Eligmodontia
Encyclopedia
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 arid
and semiarid habitat
s and in both high and low elevation areas. These rodent
s are commonly known as gerbil mice or by their local name lauchas. Sometimes they are also called silky desert mice, highland desert mice or silky-footed mice. The closest living relatives are probably the chaco mice (Andalgalomys), the leaf-eared mice (Graomys
, Paralomys and Phyllotis
), and Salinomys.
s and is derived from the Ancient Greek
eliktos (ἑλικτός, "winding") and odontas (ὀδόντας, "toothed").
The systematics
and taxonomy
of Eligmodontia have been complicated. The first specimen was acquired by Charles Darwin
in 1835 at Bahía Blanca
(Argentina
), during his five-year journey on the HMS Beagle
. It was formally described by George R. Waterhouse
as Mus elegans in February 1837, just weeks after the formal description of E. typus by Frédéric Cuvier
, from a specimen that he had received from Buenos Aires
and which was collected six months after Darwin's. The two taxa were later synonymized and represent the same species
.
and the tribe
Phyllotini. Eight species of Eligmodontia have been described, three of these containing 2 subspecies each. In a 1962 revision of the tribe Phyllotini, Philip Hershkovitz
synonymized all 10 named forms of Eligmodontia known by then into a single species with two subspecies. The lighter and larger northern populations were known as Eligmodontia typus puerulus, and the darker and smaller southern ones as E. typus typus. For nearly 30 years, Hershkovitz's approach was followed until karyotype
s and molecular data became available. Today, five distinct karyotypes have been described, and as many distinct clades have been found.
The following 5 species can be unequivocally recognized:
The case of the newly-proposed species E. bolsonensis is quite interesting. Phylogenetically it is part of the same clade as E. typus. Yet there seems to have been reproductive isolation
between these two parapatric populations – the population separated as bolsonensis occurs where the range of E. typus extends northwards and upslope into the Andes. And while splitting E. bolsonensis from E. typus would leave the latter non-monophyletic as regards because of incomplete lineage sorting, the two differ weakly but consistently in several molecular and morphological characters.
Altogether, this seems to represent a case of ongoing parapatric speciation
, with a population of E. typus becoming separated at the northern and upper limit of its range not more than a few 100,000 years ago. Whether they are to be treated as species or subspecies is essentially a matter of what species concept one prefers. Additionally, it appears that the karyotype reported for E. typus originates from the upland population, and that the karyotype of E. typus proper is unknown.
– uncalibrated due to the absence of fossil
Eligmodontia – has been applied to this genus. However, it agrees well with the emergence of key geographical features in the region. The data suggests that the genus evolved approximately in the mid-late Miocene
(Serravallian
–Tortonian
), about 13-7 mya (million years ago). Presumably, the original Eligmodontia occurred in the region now inhabited by E. typus. Increasing arid
ity as a consequence of the beginning Quaternary glaciation
combined with the uplift of the Patagonian Andes during the latter Pliocene
(late Piacenzian
to Gelasian
, about 3-1.7 mya) split the population into a lowland and a montane
lineage. The latter expanded southwards in the Gelasian, these populations becoming increasingly isolated and eventually became the E. morgani of our time. The same happened somewhat later, at the beginning of the Early Pleistocene
(about 2-1.5 mya) at the northern end of the genus' range, with the separating Altiplano
population becoming the ancestors of E. hirtipes. Finally, in the Middle Pleistocene
local uplifts in the Pampean region separated the ancestors of E. moreni and E. puerulus, and the lowlands population, isolated form its relatives since more than one million years, began also expanding into the uplands, yielding E. (t.) bolsonensis which currently well on its way to become another highly distinct species.
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...
Eligmodontia consists of five or six species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of South American sigmodontine mice
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...
restricted to Bolivia
Bolivia
Bolivia officially known as Plurinational State of Bolivia , is a landlocked country in central South America. It is the poorest country in South America...
, Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
, and 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...
. Species of Eligmodontia occur along the eastern side of the Andes Mountains, in Patagonia
Patagonia
Patagonia is a region located in Argentina and Chile, integrating the southernmost section of the Andes mountains to the southwest towards the Pacific ocean and from the east of the cordillera to the valleys it follows south through Colorado River towards Carmen de Patagones in the Atlantic Ocean...
, and in the Chaco
Gran Chaco
The Gran Chaco is a sparsely populated, hot and semi-arid lowland region of the Río de la Plata basin, divided among eastern Bolivia, Paraguay, northern Argentina and a portion of the Brazilian states of Mato Grosso and Mato Grosso do Sul, where it is connected with the Pantanal region...
thorn forest of South America. They can be found in arid
Arid
A region is said to be arid when it is characterized by a severe lack of available water, to the extent of hindering or even preventing the growth and development of plant and animal life...
and semiarid habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
s and in both high and low elevation areas. These rodent
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....
s are commonly known as gerbil mice or by their local name lauchas. Sometimes they are also called silky desert mice, highland desert mice or silky-footed mice. The closest living relatives are probably the chaco mice (Andalgalomys), the leaf-eared mice (Graomys
Graomys
Graomys is a genus of rodent in the family Cricetidae.It contains the following species:* Central Leaf-eared Mouse * Pale Leaf-eared Mouse * Edith's Leaf-eared Mouse...
