Muridae Rodent Family, Habitats & Characteristics
A molecular phylogenetic investigation of several of the taxa now classified as Murinae or Dendromurinae has never been performed. All of the genera are found in Africa, implying that the deomyines originated there. The subfamily Deomyinae includes four mouse-like rodent genera that were previously classified in the subfamilies Murinae and Dendromurinae. They are frequently referred to as the Acomyinae, especially in references that before the finding that Deomys ferruginous, the link rat, is a member of a group.
The taxonomy of southern African gerbils is still under revision as chromosomal and molecular data are expanded. Recent studies have suggested that the genus Gerbillurus should be incorporated into the genus Gerbilliscus (Colangelo et al., 2007), based on their analyses of mitochondrial genes. Knight et al. (2013) adopted the new nomenclature, naming all former Gerbillurus species as Gerbilliscus. Setzeri specimen used for the molecular analyses in the studies by Chevret and Dobigny (2005), Colangelo et al. (2007), and Granjon et al. (2012) is given as Western Cape, South Africa, whereas G. Setzeri is endemic to the Namib Desert with the southern limit of its distribution being the Kuiseb River, about 1500 km distant from the Western Cape (Dempster, Perrin, Downs, & Griffin, 1998). Setzeri used in the analyses of Colangelo et al. (2007), Chevret and Dobigny (2005), and Granjon et al. (2012).
The rare Ethiopian water mouse (Nilopegamys plumbeus) is known only from a mountain tributary of the Blue Nile, and is critically endangered (IUCN, 2006); it may even be extinct. It is the only African rodent to show the degree of adaptation to aquatic life and swimming ability evident in the Neotropical Ichthyomyinae and in the Australian Hydromyinae (Peterhans and Patterson, 1995). Goslingi or Malacomys spp., which belong to the ‘wading murid’ niche and have feet that are elongated and thin. They serve the purpose of raising the body so that these animals can hunt by wading in shallow water (Kingdon, 1974). The Muridae, or murids, are the biggest rodent and mammal family in the world, with over 700 species including many mice, rats, and gerbils found in Eurasia, Africa, and Australia.
They occupy ecosystems ranging from dry desert to wet tropical forest, from tundra to savanna to temperate woodland. Some species are semiaquatic; others live underground; yet others spend their entire lives in the canopy of tropical forest. Their food habits range from true omnivores to specialists on earthworms, subterranean fungi, even aquatic invertebrates. Some species cause millions of damage to agricultural lands and stored foods. Others are the vectors or reservoirs of a number of diseases that have periodically devasted human populations (and continue to do so). Some are important biological controls of pestiferous insects.
Nemirov et al. (2002) have examined the phylogenetic trees of hantaviruses and compared these to the D-loop region of mitochondrial DNA. These studies show a remarkable concordance between murine evolution and the evolution of hantaviruses. Focusing on the divergence of Saaremaa virus from Dobrava virus, Nemirov et al. have speculated that Saaremaa virus has evolved as a result of Dobrava virus switching host from the yellow-striped field mouse (Apodemus flavicollis) to A. The result is a virus with a reduced pathogenicity for humans compared to Dubrova virus, although there are some qualifications as to just how pathogenic the latter virus really is. Other examples include transmission of Monongahella virus from Peromyscus maniculatus to P. leucopus, eventually leading to the evolution of New York virus (Morzunov et al., 1998).
They are thought to have developed from hamster-like creatures in tropical Asia during the early Miocene and have only generated species that can survive in colder regions since then. As a result of hitching a ride alongside human migrations throughout the current geological age, they have grown notably abundant globally. Another large group, restricted to Africa and the Middle East to Central Asia. Most species inhabit dry areas with sparse vegetation, including deserts. Granivorous and herbivorous, but some also consume large numbers of insects.
They are most commonly some shade of brown in colour, although many have black, grey, or white markings. A broad range of feeding habits is found in murids, ranging from herbivorous and omnivorous species to specialists that consume strictly earthworms, certain species of fungi, or aquatic insects. Most genera consume plant matter and small invertebrates, often storing seeds and other plant matter for winter consumption. Murids have sciurognathous jaws (an ancestral character in rodents) and a diastema is present. Generally, three molars (though sometimes only one or two) are found, and the nature of the molars varies by genus and feeding habit. Murids have sciurognathous jaws (an ancestral character in rodents) and a diastema is present.[5] Murids lack canines and premolars.
Research animal vendors sell a variety of outbred stocks and inbred strains of the laboratory mouse (Mus domesticus). Different mouse strains have different coat colours and other traits. Commercially accessible mice come in a variety of species and genera.
As a result of the large number of species, there is much variation in the physical characteristics of murids. Murids breed frequently, often producing large litters several times per year. They typically give birth between 20 and 40 days after mating, although this varies greatly between species. The young are typically born blind, hairless, and helpless, although exceptions occur, such as in spiny mice. The evolution of murids, like that of many other tiny mammals, is poorly understood due to the shortage of fossils.
