Chilean Climbing Mouse
Encyclopedia
Irenomys tarsalis, also known as the Chilean Climbing Mouse, Chilean Tree Mouse, or Long-footed Irenomys, is a rodent
found in Chile, from about 36° to 46°S, and in adjacent Argentina, mainly in forests. It is a large, long-tailed, soft-furred mouse characterized by grooved upper incisor
s and specialized molar
s with transverse ridges, divided by deep valleys, which are connected by a transverse ridge along the midline of the molars.
I. tarsalis is a docile, herbivorous animal that lives in trees. It is so distinct from other species that it is placed in its own genus
, Irenomys, which was named in 1919 in reference to the end of World War I
. Although it has been generally placed in the tribe Phyllotini, genetic evidence does not support any close relationships with other genera, so that it is now classified as a member of the subfamily Sigmodontinae
incertae sedis
(of uncertain position).
in mainland Chile) and Reithrodon longicaudatus (from a small island near Chiloé), both of which are now classified as Irenomys tarsalis. Philippi's Reithrodon longicaudatus was transferred into a new genus, Irenomys, by Oldfield Thomas
in February 1919. The name, which means "peace mouse" in Greek, referred to the end of World War I
four months before. Another of the species Philippi described in 1900, Mus mochae, was later transferred to Irenomys because of a mismatch between the skin and skull, but it is in fact a member of the genus Abrothrix
and not closely related to Irenomys. In his 1943 work on The mammals of Chile, Wilfred Hudson Osgood
recognized the close relation between Philippi's Mus tarsalis and Reithrodon longicaudatus and referred them to a single species, then called Irenomys tarsalis. Osgood retained two subspecies
, Irenomys tarsalis tarsalis on the mainland and Irenomys tarsalis longicaudatus on Chiloé and nearby islands, on the basis of slight differences in pelage coloration. In the few mature specimens of the latter subspecies that Osgood had, the underparts are somewhat lighter than in examples of I. t. tarsalis, which has a pinkish color in the underparts, but Osgood stressed that further material could well indicate that the two forms could not be distinguished.
In his description of the genus, Thomas opined that Irenomys is most closely related to Phyllotis
. The group of genera related to Phyllotis was later formalized as the tribe Phyllotini, and Irenomys was often included there, but also excluded from it by some authors. In 1995, a cladistic
analysis of Phyllotini on the basis of morphology
provided evidence in favor of placement of Irenomys in the group, with some support for a close relation to Andinomys. From 1999 on, DNA sequence data cast doubt on this assignment, as studies using the mitochondrial
cytochrome b
gene and the nuclear
IRBP
gene placed Irenomys in a variety of positions, all outside Phyllotini, with Scolomys
, Sigmodon, Euneomys
, and various large clade
s of sigmodontines
all as sister groups in some analyses. Accordingly, it is now classified outside Phyllotini and considered as Sigmodontinae incertae sedis
.
includes 64 chromosome
s, with a fundamental number (FN) of 98.
The skull resembles that of some Rhipidomys
species. The interorbital region
is narrow and the incisive foramina
are long, extending between the first molar
s. The upper incisor
s are deeply grooved. The molars are strongly hypsodont
(high-crowned) and consist of transverse, diamond-shaped laminae (plates), separated by deep valleys, which are joined at the midline by narrow ridges, similar to those of the African elephant.
s are known. It generally occurs in humid and densely forested habitats, often with bamboo
vegetations, but a specimen has been reported from ripuarian
vegetation at a small stream near the southern limit of its distribution and it is also found in unforested steppe habitat with scattered Austrocedrus chilensis trees. It does not occur on high elevations. It was a common species during a population peak of small rodents evidently caused by the flowering of quila (Chusquea quila) bamboo.
