The nutria () or coypu () (Myocastor coypus) is an herbivorous, semiaquatic rodent native to South America. Classified for a long time as the only member of the family Myocastoridae, Myocastor has since been included within Echimyidae, the family of the spiny rats. The nutria lives in burrows alongside stretches of water and feeds mainly on aquatic and riparian vegetation. In its native range it forms part of South American wetland food webs and can contribute to the dispersal of aquatic plants and spores. Native to subtropical and temperate South America, it was introduced to North America, Europe and Asia, primarily by fur farmers. Although it is still hunted and trapped for its fur in some regions, introduced populations can damage wetland vegetation and infrastructure through feeding and burrowing, and the species is considered invasive in several countries. Some populations can carry some zoonotic pathogens, including pathogenic Leptospira, although their epidemiological significance is scarce and region-specific.
Etymology The genus name Myocastor derives from the two Ancient Greek words μῦς (mûs) 'rat, mouse', and κάστωρ (kástōr) 'beaver'. Therefore, the name Myocastor literally means 'mouse-beaver'. Two names are commonly used in English for Myocastor coypus. The name nutria (from the Spanish word nutria 'otter') is generally used in North America, Asia, and throughout countries of the former Soviet Union; however, in most Spanish-speaking countries, the word nutria refers primarily to the otter. To avoid this ambiguity, the name coypu or coipo (derived from Mapudungun) is used in South America, Britain and other parts of Europe. In France, the nutria is known as a ragondin. In Dutch, it is known as beverrat 'beaver-rat'. In German, it is known as Nutria, Biberratte 'beaver-rat', or Sumpfbiber 'swamp-beaver'. In Italy, the popular name is, as in North America and Asia, nutria, but it is also called castorino 'little beaver', by which its fur is known in Italy. In Swedish, the animal is known as sumpbäver 'marsh/swamp-beaver'. In Brazil, the animal is known as ratão-do-banhado 'big swamp-rat', nútria, or caxingui (the last from Tupi).
Taxonomy
The nutria was first described by Juan Ignacio Molina in 1782 as Mus coypus, a member of the mouse genus. The genus Myocastor was assigned in 1792 by Robert Kerr. Geoffroy Saint-Hilaire, independently of Kerr, named the species Myopotamus coypus, and it is occasionally referred to by this name. Four subspecies are generally recognized:
M. c. bonariensis: northern Argentina, Bolivia, Paraguay, Uruguay, southern Brazil (RS, SC, PR, and SP) M. c. coypus: central Chile, Bolivia M. c. melanops: Chiloé Island M. c. santacruzae: Patagonia M. c. bonariensis, the subspecies present in the northernmost (subtropical) part of the nutria's range, is believed to be the type of nutria most commonly introduced to other continents.
Phylogeny Comparison of DNA and protein sequences showed that the genus Myocastor is the sister group to the genus Callistomys (painted tree-rats). In turn, these two taxa share evolutionary affinities with other Myocastorini genera: Proechimys and Hoplomys (armored rats) on the one hand, and Thrichomys on the other hand.
Appearance
The nutria somewhat resembles a very large rat, or a beaver with a small, long and skinny hairless tail. Adults are typically 4–9 kg (9–20 lb) in weight, and 40–60 cm (16–24 in) in body length, with a 30 to 45 cm (12 to 18 in) tail. It is possible for nutrias to weigh up to 16 to 17 kg (35 to 37 lb), although adults usually average 4.5 to 7 kg (10 to 15 lb). Nutrias have three sets of fur. The guard hairs on the outer coat are three inches long. They have coarse, darkish brown midlayer fur with soft dense grey under fur, also called the nutria. Three distinguishing features are a white patch on the muzzle, webbed hind feet, and large, bright orange-yellow incisors. They have approximately 20 teeth with four large incisors that grow during the entirety of their lives. The orange discoloration is due to pigment staining from the mineral iron in the tooth enamel. Nutrias have prominent four inch long whiskers on each side of their muzzle or cheek area. The mammary glands and teats of female nutrias are high on her flanks, to allow their young to feed while the female is in the water. There is no visible distinction between male and female nutria. Both are similar in coloring and weight. A nutria is often mistaken for a muskrat (Ondatra zibethicus), another widely dispersed, semiaquatic rodent that occupies the same wetland habitats. The muskrat, however, is smaller and more tolerant of cold climates, and has a laterally flattened tail it uses to assist in swimming, whereas the tail of a nutria is round. It can also be mistaken for a small beaver, as beavers and nutrias have very similar anatomies and habitats. However, beavers' tails are flat and paddle-like, as opposed to the round tails of nutria.
Life history
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