Family Nesomyidae
African and Malagasy endemic rats and mice

The family Nesomyidae is a diverse group of African rodents that has recently proven to be even more diverse than originally thought, with the discovery of two new genera and species since 1995 (Carleton and Goodman 1996, 1998). Overall, this family encompasses 61 species and 21 genera in six subfamilies: the Cricetomyinae (African pouched rats), the Delanymyinae (swamp mice), the Dendromurinae (climbing mice), the Mystromyinae (white-tailed rat), the Nesomyinae (Malagasy rats and mice), and the Petromyscinae (African rock mice). (Carleton and Goodman, 1996; Carleton and Goodman, 1998; Musser and Carleton, 2005)

Nesomyid rodents range throughout sub-Saharan Africa and Madagascar. (Corbert, 1984)

Nesomyids occupy a wide range of habitats, including forests, shrublands, grasslands, savanna, agricultural fields, and wetlands. They live in both moist and dry habitats and span the tropical, subtropical, and temperate zones. Some are found in montane habitats at altitudes up to 4,300 meters. (Corbert, 1984; IUCN, 2004; Kingdon, 1974; Nowak, 1999)

As is true for many muroid rodent groups, the family Nesomyidae has a long, complicated taxonomic history. Tullberg's (1899) Nesomyidae did not include the genus Dendromus, which he placed in the family Muridae. The Nesomyidae of Chaline et al. (1977) included a subfamily now placed in Muridae, the Otomyinae, as well as the extinct subfamily Afrocricetodontinae. The classification of Chaline et al. (1977) also included the Dendromuridae as a separate family containing the subfamilies Dendromurinae and Petromyscinae. Other authors did not recognize Nesomyidae as a family, but instead classified nesomyid genera in various muroid subfamilies, including Gerbillinae (Alston 1876), Murinae (Alston 1876), Sigmodontinae (Thomas 1896), Cricetinae (Miller and Gidley 1918; Ellerman 1940, 1941), and Dendromyinae (Ellerman 1940, 1941). Simpson (1945) considered Nesomyinae a subfamily of Cricetidae and Dendromurinae a subfamily of Muridae. Still others have simply placed all muroid subfamilies, including Nesomyid subfamilies, within the family Muridae (Musser and Carleton 1993). Recent molecular evidence has shown that the subfamilies Nesomyinae, Petromyscinae, Mystromyinae, Dendromurinae, and Cricetomyinae form a distinct clade (Jansa and Weksler 2004; Steppan et al. 2004, Michaux et al. 2001), and therefore they are now grouped together in the family Nesomyidae (Steppan et al. 2004). The relationship between the nesomyid clade and the rest of Muroidea remains unclear (Jansa and Weksler 2004), but Steppan et al. (2004) date this divergence event at about 25 million years before the present. (Alston, 1876; Chaline, Mein, and Petter, 1977; Ellerman, 1940; Ellerman, 1941; Jansa and Weksler, 2004; Michaux, Reyes, and Catzeflis, 2001; Miller and Gidley, 1918; Musser and Carleton, 1993; Simpson, 1945; Steppan, Adkins, and Anderson, 2004; Thomas, 1896; Tullberg, 1899)

A survey of the physical characteristics of nesomyid species gives an idea of just how diverse this group is. The wide array of physical characteristics in this group reflects the wide array of habitats and lifestyles to which they have become adapted. Nesomyids are rat-like, vole-like or gerbil-like in overall appearance. Tail lengths range from more than twice the length of the head and body to less than half the length of the head and body, and ear lengths vary as well, from very long relative to the head to very short. In overall size, nesomyids range from the tiny Delany's swamp mouse, with a head and body length of 50 to 63 mm and a weight of 5.2 to 6.5 g, to the hefty African giant pouched rats, which can grow to 450 mm in length and weigh up to 2.8 kg. In some species, males weigh more than females, and in others, there is no detectable sexual dimorphism. Most nesomyids are thickly furred and they span a range of colors, including various shades of browns and grays. Some have nearly naked prehensile tails, and others have well-furred tails that may appear almost bushy and have tufted tips. One subfamily, the Cricetomyinae, has cheek pouches; the others do not. (Kingdon, 1974; Nowak, 1999)

