Yesterday we talked about vultures, and now a fascinating new publication by Jonathan Kingdon and colleagues working in UK, Kenya and the US has inspired me to write about another often despised group, the rat! In fact, I'm not going to be general, but just going to highlight some of their fascinating findings regarding the Crested Rat Lophiomys imhausi. This is a species of the arid and semi-arid habitats of NE Africa, just making it into some of the driest areas of northern Tanzania and the drier parts of Kenya (interestingly IUCN don't think it's in Tanzania - anyone know differently? I've never seen it here but there are lots of unsourced references I can find like here). They're a rather large, slow moving rat with distinctive black and white crest and strange-looking hairs - I've no pictures myself, but there's a nice one here. You might see them every now and again on night drives, shuffling along a little like a small porcupine. That sort of slow, unconcerned attitude is pretty unusual in small fluffy creatures that everything wants to eat, and the black and white colourings are often a warning to other animals that's they're something to be afraid of. But what defence can a rat possibly have?
Well the new research has found that these rats chew on the bark of Acokanthera schimperi and smear the chewed bark and saliva on that crest, transferring the poison there, and possibly modifying it slightly in the process to make it even more potent. Any animal taking a bite gets a mouthful of poison and either dies very fast, or gets ill enough to remember not to take another bite of this species! The posions (actually, there are several, but it seems as though the rat is only using one) in Acokanthera schimperi is capable causing a heart attack by greately increasing the force of the heart-beats. In fact, it's the same poison that used to be used by the Waliangulu of Tsavo for elephant hunting. In a neat extra adaptation, the rat's fur along this crest contains special absorbant holes for soaking up the poison rather like a sponge. The paper reports that normally the animals cover the special fur with longer normal, grey fur to protect it from light rain and sun, which could mean that they're not immediately showing their warning colours and may get bitten - but they also show several adaptations that suggest they can survive a hefty bite, with thickened skull and other bones - hopefully meaning that when the predator gets a mouthful of poison, any damage it causes to the rat is minimal.
The big question, of course, is how do the rats do it? Why doesn't chewing the bark kill them, the same way it woudl kill an elephant? And the new paper has nothing concrete to say about this (though does suggest that the large salivary glands might have something to do with it). It's interesting though - because if we can understand how the rats prevent heart-attack induced by this poison, we might have a whole new set of tools available to us to treat heart conditions (we already use the poison itself in some medical treatments).
So who said that rats were dirty and uninteresting?! This one at least has a nice series of tricks up it's fur. The question you might then have, of course, if if they're so very toxic and don't need tow orry aout predators very much, why aren't we over-run with the beasts? And it's a good question - they'r emostly vegeterian in the wild, but can certainly tuck into mean when it's available, so there shouldn't be too much food limitation either. But there must be something more to this, as they are restricted to arid areas and the tree is much more widespread, so there's obviously something else specialised going on we don't know about yet - any thoughts?!
Very interesting !
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