Gerbil mice Temporal range: Late Pleistocene to Recent | |
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Scientific classification ![]() | |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Rodentia |
Family: | Cricetidae |
Subfamily: | Sigmodontinae |
Tribe: | Phyllotini |
Genus: | Eligmodontia Cuvier, 1837 |
Type species | |
Eligmodontia typus | |
Species | |
Eligmodontia hirtipes Contents |
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 habitats and in both high and low elevation areas. These rodents 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 . [1]
The genus receives its name from the occlusal (chewing surface) pattern of the molars [2] 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 HMS Beagle. It was formally described by George R. Waterhouse as Mus elegans in February 1837, [3] 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. [4] The two taxa were later synonymized and represent the same species. [5]
Eligmodontia belongs to the subfamily Sigmodontinae and the tribe Phyllotini. Eight [6] species of Eligmodontia have been described, three of these containing 2 subspecies each. In a 1962 revision of the tribe Phyllotini, [7] 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 have been found. [8]
The following 5 species can be unequivocally recognized: [9]
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. [5]
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[ verification needed ] that the karyotype reported for E. typus originates from the upland population, and that the karyotype of E. typus proper is unknown.
A crude molecular clock – 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 aridity 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 [10] ) 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. [5]
Eligmodontia eight species.
The Muroidea are a large superfamily of rodents, including mice, rats, voles, hamsters, lemmings, gerbils, and many other relatives. Although the Muroidea originated in Eurasia, they occupy a vast variety of habitats on every continent except Antarctica. Some authorities have placed all members of this group into a single family, Muridae, due to difficulties in determining how the subfamilies are related to one another. Many of the families within the Muroidea superfamily have more variations between the families than between the different clades. A possible explanation for the variations in rodents is because of the location of these rodents; these changes could have been due to radiation or the overall environment they migrated to or originated in. The following taxonomy is based on recent well-supported molecular phylogenies.
The Muridae, or murids, are the largest family of rodents and of mammals, containing approximately 1,383 species, including many species of mice, rats, and gerbils found naturally throughout Eurasia, Africa, and Australia.
The Old World rats and mice, part of the subfamily Murinae in the family Muridae, comprise at least 519 species. Members of this subfamily are called murines. In terms of species richness, this subfamily is larger than all mammal families except the Cricetidae and Muridae, and is larger than all mammal orders except the bats and the remainder of the rodents.
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 species count numbers at least 508. Their distribution includes much of the New World, but the genera are predominantly South American, such as brucies. They invaded South America from Central America as part of the Great American Interchange near the end of the Miocene, about 5 million years ago. Sigmodontines proceeded to diversify explosively in the formerly isolated continent. They inhabit many of the same ecological niches that the Murinae occupy in the Old World.
The term spiny mouse refers to any species of rodent within the genus Acomys. Similar in appearance to mice of the genus Mus, spiny mice are small mammals with bare, scaled tails. However, their coats are endowed with unusually stiff guard hairs similar to the spines of a hedgehog; this trait is the source of the common name, spiny mouse.
Apodemus is a genus of Muridae. The name is unrelated to that of the Mus genus, instead being derived from the Greek ἀπό-δημος.
Vesper mice are rodents belonging to a genus Calomys. They are widely distributed in South America. Some species are notable as the vectors of Argentinian hemorrhagic fever and Bolivian hemorrhagic fever.
Pearson's chaco mouse is a species of rodent in the family Cricetidae. This mouse is found in the Gran Chaco ecoregion of southeastern Bolivia and western Paraguay at elevations up to 400 m. The species is named after American zoologist Oliver Payne Pearson. Its karyotype has 2n = 76 and 78 in the two subspecies. The latter is the highest diploid number of any species in the tribe Phyllotini.
The Luzon montane forest mouse is a species of rodent in the family Muridae, from the genus Apomys. It occurs only in the Philippines, where it has been found on the large northern island Luzon. It is most closely related to the large Mindoro forest mouse, which occurs on Mindoro. There may be another related species in the Sierra Madre, but this species is yet undescribed. The Luzon montane forest mouse is a relatively large, ground-dwelling rat with a tail that is quite short for its genus.
The Monte gerbil mouse or Monte laucha is a species of rodent in the family Cricetidae. It is found only in Argentina.
Morgan's gerbil mouse, also known as the western Patagonian laucha, is a South American species of rodent in the family Cricetidae. It is named for J. P. Morgan, one of the sponsors of the expedition that first identified the species.
The Andean gerbil mouse or Altiplano laucha is a species of rodent in the family Cricetidae. It is found in Argentina, Bolivia, Chile, and Peru.
Eligmodontia typus is a species of rodent in the family Cricetidae. It is found in Argentina and possibly also Chile. The northernmost population might represent a distinct species, E. bolsonensis, to which the common name highland gerbil mouse would apply. The lowland population would then be known as eastern Patagonian gerbil mouse or eastern Patagonian laucha.
The Patagonian chinchilla mouse is a species of rodent in the family Cricetidae. It was first described by George Robert Waterhouse in 1839. It is found in Tierra del Fuego and neighboring areas of southernmost Argentina and Chile.
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 incisors and specialized molars with transverse ridges, divided by deep valleys, which are connected by a transverse ridge along the midline of the molars.
The delicate salt flat mouse, Salinomys delicatus, is a sigmodontine rodent species in the family Cricetidae from South America. It is the only species in the genus Salinomys. Its habitat is scrublands bordering salt flats in the Monte Desert area of central western Argentina at elevations around 400 m. The closest relatives of the species are the chaco mice (Andalgalomys).
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. Many members of the family lack them or have only simple pits, but Arvicolinae and Oryzomyini have more highly developed posterolateral palatal pits. Posterolateral palatal pits are also present in some other rodents, including Glis, Jaculus, Hystrix, Abrocoma, Ctenomys, Chinchilla, and Lagidium.