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Brief Summary

    Sigmodontinae: Brief Summary
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    The rodent 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 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 "Thomasomyini" from the Atlantic Forest of Brazil are generally thought to be not especially related to the "real" Thomasomyini from the northern Andes and the Amazon rainforest. The genera Wiedomys and Sigmodon are generally placed in their own tribe, and the "phyllotines" Irenomys, Punomys, Euneomys, and Reithrodon are considered incertae sedis.

    The name "Sigmodontinae" is based on the name of the type genus, Sigmodon. This name in turn derives from the Greek roots for "S-tooth" (sigm- for "S" and odont- for "tooth", as in orthodontist) for the characteristic of the molars having an S-shape when viewed from above.

Comprehensive Description

Distribution

    Distribution
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    Sigmodontines range from Tierra del Fuego north throughout South America, Central America, and Mexico, and into the United States as far north as Nebraska and New Jersey. They are also found on the Galapagos Islands.

    Biogeographic Regions: nearctic (Native ); neotropical (Native )

Morphology

    Morphology
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    Sigmodontines are small to medium-large muroid rodents--head and body length ranges from 62 to 360 mm, tail length ranges from 30 to 330 mm, and they weigh 7 to 455 grams. They are extremely diverse in body form, resembling mice, rats, voles, moles, gerbils, gophers, and shrews. They have short to long fur, ranging from soft to coarse and including spiny forms. Fur colors include many different shades of brown, gray, reddish, and yellow, with the pelage generally paler, even white, on the underparts. Some populations are polymorphic in fur color or pattern. Sigmodontine tails are naked to well-furred, and some have tufted tips. Ears can be very short and nearly hidden in the fur, to very long--almost 1/3 the length of the head and body. Most sigmodontines have feet adapted for cursorial locomotion, but some have specializations for digging (such as long, heavy foreclaws) or swimming (such as webbed hind feet). Many male sigmodontines have prominant ventral sebaceous glands, but they usually lack rump, hip, and flank glands.

    The sigmodontine dental formula is 1/1, 0/0, 0/0, 3/3 = 16, except for one species, Neusticomys oyapocki, which has the formula 1/1, 0/0, 0/0, 2/2 = 12. The incisors are usually orthodont or opisthodont, and the molars are rooted and have a biserial cusp arrangement (in contrast to the triserial cusp arrangement of most murines). Each molar has a longitudinal enamel crest (mure or murid). The molars range from brachydont to hypsodont, and the third molars are usually smaller than the second molars. Sigmodontine skulls generally have flat pterygoid fossae, and small to medium-sized auditory bullae. In addition, the mastoid bullae are not hypertrophied, and an accessory tympanum is always present. The malleus is of parallel construction. All other sigmodontine skull characteristics vary widely. A skeletal characteristic shared by most sigmodontines is the presence of a prominant neural spine on the second thoracic vertebra. Finally, sigmodontines have one- or two-chambered stomachs, and the tongue bears a single circumvallate papilla.

    Other Physical Features: endothermic ; homoiothermic; bilateral symmetry ; polymorphic

    Sexual Dimorphism: sexes alike

Habitat

    Habitat
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    Sigmodontines live in a wide range of habitat types, including grasslands, deserts, wet and dry forests, scrub forests, savannahs, steppes, agricultural areas, marshes, swamps, streams, sandy coastlines, barren highlands, alpine meadows, and human habitations. They live at elevations from sea level to over 5,500 meters.

    Habitat Regions: temperate ; tropical ; terrestrial

    Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest ; mountains

    Aquatic Biomes: rivers and streams

    Wetlands: marsh ; swamp

    Other Habitat Features: urban ; suburban ; agricultural ; riparian

Trophic Strategy

    Trophic Strategy
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    These rodents are herbivorous, omnivorous, or carnivorous. Foods consumed by the group as a whole include: grasses, seeds, fruit, berries, fungi, lichen, insects, crustaceans, other arthropods, mollusks, worms, small fish, tadpoles, and bird eggs.

    Primary Diet: carnivore (Eats terrestrial vertebrates, Piscivore , Eats eggs, Insectivore , Eats non-insect arthropods, Molluscivore ); herbivore (Folivore , Frugivore , Granivore ); omnivore ; mycophage

Associations

    Associations
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    Sigmodontines are primary and higher-level consumers, and they are food for a wide range of other animals. Some species are commensal with humans, depending on human food stores or agriculture to survive. Others take advantage of burrows made by other animals, such as armadillos (Dasypus novemcinctus) and tuco-tucos Ctenomys, or nests made by birds. Some, as mentioned in the previous section, rely on other animals to help them avoid predation. Finally, sigmodontines may be important dispersers of mycorrhizal fungi (Mangan and Adler 2000).

