genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
''Eligmodontia'' consists of five or six
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
Chile
Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
, and
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
. Species of ''Eligmodontia'' occur along the eastern side of the Andes Mountains, in
Patagonia
Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...
, and in the Chaco thorn forest of South America. They can be found in
arid
A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ...
and
semiarid
A semi-arid climate, semi-desert climate, or steppe climate is a dry climate sub-type. It is located on regions that receive precipitation below potential evapotranspiration, but not as low as a desert climate. There are different kinds of semi- ...
habitat
In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
s and in both high and low elevation areas. These
rodent
Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...
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'' is a genus of rodent in the family Cricetidae. It contains the following species:
* Central leaf-eared mouse (''Graomys chacoensis'')
* Pale leaf-eared mouse
The pale leaf-eared mouse (''Graomys domorum'') is a species of rodent i ...
The genus receives its name from the occlusal (chewing surface) pattern of the molars and is derived from the
Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic p ...
''eliktos'' (ἑλικτός, "winding") and ''odontas'' (ὀδόντας, "toothed").
The systematics and
taxonomy
Taxonomy is the practice and science of categorization or classification.
A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...
of ''Eligmodontia'' have been complicated. The first specimen was acquired by
Charles Darwin
Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended ...
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
), during his five-year journey on
HMS Beagle
HMS ''Beagle'' was a 10-gun brig-sloop of the Royal Navy, one of more than 100 ships of this class. The vessel, constructed at a cost of £7,803 (roughly equivalent to £ in 2018), was launched on 11 May 1820 from the Woolwich Dockyard on t ...
. 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
Georges-Frédéric Cuvier (28 June 1773 – 24 July 1838) was a French zoologist and paleontologist. He was the younger brother of noted naturalist and zoologist Georges Cuvier.
Career
Frederic was the head keeper of the menagerie at the Musé ...
, from a specimen that he had received from
Buenos Aires
Buenos Aires ( or ; ), officially the Autonomous City of Buenos Aires ( es, link=no, Ciudad Autónoma de Buenos Aires), is the capital and primate city of Argentina. The city is located on the western shore of the Río de la Plata, on South ...
and which was collected six months after Darwin's. The two
taxa
In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
were later synonymized and represent the same
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
Sigmodontinae
The rodent subfamily Sigmodontinae 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 specie ...
and the
tribe
The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide usage of the term in English is in the discipline of anthropology. This definition is contested, in part due to confli ...
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 karyotypes and molecular data became available. Today, five distinct karyotypes have been described, and as many distinct
clades
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
have been found.
The following 5 species can be unequivocally recognized:
* Monte Gerbil Mouse or Monte Laucha, ''Eligmodontia moreni''
*
Andean Gerbil Mouse
The Andean gerbil mouse or Altiplano laucha (''Eligmodontia puerulus'') is a species of rodent in the family Cricetidae.
It is found in Argentina, Bolivia, Chile, and Peru
, image_flag = Flag of Peru.svg
, image_coat ...
or Altiplano Laucha, ''Eligmodontia puerulus''
* '' Eligmodontia hirtipes'' (Thomas, 1902) (recently separated from ''E. puerulus'')
* Morgan's Gerbil Mouse or Western Patagonian Laucha, ''Eligmodontia morgani''
* Eastern Patagonian Laucha, ''Eligmodontia typus''
* Highland Gerbil Mouse, ''Eligmodontia bolsonensis'' Mares, Braun, Coyner & van den Bussche, 2008
The case of the newly proposed species ''E. bolsonensis'' is quite interesting.
Phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
ally it is part of the same clade as ''E. typus''. Yet there seems to have been reproductive isolation between these two
parapatric
In parapatric speciation, two subpopulations of a species evolve reproductive isolation from one another while continuing to exchange genes. This mode of speciation has three distinguishing characteristics: 1) mating occurs non-randomly, 2) gene ...
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
Incomplete lineage sorting, also termed hemiplasy, deep coalescence, retention of ancestral polymorphism, or trans-species polymorphism, describes a phenomenon in population genetics when ancestral gene copies fail to coalesce (looking backwards i ...
, 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
The species problem is the set of questions that arises when biologists attempt to define what a species is. Such a definition is called a species concept; there are at least 26 recognized species concepts. A species concept that works well for se ...
