Fourth Floor Studio

October 14, 2006

Mus cypriacus, and four reasons you should care

Filed under: genetics — chris @ 1:42 am

A new species of mouse, Mus cypriacus, has been announced (although it was originally reported by the same authors in french in 2004). The mouse is apparently endemic to the vineyards and fields of the foothills leading up to the Troodos mountains in Cyprus. It’s not yet clear whether it’s commensal with humans, although mice generally are. It shares its range with the far more common Mus musculus domesticus, the western european house mouse, although it is anatomically and genetically distinct.

Why, one might ask, is this remotely interesting? Several reasons, actually:

– First, it’s rather rare that a new mammal is described in Europe. The taxonomy craze beginning in the mid-1700s naturally turned its sights to its own back yard first, so that even by the time of Goethe and Darwin one had to travel to remote and exotic continents to find new species. Mammals, being (along with large trees) the most conspicuous group of organisms, have come under particular scrutiny, so new mammals are a real find (and perhaps, an ironic one given their hiding in plain sight).

– Second, the mouse is one of the most widely used model organisms, finding employment in genetics, cancer, immunology, toxicology, and several other -ologies. Factor in the rat, and rodents become far and away the most common model – although the proverbial guinea pig has in fact been largely abandoned. In the context of the lab, by “mouse” we generally mean M. m. domesticus, and more specifically the laboratory lines of mice derived from it. This is where things get a little complicated: these lines were derived largely from fancy mouse stocks imported from south-east Asia at the beginning of the 20th century, with others being added later from wild captures in Switzerland and Japan. As it turns out, however, things are a little bit more complicated, and an explanation first requires a detour through the murky taxonomy of mouse species:

mice belong to the order Rodentia (the rodents), and to the genus Mus. Since it’s such a large genus, it is split into a number of subgenii based on the relationships between the species that comprise it. Lab mice (Mus musculus), along with M. cypriacus, belong to the subgenus Mus – the archetypical grouping within the genus. It turns out that M. musculus is so diverse, it can be further split into a number of subspecies, such as M. m. domesticus mentioned above.

Now, back to our fancy mice: it turns out they were themselves derived by breeding bewteen Mus musculus subspecies, and also with Mus subgenii, primarily M. spretus. So what we call “lab mouse” is actually a complex mixture of several species and sub-species of mouse, bound together under the general rubrik of Mus. This mess actually works in our favour, as having a new species to play with gives us another set of genetic variations to inject into the mix, and generate interesting (ie medically relevant) traits. It will also provide us with more data on what the mouse precursor looked like, allowing us to ask questions about the evolution of mice and in particular, some of their traits that they share with humans.

– Third, stemming from this complicated mess, the new species allows us to ask some interesting questions about how species arise. I mentioned above that M. cypriacus shares its range with M. m. domesticus, from which it diverged 500,000 to 1 million years ago. This raises the question of how and where the newly discovered species evolved. One definition of a species is as a reproductively isolated group of organisms: that is, they can mate between themselves, but not (fertilely) with other groups/species. The easiest way to isolation and speciation is geographic separation, or allopatry: a group of individuals is split into two by migration or some barrier, and over time diverges genetically to the point where reproduction between individuals from the two groups is no longer possible. A slightly trickier scenario is sympatry, where individuals within a population don’t mate at random but choose one of (usually) two subgroups, according to some set of characteristics. Eventually these groups become so genetically different that, although they live together, they can no longer produce viable offspring and are therefore, by definition, different species. Sympatry is still a hotly contested phenomenon in animals, particularly mammals, which move around a lot and can have rather a wide range of characteristics to begin with. There are some intriguing hints that some fish species have speciated sympatrically, but no definitive evidence has been given for mammals, so M. cypriacus may take the cake here, particularly if genetic analysis shows it’s more related to M. m. domesticus than other Mus sub/species. Alternatively, if it evolved allopatrically, finding its continental relatives (living or fossil) will tell us where and when the species evolved.

– Fourth, the species can tell us about Cyprus archaeology. Cyprus has an interesting, but still largely unknown, prehistory: the first human traces on the island apparently date to before the 10th century BC and are in a cliff cave, where mounds of pygmy hippo and elephant bones have been found. The site itself appears transient, so it’s not clear if this represents the first settlement or simply an opportunistic cull of native fauna by passers-by. Evidence for settlement then starts around the 10th/9th century BC with preceramic neolithic settlements, which disappear abruptly around 6000 BC. Ceramic neolithic settlements then crop up around 4500 BC, followed by Bronze and Iron Ages, at which point the period of recorded history starts. If M. cypriacus evolved allopatrically and was introduced during one of the waves of settlement, that would tell us when, from where, and by extension who introduced the species, and therefore where at least one of these civilisations came from. It would also give us insight into exactly what the starting parameters of that civilisation were; for example, rodents imply grain and its storage, so this people would have to already be adroit farmers, rather than hunter gatherers who settle down and learn to live off the land later.

Here endeth the lesson: I hope I’ve convinced you why you should care about an obscure new rodent, and also shown you a little of how science is interconnected and cross-fertilises: we’ve touched on molecular genetics and genomics, evolution and evo-devo, archaeology, taxonomy, ecology, geography, and history in this brief tour, although we’ve barely scratched the surface on any of them. These confluences of ideas is why I chose my profession, and I have a sneaking suspicion that’s true for many of my peers.

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1 Comment »

  1. [...] Another Cypriot mammal has much more to say about this [...]

    Pingback by New mouse « What You’re Doing Is Rather Desperate — October 14, 2006 @ 4:26 am

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