, Paralomys 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...
), and Salinomys.
Taxonomy, systematics and evolution
The genus receives its name from the occlusal (chewing surface) pattern of the molarMolar (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 and is derived from the Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
eliktos (ἑλικτός, "winding") and odontas (ὀδόντας, "toothed").
The systematics
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...
and taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
of Eligmodontia have been complicated. The first specimen was acquired by Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
in 1835 at Bahía Blanca
Bahía Blanca
Bahía Blanca is a city located in the south-west of the province of Buenos Aires, Argentina, by the Atlantic Ocean, and seat of government of Bahía Blanca Partido. It has a population of 274,509 inhabitants according to the...
(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...
), during his five-year journey on the HMS Beagle
HMS Beagle
HMS Beagle was a Cherokee-class 10-gun brig-sloop of the Royal Navy. She was launched on 11 May 1820 from the Woolwich Dockyard on the River Thames, at a cost of £7,803. In July of that year she took part in a fleet review celebrating the coronation of King George IV of the United Kingdom in which...
. It was formally described by George R. Waterhouse
George Robert Waterhouse
George Robert Waterhouse was an English naturalist.In 1833, Waterhouse was elected as the Royal Entomological Society of London's librarian and curator of insects and records....
as Mus elegans in February 1837, just weeks after the formal description of E. typus by Frédéric Cuvier
Frédéric Cuvier
Frédéric Cuvier was a French zoologist. He was the younger brother of noted naturalist and zoologist Georges Cuvier....
, from a specimen that he had received from Buenos Aires
Buenos Aires
Buenos Aires is the capital and largest city of Argentina, and the second-largest metropolitan area in South America, after São Paulo. It is located on the western shore of the estuary of the Río de la Plata, on the southeastern coast of the South American continent...
and which was collected six months after Darwin's. The two taxa were later synonymized and represent the same species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
.
Systematics
Eligmodontia belongs to the subfamily SigmodontinaeSigmodontinae
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 tribe
Tribe (biology)
In biology, a tribe is a taxonomic rank between family and genus. It is sometimes subdivided into subtribes.Some examples include the tribes: Canini, Acalypheae, Hominini, Bombini, and Antidesmeae.-See also:* Biological classification* Rank...
Phyllotini. Eight species of Eligmodontia have been described, three of these containing 2 subspecies each. In a 1962 revision of the tribe Phyllotini, Philip Hershkovitz
Philip Hershkovitz
Philip Hershkovitz was an American mammalogist. Born in Pittsburgh, he attended the Universities of Pittsburgh and Michigan and lived in South America collecting mammals. In 1947, he was appointed a curator at the Field Museum of Natural History in Chicago and he continued to work there until his...
synonymized all 10 named forms of Eligmodontia known by then into a single species with two subspecies. The lighter and larger northern populations were known as Eligmodontia typus puerulus, and the darker and smaller southern ones as E. typus typus. For nearly 30 years, Hershkovitz's approach was followed until 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...
s and molecular data became available. Today, five distinct karyotypes have been described, and as many distinct clades have been found.
The following 5 species can be unequivocally recognized:
- Monte Gerbil MouseMonte Gerbil MouseThe Monte Gerbil Mouse or Monte Laucha is a species of rodent in the family Cricetidae.It is found only in Argentina.-References:* Baillie, J. 1996. . Downloaded on 19 July 2007....
or Monte Laucha, Eligmodontia moreni - Andean Gerbil MouseAndean Gerbil MouseThe Andean Gerbil Mouse or Altiplano Laucha is a species of rodent in the family Cricetidae.It is found in Argentina, Bolivia, Chile, and Peru.-References:* Baillie, J. 1996. . Downloaded on 19 July 2007....
or Altiplano Laucha, Eligmodontia puerulus - Eligmodontia hirtipes (Thomas, 1902) (recently separated from E. puerulus)
- Morgan's Gerbil MouseMorgan's Gerbil MouseMorgan's Gerbil Mouse , also known as the Western Patagonian Laucha, is a species of rodent in the family Cricetidae.It is found in Argentina and Chile.-References:* Baillie, J. 1996. . Downloaded on 19 July 2007....