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 clock
The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleo ...
– uncalibrated due to the absence of
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
''Eligmodontia'' – has been applied to this genus. However, it agrees well with the emergence of key
geographical
Geography (from Greek: , ''geographia''. Combination of Greek words ‘Geo’ (The Earth) and ‘Graphien’ (to describe), literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and ...
features in the region. The data suggests that the genus evolved approximately in the mid-late
Miocene
The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
(
Serravallian
The Serravallian is, in the geologic timescale, an age or a stage in the middle Miocene Epoch/Series, which spans the time between 13.82 Ma and 11.63 Ma (million years ago). The Serravallian follows the Langhian and is followed by the Tortonian ...
–
Tortonian
The Tortonian is in the geologic time scale an age or stage of the late Miocene that spans the time between 11.608 ± 0.005 Ma and 7.246 ± 0.005 Ma (million years ago). It follows the Serravallian and is followed by the Messinian.
The Torto ...
), about 13-7 mya (
million years ago
The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds.
Usage
Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago) ...
). Presumably, the original ''Eligmodontia'' occurred in the region now inhabited by ''E. typus''. Increasing
arid
A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ...
ity as a consequence of the beginning
Quaternary glaciation
The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial and interglacial periods during the Quaternary period that began 2.58 Ma (million years ago) and is ongoing. Although geologists describ ...
combined with the uplift of the
Patagonian Andes
Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...
during the latter
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Piacenzian to
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 2.58 Ma (million ye ...
, about 3-1.7 mya) split the population into a lowland and a
montane
Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial ...
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''
Lapsus
In philology, a lapsus (Latin for "lapse, slip, error") is an involuntary mistake made while writing or speaking.
Investigations
In 1895 an investigation into verbal slips was undertaken by a philologist and a psychologist, Rudolf Meringer and ...
'' in Mares ''et al.'' (2008).) at the northern end of the genus' range, with the separating
Altiplano
The Altiplano (Spanish for "high plain"), Collao (Quechua and Aymara: Qullaw, meaning "place of the Qulla") or Andean Plateau, in west-central South America, is the most extensive high plateau on Earth outside Tibet. The plateau is located at the ...
population becoming the ancestors of ''E. hirtipes''. Finally, in the
Middle Pleistocene
The Chibanian, widely known by its previous designation of Middle Pleistocene, is an age in the international geologic timescale or a stage in chronostratigraphy, being a division of the Pleistocene Epoch within the ongoing Quaternary Period. Th ...
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.
n French
N, or n, is the fourteenth letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''en'' (pronounced ), plural ''ens''.
History
...
* (1962): Evolution of the Neotropical cricetine rodents (Muridae) with special reference to the phyllotine group. '' Fieldiana Zool.'' 46: 1-524 PDF fulltext * (1997): Mitochondrial DNA analysis and zoogeography of two species of silky desert mice, ''Eligmodontia'', in Patagonia. ''Zeitschrift für Säugetierkunde'' 62(5): 281—292.
* (2005): Citotaxonomía y distribución del género ''Eligmodontia'' (Rodentia, Cricetidae, Sigmodontinae) Cytotaxonomy and distribution of the genus ''Eligmodontia''" ''Mastozoología Neotropical'' 12(1): 73-77
n Spanish
N, or n, is the fourteenth Letter (alphabet), letter in the Latin alphabet, used in the English alphabet, modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is English alphabet# ...
br>PDF fulltext * (2008): Phylogenetic and biogeographic relationships of gerbil mice ''Eligmodontia'' (Rodentia, Cricetidae) in South America, with a description of a new species. ''
Zootaxa
''Zootaxa'' is a peer-reviewed scientific mega journal for animal taxonomists. It is published by Magnolia Press (Auckland, New Zealand). The journal was established by Zhi-Qiang Zhang in 2001 and new issues are published multiple times a week ...
Tree of Life Web Project
The Tree of Life Web Project is an Internet project providing information about the diversity and phylogeny of life on Earth.
This collaborative peer reviewed project began in 1995, and is written by biologists from around the world. The site ...
Tree of Life Web Project
The Tree of Life Web Project is an Internet project providing information about the diversity and phylogeny of life on Earth.
This collaborative peer reviewed project began in 1995, and is written by biologists from around the world. The site ...