Muridae an overview

Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Several studies have described anatomical peculiarities within this species. Both males and females possess a well-developed prostate gland, which has previously been exploited to develop an experimental model of infectious prostatitis (Jantos et al., 1990).

The rodent family Muridae encompasses at least 1326 species grouped in 281 genera [11]. The establishment of the evolutionary systematics in this group has also been controversial because of similarities in size and shape of the different species. Here again, studies making use of DNA sequences of various types have greatly contributed to clarify the situation [11–15]. Figure 1.1.2 represents the evolutionary relationships among a sample of 32 species of rodents including the mouse (Mus musculus) and rat (Rattus norvegicus). The divergence between the Mus and Rattus genera probably occurred around 10–12 Myr ago [14, 15], while the divergence of these two genera from Peromyscus maniculatus, the deer mouse (subfamily Sigmodontinae), occurred around 25 Myr ago.

Others may be essential (“keystone”) species in maintaining the health of our forests, through their role in spreading mycorrhizal fungi or dispersing seeds. And a few species play an essential role as “domestic animals” used in medical research that has been enormously beneficial to mankind. Switching to a new rodent species can have a profound effect on the evolution of hantaviruses. Adaptation to the new host can stimulate modifications of virus phenotype and expansion into new ecological niches, eventually giving rise to “new” hantaviruses sufficiently distinct that are able to exploit new geographical areas. At least three instances of this happening have now been recorded.

Incisors without apposition may be removed, although the extraction procedure may prove challenging due to the length of the tooth roots (Donnelly, 1997). Murids feature in literature, including folk tales and fairy stories. In the Pied Piper of Hamelin, retold in many versions since the 14th century, including one by the Brothers Grimm, a rat-catcher lures the town’s rats into the river, but the mayor refuses to pay him. In revenge, the rat-catcher lures away all the children of the town, never to return. Mice feature in some of Beatrix Potter’s small books, including The Tale of Two Bad Mice (1904), The Tale of Mrs Tittlemouse (1910), The Tale of Johnny Town-Mouse (1918), and The Tailor of Gloucester (1903), which last was described by J. R. R. Tolkien as perhaps the nearest to his idea of a fairy story, the rest being “beast-fables”.

Much variation present in external and internal morphology, and also in habitat and other aspects of natural history; members of the group are linked primarily by dental characteristics. All other rats, mice, and relatives vary widely in physical characteristics. Most species are small, usually with somewhat long tails and brownish fur. This African rodent is also in the family Muridae and used to be included in the genus Rattus (Williams, 1980). Its small size (40 to 80 g) has caused it to also be known as the multimammate mouse.

Even though most genera have lifespans of less than two years, murids have a high reproductive capacity, and their populations tend to grow quickly until rapidly decreasing when food supplies are depleted. This occurs in a three- to four-year cycle most of the time. This tail is exceptionally small in comparison to the body length (37%) and is regarded as a key diagnostic trait.

Many providers provide mice that are devoid of murine infectious illnesses and parasites. Healthy and sick mice have similar acquisition costs, but there are likely to be substantial changes in the experimental result and data reliability between the two groups. Many subfamilies, including hamsters, were once thought to be part of a distinct family from Muridae, although they are now most commonly regarded as muroid subfamilies. Pending better resolution of the relationships between these problem groups, some specialists prefer to retain them as subfamilies within Muridae, but others still separate them as families under the umbrella of Muroidea. Fossil evidence may support the single-family arrangement because clearly diagnosable groups of living species, such as mole rats and bamboo rats, lose their distinction when their lineages are traced far back in time.

Other sites of vascular access may be used to collect blood from an anesthetized mouse during a terminal surgical procedure. Methoxyflurane is a safe, easily administered inhalant anesthetic agent for mice. The injectable anesthetic agents most often used in mice include pentobarbital (40–60 mg/kg i.p. after dilution in saline) and 2% tribromoethanol solution (0.2 ml/10 g i.p.).

A second Afrotropical niche includes carnivorous semi-aquatic rodents that display significant adaptations to water. Among them are species of the genera Lophuromys, Malacomys and Deomys, Nilopegamys plumbeus and Colomys goslingi. Both feed on molluscs, worms, and crustaceans, and occur in forested parts of central Africa with C. Goslingi having a more eastern distribution, whereas Malacomys is commoner in the west. The former replaces the latter in wetter habitats where ranges overlap, and is found along muddy rivers and in swamps that flood regularly (Kingdon, 1974). Colomys goslingi hunts in water where it wades and sifts sediment with the front paws.

Muridae is derived from the Latin mus (genitive murids), which means “mouse.” Murids are found almost everywhere on the planet, however many subfamilies have more limited distributions. Antarctica and numerous maritime islands are devoid of murids. Even though none of them is native to the Americas, a few species, such as the house mouse and black rat have been transported to other parts of the world.

For instance, some assemblages, such as blind mole rats and bamboo rats, are very distinctive and have been treated in the past as separate families. The Malabar spiny tree mouse was originally described as a kind of dormouse (Myoxidae) but was reclassified as a murid similar to blind tree mice. Many subfamilies, including hamsters, were formerly considered as part of a family separate from Muridae, but these groups are now most often viewed as muroid subfamilies. This would be satisfactory if each group could be clearly demonstrated to have a common ancestor (i.e., to be monophyletic).

Originally classified as a dormouse (Myoxidae), the Malabar spiny tree mouse was reclassified as a murid, comparable to blind tree mice. Muridae, (family Muridae), largest extant rodent family, indeed
the largest of all mammalian families, encompassing more than 1,383 species of the “true” mice and rats. Two-thirds of all rodent species and genera belong to family Muridae.

