Calomys musculinus - Drylands Vesper Mouse
Members of this genus are small mostly granivorous
rodents (Salazar-Bravo et al. 2001). The characteristics of C.
musculinus include a mouse-like body form, with prominent ears, narrow
hands and feet, and a moderately haired tail. The total body length
ranges from 60-125 mm; tail length 30-90 mm. Generally, the tail is
shorter and the head and body are rarely longer. In specific localities
this species does not normally exceed 100 mm, which can be used as a
diagnostic character (Braun and Diaz 1999). The pelage is thin, and
coloration varies from buff, tawny, grayish buff, grayish to dark brown.
Ventral coloration is typically gray to white (Nowak 1999).
Range of C. musculinus includes northern and central
Argentina (Nowak 1999). Formally it was thought that this species was
only found in eastern Paraguay; however, research has found C.
musculinus inhabiting the central Paraguayan Chaco region (Myers 1982;
Yahnke 1999). There may also be reason to suspect that the range
includes south central Bolivia to central Brazil (Salazar-Bravo et al.
Calomys musculinus like other members of the family
Muridae possesses a Type III ovarian cycle. This is typified by a
combination of spontaneous ovulation, short luteal phases in females
that did not copulate and the development of fully functional
progestational phase if copulation occurs. This reproductive strategy
may have evolved due to predation pressure increasing the probability
that females will become pregnant by returning to estrus quickly if
breeding does not take place (Cutrera et al. 1998).
typical breeding season includes most of the summer continuing into the
autumn. The average time of reproductive stages was determined by
laboratory studies of captive colonies. The average estrous cycle is 5.7
days. The gestation is 24.5 days, and their litter size is 5.4- 7.60.
Females reach sexual maturity at 72.5 days, and males reach sexual
maturity at 82 days (Nowak 1999; Mills 1992). These values characterize
the opportunistic life history of the species, enabling it to colonize
unstable crop habitats (Mills 1992).
have provided evidence in support of the hypothesis that C. musculinus
is a polygamous species with a solitary social structure (Laconi and
Castro-Vazquez 1999). In contrast, the closely related C. laucha is a
more monogamous species. C. musculinus females have been observed to
interact with more than one male in their home range, which overlaps the
range of several neighboring males (Laconi et al. 2000). Copulation
with more than one male may take place. The presence of a male, even the
siring male, is deleterious for the young, both in reduced survival and
protracted growth. Laboratory results show that maternal nesting
behavior includes aggressively excluding the male both pre and
postpartum (Laconi et al. 2000). Again compared with C. laucha, C.
musculinus had a lower frequency of co-occupancy (Laconi and
Castro-Vazquez 1999). Aggressive behavior such as combat may be
responsible for the reduced growth rate and survival due to the heat
loss of the highly altricial pups during maternal absence.
changes influence reproduction in C. musculinus. Male reproductive
systems are responsive to unfavorable environmental conditions of fall
and winter, yet some reproduction does take place during this time
(Mills et al. 1992). Animals, males in particular, that are born in the
autumn do not usually become active until the following spring (Mills et
al. 1992). Mass is more significant than age when determining sexual
maturity (Mills et al. 1992).
Growth takes place in
three distinct phases: the maximum instantaneous growth rate located
between the birth and 30 days old, a lower growth rate between 60 and 90
days, and then a progressive decline in growth rate from 90 to 180
days. These growth rates tend to differ between the sexes (Provensal
and Polop 1993).
Ecology and Behavior:
This nocturnal, secretive, rodent selects open
vegetation habitat, with a wider niche than other coexisting rodent
species. Expansion of human agricultural activities may be contributing
to an increase in the abundance of C. musculinus by indirectly creating
more edge or a boarder habitat (Busch & Kravetz 1992). C. musculinus
preferentially selects boarders of fields over crop fields indicated by
differences in abundances (Busch et al. 2000). Boarder habitats are
more attractive for rodent species because of increased stability (Ellis
et al. 1998). Activities that cause mortality such as sowing and
harvesting do not affect these areas (Busch & Kravetz 1992). Crop
type influences the abundance of this species, with higher densities
present in corn than in soy beans, with population dynamics synchronized
with corn (Busch et al. 2000). Vegetation reducing predatory risk may
be more of an influence than dietary limitations of this more
omnivorous, generalist species. The availability of green plant cover
may be favored by reproductive individuals in early autumn when the
boarders provide a more protected microhabitat for large, above ground
nests that would otherwise be exposed in crop fields (Yunes et al.