It is found in association with other rodents such as Abrothrix olivaceus, Abrothrix longipilis, Oligoryzomys longicaudatus, Geoxus valdivianus, and Auliscomys pictus, as well as the marsupials Rhyncholestes raphanurus and Dromiciops gliroides. Remains of Irenomys have been found in owl pellets
of the Great Horned Owl
(Bubo virginianus), Rufous-legged Owl
(Strix rufipes), and Barn Owl
(Tyto alba); other potential predators include another owl, the Austral Pygmy-owl
(Glaucidium nanum), and the South American Gray Fox (Pseudalopex griseus), Darwin's Fox
(Pseudalopex fulvipes) and Kodkod
(Leopardus guigna).
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
found in Chile, from about 36° to 46°S, and in adjacent Argentina, mainly in forests. It is a large, long-tailed, soft-furred mouse characterized by grooved upper incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
s and specialized molar
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
s with transverse ridges, divided by deep valleys, which are connected by a transverse ridge along the midline of the molars.
I. tarsalis is a docile, herbivorous animal that lives in trees. It is so distinct from other species that it is placed in its own genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
, Irenomys, which was named in 1919 in reference to the end of World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
. Although it has been generally placed in the tribe Phyllotini, genetic evidence does not support any close relationships with other genera, so that it is now classified as a member of the subfamily Sigmodontinae
Sigmodontinae
The subfamily Sigmodontinae is one of the most diverse groups of mammals. It includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the species count...
incertae sedis
Incertae sedis
, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
(of uncertain position).
Taxonomy
In 1900, Rodolfo Armando Philippi named both Mus tarsalis (from Valdivia ProvinceValdivia Province
Valdivia Province is one of two provinces of the southern Chilean region of Los Ríos . The provincial capital is Valdivia. Located in the province are two important rivers, the Calle-Calle / Valdivia River and the Cruces River.It is part of Northern Patagonia and its wild virgin forest embrace the...
in mainland Chile) and Reithrodon longicaudatus (from a small island near Chiloé), both of which are now classified as Irenomys tarsalis. Philippi's Reithrodon longicaudatus was transferred into a new genus, Irenomys, by Oldfield Thomas
Oldfield Thomas
Oldfield Thomas FRS was a British zoologist.Thomas worked at the Natural History Museum on mammals, describing about 2,000 new species and sub-species for the first time. He was appointed to the Museum Secretary's office in 1876, transferring to the Zoological Department in 1878...
in February 1919. The name, which means "peace mouse" in Greek, referred to the end of World War I
Armistice with Germany (Compiègne)
The armistice between the Allies and Germany was an agreement that ended the fighting in the First World War. It was signed in a railway carriage in Compiègne Forest on 11 November 1918 and marked a victory for the Allies and a complete defeat for Germany, although not technically a surrender...
four months before. Another of the species Philippi described in 1900, Mus mochae, was later transferred to Irenomys because of a mismatch between the skin and skull, but it is in fact a member of the genus Abrothrix
Abrothrix
Abrothrix is a genus of rodent in the tribe Abrotrichini of family Cricetidae.It contains the following living species:*Abrothrix andinus*Abrothrix hershkovitzi*Abrothrix illuteus*Abrothrix jelskii*Abrothrix lanosus...
and not closely related to Irenomys. In his 1943 work on The mammals of Chile, Wilfred Hudson Osgood
Wilfred Hudson Osgood
Wilfred Hudson Osgood was an American zoologist.Osgood was working as a biologist in the United States Department of Agriculture from 1897 to 1909. Then he moved to the Field Museum of Natural History in Chicago, where he was assistant curator of mammalogy and ornithology from 1909 to 1921, and...
recognized the close relation between Philippi's Mus tarsalis and Reithrodon longicaudatus and referred them to a single species, then called Irenomys tarsalis. Osgood retained two subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
, Irenomys tarsalis tarsalis on the mainland and Irenomys tarsalis longicaudatus on Chiloé and nearby islands, on the basis of slight differences in pelage coloration. In the few mature specimens of the latter subspecies that Osgood had, the underparts are somewhat lighter than in examples of I. t. tarsalis, which has a pinkish color in the underparts, but Osgood stressed that further material could well indicate that the two forms could not be distinguished.
