Spegazzini's Grass Mouse
Encyclopedia
Akodon spegazzinii, also known as Spegazzini's Akodont or Spegazzini's Grass Mouse, is a rodent
in the genus Akodon
found in northwestern Argentina
. It occurs in grassland and forest at 400 to 3500 m (1300 to 11500 ft) above sea level. After the species was first named in 1897, several other names were given to various populations now included in A. spegazzinii. They are now all recognized as part of a single, widespread and variable species. Akodon spegazzinii is related to Akodon boliviensis and other members of the A. boliviensis species group
. It reproduces year-round. Because it is widely distributed and common, Akodon spegazzinii is listed as "Least Concern
" on the IUCN Red List
.
Akodon spegazzinii is medium in size for the A. boliviensis species group. The coloration of its upperparts varies considerably, from light to dark and from yellowish to reddish brown. The underparts are yellow-brown to gray. The eyes are surrounded by a ring of yellow fur. The skull contains a hourglass-shaped interorbital region
(between the eyes) and various features of the skull distinguish the species from its close allies. Head and body length is 93 to 196 mm (3.7 to 7.7 in) and body mass is 13.0 to 38.0 g (0.46 to 1.34 oz). A. spegazzinii has 40 chromosome
s.
by Oldfield Thomas
on the basis of a collection made in late 1896 or early 1897 by mycologist Carlos Luigi Spegazzini
, after whom the species was named. Four years later, Joel Asaph Allen
named Akodon tucumanensis from Tucumán Province
, comparing it to various species now synonymized
under Abrothrix olivaceus. Thomas named an additional species, Akodon alterus, from La Rioja Province
in 1919, and considered it closely related to A. spegazzinii. A fourth species, Akodon leucolimnaeus, was described by Ángel Cabrera
from Catamarca Province
in 1926, but after 1932 it was associated with Akodon lactens (now Necromys lactens) as a subspecies
.
In 1961, Cabrera listed both spegazzinii and tucumanensis as subspecies of Akodon boliviensis, with alterus as a full synonym of A. boliviensis tucumanensis. In 1990, Philip Myers and colleagues reviewed the Akodon boliviensis species group. They provisionally kept Akodon spegazzinii as a species separate from A. boliviensis, with tucumanensis as a subspecies, and suggested that alterus was likely related to spegazzinii and tucumanensis. Subsequently, the treatment of these species in systematic
works became variable. A 1992 paper suggested that alterus and tucumanensis were, at best, very similar to each other, but in 1997, Michael Mares and colleagues listed each of the three as distinct species in a compendium of the mammals of Catamarca, citing differences in habitat and fur coloration. They were followed by Mónica Díaz and Rubén Bárquez in 2007, among others. However, in 2000 Díaz and colleagues listed alterus and tucumanensis as subspecies of spegazzinii in a review of the mammals of Salta. Guy Musser
and Michael Carleton, in the 2005 third edition of Mammal Species of the World
, also considered the three to represent the same species, as did Ulyses Pardiñas and colleagues in a 2006 review of Argentinean Akodontini
. Meanwhile, Carlos Galliari and Pardiñas had recognized Akodon leucolimnaeus as a true Akodon, not a Necromys, in 1995. Although associated with the Akodon boliviensis group, its precise status remained unclear. The common name
"Catamarca Akodont" was proposed for this species.
In 1980, Julio Contreras and María Rosi identified an Akodon from the province of Mendoza
as Akodon varius neocenus (now Akodon neocenus), but the following year, they identified it as a new species, named Akodon minoprioi in a presentation at a scientific meeting. However, this name was never formally validated. In 2000, Janet Braun and colleagues formally named this species Akodon oenos and allied it to the Akodon varius species group. The specific name, oenos, is Greek for "wine" and refers to the animal's occurrence in the wine-producing region of Mendoza. The common names "Monte Akodont" and "Wine Grass Mouse" were proposed for this species.
