of rice fields on a huge scale;
10,000 tonnes a year of rat meat is collected, taken through to the big cities where it's processed
in various ways and then sold in various products, some of which tourists are probably familiar
with...I shouldn't be saying this, should I, I'll probably end up...

Robyn Williams: What do you mean? Street food that I might pick up somewhere could contain Rattus

Ken Aplin: There is one well known street in Ho Chi Minh City that specialises in rats on their
menu, so you can go there and buy things that are clearly labelled as rat products. I've eaten rats
in many different places. I prefer rat meat to most other meats. It's a fine meat, and they're very
clean animals, despite their reputation for being filthy. Having now observed them much more
closely than I could ever do before, I appreciate how hygienic and clean they actually are.

Robyn Williams: What do you like about the flavour?

Ken Aplin: It's a distinctive flavour, it's a mild meat, but particularly barbequed and served up
with a good Vietnamese beer, it can't be beaten.

Robyn Williams: Very low in cholesterol, I'd imagine.

Ken Aplin: Very low in cholesterol, they don't have time to accumulate fat, they're constantly

Robyn Williams: Of course they've changed history, and one of the things that you highlight is
these streams going out with human beings to Europe, for example, where during the Black Death, the
1340s and various other times during European history, they wiped out something like 80% of the
population. Is there a way to assess their effect on human health these days?

Ken Aplin: There is, and there's a big research effort worldwide now to look into rodent-borne
diseases, and as that research develops we're probably on a daily basis adding to the diseases that
can be shared between rats and humans. Some of those diseases probably didn't originate in rats but
it came either from people originally or livestock. But the trilogy of rats, people and livestock
is a really deadly one. We can share a large number of different kinds of diseases and we do. Many
of those are still relatively restricted in their geographic distributions, but as rats move
increasingly and the volume of global transport and trade increases, the numbers of rats moving is
on the increase constantly, then the movement of disease must follow.

Robyn Williams: What about these days? What about the rats in my house? Do they carry much?

Ken Aplin: The rats in your house may well carry 100 or so different diseases that could
potentially be transmitted through to people in your household. Some of them are transmitted
through fleas or ticks or mites or other parasites, but many of them are also transmitted through
saliva, urine and faeces, and it's that contamination when a rat comes out and piddles on the bench
or on food which you then come along and consume yourself, or even just touch with a cut on your
finger, that's probably the main threat for disease transmission from rats.

Robyn Williams: What do you do to keep your own Aplin house free of them?

Ken Aplin: I don't think I do. Actually some people would probably accuse me of encouraging

Robyn Williams: That means you're relaxed about it, that's reassuring. But what are you going to do
with the next phase of the research? You say it's an ongoing thing, how are you going to follow it

Ken Aplin: Look at the current distributions and taxonomy in much greater detail using many more
different genetic markers, but also to look at the history of black rat movement and their impacts
using ancient DNA technologies to really get into this fascinating 4,000 or 5,000-year relationship
that's existed between people and these lovely creatures.

Robyn Williams: Lovely creatures! Finally, if these lovely creatures do confront one in one's
garden, in the compost, say, or running through the house, what should the average Australian do?

Ken Aplin: Applaud yourself that you've actually seen one because sightings are relatively rare.
They're so shy that most people wouldn't see the animals that have lived with them for ten years or

Robyn Williams: Dr Ken Aplin of CSIRO Sustainable Ecosystems in Canberra.