Calomys callosus - Large Vesper Mouse
Calomys callosus is the largest species in the genus
Calomys. The large vesper mouse is a generalist species. They are dark
gray-brown on the dorsal surfaces and gray on the ventral surfaces.
The tail is sparsely haired and bicolored. The vesper mouse has tan
feet and large prominent ears. The total body length is 60-125 mm and
the tail length is anywhere from 30-90 mm (Nowak 1999). The tail is
usually shorter than the head and body. Their teeth are low-crowned.
The chromosome number of the Calomys callosus is 2N=36, FN=48 (Bravo et
al. 2001). Large vesper mice have either 8, 10 or 14 mammae (Nowak
Calomys callosus is widely distributed across
South America from Argentina to eastern and southwestern Brazil and
into Paraguay. They are one of the most widespread genera of the
Neotropical rodents (Bravo et al. 2001).
Females undergo post-partum estrus, which
lasts for approximately 6 days. After a 21.8 day gestation, they have a
litter of 4-5 young. The offspring weigh approximately 2 grams at
birth. The babies are weaned at 15-21 days, and sexual maturity is
reached when the mouse is 45-50 days old (Nowak 1999, Redford and
Ecology and Behavior:
Calomys callosus are a nocturnal species
that tend to live in montane grasslands, brushy areas, and forest
fringes (Nowak 1999). In Paraguay, the large vesper mouse is found in
palm savannas, bunchgrass meadows, and dry marshes (Redford and
Eisenberg 1992). They shelter in bunchgrass, holes in the ground,
rotting tree stumps, and among rocks.
Calomys callosus are opportunistic of fire in open pasture
habitats (Briani 2004). When pasture fires occur, they are one of the
first species to recolonize the area. The vesper mouse is able to adapt
their diet to include more invertebrates, which are more readily
available after a fire (Briani 2004). While the large vesper mouse is
primarily an insectivore that feeds on arthropods, they also feed on
Calomys callous was identified as the
rodent reservoir of the Machupo virus, which causes BHF, or Hantavirus
(Dragoo et al. 2002). BFH is a disease endemic to Bolivia. Because of
their unique DNA sequence, the large vesper mouse failed to develop
antibodies against the virus. The virus is transferred from mouse to
mouse venereally as well as through wounds sustained during
intraspecific fighting (Johnson 2004). Humans contract BHF through the
inhalation of aerosolized virus, bites from infected mice, or through
contact with the urine, saliva, or droppings of infected mice (Johnson
Bravo, J.S., Dragoo, J.W., Tinnin, D.S., Yates, T.L.
2001. Phylogeny and Evolution of the Neotropical Rodent Genus Calomys:
Inferences from Mitochondrial DNA Sequence Data. Academic Press.
Molecular Polygenetic and Evolution 20(2):173-184.
Briani, D. 2004. Fire and Small Mammals. Institution of Conservation
Accessed 1 December 2004).
Dragoo, J. W., Bravo, J., Layne, L. J., and Yates, T. L. 2002.
Relationships within the Calomys callosus species group based on
amplified fragment length polymorphisms. Biochemical Systematic and
Johnson, K. 2004. The Discovery of Hantaan Virus: Comparative Biology
and Serendipity in a World at War. Journal of Infectious Diseases
Nowak, M. 1999. Walker’s Mammals of the World, 6th Edition, Volume 2. Johns Hopkins University Press. pp 1402-1404.
Redford, K. and J. Eisenberg. 1992. Mammals of the Neotropics the
Southern Cone, Volume 2. The University of Chicago Press. pp 278-279.
Reference written by Desiree Dahl, Biol 378 (Mammalogy), University of
Wisconsin – Stevens Point: Edited by Chris Yahnke. Page last updated