In 2010, Pablo Jayat and colleagues reviewed the members of the Akodon boliviensis species group, including A. spegazzinii, in Argentina. They could not find clear differentiation in either morphological or molecular characters between animals belonging to A. alterus, A. leucolimnaeus, A. spegazzinii, and A. tucumanensis, and consequently concluded that they all represent a single species. Although genetic variation is relatively high within A. spegazzinii, there is no clear geographic structure among haplotype
s from different regions. The next year, Ulyses Pardiñas and colleagues concluded that A. oenos, which had formerly, and incorrectly, been placed in the A. varius species group, was in fact another synonym
of A. spegazzinii. The proliferation of scientific names for this one species occurred because of the terseness of the original description of A. spegazzinii, and a lack of large samples and of appreciation of the substantial variation occurring within A. spegazzinii.
According to phylogenetic analysis of sequences
from the mitochondrial
cytochrome b
gene, Akodon spegazzinii is most closely related to A. boliviensis and more distantly to other members of the A. boliviensis species group, including Akodon polopi and Akodon sylvanus. The boliviensis group is part of the highly diverse genus Akodon
and thereby of the tribe Akodontini
, which includes about 90 species of South American rodents. Akodontini is one of several tribes within the subfamily Sigmodontinae
and the family Cricetidae
, which includes hundreds of mainly small rodents distributed chiefly in Eurasia and the Americas.
The coloration of the upperparts is generally uniform, with some scattered darker hairs. There is a yellow ring around the eyes, which is more prominent than in A. sylvanus. The underparts are not strongly demarcated from the upperparts in color and are yellow-brown to gray. There are some scattered white hairs on the chin. Although this white spot is better developed than in A. sylvanus, A. spegazzinii lacks the conspicuous white spot seen in A. simulator. The color of the feet ranges from white and yellow-brown to gray. Ungual tuft
s of hairs cover the claws; these hairs are grayish-brown at the bases and whitish at the tips. The amount of hair on the tail is variable, but it is dark brown above and white to yellow-brown below. High-altitude animals tend to have hairier ears and tails.
In the skull, the front part (rostrum) is large, but not as long as in A. budini. The skull is more robust than in the very similar Akodon boliviensis, but less so than in A. simulator. The hourglass-shaped interorbital region
(between the eyes) is narrower than in A. caenosus and not as squared as in A. polopi. Members of the Akodon varius group, with which Akodon oenos was formerly associated, tend to have much broader interorbital regions. The braincase is somewhat inflated and bears well-developed temporal and lambdoid crests relative to the situation in A. caenosus; Akodon polopi, however, has even better developed crests.
Although the zygomatic plate
s (plates of bone at the side of the skull) are variable, their size is generally intermediate for the Akodon boliviensis group and their front margin ranges from straight to a little concave. The zygomatic notches, projections at the front of the plates, are better developed than in A. caenosus and A. sylvanus. The incisive foramina (openings in the front part of the palate
) are long, sometimes extending between the first upper molars
. Tiny posterolateral palatal pits
are located at the back of the palate. The back margin of the palate is squared to rounded, with a spine in the middle (medial process) sometimes present. The opening behind the palate, the mesopterygoid fossa, is of intermediate width, being narrower than in A. sylvanus, A. simulator, and A. budini but broader than in A. caenosus.
The masseteric crests (crests on the outer sides of the mandible
s) reach their front ends below the front border of the first molars. Usually, the capsular process
(a projection at the back of the mandible housing the root of the lower incisor
) is well-developed. The enamel
of the upper incisors is yellowish-orange and the incisors are orthodont (with their cutting edge perpendicular to the plane of the toothrow) or slightly opisthodont (with the cutting edge inclined backwards). In contrast, Akodon simulator has more proodont incisors (with the cutting edge oriented forwards) and Akodon neocenus has more opisthodont incisors. The molars
are more hypsodont
(high-crowned) than in A. caenosus, but are unlike the very hypsodont molars of A. budini. The molar rows are relatively longer than in A. polopi. There are 13 or 14 thoracic (chest), 7 or 8 lumbar (abdomen), and 23 or 26 caudal (tail) vertebrae.