1991). Large above ground nest may serve a thermoregulatory purpose in
addition to their breeding purposes (Yunes et al. 1991). Nest building
for thermoregulatory purposes may correspond to breeding, since the
insulation conserves energy, which can then be delegated to reproduction
(Yunes et al. 1991).
Seasonal distribution within the
habitat may be influenced by the presence of other species, such as
Akodon azarae and Calomys laucha, through competition. During winter and
autumn, the presence of C. lucha and A. azarae has a negative
relationship to C. musculinus (Busch et al. 2000) Distribution within
the more arid portions of its range may be dictated by proximity to
water (Cutrera et al. 1998).
Seasonality may also
dictate the proportions of major dietary items such as insects, leaves
and seeds the animals consume (Ellis et al. 1998). Leaves make up a
small portion of the diet throughout the year. During the winter, seeds
make up a larger proportion of the diet compared with arthropods. In the
spring and summer, this is revered with the arthropods making the
largest contribution to diet. The diet is the most diverse in the spring
and summer and autumn; lowest in winter and spring. Corn and soybeans
are the most important plants in the diet of C. musculinus, and they are
consumed in high proportions during the fall and winter. Other plants
growing in boarders made more of a contribution in the spring and
summer. Specific preferences are not present with most plant species
consumed in proportion to availability. Dietary studies have yielded
information about parasites with the nematodes as the most common
parasite of the stomach (Ellis et al. 1998).
This species serves as a vector for Argentine
Haemorrhagic fever (Junin Virus). The mode of transmission is thought to
be predominantly through airborne virus-containing aerosols of rodent
excreta. First recognized in 1955, the disease was initially localized
in rural populations in the northwestern Buenos Aries province of
Argentina. Annually 100-4,000 cases are reported, with the exception of
1993 when 24,000 cases were reported. Outbreaks of the disease are
seasonal corresponding to the harvest of corn in March through June.
Disease outbreaks have been strongly correlated with rodent density.
Significant increases in the density of C. musculinus immediately
preceded an outbreak of the disease (Mills et al. 1992). The common
symptoms of the disease include gradual onset of fever, sore throat,
myalgias, low back pain, and abdominal pain. The fatality rate is 15-30%
In addition to the Junin Virus, C.
musculinus may also become infected with Trypanosoma cruzi, the
protozoan parasite responsible for Chagas-Mazza disease (Cutrera et al.
The drylands vesper mouse belongs to the murid genus
Calomys Waterhouse 1873 Rodentia: Sigmodontinae (Salazar-Bravo et al.
2001). Synonyms for Calomys musculinus, Thomas 1913 include, Calomys
cordovensis, Calomys cortensis, Calomys murillus. Members of this genus,
including C. musculinus, have been referred to as “lauchas” or vesper
mice (Salazar-Bravo et al. 2001). A frequently used alternative common
name for this species is the corn mouse.
there are two distinct clades within Calomys. C. musculinus belongs to
the clade containing three total species, including C. lepidus and C.
sorellus (Salaza-Bravo et al. 2001).
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(Copyright © 2004 NatureServe, 1101 Wilson Boulevard, 15th Floor, Arlington Virginia 22209, U.S.A. All Rights Reserved. Each document delivered from this server or web site may contain other proprietary notices and copyright information relating to that document. The following citation should be used in any published materials which reference the web site.)
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Reference written by Sarah Orlofske, Biol 378 (Mammalogy), University of Wisconsin – Stevens Point: Edited by Kim Moore. Page last updated 12-20-04.