''Oligoryzomys microtis'', also known as the small-eared colilargo or small-eared pygmy rice rat, is a species of

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

in the genus ''

Oligoryzomys ''Oligoryzomys'' is a genus of rodents in the tribe Oryzomyini of family Cricetidae. Many species are known as pygmy rice rats or colilargos.Musser and Carleton, 2005 The genus is found from Mexico to Tierra del Fuego and includes approximately 1 ...

'' of family

Cricetidae The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and New World rats and mice. At over 870 species, it is either the largest or second-largest family ...

. It is found in western

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

, eastern

Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...

Bolivia Bolivia, officially the Plurinational State of Bolivia, is a landlocked country located in central South America. The country features diverse geography, including vast Amazonian plains, tropical lowlands, mountains, the Gran Chaco Province, w ...

, and northern

Paraguay Paraguay, officially the Republic of Paraguay, is a landlocked country in South America. It is bordered by Argentina to the Argentina–Paraguay border, south and southwest, Brazil to the Brazil–Paraguay border, east and northeast, and Boli ...

Description

''Oligoryzomys microtis'' has a total length of including a tail of . It weighs about and is the smallest species in the genus. In proportion to the head and body length, the hind feet are relatively long, being 28.5% of their length. This compares with the rather similar ''

Oligoryzomys nigripes ''Oligoryzomys nigripes'', also known as the black-footed colilargo or the black-footed pygmy rice rat, is a rodent in the genus ''Oligoryzomys'' of family Cricetidae. Oligoryzomys nigripes is a species that has been further divided into differen ...

'' where the proportion is 24.5%. The ears are small and densely furred inside. The cheeks may be grey or orangeish-brown. The back is brownish and the underparts are whitish or greyish, sometimes tinged with buff. The tail is rather darker on the upper surface than the lower surface. Its

karyotype A karyotype is the general appearance of the complete set of chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes. Karyotyping is the process by which a karyotype is discerned by de ...

has 2n = 64 and FNa = 66.

Distribution and habitat

''O. microtis'' is native to South America, its range extending from northwestern Brazil, south of the

Solimões River Solimões () is the name often given to upper stretches of the Amazon River in Brazil from its confluence with the Rio Negro upstream to the border of Peru. The Solimões flows for about 1,600 km (1,000 miles) through a floodplain about 80 km ...

and Amazon River, to the adjoining lowlands of Peru and Bolivia, northern Argentina, eastern Paraguay and the

Gran Chaco The Gran Chaco or simply Chaco is a sparsely populated, hot and semiarid lowland tropical dry broadleaf forest natural region of the Río de la Plata basin, divided among eastern Bolivia, western Paraguay, northern Argentina, and a portion o ...

plain. Its typical habitat is marshes and wet grassland, but in Brazil it is more associated with forest borders, gallery woodland and secondary forest. In the Paraguayan Chaco it is associated with both dry and wet marshland, and has been reported from floating masses of vegetation.

Ecology

Breeding starts at a young age, even while still in juvenile coat, and pregnancy rates are high. In Bolivia, pregnant females have been found in March, May, August and September, and the number of embryos varied from two to eight. The Rio Mamore virus has been isolated from this species in Bolivia.

Status

This is a common species over much of its wide range. It is an adaptable species, able to tolerate some habitat degradation. No particular threats have been recognised and the population seems to be stable, so the

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...

has rated its conservation status as being of

least concern A least-concern species is a species that has been evaluated and categorized by the International Union for Conservation of Nature (IUCN) as not being a focus of wildlife conservation because the specific species is still plentiful in the wil ...

References

{{Taxonbar, from=Q1769195 Oligoryzomys Mammals of Bolivia Rodents of Brazil Mammals of Paraguay Mammals of Peru Mammals described in 1916 Taxa named by Joel Asaph Allen