Friday Weird Science: When studying species, know your Roo Poo.

Jun 14 2013 Published by under Friday Weird Science

Ecologists have to know their s**t. Sure, you might think, people who study ecology have to learn a lot of stuff about the area, they need to learn lots of different kinds of information. And that's all true. But what's also true is that many ecologists really DO need to know their s**t. Literally. It's hard to study species in the wild, and this means that often, you are stuck studying not the species directly, but what the species left behind. Tracks, scents, and s**t. Scat. Crap. Many ecologists can tell wolf poop from deer from rabbit from squirrel instantly.

Studying scat is not just about where an animal has been. Yes, it can tell you a lot about the distribution of populations, but it can also give you a rough idea of population size, what they eat, where they've been before, and even where an animal might be in its life cycle. Clearly, it's important to know your crap.

Many poop samples are pretty easy to tell apart (if you can mix up a wolf and a squirrel, it's safe to say that one of those species is having some tummy trouble), but what about species that are very closely related? One species of squirrel from another? Or...one type of kangaroo from another?

Wadley et al. "Rapid species identification of eight sympatric northern
Australian macropods from faecal-pellet DNA" Wildlife Research, 2013.

Eastern_grey_kangaroo_dec07_02
(This 'roo wants to know the deal with its poo. Source)

The savannahs of Australia boast 9 of the 13 species of macropods (the marsupial group that includes wallabies and kangaroos). Environmental scientists and ecologists have become very worried about the animal diversity on the savannah, as things like mining and farming encroach on the land that the macropods usually use to survive. It's possible that some species may be more affected than others.

But how to tell? You can go over in a plane (if you have the money), you can drive all over the savannah counting (if you have the time and the gas), you can maybe hunker down in a blind for a very, very, very long time. Or, you can take a look at the local crap.

But when you're dealing with kangaroos and wallabies, you are dealing with species that have very similar diets and that are usually very similar in size, and often which occupy a similar range. And if they are similar species that are sized alike and eat alike, it's a good bet they poop alike. It's probably relatively simple to tell squirrel scat from panther poo, but a kangaroo from a wallaby?

So how do you tell? Well, why just look at and puzzle over your roo poo, when you can bring it in to the lab and...look at its DNA.

Yes, there's DNA in poop. And not just the DNA of the stuff the animal was eating. When we digest, some of our stomach and intestinal cells end up as a sacrifice to a good meal, and will get incorporated into your poop. If you can isolate the DNA from those cells (preferably with a DNA bit that is not going to be mixed up in what the animal was eating), that differs between the species, you might be able to amplify that up with polymerase chain reaction (which uses an enzyme to copy a specific set of DNA over and over and over), and then be able to tell what species you have.

And that's what this group did. They took a segment of mitochondrial DNA that differs between the species. They took 8 different species of wallabies and kangaroos, and PCRd up the DNA. Then they used enzymes to cut it at the places where it differed between species, resulting in DNA bands of different sizes.

Screen shot 2013-06-11 at 4.31.55 PM

Above in Fig 1 you can see the bands, a different size for each species. Using this, the authors took a large number of samples (406) from all over the savannah, and PCRd them up, and were able to identify the vast majority (except for a couple of really bad samples, and three that were accidentally from sheep. Oops).

Screen shot 2013-06-11 at 4.33.27 PM

You can see in table 2 you've got your kangaroos, your wallabies, but the big winner was the "wallaroo". Kangaroos are big. Wallabies are small. Wallaroos are right in the middle.

Macropus_robustus
(But also, apparently, a species of severe cuteness. Source)

Hopefully, this method can be used to keep an eye on the macropod populations in Australia. A little s**t can go a long way.

2 responses so far

  • bret says:

    A slight correction - there isn't any savannah in Australia (apart from farmland) Its desert, or arid scrubland - mostly anyway, there is a thin strip of green around the caost :)

    • scicurious says:

      So I actually called it "savannah" because that's what the authors of the paper called it. Is there a specific definition?