The karyotype
includes 40 chromosome
s, with a fundamental number of 40 major chromosomal arms and resembles that of other members of the A. boliviensis group. Head and body length is 93 to 196 mm (3.7 to 7.7 in), averaging 158 mm (6.2 in); tail length is 46 to 83 mm (1.8 to 3.3 in), averaging 66 mm (2.6 in); hindfoot length is 18 to 25 mm (0.7 to 1 in), averaging 23 mm (0.9 in); ear length is 12 to 21 mm (0.5 to 0.8 in), averaging 14 mm (0.6 in); and body mass is 13.0 to 38.0 g (0.46 to 1.34 oz), averaging 21.6 g (0.76 oz). Like other members of the Akodon boliviensis group, individuals of Akodon spegazzinii continue to grow in adulthood.
(Lujanian
); it is among the most common species there. The species occurs in the Yungas
forest as well as the drier Monte Desert
and Puna
, where it is found only along streams. In the cloud grasslands of the higher portions of the Yungas, it is the dominant species of sigmodontine rodent.
Although reproduction occurs around the year, there is a peak during the summer (November to April). Molting mostly occurs during autumn and winter (April to August). At one locality in Mendoza, Akodon spegazzinii occurs at an estimated density of 21 individuals per hectare (8.5 per acre) and has a home range size of about 300 m2 (3200 sq ft). A number of sigmodontines have been recorded as occurring with A. spegazzinii, including A. caenosus, A. simulator, Neotomys ebriosus, Abrothrix illuteus, Reithrodon auritus, Andinomys edax, and various species of Eligmodontia
, Necromys
, Calomys, Oligoryzomys
, Oxymycterus
, and Phyllotis
. The tick Ixodes sigelos has been recorded on A. spegazzinii in Tucumán. In addition, the mites Androlaelaps fahrenholzi
, Androlaelaps rotundus, and Eulaelaps stabularis and the flea Cleopsylla townsendii are known from the species.
" on the IUCN Red List
in view of its wide distribution and apparently stable population; in addition, it occurs in several protected area
s. However, both Akodon oenos and Akodon leucolimnaeus are listed as "Data Deficient
" with a trend of declining populations; they are said to be threatened by agricultural development.
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....
in the genus Akodon
Akodon
Akodon is a genus consisting of South American grass mice. They mostly occur south of the Amazon Basin and along the Andes north to Venezuela, but are absent from much of the basin itself, the far south of the continent, and the lowlands west of the Andes. Akodon is one of the most species-rich...
found in northwestern Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
. It occurs in grassland and forest at 400 to 3500 m (1300 to 11500 ft) above sea level. After the species was first named in 1897, several other names were given to various populations now included in A. spegazzinii. They are now all recognized as part of a single, widespread and variable species. Akodon spegazzinii is related to Akodon boliviensis and other members of the A. boliviensis species group
Species group
A species group is an informal taxonomic rank into which an assemblage of closely related species within a genus are grouped because of their morphological similarities and their identity as a biological unit with a single monophyletic origin.-Use:...
. It reproduces year-round. Because it is widely distributed and common, Akodon spegazzinii is listed as "Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
" on the IUCN Red List
IUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...
.
Akodon spegazzinii is medium in size for the A. boliviensis species group. The coloration of its upperparts varies considerably, from light to dark and from yellowish to reddish brown. The underparts are yellow-brown to gray. The eyes are surrounded by a ring of yellow fur. The skull contains a hourglass-shaped 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....
(between the eyes) and various features of the skull distinguish the species from its close allies. Head and body length is 93 to 196 mm (3.7 to 7.7 in) and body mass is 13.0 to 38.0 g (0.46 to 1.34 oz). A. spegazzinii has 40 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.
Taxonomy
Akodon spegazzinii was first described in 1897 from Salta ProvinceSalta Province
Salta is a province of Argentina, located in the northwest of the country. Neighboring provinces are from the east clockwise Formosa, Chaco, Santiago del Estero, Tucumán and Catamarca. It also surrounds Jujuy...
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...
on the basis of a collection made in late 1896 or early 1897 by mycologist Carlos Luigi Spegazzini
Carlos Luigi Spegazzini
Carlos Luis Spegazzini, or Carlo Luigi Spegazzini, was an Italian-Argentinian botanist and mycologist. Spegazzini published about 100 scientific papers on vascular plants, describing around 1000 new taxa...