The hind feet are long and very large, with compressed lateral digits; these water mice often catch fish (Nowak, 1999). The South American water mice, placed in the genus Neusticomys, are typically found along fast-flowing streams in the eastern Andes (Table VI). They have sharp incisors with surfaces inclined towards each other allowing them to catch and hold slippery aquatic prey (Nowak, 1999).

For their size, they can be very aggressive to predators and even to other members of their species. The rodents can be vocal, with various communicative sounds such as chattering, screaming, and whistling. Murids are sometimes found alone, but often are social, and are found traveling and sleeping together. Some species breed throughout the year but others only during certain seasons. Murid rodents generally have high reproduction rates (lots of offspring) and large populations.

The yellow-rumped leaf-eared mouse (Phyllotis xanthopygus) has the world’s biggest elevation range of any animal, at more than 20,000 feet. The Muridae are classified into five subfamilies, around 150 genera, and about 834 species. Not surprisingly, even the most basic characters are subject to continuing evolutionary change; most of the characters listed as diagnostic in the next paragraph do in fact show some variation within the group. All, however, are believed to have characterized primitive murids. Previously, these animals were used extensively in pesticide research (Gill and Redfern, 1979) because they constitute a significant agricultural pest in Africa.

Parenteral agents usually provide 20–30 min of general anesthesia in the mouse and can be re-dosed to prolong their effects. Recommended methods of euthanasia for mice include carbon dioxide inhalation, cervical dislocation, and i.p. It is the only animal known to use and store poisons from other species in nature for self-defence, with no known negative consequences. In the wild, it eats mostly leaves, fruit, and other plant material, but in captivity, it has been known to consume meat, grains, root vegetables, and insects. It eats by sitting on its haunches and bringing food to its mouth with its forepaws.

The submaxillary salivary glands are considered one of the richest natural sources of nerve growth factor (Aloe et al., 1981; Burcham et al., 1991). Females of the wild-colored inbred strain, MWC, have a unique adrenal border zone between the zona fasciculata and the zona reticularis (Tanaka et al., 1996). The MCC strain was observed to have lysosomal glycolipid storage within the renal proximal tubular epithelium (Fujimura et al., 1996). Another active area of research utilizing Mastomys is in the study of microfilarial infections and development of antifilarial agents (Tripathi et al., 2000).

Distinctive row of stiffened hairs along the sides of the head, effectively increasing its breadth and probably helpful in digging. Number of species and their relationships have proved very difficult to work out. In general, infection of the rodent hosts by their respective hantaviruses is thought to be asymptomatic and no overt disease is produced. Infection of hantavirus in the rodent host may also cause growth retardation as observed in Rattus norvegicus infected Opportunities for innovation in animal diets with SEOV (Childs et al., 1989) and P. maniculatus infected with SNV (Kanerva et al., 1998). Nevertheless, the general absence of an overt illness in rodent hosts despite a persistent and lifelong infection is believed to be a smart way of survival for hantaviruses, by which they avoid killing their own hosts. It also highlights an amicable relationship between the virus and its host that was developed over hundreds of thousands of years of mutual interaction.

The Neotropical web-footed marsh rats (Holochilus spp.) are distinctive in that they feed almost exclusively on grass and herbs on floodplains, along stream banks or in marshes, occasionally they may take molluscs. Fish-eating rats (Ichthyomys spp.) are widely distributed in tropical America (Table VI). They have large, partially-webbed hind feet, stout whiskers, small eyes and ears, and a tail with a bristly underface. Venezuelan Ichthyomys pittieri sometimes capture small fish but more often feed on crustaceans and other aquatic invertebrates. Underwoodi, which is well adapted to life in water and has dorsally-situated nostrils that have posterior valves that exclude water (Starret and Fisler, 1970).

Muridae (rat family) is the biggest extant rodent family, and indeed the biggest of all animal families, with over 1,383 species of “real” mice and rats. The use of nuclear and mitochondrial DNA, as well as DNA-DNA hybridization, has provided strong statistical support for these claims. Due to the absence of physical traits that support this group, the subfamily as it is now classified will likely expand.

The hairs in this region resemble normal hair at the tips, but they are otherwise spongy, fibrous, and absorbent, with a honeycomb structure. A thick, white-bordered band of hairs surrounds a region of glandular skin in this mane.

Some specialists want to keep these issue groups as subfamilies under Muridae until a better clarification of their connections, while others continue to split them as families under the umbrella of Muroidea. The live members of these 18 groups demonstrate an impressive range of variety in body structure, movement, and ecology. The murids are small mammals, typically around 10 cm (3.9 in) long excluding the tail, but ranging from 4.5 to 8 cm (1.8 to 3.1 in) in the African pygmy mouse to 48 cm (19 in) in the southern giant slender-tailed cloud rat. They typically have slender bodies with scaled tails longer than the body, and pointed snouts with prominent whiskers, but with wide variation in these broad traits. Some murids have elongated legs and feet to allow them to move with a hopping motion, while others have broad feet and prehensile tails to improve their climbing ability, and yet others have neither adaptation.

Litters (groups of young born at the same time from the same mother) have one to seventeen offspring. Young are born blind and naked, although they develop fast, are weaned (stop drinking their mother’s milk) quickly, and are able to reproduce within weeks or months. Murids include most of the familiar rats and mice, but the family also encompasses an enormously diverse array of other rodents. Here, we follow recent authorities in treating murids as members of a single, very large family with a number of subfamilies. The systematic relationships of these groups among themselves and with other rodents has proved to be an extremely difficult problem, one that is by no means resolved.