Download Calomys musculinus

Sarah Orlofske
Calomys musculinus
Drylands Vesper Mouse
Description
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 rarely longer. In specific localities this species does not normally exceed 100mm,
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).
Distribution
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. 2001).
Ontogeny and Reproduction
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).
The 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, 5.7 days; gestation, 24.5 days; litter size, 5.4- 7.60;
female sexual maturity, 72.5 days; and male sexual maturity 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).
Several studies 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 cooccupancy (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 altrical pups during maternal absence.
Seasonal 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 were born in the autumn do not usually become active until the following
spring (Mills et. a. 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, although these differed
between the sexes (Provensal and Polop 1993).
Ecology and Behavior
This nocturnal, secretive, rodent selects open vegetation habitat, with a wider niche than
other coexiting 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 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 through out 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 were the
most important plants in the diet of C. musculinus consumed in high proportions during
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).
Remarks
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 1004,000 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% (CIDRP 2004).
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. 1998).
Nomenclature
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.
Phylogenically there are two distinct clades within Calomys. C. musculinus belongs to
the clade containing three total species, including C. lepidus and C. sorellus (SalazaBravo et al. 2001).
Literature Cited
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selection by Calomys musculinus (Muridae, Sigmodontinae) in crop areas of the pampean
region, Argetina. Ecologia Austral 10:15-26.
Busch, M. and Kravetz, F.O. 1992. Competitive interactions among rodents (Akodon
azarae, Calomys laucha, Calomys musculinus and Oligoryzomys flavescens) in a twohabitat system. II. Effect of species removal. Mammalia Vol. 56. (4) : 541-554.
Center for Infectious Disease Research & Policy Academic Health Center -- University
of Minnesota Copyright © 2004 Regents of the University of Minnesota
http://www.cidrap.umn.edu/cidrap/content/bt/vhf/biofacts/vhffactsheet.html#Modes
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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
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Reference written by Sarah Orlofske, Biology 378 student. Edited by Christopher Yahnke.
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