In his description of the genus, Thomas opined that Irenomys is most closely related to Phyllotis
Phyllotis
Phyllotis is a genus of rodent in the family Cricetidae.It contains the following species:* Phyllotis alisosiensis* Friendly Leaf-eared Mouse * Andean Leaf-eared Mouse...
. The group of genera related to Phyllotis was later formalized as the tribe Phyllotini, and Irenomys was often included there, but also excluded from it by some authors. In 1995, a cladistic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
analysis of Phyllotini on the basis of morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
provided evidence in favor of placement of Irenomys in the group, with some support for a close relation to Andinomys. From 1999 on, DNA sequence data cast doubt on this assignment, as studies using the mitochondrial
Mitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
cytochrome b
Cytochrome b
Cytochrome b/b6 is the main subunit of transmembrane cytochrome bc1 and b6f complexes. In addition, it commonly refers to a region of mtDNA used for population genetics and phylogenetics.- Function :...
gene and the nuclear
Nuclear DNA
Nuclear DNA, nuclear deoxyribonucleic acid , is DNA contained within a nucleus of eukaryotic organisms. In mammals and vertebrates, nuclear DNA encodes more of the genome than the mitochondrial DNA and is composed of information inherited from two parents, one male, and one female, rather than...
IRBP
RBP3
Retinol-binding protein 3, interstitial , also known as IRBP is a protein that in humans is encoded by the RBP3 gene. RBP3 orthologs have been identified in most eutherians except tenrecs and armadillos.- Function :...
gene placed Irenomys in a variety of positions, all outside Phyllotini, with Scolomys
Scolomys
Scolomys is a genus of rodent in the tribe Oryzomyini of family Cricetidae. Some evidence suggests that it is related to Zygodontomys. It is characterized, among other traits, by spiny fur. It contains two species, Scolomys melanops and Scolomys ucayalensis.-Literature cited:*Musser, G.G. and...
, Sigmodon, Euneomys
Euneomys
Euneomys is a genus of rodent in the family Cricetidae.It contains the following species:* Patagonian Chincilla Mouse * Burrowing Chincilla Mouse * Biting Chincilla Mouse...
, and various large clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
s of sigmodontines
Sigmodontinae
The subfamily Sigmodontinae is one of the most diverse groups of mammals. It includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the species count...
all as sister groups in some analyses. Accordingly, it is now classified outside Phyllotini and considered as Sigmodontinae incertae sedis
Incertae sedis
, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
.
Description
Irenomys is a large mouse with a long, hairy tail, large eyes, and long and soft fur. The upperparts are rufous with fine dark lines and the underparts are buff, with the exact color varying by subspecies. The densely haired ears are medium-sized and blackish in color. The feet, which are large and broad, are nearly white. The tail, which ends in a slight pencil, is dark brown, with a somewhat lighter area present on the ventral side in some individuals. The total length is 270 to 326 mm (10.6 to 12.8 in), averaging 280 millimetres (11.02 in), the tail length is 162 to 196 mm (6.4 to 7.7 in), averaging 165 millimetres (6.5 in), the hindfoot length is 28 to 32 mm (1.1 to 1.3 in), averaging 30 millimetres (1.18 in), the ear length is 20 to 25 mm (0.78740157480315 to 0.984251968503937 in), averaging 22 millimetre (0.866141732283465 in), and weight is 40 to 59 g (1.4 to 2.1 oz), averaging 42 grams (1.5 oz). The karyotypeKaryotype
A karyotype is the number and appearance of chromosomes in the nucleus of an eukaryotic cell. The term is also used for the complete set of chromosomes in a species, or an individual organism.p28...
includes 64 chromosome
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
s, with a fundamental number (FN) of 98.