    Mutualist Species:

    • viscachas Lagidium
    • birds Aves
    • tuco-tucos Ctenomys
    • armadillos Dasypus novemcinctus
    • humans Homo sapiens
    Associations
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    Sigmodontines are preyed upon by a variety of other animals, including hawks, owls, snakes, and carnivorous mammals. The neutral-colored coats of sigmodontines may help them blend in with their background. Most species are vigilant and agile, helping them to avoid predation. Semiaquatic species avoid predation by quickly diving into the water when threatened. One sigmodontine species, Auliscomys boliviensis, avoids predation by associating with viscachas (Lagidium) and dashing for cover when the viscachas give alarm calls.

    Known Predators:

    • hawks Accipitridae
    • owls Strigiformes
    • snakes Serpentes
    • carnivorous mammals Carnivora

    Anti-predator Adaptations: cryptic

Behavior

    Behavior
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    Sigmodontines perceive their environment using vision, hearing, touch, smell, and taste. Hearing and olfaction may be especially important, as auditory and chemical cues are often used for communication. Sigmodontines make a variety of squeaking sounds in social contexts, and they can detect and produce ultrasounds. Territorial males use their urine and feces to scent-mark their domains.

    Communication Channels: acoustic ; chemical

    Other Communication Modes: scent marks

    Perception Channels: visual ; tactile ; acoustic ; chemical

Life Expectancy

    Life Expectancy
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    Sigmodontines have short lives. Most do not make it past their first birthday. In captivity, some species have lived as long as five years.

Reproduction

    Reproduction
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    Most sigmodontines have a promiscuous mating system. During mating, a copulatory plug forms and seals the female's reproductive tract, preventing subsequent males from successfully fertilizing the female's eggs.

    Mating System: polygynandrous (promiscuous)

    Many rodents are prolific breeders and sigmodontines are no exception. They breed year round or seasonally, and during a year or season females often have two to three, or even six to seven litters. Ovulation is spontaneous, and females of many species have a postpartum estrus, becoming pregnant again just a few hours after giving birth. In some species, the embryos do not implant until the current litter is weaned; gestation after implantation occurs usually lasts 20 to 30 days. Some species can have as many as 13 young in a litter, although many have just three to five. The young are altricial and open their eyes anywhere from 1 to 11 days after birth. They are weaned as early as five and as late as 30 days. Female sigmodontines reach sexual maturity several weeks before males do. Some have been known to give birth at just four weeks of age. Other species mature much later, and do not reproduce until they are at least four months old.

    Key Reproductive Features: iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous ; delayed implantation ; post-partum estrous

    Sigmodontine females generally do not have any help in caring for their young. Most build nests out of plant material where they raise their babies. The young are altricial, and they nurse for 5 to 30 days. In a few species, the young remain with the mother for a few days after weaning is complete.

    Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Protecting: Female)

Conservation Status

    Conservation Status
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    There are currently 18 lower risk, 1 near threatened, 13 vulnerable, 11 endangered (aquatic rats, Anotomys leander, 4 Neusicomys species, Cleber's arboreal rice rats, Oecomys cleberi, St. Vincent pygmy rice rats, Oligoryzomys victus, Rushi's rats, Abrawayaomys ruschii, Rio de Janeiro arboreal rats, Phaenomys ferrugineus, and both Scolomys species), and 4 critically endangered (small-footed bristly mice, Nectomys rattus, Gorgas' rice rats, Oryzomys gorgasi, Harris's rice water rats, Sigmodontomys aphrastus, and Brazilian arboreal mice, Rhagomys rufescens) sigmodontine species on the IUCN's Red List of Threatened Species. In addition, three species are lacking sufficient data to be assessed, and five species have gone extinct recently (both Megalomys species, Darwin's Galapagos mice, Nesoryzomys darwini, indefatigable Galapagos mice, Nesoryzomys indefessus, and Nelson's rice rats, Oryzomys nelsoni). Sigmodontines with restricted ranges are vulnerable to habitat loss and destruction, and those that dwell on islands are especially vulnerable to predation or competition by invasive species, such as rats, cats, and mongooses.

Benefits

    Benefits
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    Several sigmodontine species are considered household or agricultural pests. They raid buildings, gnawing on and destroying household goods and food stores, and they damage crops. Some also carry diseases such as haemorrhagic fever.

    Negative Impacts: injures humans (carries human disease); crop pest; household pest

    Benefits
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    Some sigmodontines are used in laboratory disease research. Others are trapped for their fur.

    Positive Impacts: body parts are source of valuable material; research and education

Other Articles

    Untitled
    provided by Animal Diversity Web

    The earliest fossils of existing sigmodontine genera are from the late Miocene of North America.