, after whom the species was named. Four years later, Joel Asaph Allen
Joel Asaph Allen
Joel Asaph Allen was an American zoologist and ornithologist, born in Springfield, Massachusetts.He studied at Harvard University under Louis Agassiz...
named Akodon tucumanensis from Tucumán Province
Tucumán Province
Tucumán is the most densely populated, and the smallest by land area, of the provinces of Argentina. Located in the northwest of the country, the capital is San Miguel de Tucumán, often shortened to Tucumán. Neighboring provinces are, clockwise from the north: Salta, Santiago del Estero and...
, comparing it to various species now synonymized
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
under Abrothrix olivaceus. Thomas named an additional species, Akodon alterus, from La Rioja Province
La Rioja Province (Argentina)
La Rioja is a one of the provinces of Argentina and is located in the west of the country. Neighboring provinces are from the north clockwise Catamarca, Córdoba, San Luis and San Juan.-History:...
in 1919, and considered it closely related to A. spegazzinii. A fourth species, Akodon leucolimnaeus, was described by Ángel Cabrera
Ángel Cabrera (naturalist)
Ángel Cabrera was a Spanish zoologist.Cabrera was born in Madrid and studied at the city's university. He worked the National Museum of Natural Sciences from 1902, going on several collecting expeditions to Morocco....
from Catamarca Province
Catamarca Province
Catamarca is a province of Argentina, located in the northwest of the country. The province has a population of 334,568 as per the , and covers an area of 102,602 km². Its literacy rate is 95.5%. Neighbouring provinces are : Salta, Tucumán, Santiago del Estero, Córdoba, and La Rioja...
in 1926, but after 1932 it was associated with Akodon lactens (now Necromys lactens) as a 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...
.
In 1961, Cabrera listed both spegazzinii and tucumanensis as subspecies of Akodon boliviensis, with alterus as a full synonym of A. boliviensis tucumanensis. In 1990, Philip Myers and colleagues reviewed the Akodon boliviensis species group. They provisionally kept Akodon spegazzinii as a species separate from A. boliviensis, with tucumanensis as a subspecies, and suggested that alterus was likely related to spegazzinii and tucumanensis. Subsequently, the treatment of these species in systematic
Systematics
Biological systematics is the study of the diversification of terrestrial life, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...
works became variable. A 1992 paper suggested that alterus and tucumanensis were, at best, very similar to each other, but in 1997, Michael Mares and colleagues listed each of the three as distinct species in a compendium of the mammals of Catamarca, citing differences in habitat and fur coloration. They were followed by Mónica Díaz and Rubén Bárquez in 2007, among others. However, in 2000 Díaz and colleagues listed alterus and tucumanensis as subspecies of spegazzinii in a review of the mammals of Salta. Guy Musser
Guy Musser
Guy Graham Musser is an American zoologist. His main research field is the subfamily Murinae, in which he has described many new species.Musser was born in Salt Lake City, Utah...
and Michael Carleton, in the 2005 third edition of Mammal Species of the World
Mammal Species of the World
Mammal Species of the World, now in its 3rd edition, is a standard reference work in zoology giving descriptions and bibliographic data for the known species of mammals.An updated Third Edition of Mammal Species of the World was published late in 2005:...
, also considered the three to represent the same species, as did Ulyses Pardiñas and colleagues in a 2006 review of Argentinean Akodontini
Akodontini
Akodontini is the second most speciose tribe of the subfamily Sigmodontinae. It includes at least 106 living species in 19 genera and is distributed mainly in the southern half of South America, with only two genera extending into Guyana and Venezuela . It also includes genera previously placed in...
. Meanwhile, Carlos Galliari and Pardiñas had recognized Akodon leucolimnaeus as a true Akodon, not a Necromys, in 1995. Although associated with the Akodon boliviensis group, its precise status remained unclear. The common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
"Catamarca Akodont" was proposed for this species.
