Andalgalomys pearsoni
Pearson’s Chaco Mouse
Description:
Andalgalomys pearsoni is a medium-sized mouse that has a relatively long tail.
The tail is slightly hairy and bi-colored with a pale brown dorsal surface. The rest of the
mouse is reddish-brown with strands of black hair scattered throughout the dorsal region
(Nowak and Paradiso 1999). The face is essentially the same color as the dorsum but
lacks the black hair and is outlined in an orange color (Eisenberg and Redford 1992).
The bottoms of the feet are white with no hair or cushions. The ears are slightly hairy
and medium-sized (Nowak and Paradiso 1999). They appear dark brown on the outside
with pale edges (Anderson and Yates 2000). A. pearsoni resembles other members of the
same genus but differs in dorsal coloration. A. olrogi has a yellowish-brown dorsum and
A. roigi has a grayish-brown dorsum (Braun and Mares 1996). The total body length of
this species is 236 mm with a tail length of 124 mm, a hind foot length of 25 mm, and an
ear length of 20 mm (Myers 1977).
The skull tends to be somewhat slender in the tribe Phyllotini (Anderson
and Yates 2000). The supraorbital borders (which are clearly ridged) in genus
Andalgalomys are generally far apart and come together towards the back of the skull.
The temporal ridges are well-defined and tend to hang over the orbits. The zygomatic
plate of Andalgalomys is slightly concave when compared to other species in the tribe
Phyllotini. The auditory bullae are relatively large in this genus. The tooth morphology
is brachydont. The penis contains preputial glands, which are derived characteristics
exclusive to the tribe Phyllotini (Tree of Life date).
Distribution:
A. pearsoni is a species endemic to the chaco of South America, found
exclusively in the western region of Paraguay (Yahnke 1999). Other species in the
Andalgalomys genus are located farther south.
Ontogeny and Reproduction:
Andalgalomys pearsoni tend to breed often and have a short gestation period. The
young are tiny and numerous, with an average litter size of 5. Parental care is limited.
Winter breeding is thought to occur, as females trapped in July exhibited no signs of
breeding. The males that were captured at this time did, however, have large scrotal
testes (Myers 1977).
Ecology and Behavior:
Andalgalomys pearsoni inhabit "islands" of dry grasslands within the Chaco
(Myers 1977). There is an overall complexity to the distribution of animals in the Chaco.
The Pearson's mouse is affiliated with areas of bare soil. The ground coverage consists
of low herbaceous plants and very few woody plants. They do not appear to choose their
habitat based on a high amount of litter. They are exclusive to the regions of the western
Chaco that are dry and sandy, possibly due to the division of resources (food) among the
various rodent populations (Yahnke 1999). A. pearsoni feeds mainly on plant material,
as do all members of the tribe Phyllotini. Arthropods are an insignificant portion of their
diet (MacDonald 2001).
Remarks:
A. pearsoni is a known carrier of hantavirus pulmonary syndrome (HPS). A large
outbreak of the disease occurred in Paraguay in 1995 (Yahnke 1999). This disease is
deadly to humans. It is transmitted by various means, including through the droppings,
urine or saliva of the infected rodent (National Center for Infectious Diseases date).
Andalgalomys was formerly included in the genus Graomys, as of its discovery in
1977. In 1978 the genus was changed to Andalgalomys (Braun and Mares 1996). There
is still strong support for changing the mouse back to the genus Graomys (Braun and
Mares 2000). DNA evidence, however; shows that these two genuses are not the same,
so the two should not be placed in synonymy. One of the DNA disparities is the differing
number of diploids (Anderson and Yates 2000).
Literature Cited:
Anderson S., and T.L. Yates. 2000. A new genus and species of Phyllotine rodent
from Bolivia. Journal of Mammalogy 81(1):18-36.
Braun, J. K., and M. A. Mares. 1996. A new species of Phyllotine rodent, genus
Andalgalomys (Muridae: Sigmodontinae) from Argentina. Journal of
Mammalogy 77(4): 928-941.
________________________. 2000. Graomys, the genus that ate South America: a
reply to Steppan and Sullivan. Journal of Mammalogy 81(1):271-276.
Eisenberg, J. F., and K. H. Redford. 1992. Mammals of the Neotropics-The Southern
Cone Volume 2. University of Chicago Press, Chicago, Illinois.
MacDonald, D. 2001. Encyclopedia of Mammals. Andromeda Oxford Limited, New
York, New York.
Myers, P. 1977. A new Phyllotine rodent (genus Graomys) from Paraguay. Occasional
Papers of the Museum of Zoology, University of Michigan. 676:1-7.
National Center for Infectious Diseases. Date
http://www.cdc.gov/ncidod/diseaes/hanta/hps . (Accessed 3 December 2004).
Nowak, R. M. and J. L. Paradiso. 1999. Walker’s Mammals of the World, 4th ed.
Johns Hopkins University Press, Baltimore, Maryland.
“Tree of Life Web Project: Phyllotini.” Date http://www.tolweb.org/tree/phylogeny.html.
(Accessed 3 December 2004).
Yahnke, C. J. 1999. Community ecology and habitat associations of small mammals in
the endemic region of Hantavirus Pulmonary Syndrome in the central Paraguayan
Chaco.” Diss., Northern Illinois University.
Figure 1. Distribution of Andalgalomys pearsoni
Source: http://www.natureserve.org/infonatura/index.html