Old World rats and mice have long tails (sometimes longer than the body) that are either furry or scaly; strong feet; long hind feet; and opposable digits on their front feet. Adults have a length of 1.9 to 14.7 inches (5 to 36 centimeters) and a weight of 0.2 to 52.9 ounces (5 grams to 1.5 kilograms). Persistently infected rodents shed the virus in urine, feces, and saliva. Inhalation of virus-contaminated aerosols is the major route of transmission to humans. However, the general view that rodents are the only infection source for humans has been disputed by Zeier et al. (2005). It has been suggested that the close proximity of domestic animals such as cats, dogs, pigs, and cattle with rodents may cause some transmission events of hantaviruses to these animals.
A second example is Puumala virus from Clethrionomys “host-switching” species to Lemmus and then onto Microtus species, thence establishing lineages to the present day Topografov and Khabarovsk viruses (Vapalahti et al., 1999b). Upper molars are hypsodont and strongly lophodont or loxodont; individual teeth appear to be made up of transverse laminae; third molar larger than the first two. Unusually strongly developed zygomatic spine and notch, and zygomatic arch strong and bowed. A number of other unusual characteristics of cranium and mandible. Medium sized rats, primarily terrestrial, and mainly herbivorous.
They have front paws with four digits and a short thumb, and hind feet with five digits. Their soft, thick fur varies in color (depending on the species) from gray to reddish brown, and their underparts can be white, gray, or black. They have excellent senses of hearing and smell, but poor eyesight (even though they have large, round eyes). Adults are 2 to 13.4 inches (5 to 34 centimeters) long and weigh between 0.9 and 31.7 ounces (25 to 900 grams).
The Murids are classified in four subfamilies, and about 140 genera. The family name Muridae is sometimes used in a broader sense to include all members of the superfamily Muroidea. The rat is commonly transmitted poison from the bark of the poison arrow tree, Acokanthera schimperi, on which it eats, on these hairs, forming a defensive mechanism that can sicken or even kill predators that try to bite it. The forefeet are big, and digit 1 does not have a claw, but digits 2–5 have a well-developed claw. The maned rat, also known as the (African) crested rat (Lophiomys imhausi), is a nocturnal, long-haired, bushy-tailed East African rodent with a porcupine-like appearance. Rats, mice, and relatives are found throughout the world except for the extreme polar regions of Earth.
Above, the animal is dark to grey-brown, and below, it is pale grey-brown. The zygomatic plate is massive, the snout is long and wide, and the interorbital breadth is broad). The Togo mouse is thought to be insectivorous based on its skull anatomy. Mice are members of the Rodentia order’s Muridae rat family.
Although none of them is native to the Americas, a few species, notably the house mouse and black rat, have been introduced worldwide. Fossorial, arboreal, and semiaquatic murid species occur, though most are terrestrial. The extensive list of niches filled by murids helps to explain their relative abundance.
The Ecuador fish-eating rat (Anotomys leander) is an endangered rodent (IUCN, 2006) confined to high altitude streams and wetlands. It has well-developed vibrissae, velvety fur, and the ears are sealed during immersion by a muscular membrane. The broad hind feet are not fully webbed but have stiff hairs which aid in swimming (Nowak, 1999). These and other Neotropical mice and rats listed in Table VI are sometimes treated as distinct from the Muridae, and most are placed in the Sigmodontinae within the Cricetidae which contains all endemic South American rodents.
Among Aesop’s Fables are The Cat and the Mice and The Frog and the Mouse. In James Herbert’s first novel, The Rats, (1974), a vagrant is attacked and eaten alive by a pack of giant rats; further attacks follow. The name Muridae comes from the Latin mus (genitive muris), meaning “mouse”, since all true mice belong to the family, with the more typical mice belonging to the genus Mus. Four clawed digits are found on each forefoot (the pollex or “thumb” is small and bears a nail); the hind foot in most has five clawed digits (but sometimes the hallux or first toe has a nail). Other external features (ears, eyes, tail, pelage, etc.) are extremely variable.
Deomyinae is the older term, hence it takes priority over Acomyinae. Although modest elements of the third upper molar have been postulated, deomyines share no morphological traits that may be utilised to distinguish them from other muroids. The only thing that binds this subfamily together is a set of genetic mutations. They are found from dry temperate (mild) climates to wet tropical environments. It has also been touted as a model of autoimmune thyroiditis (Solleveld et al., 1985) and as a potentially useful model for reproductive biology with the successful development of an in vitro fertilization procedure (Nohara et al., 1998). Mastomys has been used most extensively as a model of gastric neoplasia (Nilsson et al., 1992; Gilligan et al., 1995).
One study reported that this species had an abnormally high occurrence of gastric adenocarcinoma (Oettle, 1957). Further studies have determined these masses to be gastric carcinoids (Snell and Stewart, 1969). As a result, this species is actively used in the study of mechanisms of gastric hyperplasia and carcinoid formation (Kidd et al., 2000). Around 1150 living species of murid rodents have been described, but surely many more remain to be discovered. These are placed in around 260 genera, which are distributed among 17 subfamilies.
