The Grisons

Spend a bit of time following discussions of nature documentaries and other popular representations of biodiversity, and one topic you're likely to see come up is the biases that tend to exist in what gets represented. Images from eastern and southern Africa predominate while the west and north of that continent get overlooked. Europe and North America receive much more attention than the temperate regions of Asia. Another region whose diversity tends to go underrepresented is South America. The casual observer might think this continent is all monkeys and jaguars but South America is also home to notable radiations of dogs, deer, rodents, and other animals that many people would associate more with other parts of the world. Among these overlooked elements of the South American fauna are the local species of mustelid, including the grisons of the genus Galictis.

Greater grison Galictis vittata, copyright Tony Hisgett.

Grisons are somewhat ferret- or skunk-like animals found across almost the entirety of South America, and north into southern Mexico. They are greyish in colour dorsally (the name 'grison' itself means 'grey') with a black face and underparts. A pale stripe separates the upper and lower parts across the top of the face and continues diagonally back to the shoulders. They feed on small vertebrates and tend to be solitary hunters though they may sometimes form small family groups. They are primarily terrestrial and diurnal in habits. They have a reputation for ferocity; residents of Chile apparently have a history of using comparisons to grisons to describe unchecked rage (Yensen & Tarifa 2003b), in a similar manner to references to wolverines and honey badgers in other parts of the world. Contrasting colour patterns like those of the grisons are associated in other musteloids (such as skunks) with the production of offensive odours for defence, and grisons also produce strong-smelling secretions from their anal glands. Though some sources have claimed the odour produced by the lesser grison to be worse than a skunk's, it appears that these reports are exaggerated (Yensen & Tarifa 2003b).

Lesser grison Galictis cuja, copyright Ken Erickson.

Most authors have recognised two species of grison, the greater grison Galictis vittata and the lesser grison G. cuja*, as corroborated by a recent taxonomic study of the genus by Bornholdt et al. (2013). As their names indicate, the greater grison is generally larger and more robust than the lesser, being about 60 to 76 cm in total length versus 44 to 68 cm for the lesser grison (Yensen & Tarifa 2003b). The tail is also proportionately shorter in the greater grison (30% of the total length for the greater, 40% for the shorter). Fur is relatively longer and denser in the lesser grison, giving it more of a fluffy look. Whereas the dorsal fur is always a plain grey in the greater grison, it may often have a yellowish tinge in the lesser (not always, though). The two are generally distinct in range and habitat, as well. The greater grison is an animal of tropical forests and inhabits the northern part of the genus' range in Central America and northern and western South America. The lesser grison inhabits drier habitats, in arid or temperate regions, and so occupies the southern and eastern parts of the continent. The ranges of the species are known to overlap in Bolivian and Paraguay where their respective biomes approach each other.

*Some sources have listed a third species G. allamandi but this seems have been something of a 'ghost' taxon born from confusion whether the name 'G. vittata' applied to the greater or lesser species.

The genus Galictis arrived in South America as part of the Great American Biotic Interchange, about three million years ago. The general consensus is that it is derived from the genus Trigonictis of the North American Pliocene. Indeed, it has even been suggested that the two North American species of Trigonictis might represent independent ancestors of Galictis, with the larger T. macrodon giving rise to the greater grison and the smaller T. cookii birthing the lesser grison (Yensen & Tarifa 2003a). This certainly would seem overly complicated, though, and molecular data are more in line with a more recent separation of the species.

REFERENCES

Bornholdt, R., K. Helgen, K.-P. Koepfli, L. Oliveira, M. Lucherini & E. Eizirik. 2013. Taxonomic revision of the genus Galictis (Carnivora: Mustelidae): species delimitation, morphological diagnosis, and refined mapping of geographical distribution. Zoological Journal of the Linnean Society 167: 449–472.

Yensen, E., & T. Tarifa. 2003a. Galictis vittata. Mammalian Species 727: 1–8.

Yensen, E., & T. Tarifa. 2003b. Galictis cuja. Mammalian Species 728: 1–8.