Sunday, 17 July 2011

Badger Badger Badger

The European badger (Meles meles) is a very familiar animal across Europe, the animal we immediately think of when we think of "badgers". Its distinctive black-and-white face markings make it instantly recognisable, but, in fact, it has quite a range of different appearances, with variations in size, fur colour, and skeletal anatomy that allow it to be divided into a number of subspecies. This variation has been the source of some confusion when it comes to separating this species from its closest relatives.

It used to be thought that the European badger could be found throughout almost the whole of Europe and Asia, avoiding only the tropics, deserts, and the depths of Siberia. As a result it was called, quite reasonably, the "Eurasian badger". Over the last decade, that view has changed. Firstly, it became clear that the badgers of Europe and Asia were different enough to be considered separate species, and then that the badgers of Japan were likely different from those elsewhere in Asia. The suggestion has a venerable history; it was first made in the 1840s, but subsequently ignored when scientists decided that Eurasian badgers were really just one species that happened to be quite variable in appearance.

The scientific names had been hanging around unused for decades, and have now been brought back, so that we have three species of Eurasian badger, with the 'new' ones being Meles leucurus in mainland Asia, and Meles anakuma in Japan. There are significant genetic differences between the three, suggesting that the physical differences we're seeing aren't just in our imagination. It also means that they probably don't interbreed, although its entirely possible that they could if they wanted (which brings us to the whole what is a species? question). In fact, it may not even end there, because a genetic analysis conducted just last year suggested that the badgers of the Middle East may represent a fourth species. That hasn't yet percolated through to most of the usual directories of species, and shows how rapidly our knowledge can change in the light of new information, even about an animal that's fairly well known.

European     Asian        Japanese
 Badger      Badger        Badger
   |           |             |
   |           |             |       Meles thorali
   |           |             |             |
   |           ---------------             |          Hog badger
   |                  |                    |               |
   |                  |                    |               |
   --------------------                    |               |
            |                              |               |
            |                              |               |
            --------------------------------               |
                           |                               |
                   (Eurasian badgers)                      |
                           |                               |

By 'Eurasian badgers' I am referring here only to the genus Meles, of which the Eurasian badger was previously thought to be the only living species. There are at least seven other animals that could reasonably be called badgers and that live in Eurasia (including the hog badger). The American badger, however, is a completely different animal that merely happens to look a bit like the European sort, and isn't a particularly close relative.

If we're still working out how many species there are today, its scarcely surprising that the picture is even muddier when we come to reconstruct the history of the genus, and how many extinct species there may have been. The best evidence for the separation of the living species comes from their genetics, which we can't study in fossils. There are also variations in their coat pattern, with Japanese badgers, for example, being browner with fainter markings than the European sort. Again, not a lot of use with a fossil.

That leaves us with the shape of the skull and teeth, and, to a lesser extent, of the baculum, a bone found in the penis of most mammals (with humans being an obvious exception). Although fossils are rarely complete enough to include the baculum, there are enough differences in the teeth and skull alone to have led us to identify at least five species of fossil badger from Europe. But, bearing in mind the difficulty of counting species of the living animal, how sure can we be that these are real?

Together with publishing a description of some new specimens from Spain, Joan Madurell-Malepiera and co-workers of the Autonomous University of Barcelona conducted a review of fossil badgers across Europe. Given the issues involved, there is, perhaps, no particular reason to assume that this will be the absolute final word on the matter, but it does present a simpler and clearer picture than we've had before. They compiled a list of nine characteristics of badger skulls that should enable us to identify the skull of a European badger (in particular, telling it apart from that of an Asian badger) and looked at how many of them they could find in European fossils.

They concluded that fossils of two different Ice Age species from Italy and Germany were nothing of the sort. Instead, they argue that they represent individuals of the modern European badger, with seven out of the eight diagnostic features being found in the skulls - enough difference, perhaps, to represent a different subspecies, but no more. This would mean that the oldest fossils of our modern, familiar, badger date back to one-and-a-half million years ago, during the early Ice Ages.

Of course, if identifying a species is hard, identifying a subspecies is harder, and one could argue whether the differences that do exist are enough to warrant a separate species. Perhaps, if we could only travel back in time, have a good look at the animals, and take blood samples, we'd see further differences, but since we can't, and since living badgers are pretty variable, putting the fossil ones together seems reasonable to me when you consider how slight the differences are.

Going further back, there are few European fossils of badgers that date to the Pliocene, the warmer epoch that immediately pre-dates the Ice Ages. But when the authors looked at the fossils that do exist, the found quite a different pattern. Again, the fossils, supposedly belonging to three different species, were so similar that they probably represented just one. But the features of the skull were noticeably different from those of living European badgers. Not only that, but, compared with modern skulls, they had some features found only in European badgers, and some found only in Asian ones. So, these are not modern European badgers, but something else, and, following the usual rules for this sort of thing, the species name they get to keep is the first one they were given, which happens to be Meles thorali.

Together with fossil records from elsewhere, and the genetic analysis of living species, this enables us to put together a picture of how Eurasian badgers got to where they are today. Meles thorali is, perhaps, the earliest Eurasian badger, or at least closely related to it. It first appeared around four million years ago, when it diverged from the ancestors of the hog badger, which today lives in China and south-east Asia.

From its original home, which was presumably also in Asia, it spread throughout the continent, eventually reaching Europe. Then the Ice Ages began. Badgers retreated south to avoid the tundra, where they had little to eat, just as today they are not found in Siberia or Lapland. At one point, the tundra reached the northern coasts of the Black and Caspian Seas, cutting off the badgers in Europe from those in Asia. Unable to interbreed, they went their separate ways, and became the two continental species that we have today. That's why Meles thorali has a mixture of European and Asian features: its the ancestor of them both.

Unlike black bears, badgers don't travel so far, and the two species remained separate. Much later, during one of the periodic warm spells in between the Ice Ages, badgers in Japan found themselves cut off from the mainland by rising sea levels, and they too, became a separate species.

We used to think that there was only one species of living Eurasian badger, but as many as five extinct ones. Now we know there are three (or four) living ones, and perhaps only one that's extinct... but that one could be the ancestor of all the others.

[Picture from Wikimedia Commons. Cladogram adapted from Kurose et al. 2001]

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