or Western Patagonian Laucha, Eligmodontia morgani - Eastern Patagonian Laucha, Eligmodontia typus
- Highland Gerbil Mouse, Eligmodontia (typus) bolsonensis Mares, Braun, Coyner & van den Bussche, 2008
The case of the newly-proposed species E. bolsonensis is quite interesting. Phylogenetically it is part of the same clade as E. typus. Yet there seems to have been reproductive isolation
Reproductive isolation
The mechanisms of reproductive isolation or hybridization barriers are a collection of mechanisms, behaviors and physiological processes that prevent the members of two different species that cross or mate from producing offspring, or which ensure that any offspring that may be produced is not...
between these two parapatric populations – the population separated as bolsonensis occurs where the range of E. typus extends northwards and upslope into the Andes. And while splitting E. bolsonensis from E. typus would leave the latter non-monophyletic as regards because of incomplete lineage sorting, the two differ weakly but consistently in several molecular and morphological characters.
Altogether, this seems to represent a case of ongoing parapatric speciation
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
, with a population of E. typus becoming separated at the northern and upper limit of its range not more than a few 100,000 years ago. Whether they are to be treated as species or subspecies is essentially a matter of what species concept one prefers. Additionally, it appears that the karyotype reported for E. typus originates from the upland population, and that the karyotype of E. typus proper is unknown.
Evolution
A crude molecular clockMolecular clock
The molecular clock is a technique in molecular evolution that uses fossil constraints and rates of molecular change to deduce the time in geologic history when two species or other taxa diverged. It is used to estimate the time of occurrence of events called speciation or radiation...
– uncalibrated due to the absence of fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
Eligmodontia – has been applied to this genus. However, it agrees well with the emergence of key geographical features in the region. The data suggests that the genus evolved approximately in the mid-late Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
(Serravallian
Serravallian
The Serravallian is in the geologic timescale an age or a stage in the middle Miocene epoch/series, that spans the time between 13.65 ± 0.05 Ma and 11.608 ± 0.005 Ma...
–Tortonian
Tortonian
The Tortonian is in the geologic timescale an age or stage of the late Miocene that spans the time between 11.608 ± 0.005 Ma and 7.246 ± 0.005 Ma . It follows the Serravallian and is followed by the Messinian....
), about 13-7 mya (million years ago). Presumably, the original Eligmodontia occurred in the region now inhabited by E. typus. Increasing arid
Arid
A region is said to be arid when it is characterized by a severe lack of available water, to the extent of hindering or even preventing the growth and development of plant and animal life...
ity as a consequence of the beginning Quaternary glaciation
Quaternary glaciation
Quaternary glaciation, also known as the Pleistocene glaciation, the current ice age or simply the ice age, refers to the period of the last few million years in which permanent ice sheets were established in Antarctica and perhaps Greenland, and fluctuating ice sheets have occurred elsewhere...
combined with the uplift of the Patagonian Andes during the latter Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
(late Piacenzian
Piacenzian
The Piacenzian is in the international geologic timescale the upper stage or latest age of the Pliocene. It spans the time between 3.6 ± 0.005 Ma and 2.588 ± 0.005 Ma...
to Gelasian
Gelasian
The Gelasian is an age in the international geologic timescale or a stage in chronostratigraphy, being the earliest or lowest subdivision of the Quaternary period/system and Pleistocene epoch/series. It spans the time between 2.588 ± 0.005 Ma and 1.806 ± 0.005 Ma...
, about 3-1.7 mya) split the population into a lowland and a montane
Montane
In biogeography, montane is the highland area located below the subalpine zone. Montane regions generally have cooler temperatures and often have higher rainfall than the adjacent lowland regions, and are frequently home to distinct communities of plants and animals.The term "montane" means "of the...
lineage. The latter expanded southwards in the Gelasian, these populations becoming increasingly isolated and eventually became the E. morgani of our time. The same happened somewhat later, at the beginning of the Early Pleistocene
Early Pleistocene
Calabrian is a subdivision of the Pleistocene Epoch of the Geologic time scale. ~1.8 Ma.—781,000 years ago ± 5,000 years, a period of ~.The end of the stage is defined by the last magnetic pole reversal and plunge in to an ice age and global drying possibly colder and drier than the late Miocene ...
(about 2-1.5 mya) at the northern end of the genus' range, with the separating Altiplano
Altiplano
The Altiplano , in west-central South America, where the Andes are at their widest, is the most extensive area of high plateau on Earth outside of Tibet...
population becoming the ancestors of E. hirtipes. Finally, in the Middle Pleistocene
Middle Pleistocene
The Middle Pleistocene, more specifically referred to as the Ionian stage, is a period of geologic time from ca. 781 to 126 thousand years ago....
local uplifts in the Pampean region separated the ancestors of E. moreni and E. puerulus, and the lowlands population, isolated form its relatives since more than one million years, began also expanding into the uplands, yielding E. (t.) bolsonensis which currently well on its way to become another highly distinct species.