In 1980, Julio Contreras and María Rosi identified an Akodon from the province of Mendoza
Mendoza Province
The Province of Mendoza is a province of Argentina, located in the western central part of the country in the Cuyo region. It borders to the north with San Juan, the south with La Pampa and Neuquén, the east with San Luis, and to the west with the republic of Chile; the international limit is...
as Akodon varius neocenus (now Akodon neocenus), but the following year, they identified it as a new species, named Akodon minoprioi in a presentation at a scientific meeting. However, this name was never formally validated. In 2000, Janet Braun and colleagues formally named this species Akodon oenos and allied it to the Akodon varius species group. The specific name, oenos, is Greek for "wine" and refers to the animal's occurrence in the wine-producing region of Mendoza. The common names "Monte Akodont" and "Wine Grass Mouse" were proposed for this species.
In 2010, Pablo Jayat and colleagues reviewed the members of the Akodon boliviensis species group, including A. spegazzinii, in Argentina. They could not find clear differentiation in either morphological or molecular characters between animals belonging to A. alterus, A. leucolimnaeus, A. spegazzinii, and A. tucumanensis, and consequently concluded that they all represent a single species. Although genetic variation is relatively high within A. spegazzinii, there is no clear geographic structure among haplotype
Haplotype
A haplotype in genetics is a combination of alleles at adjacent locations on the chromosome that are transmitted together...
s from different regions. The next year, Ulyses Pardiñas and colleagues concluded that A. oenos, which had formerly, and incorrectly, been placed in the A. varius species group, was in fact another synonym
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
of A. spegazzinii. The proliferation of scientific names for this one species occurred because of the terseness of the original description of A. spegazzinii, and a lack of large samples and of appreciation of the substantial variation occurring within A. spegazzinii.
According to phylogenetic analysis of sequences
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
from 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, Akodon spegazzinii is most closely related to A. boliviensis and more distantly to other members of the A. boliviensis species group, including Akodon polopi and Akodon sylvanus. The boliviensis group is part of the highly diverse genus Akodon
Akodon
Akodon is a genus consisting of South American grass mice. They mostly occur south of the Amazon Basin and along the Andes north to Venezuela, but are absent from much of the basin itself, the far south of the continent, and the lowlands west of the Andes. Akodon is one of the most species-rich...
and thereby of the tribe Akodontini
Akodontini
Akodontini is the second most speciose tribe of the subfamily Sigmodontinae. It includes at least 106 living species in 19 genera and is distributed mainly in the southern half of South America, with only two genera extending into Guyana and Venezuela . It also includes genera previously placed in...
, which includes about 90 species of South American rodents. Akodontini is one of several tribes within 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...
and the family Cricetidae
Cricetidae
The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, and New World rats and mice...
, which includes hundreds of mainly small rodents distributed chiefly in Eurasia and the Americas.
Description
The species is intermediate in size for the Akodon boliviensis species group; it is smaller than A. polopi and A. sylvanus, but larger than A. boliviensis and A. caenosus. The more distantly related A. budini and A. simulator, which occur in the same area, are larger. Akodon spegazzinii is variable in coloration, ranging from light to dark and from reddish to yellowish brown. In general, animals in wetter, lower-lying areas are darker, and those in open, dry environments are paler. However, there is also variation within populations, and sometimes young mice are darker and lactating females are more reddish. The formerly recognized species Akodon tucumanensis corresponds to the dark, low-altitude populations, while A. leucolimnaeus and A. alterus represent more reddish, high-altitude animals.The coloration of the upperparts is generally uniform, with some scattered darker hairs. There is a yellow ring around the eyes, which is more prominent than in A. sylvanus. The underparts are not strongly demarcated from the upperparts in color and are yellow-brown to gray. There are some scattered white hairs on the chin. Although this white spot is better developed than in A. sylvanus, A. spegazzinii lacks the conspicuous white spot seen in A. simulator. The color of the feet ranges from white and yellow-brown to gray. Ungual tuft
Ungual tuft
In mammals, ungual tufts are tufts of hairs at the base of claws of the fore- and hindfeet. Their presence has been used as a character in cladistic studies of Cricetidae....
s of hairs cover the claws; these hairs are grayish-brown at the bases and whitish at the tips. The amount of hair on the tail is variable, but it is dark brown above and white to yellow-brown below. High-altitude animals tend to have hairier ears and tails.
In the skull, the front part (rostrum) is large, but not as long as in A. budini. The skull is more robust than in the very similar Akodon boliviensis, but less so than in A. simulator. The hourglass-shaped 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....
