Akodon azarae - Azara's Grass Mouse

Description:

Azara’s Grass Mouse (Akodon azarae) is a small, omnivorous rodent weighing approximately 24 grams as an adult (Antinuchi and Busch 2000).  Total body length is 75-140 mm and tail length is 50-100 mm.  The pelage is soft and full, ranging in color from gray to dark brown.  Some individuals exhibit a red tinge to their fur.  The underside of the mouse ranges in color from white to dark gray.  All members of the Akodon genus are described as heavy-bodied, short-limbed and short-tailed (Dalby 1975).

Distribution:

Akodon azarae is the most numerically-represented mammal of the Pampas grasslands.  It is found in South America from extreme southern Bolivia, Paraguay, northern Argentina, southern Brazil, and Uruguay (Antinuchi and Busch 2000).  They primarily inhabit agroecosystems, especially less-disturbed crop/field borders (Cittadino 2002).  Akodon azarae have a minimum home range of 98 square meters and exhibit peak densities of 200 animals/hectare (Carlson 2003, Brooks and Fielder 1999). Their distribution is strongly influenced by the availability of plant material, and they show a general preference for grassy habitats (Suarez and Bonaventura 2001). There is evidence for strong seasonal variation in abundance throughout its distribution, with a minimum abundance in spring and a maximum abundance in late autumn and early winter.  Females have more restricted movements due to maternal care, while males make large movements, overlapping their home ranges with those of multiple females (Cittadino 2002).  The mice are found from near sea level up to approximately 5000 meters in elevation (Dalby 1975).  The mean annual temperature of the Pampean ecosystem in which Akodon azarae is most common is 16oC with a mean annual rainfall of 94.6 cm (Busch et al. 2001). 

Ontogeny and Reproduction:

Akodon azarae experience a population turnover each year.  The breeding season begins in spring (late September) and lasts through autumn (April/May) (Cittadino 2002). The gestation period is 22.7 days, producing an average litter size of 4.6 offspring.  After 14-15 days the young are weaned, and they become sexually mature at 2 months.  Those young born late in the breeding season do not become sexually mature until the following year (Dalby 1975).

Ecology and Behavior:

Akodon azarae is an omnivorous rodent.  Different species and parts of plants as well as insects are included in its diet.  The most important plant species in their diet are corn, soybeans, and chickweed as well as a variety of other seed bearing plants.  In all seasons, 41-62 % of their diet is arthropods (Antinuchi and Busch 2000, Ellis 1998).  The mice vary the proportion of plants, seeds and invertebrates in their diet according to their availability throughout the year (Busch et al. 2001). To digest both plant and insect material, they have unicellular stomachs with glandular and non-glandular areas divided by a bordering line. (Rouaux 2000).

Azara's grass mice are terrestrial animals and are known to construct burrows 12-15 cm below-ground (Antinuchi and Busch 2000, Dalby 1975).  Various species of Akodon have been reported as diurnal, nocturnal, crepuscular, or active throughout the day (Dalby 1975).  Throughout the year, males and females inhabit separate home ranges.  In early fall the population restructures with increasing population densities, causing competition for vacant sites that appear after the over-winter deaths of adults.  At this time, less competitive, smaller females who did not gain territory may disperse in an attempt to breed before winter.  Males inhabit a larger range during the reproductive period, overlapping the territories of many females to enhance the probability of mating (Cittadino 2002).

Remarks:

Three rodents including Akodon azarae have been noted as carriers of the Junin virus, the etiological agent of Argentine hemorrhagic fever.  This disease is deadly to humans (Salzar et al. 2002).

Female Azara's grass mice with an XY sex chromosome are unique in that they are fully viable and fertile, while the vast majority of other mammals with the same condition are not.  Although the XY females are fertile, the Y chromosome is inherited in a way that results in a decrease in XY females in each generation (Hoekstra and Hoekstra 2001).

Literature Cited:

Antinuchi, D. and C. Busch.  2000.  Metabolic rates and thermoregulatory characteristics of Akodon Azarae.  Revistita Chilena de Historia Natural 73(1):200.

Brooks J. and L. Fielder.  1999.  United States Department of Agriculture Post Harvest Management Group, accessed online October 16, 2004,  http://www.fao.org/info/compend/text/ch.03-01.htm.

Busch, M., M. Mino, J. Dadon and K. Hodara.  2001.  Habitat selection by Akodon    azarae and Calomys laucha (Rodentia, Muridae) in pampean agroecosystems.    Mammalia 65(1):29-48.

Carlson T.  2003.  The spatial extent contaminants and the landscape scale.  Journal of Environmental Toxicology and Chemistry.

Cittadino E.  2002.  Characteristics of dispersing pampean grassland mice (Akodon      Azarae) in agroecosystems of central Argentina.  Studies on Neotropical Fauna           and Environment 37(1):1-7. 

Dalby, P. L.  1975.  Biology of pampa rodents.  Balcarce Area, Argentina.  Publications           of the Museum, Michigan State University, Biological Series 5:149-272.

Ellis, B.  1998.  Dietary habits of the common rodents in an agroecosystem in Argentina.            Journal of Mammology  19(4):1203-1220.

Hoekstra, H. and J. Hoekstra.  2001.  An unusual sex-determination system in South     American field mice (Genus: Akodon): the role of mutation, selection, and meiotic     drive in maintaining XY females.  Evolution 55(1):190-197.

Rouaux, R.  2003.  Estuctura del estomago en Akodon azarae.  Journal of Neotropical             Mammals 10(1):115-121.

Salzar, B., L. Ruedas and T. Yates.  2002.  Mammalian Reservoirs of Arenaviruses:25-63.     

Suarez, O. and S. Bonaventura.  2001.  Habitat use and diet in sympatric species of      rodents of the low Parana delta, Argentina.  Mammalia 65(2):161-176.

Reference written by Dan Liebergen, Biol 378 (Mammalogy), University of Wisconsin – Stevens Point:  Edited by Chris Yahnke. Page last updated 7-25-05.