Calomys laucha - Small Vesper Mouse
Calomys laucha is similar in appearance to a house
mouse, with a tail length approximately 40% of total body length. The
dorsal pelt is a mixture of light brown, orange/gold, and black. The
ventral pelage is grey/white. An identifying characteristic of Calomys
laucha is a small area of white fur behind both ears. The mean length
of total body, tail, hind foot, and ear are 127.0 mm, 54.9 mm, 16.5 mm,
and 13.1mm respectively (Redford & Eisenberg 1992). Calomys laucha
adults weigh approximately 12.8g (Yahnke et al. 2001).
Calomys laucha is found in the Chaco regions of South
America, including those of Paraguay, central Argentina, southern
Bolivia, southeastern Brazil, and Uruguay (Bilenca and Kravetz 1999).
The Chaco can be divided into two sub-regions, the Chaco Austral of
Argentina and the Chaco Boreal of Paraguay and Bolivia. The topography
of the Chaco is primarily flat. It includes a wide variety of
vegetative habitats. Calomys laucha is thought to primarily inhabit the
western Chaco where conditions are drier and the soils sandier (Myers 1982).
The small vesper mouse has a fairy short oesterous
cycle, which makes them a popular choice for research in reproductive
physiology. Females are easily bred, have large litters, and ovulate
multiple times throughout the year. The males also have a noteworthy
reproductive characteristic. The sperm of the small vesper mouse has a
flat, rather than the more common hooked head. The tail of the
spermatozoa is attached to the center of this flat head, and the nucleus
of the sperm is asymmetrical (Lasserre et al. 2000). Calomys laucha
produces an average of 5.15 young per litter. The most productive
periods for Calomys laucha are the colder months of the year (Yahnke et
al. 2001). Nests are cup-shaped and made of soft materials including
grasses, leaves, stems and various man-made items. The small vesper
mouse has a monogamous mating system (Chiappero et al. 2002).
Ecology and Behavior:
The habitat selection of Calomys laucha changes
seasonally. During the summer the small vesper mouse selects habitats
with high levels of vegetation. In the winter months the small vesper
mouse takes refuge in border habitats with less vegetative cover and
more open spaces (Bilenca & Kravetz 1999). Calomys laucha are found
at the highest densities in crop fields, possibly because of the high
level of disturbance experienced there. Many studies have shown that
Calomys laucha are broad-based omnivores, with diets including seeds,
leaves, grains and arthropods. A food item that Calomys laucha seems to
prefer is the E. indica seed (Castellarini et al. 2003). The diet of
the small vesper mouse is hypothesized to be a function of their
relationship with coexisting species with similar diets as well as the
disturbance level of their habitat. Many rodent communities of South
America are constructed in a hierarchical manner. There have been
significant findings supporting the concept of interspecific competition
as a determinant of niche habitat partitioning between Calomys laucha
and its conspecifics. The Akodon azarae, for example, seem to
out-compete Calomys laucha in the winter months for control of the ideal
habitat space. Calomys laucha is forced to wait out the winter months
in less ideal habitats (Bilenca & Kravetz 1999, Castellarini et al.
As with other members of the order Rodentia, Calomys
laucha plays a crucial role in ecosystem dynamics. The members of order
Rodentia are the “main course” to many predators higher up on the food
chain. The predators of the small vesper mouse include birds of prey
and other carnivores.
Hantavirus is a zoonotic disease, which means that it
spread from animal reservoir to humans. One such reservoir is Calomys
laucha. Small vesper mice males that have reached reproductive age are
physically aggressive with one another. This aggression leads to biting
and other physical injuries, which is how some researchers believe the
Hantavirus is spread within the Calomys laucha population (Yahnke et al.
2001). The virus is found in rodent urine, saliva, and feces. The
inhalation of micro-particles (dust) is the most common means of
infection, although fomite surfaces (dirt) can also harbor the virus.
The virus can be destroyed with disinfectants, such as bleach or
Bilenca, D. N. and F. O. Kravetz. 1999. Seasonal
changes in microhabitat use and niche overlap between Akodon Azarae and
Calomys laucha in agroecosystems of central Argentina. Study of
Neotropical Fauna and Environment 34:129-136.
Castellarini, F., C. Dellafiore and J. Polop. 2003. Feeding habits of
small mammals in agroecosystems of central Argentina. Mammalian
Chiappero, M. B., A.
Blanco, G. E. Calderon, M. S. Sabattini and C. N. Gardenal. 2002.
Genetic structure of populations of Calomys laucha from central
Argentina. Biochemical Systematics and Ecology 30:1023-1036.
A., E. Cebral and A.D. Vitullo. 2000. Successful capacitation and
homologous fertilization in vitro in Calomys musculinus and Calomys
laucha. Journal of Reproduction and Fertility120:41-47.
Myers, P. 1982. Origins and affinities of the mammal fauna of Paraguay.
Mammalian Biology in South America 6:85-93.
K. H. and J. F. Eisenberg. 1992. Mammals of the Neotropics, Volume
2. University of Chicago Press, Chicago. pp 279-280.
C. J., P. L. Meserve, T. G. Ksiazek and J. N. Mills. 2001. Patterns
of infection with Laguna Negra virus in wild populations of Calomys
laucha in the central Paraguayan Chaco. American Journal of Tropical
Medicine and Hygiene 65(6):768-776.
Reference written by
Jahna Cook, Biol 378 (Mammalogy), University of Wisconsin – Stevens
Point: Edited by Chris Yahnke. Page last updated 07-25-05.