(between the eyes) is narrower than in A. caenosus and not as squared as in A. polopi. Members of the Akodon varius group, with which Akodon oenos was formerly associated, tend to have much broader interorbital regions. The braincase is somewhat inflated and bears well-developed temporal and lambdoid crests relative to the situation in A. caenosus; Akodon polopi, however, has even better developed crests.
Although the zygomatic plate
Zygomatic plate
In rodent anatomy, the zygomatic plate is a bony plate derived from the flattened front part of the zygomatic arch . At the back, it connects to the front root of the zygomatic arch, and at the top it is connected to the rest of the skull via the antorbital bridge. It is part of the maxillary...
s (plates of bone at the side of the skull) are variable, their size is generally intermediate for the Akodon boliviensis group and their front margin ranges from straight to a little concave. The zygomatic notches, projections at the front of the plates, are better developed than in A. caenosus and A. sylvanus. The incisive foramina (openings in the front part of the palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
) are long, sometimes extending between the first upper molars
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"....
. Tiny posterolateral palatal pits
Posterolateral palatal pits
In anatomy, posterolateral palatal pits are gaps at the sides of the back of the bony palate, near the last molars. Posterolateral palatal pits are present, in various degrees of development, in several members of the rodent family Cricetidae...
are located at the back of the palate. The back margin of the palate is squared to rounded, with a spine in the middle (medial process) sometimes present. The opening behind the palate, the mesopterygoid fossa, is of intermediate width, being narrower than in A. sylvanus, A. simulator, and A. budini but broader than in A. caenosus.
The masseteric crests (crests on the outer sides of the mandible
Mandible
The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...
s) reach their front ends below the front border of the first molars. Usually, the capsular process
Capsular process
In rodents, the capsular process or projection is a bony capsule that contains the root of the lower incisor. It is visible on the labial side of the mandible as a raising in the bone...
(a projection at the back of the mandible housing the root of the lower incisor
Incisor
Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...
) is well-developed. The enamel
Tooth enamel
Tooth enamel, along with dentin, cementum, and dental pulp is one of the four major tissues that make up the tooth in vertebrates. It is the hardest and most highly mineralized substance in the human body. Tooth enamel is also found in the dermal denticles of sharks...
of the upper incisors is yellowish-orange and the incisors are orthodont (with their cutting edge perpendicular to the plane of the toothrow) or slightly opisthodont (with the cutting edge inclined backwards). In contrast, Akodon simulator has more proodont incisors (with the cutting edge oriented forwards) and Akodon neocenus has more opisthodont incisors. The molars
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"....
are more 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) than in A. caenosus, but are unlike the very hypsodont molars of A. budini. The molar rows are relatively longer than in A. polopi. There are 13 or 14 thoracic (chest), 7 or 8 lumbar (abdomen), and 23 or 26 caudal (tail) vertebrae.
The karyotype
Karyotype
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 40 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 of 40 major chromosomal arms and resembles that of other members of the A. boliviensis group. Head and body length is 93 to 196 mm (3.7 to 7.7 in), averaging 158 mm (6.2 in); tail length is 46 to 83 mm (1.8 to 3.3 in), averaging 66 mm (2.6 in); hindfoot length is 18 to 25 mm (0.7 to 1 in), averaging 23 mm (0.9 in); ear length is 12 to 21 mm (0.5 to 0.8 in), averaging 14 mm (0.6 in); and body mass is 13.0 to 38.0 g (0.46 to 1.34 oz), averaging 21.6 g (0.76 oz). Like other members of the Akodon boliviensis group, individuals of Akodon spegazzinii continue to grow in adulthood.
Distribution and ecology
Akodon spegazzinii is found in northwestern Argentina, in the provinces of Salta, Catamarca, Tucumán, La Rioja, and Mendoza, at altitudes of 400 to 3500 m (1300 to 11500 ft). Although its main distribution is in the northern provinces of Salta, Tucumán, and Catamarca, there are also scattered records from the more southern provinces of La Rioja and Mendoza, where it is likely restricted to patches of wet habitat. Akodon alterus has been reported from Jujuy, but this record was likely based on misidentified specimens of A. boliviensis, and records of Akodon spegazzinii from Jujuy were based on misidentified A. sylvanus. Akodon spegazzinii is known from a paleontological site in Tucumán Province dated to the latest PleistocenePleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
(Lujanian
Lujanian
The Lujanian age is a period of geologic time within the Pleistocene and Holocene epochs of the Neogene used more specifically with South American Land Mammal Ages...
