Friday, 8 March 2013

Whose Genes Are In My Chinchilla?

We are a family of rodentophiles. The current family champion in this pursuit is #2 son, who, for the past ten years, has kept chinchillas, first the late Misses Inca and Chimu and, at present, the ridiculously tame Miss Picchu. It may seem incongruous to keep inhabitants of the Andes in the heat and humidity of Hong Kong but chinchillas are popular pets there, living in air-conditioned comfort for six months of the year and waking up to entertain their diurnal keepers after the latter’s dinner.

When we visit and displace the chinchillas to the dining room from the spare bedroom, talk is inevitably of chinchillas when they are let out each night for a run around the room. We have often talked about the origins of the domestic chinchilla but found that evidence-based information on chinchillas is surprisingly hard to find, especially on the genetic origins of the domestic population and current status in the wild.

Most rodents which are kept as pets were either commensals (mice and rats) or spilled over from laboratory colonies (golden hamster, Mongolian gerbil). By contrast, the chinchilla was bred for its fur and, only later, became a desirable pet, and, even later still, a laboratory animal.

A number of different colour varieties have been bred. This is Picchu, a ridiculously tame Black Ebony chinchilla with aspirations to becoming a supermodel.

While the story of how M.F. Chapman hired 23 men to capture as many chinchillas as possible and that it took these men three years to capture eleven adults is well known, as is the story of their arrival in the U.S.A. in 1923, it is more difficult to find out what happened as the stock was built up in the ranch Chapman built and in the chinchilla ranches that followed in terms of genetic origins.

The general view is that Chapman’s eleven original chinchillas were a montane form of Chinchilla laniger or lanigera (see below on spelling) — the Long-tailed Chinchilla. A smaller form, from lower altitudes (costina) was said to have been trapped out by the time Chapman started his collection.

However, one also reads that, later, some costina form and a few brevicaudata were imported into the U.S.A. and crossed with the chinchillas in ranches. Chinchilla brevicaudata (now known as Chinchilla chinchilla under the rules of priority) — the Short-tailed Chinchilla — is recognised as a separate species. It is written (and repeated) that the male brevicaudata x laniger(a) crosses were sterile but that the females were fertile. When the females were back-crossed, two-thirds of the offspring were sterile.

Because it is said that all chinchillas in the fur and pet trades are derived from the chinchilla ranches of North America, it has been inferred that to a greater or lesser extent the captive population is of an interspecific hybrid derivation. The implication of this inference has, of course, been that the present population must be discounted as a source of animals for possible re-introduction into the wild.

This view also appears to have gained some credence from the breeding of chinchillas for their brevicaudata-type appearance. However, artificial selection can result in markedly changed morphology and the appearance of animals with some of the characters of C. brevicaudata (C. chinchilla) does not mean that the latter species was present in a hybrid ancestry.

However, more recently, and with the ‘re-discovery’ of C. chinchilla in the wild, the conclusions on the hybrid nature of the captive, domestic population have not been supported.

All the information on Chinchilla laniger(a) has been pulled together by Angel E. Spotorno, Carlos A. Zuleta, J. Pablo Valladares, Amy L. Deane, and Jaime E. Jiménez in Mammalian Species Number 758, pages 1-9, published on 15 December 2004 by the American Society of Mammalogists.

Incidentally, and to get nomenclature out of the way, these authors consider the correct name for this species to be Chinchilla laniger — not lanigera. I would say hooray to that since I always knew the species as C. laniger. My edition (4th) of Walker’s Mammals of the World (1983) uses laniger. E.T. Bennett in 1829 changed Molina’s (1782) laniger to lanigera seemingly in a fit of cod-latinitis and recent authors have tended to use lanigera. To add to the confusion, Corbet & Hill’s World List of Mammalian Species (3rd edition, OUP 1991) gives lanigera in the text and laniger as a caption to a drawing. I shall stick with Chinchilla laniger.

To get to the main point of this post and quoting from the paper on the species by Spotorno and colleagues, cytochrome-b gene sequences from mitochondrial DNA showed: no traces of C. brevicaudata variants... were found in any of 5 domestic C. laniger (Spotorno et al. 2004 [Journal of Mammalogy 85:384–388]).

In other words, current evidence favours the view that the domestic chinchilla is pure Chinchilla laniger. That finding, especially if confirmed with larger numbers from diverse sources, does have implications for the conservation of this species. Conservation of the two species is a topic I will turn to in a future post.