The skull resembles that of some Rhipidomys
Rhipidomys
Rhipidomys is a genus of rodents in the family Cricetidae, comprising at least 18 species of climbing mouse:* Southern Climbing Mouse * Cariri Climbing Mouse...
species. The interorbital region
Interorbital region
The interorbital region of the skull is located between the eyes, anterior to the braincase. The form of the interorbital region may exhibit significant variation between taxonomic groups....
is narrow and the incisive foramina
Incisive foramen
The fossa incisiva is an opening in the bone of the oral hard palate where blood vessels and nerves may pass. There are four of these openings in the incisive fossa.-Formation:...
are long, extending between the first molar
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
s. The upper incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
s are deeply grooved. The molars are strongly hypsodont
Hypsodont
Hypsodont dentition is characterized by high-crowned teeth and enamel which extends past the gum line. This provides extra material for wear and tear. Some examples of animals with hypsodont dentition are cows, horses and deer; all animals that feed on gritty, fibrous material. The opposite...
(high-crowned) and consist of transverse, diamond-shaped laminae (plates), separated by deep valleys, which are joined at the midline by narrow ridges, similar to those of the African elephant.
Distribution and ecology
Irenomys tarsalis is restricted to forested habitats in Chile and western Argentina. In the northern part of its range, its distribution falls into two segments, one in coastal Chile and one further east in Chile and in adjacent Argentina, both of which extend north to about 36°S. Further south, it also occurs in Chile and adjacent Argentina, and also on numerous Chilean islands, including Chiloé. The southernmost records are at about 46°S. No fossilFossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s are known. It generally occurs in humid and densely forested habitats, often with bamboo
Bamboo
Bamboo is a group of perennial evergreens in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae. Giant bamboos are the largest members of the grass family....
vegetations, but a specimen has been reported from ripuarian
Ripuarian
Ripuarian is a German dialect group, part of the West Central German language group....
vegetation at a small stream near the southern limit of its distribution and it is also found in unforested steppe habitat with scattered Austrocedrus chilensis trees. It does not occur on high elevations. It was a common species during a population peak of small rodents evidently caused by the flowering of quila (Chusquea quila) bamboo.
It is found in association with other rodents such as Abrothrix olivaceus, Abrothrix longipilis, Oligoryzomys longicaudatus, Geoxus valdivianus, and Auliscomys pictus, as well as the marsupials Rhyncholestes raphanurus and Dromiciops gliroides. Remains of Irenomys have been found in owl pellets
Pellet (ornithology)
A pellet, in ornithology, is the mass of undigested parts of a bird's food that some bird species occasionally regurgitate. The contents of a bird's pellet depend on its diet, but can include the exoskeletons of insects, indigestible plant matter, bones, fur, feathers, bills, claws, and teeth...
of the Great Horned Owl
Great Horned Owl
The Great Horned Owl, , also known as the Tiger Owl, is a large owl native to the Americas. It is an adaptable bird with a vast range and is the most widely distributed true owl in the Americas.-Description:...
(Bubo virginianus), Rufous-legged Owl
Rufous-legged Owl
The Rufous-legged Owl is a medium sized owl with no ear tufts. Its upper parts are rufous brown barred with white with more white on the head and nape. It has a rufous facial disk and dark eyes, and its legs and feet are orange-brown to cinnamon. It grows to a size about 33-38 cm long and weighs...
(Strix rufipes), and Barn Owl
Barn Owl
The Barn Owl is the most widely distributed species of owl, and one of the most widespread of all birds. It is also referred to as Common Barn Owl, to distinguish it from other species in the barn-owl family Tytonidae. These form one of two main lineages of living owls, the other being the typical...
(Tyto alba); other potential predators include another owl, the Austral Pygmy-owl
Austral Pygmy-owl
The Austral Pygmy Owl is a species of owl in the Strigidae family.It is found in Argentina and Chile.Its natural habitat is temperate forests.-References:* BirdLife International 2004. . Downloaded on 24 July 2007....
(Glaucidium nanum), and the South American Gray Fox (Pseudalopex griseus), Darwin's Fox
Darwin's Fox
Darwin's fox or Darwin's Zorro is a small Critically endangered canine from the genus Lycalopex. It is also known as the Zorro Chilote or Zorro de Darwin in Spanish and lives on Chiloé Island and Nahuelbuta National Park in mainland Chile .Darwin's fox was first collected from San Pedro Island off...