); it is among the most common species there. The species occurs in the Yungas
Yungas
The Yungas is a stretch of forest along the eastern slope of the Andes Mountains from southeastern Peru through central Bolivia. It is a transitional zone between the Andean highlands and the eastern forests. Like the surrounding areas, it has characteristics of the Neotropic ecozone...
forest as well as the drier Monte Desert
Monte Desert
The Monte Desert is a South American desert, located within the country of Argentina. The desert lies southeast of the Atacama Desert in Chile, north of the larger Patagonian Desert, and east of the Andes.-Geography and climate:...
and Puna
Puna grassland
The Puna grassland ecoregion, of the montane grasslands and shrublands biome, is found in the central Andes Mountains of South America. It is considered one of the eight Natural Regions in Peru, but extends south as far as northern Argentina and Chile....
, where it is found only along streams. In the cloud grasslands of the higher portions of the Yungas, it is the dominant species of sigmodontine rodent.
Although reproduction occurs around the year, there is a peak during the summer (November to April). Molting mostly occurs during autumn and winter (April to August). At one locality in Mendoza, Akodon spegazzinii occurs at an estimated density of 21 individuals per hectare (8.5 per acre) and has a home range size of about 300 m2 (3200 sq ft). A number of sigmodontines have been recorded as occurring with A. spegazzinii, including A. caenosus, A. simulator, Neotomys ebriosus, Abrothrix illuteus, Reithrodon auritus, Andinomys edax, and various species of Eligmodontia
Eligmodontia
The genus Eligmodontia consists of five or six species of South American sigmodontine mice restricted to Bolivia, Chile, and Argentina. Species of Eligmodontia occur along the eastern side of the Andes Mountains, in Patagonia, and in the Chaco thorn forest of South America. They can be found in...
, Necromys
Necromys
Necromys is a genus of South American sigmodontine rodents allied to Akodon. This genus has also been known as Cabreramys or more recently Bolomys. N. urichi has recently been transferred from Akodon....
, Calomys, Oligoryzomys
Oligoryzomys
Oligoryzomys is a genus of rodents in the tribe Oryzomyini of family Cricetidae. Many species are known as pygmy rice rats or colilargos...
, Oxymycterus
Oxymycterus
Oxymycterus is the genus of hocicudos. They are rat-like animals endemic to South America.Species listing:Oxymycterus is the genus of hocicudos. They are rat-like animals endemic to South America.Species listing:...
, and 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 tick Ixodes sigelos has been recorded on A. spegazzinii in Tucumán. In addition, the mites Androlaelaps fahrenholzi
Androlaelaps fahrenholzi
Androlaelaps fahrenholzi is a species of mite in the genus Androlaelaps of the family Laelapidae. It occurs throughout the contiguous United States, where it has been recorded on the mammals Arborimus albipes, Arborimus longicaudus, Bassariscus astutus, Blarina brevicauda, Blarina carolinensis,...
, Androlaelaps rotundus, and Eulaelaps stabularis and the flea Cleopsylla townsendii are known from the species.
Conservation status
Akodon spegazzinii is listed as "Least ConcernLeast Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
" on the IUCN Red List
IUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...
in view of its wide distribution and apparently stable population; in addition, it occurs in several protected area
Protected area
Protected areas are locations which receive protection because of their recognised natural, ecological and/or cultural values. There are several kinds of protected areas, which vary by level of protection depending on the enabling laws of each country or the regulations of the international...
s. However, both Akodon oenos and Akodon leucolimnaeus are listed as "Data Deficient
Data Deficient
Data Deficient is a category applied by the IUCN, other agencies, and individuals to a species when the available information is not sufficient for a proper assessment of conservation status to be made...
" with a trend of declining populations; they are said to be threatened by agricultural development.
Literature cited
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