Calomys laucha
Small Vesper Mouse
Description:
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).
Distribution:
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).
Ontogeny and Reproduction:
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 (Brooks & Fiedler date?). 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.
2003).
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.
Remarks:
The Hantavirus a zoonosis disease, which means that it has an animal reservoir
and can be spread 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 microparticles (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 alcohol (Brooks & Fiedler date?). Hantavirus is up to 60% fatal, even when prompt
medical treatment is sought.
Literature Cited:
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.
Brooks, J. E. and L. A. Fiedler. date? CHAPTER III Vertebrate Pests: Damage
on stored foods. United States Department of Agriculture (USDA)
http://www.fao.org/inpho/compend/text/ch03.htm (I don't know how this should be
structured...)
Castellarini, F., C. Dellafiore and J. Polop. 2003. Feeding habits of small
mammals in agroecosystems of central Argentina. Mammalian Biology 68:91-101.
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.
Lasserre, 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.
Redford, K. H. and J. F. Eisenberg. 1992. Mammals of the Neotropics, Volume
2. University of Chicago Press, Chicago. pp 279-280.
Yahnke, 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.