(Pseudalopex fulvipes) and Kodkod
Kodkod
The Kodkod , also called Guiña, is the smallest cat in the Americas and also has the smallest distribution, being found primarily in central and southern Chile and marginally in adjoining areas of Argentina...
(Leopardus guigna).
Natural history and behavior
Irenomys lives mainly in trees, but has also been caught on the ground. It climbs by moving both forefeet and both hindfeet alternately. It is docile, but will not readily enter a trap. The breeding season is in the Southern Hemisphere spring, extending into late summer. Litter size is three to six. The animal mostly eats seeds and fruits, but its diet also includes various other plant and fungal materials.Conservation status
Irenomys is not currently threatened and it is classified as "least concern" by the International Union for the Conservation of Nature. It occurs in several protected areas, but destruction of its forest habitat may pose a threat to some populations.Literature cited
- D'Elía, G., Luna, L., González, E.M. and Patterson, B.D. 2006. On the sigmodontine radiation (Rodentia, Cricetidae): An appraisal of the phylogenetic position of Rhagomys. Molecular Phylogenetics and Evolution 38:558–564
- D'Elía, G., González, E.M. and Pardiñas, U.F.J. 2003. Phylogenetic analysis of sigmodontine rodents (Muroidea), with special reference to the akodont genus Deltamys. Mammalian Biology 68:351–364.
- D'Elía, G. 2003. Phylogenetics of Sigmodontinae (Rodentia, Muroidea, Cricetidae), with special reference to the akodont group, and with additional comments on historical biogeography. Cladistics 19:307–323.
- Hershkovitz, P. 1962. Evolution of Neotropical cricetine rodents (Muridae) with special reference to the phyllotine group. Fieldiana Zoology 46:1–524.
- Kelt, D.A. 1993. Irenomys tarsalis. Mammalian Species 447:1–3.
- Kelt, D.A., Engilis, A., Jr., Torres, I.E. and Hitch, A.T. 2006. Ecologically significant range extension for the Chilean tree mouse, Irenomys tarsalis. Mastozoología Neotropical 15(1):125–128.
- Martínez, D.R. 1993. Food habits of the rufous-legged owl (Strix rufipes) in temperate rainforests of southern Chile. Journal of Raptor Research 27(4):214–216.
- Musser, G.G. and Carleton, M.D. 2005. Superfamily Muroidea. Pp. 894–1531 in Wilson, D.E. and Reeder, D.M. (eds.). Mammal Species of the World: a taxonomic and geographic reference. 3rd ed. Baltimore: The Johns Hopkins University Press, 2 vols., 2142 pp. ISBN 978-0-8018-8221-0
- Ojeda, A.A., Ríos, C.A. and Gallardo, M.H. 2004. Chromosomal characterization of Irenomys tarsalis (Rodentia, Cricetidae, Sigmodontinae). Mastozoología Neotropical 11(1):95–98.
- Osgood, W.H. 1943. The mammals of Chile. Fieldiana Zoology 30:1–268.
- Pardinas, U., Patterson, B., D'Elia, G. and Teta, P. 2008. . In IUCN. IUCN Red List of Threatened Species. Version 2009.2. <www.iucnredlist.org>. Downloaded on November 6, 2009.
- Smith, M.F. and Patton, J.L. 1999. Phylogenetic relationships and the radiation of sigmodontine rodents in South America: Evidence from cytochrome b. Journal of Mammalian Evolution 6(2):89–128.
- Steppan, S.J. 1995. Revision of the tribe Phyllotini (Rodentia: Sigmodontinae), with a phylogenetic hypothesis for the Sigmodontinae. Fieldiana Zoology 80:1–112.
- Thomas, O. 1919. On small mammals collected by Sr. E. Budin in North-western Patagonia. Annals and Magazine of Natural History (9)3:199–212.