Gerbils, jirds, and sand rats are all members of the Gerbillinae subfamily of the Muridae rodent family. Almost 450 species of murids are listed on the World Conservation Union’s (IUCN) Red List. Animals that use metabolically generated heat to regulate body temperature independently of ambient temperature.
Murids have sciurognathous jaws (a rodent ancestral trait), as well as a diastema. Three molars are usually present (but one or two are occasionally seen), and the nature of the molars varies by genus and eating style. They have a head and body length of 2.4 to 11.4 inches (6.1 to 29.0 centimeters); tail length of 1 to 6.3 inches (3 to 16 centimeters); and weight of 0.4 to 18 ounces (12 to 510 grams). An apparent coevolution of hantaviruses with their reservoir hosts is evident by the commonly observed close association of each hantavirus species with a certain rodent species. Depending on the population density, up to 50% of any given population of rodents are seropostive and considered as silent carriers for hantaviruses.
Murids are found nearly everywhere in the world, though many subfamilies have narrower ranges. Although none of them are native to the Americas, a few species, notably the house mouse and black rat, have been introduced worldwide. Murids occupy a broad range of ecosystems from tropical forests to tundras. Fossorial, arboreal, and semiaquatic murid species occur, though most are terrestrial animals.[4] The extensive list of niches filled by murids helps to explain their relative abundance.
Monophyletic groupings are known to exist (hamsters, voles, African pouched rats, gerbils, Old World rats and mice, African spiny mice, platacanthomyines, zokors, blind mole rats, and bamboo rats). Other groupings, on the other hand, are difficult to classify and may or may not be a jumble of unrelated genera and species (New World rats and mice, dendromurines, and Malagasy rats and mice). The affiliations of subfamilies with only one genus are also unknown (mouselike hamsters, the maned rat).
The murids are tiny mammals that range in size from 4.5 to 8 cm in length (without the tail) in the African pygmy mouse to 48 cm (19 in) in the southern giant slender-tailed cloud rat. They have thin bodies, scaled tails that are longer than the body, and pointed snouts with prominent whiskers, however, these characteristics vary greatly. Some murids have lengthened legs and feet to allow them to hop around, while others have broad feet and prehensile tails to help them climb, and yet others have neither adaptation. This would be OK if each group’s common progenitor could be proven.
There are roughly 250 more species in two more subfamilies (Arvicolinae and Gerbillinae), with the remaining 14 subfamilies housing various other genera, some of which have only one species. Not all experts believe in the number of subfamilies or if they should all be classified as Muridae. Some assemblages, such as blind mole rats and bamboo rats, are quite different and have been considered as different families in the past.
Having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. The mane erects when the animal is scared or agitated, stripping portions and exposing the glandular region.
Mastomys has been promoted as a model of other types of neoplasia as well. Madarame et al. (1995) reported on spontaneous rhabdomyosarcomas, and Pruthi et al. (1983) described intracutaneous cornifying epitheliomas. Papillomavirus has been used to experimentally induce keratoacanthomas and squamous cell carcinomas, although the classification of these lesions has been questioned (Rudolph and Busse, 1981; Rudolph et al., 1981). A histopathological survey of aged Mastomys displayed a wide range of spontaneous neoplastic and preneoplastic lesions (Solleveld et al., 1982). Overgrown incisors are treated by physically reducing the length of the tooth or teeth involved. Clippers or rongeurs may be used to quickly treat conscious rats, but must be used with caution as the teeth tend to split longitudinally, producing jagged edges and predisposing to apical abscess formation (Emily, 1991).
Some groups are known to be monophyletic (hamsters, voles, African pouched rats, gerbils, Old World rats and mice, African spiny mice, platacanthomyines, zokors, blind mole rats, and bamboo rats). Other groups, however, cannot be classified with certainty and may or may not be a hodgepodge of unrelated genera and species (New World rats and mice, dendromurines, The role of technology in animal nutrition and Malagasy rats and mice). Also unresolved are the affinities of subfamilies containing only one genus (mouselike hamsters, the maned rat). The Muridae is the largest family of mammals (numbering over 1300 species), with a great variety of adaptations to life in and around water. Oddly, however, there are no water rats in the Asian tropics.
Mammals display the full range of lung maturity at birth from the Muridae and dogs, where alveolarization is entirely postnatal, to the guinea pig where the full complement of alveoli appears to be present at birth. Likewise, it is clear that in some species (mice, rats, primates, pigs, rabbits) new alveoli form into early adulthood while in other species postnatal neoalveolarization is limited (guinea pigs, sheep) (Figure 1). There still remain significant gaps in our knowledge of species-specific changes in lung structure with age, and research is required in this field. In particular, studies on the “normal” changes in lung structure into senescence are warranted. In contrast, in species where environmental exposures and infection are not controlled (e.g., dog, nonhuman primates), there is evidence of emphysematous changes in lung structure in the latter stages of life (Figure 1).