As is the case with many rodents, nesomyids have short lifespans in the wild. Most probably do not live more than two years, but lifespan may be considerably longer in captivity. (Kingdon, 1974; Nowak, 1999)

Nesomyids range from exclusively arboreal species to exclusively terrestrial species. Many are adept climbers, and even those that are mainly terrestrial may forage in shrubs or small trees. Some are exlusively nocturnal, some are exclusively diurnal, and some are active for at least part of the night and day. They either dig burrows or use burrows made by other animals or tree cavities in which they often build nests and store food. None are reported as being highly social, although some may live in pairs or small family groups, and many are solitary. Degree of territoriality varies, as does degree of sedentariness: some have been reported to migrate between different habitats with the changing of the seasons. Others cope with hot, dry seasons by aestivating in their burrows. (Kingdon, 1974; Nowak, 1999)

All nesomyids perceive the world using vision, hearing, smell, and touch, but the relative importance and the acuteness of each of these senses varies among species. The evolution of certain modes of communication is closely tied with sensory abilities, and thus, communication among nesomyids is probably highly variable as well, with different species depending to varying degrees on visual, acoustic, chemical, and tactile cues. (Kingdon, 1974; Nowak, 1999)

The food habits within this family range from strictly herbivorous to strictly insectivorous, with varying degrees of omnivory in between. Foods eaten by nesomyid species include seeds, roots, stems, nuts, berries, fruit, leaves, insects, small reptiles, bird eggs, bird nestlings, crabs, and snails. Many nesomyid species, especially those that are primarily granivorous, create food caches in their burrows. (Kingdon, 1974; Nowak, 1999)

As small to medium-sized rodents, nesomyids are potential prey for a large array of predators, including mammalian carnivores, snakes, eagles, and owls. Many nesomyid species avoid predation by building nests in inaccessible burrows and relying on their speed and agility to escape. (Kingdon, 1974; Nowak, 1999)

Given their range of food habits, it is apparent that nesomyids as a group, and in some cases even individual nesomyid species, occupy several trophic levels, including those of primary, secondary, and tertiary consumer. Also, as mentioned above, they are prey for a variety of mammalian, reptilian, and avian predators. Because many nesomyid species include seeds and fruits as a primary component of their diet, these rodents may be important seed dispersers. Finally, nesomyids are parasitized by fleas, ticks, earwigs, and nematodes. (Durette-Desset, Lehtonen, and Haukisalmi, 2002; Hubbard, 1972; Kingdon, 1974; Nowak, 1999)

One nesomyid species, Cricetomys gambianus, is a pest in urban areas, where it inhabits sewers alongside Rattus. A few species carry the plague. (Hubbard, 1972; Kingdon, 1974; Nowak, 1999)

Some nesomyid species, including those in the genus Steatomys and the Gambian rat, Cricetomys gambianus, are prized as food items by local peoples. Gambian rats are also kept as pets by rodent enthusiasts. Additionally, the species Mystromys albicaudatus is bred in captivity and used for disease research. (Hallett and Meester, 1971; Kingdon, 1974; Nowak, 1999)

The IUCN lists three species in this family as critically endangered (Eliurus penicillatus, Macrotarsomys ingens, and Dendromus kahuziensis), four as endangered (Eliurus majori, Hypogeomys antimena, Delanymys brooksi, and Mystromys albicaudatus), four as vulnerable (Gymnuromys roberti, Dendromus lovati, Dendromus oreas, and Steatomys jacksoni), two as near threatened (Beamys major and Beamys hindei), three as lower risk (Brachyuromys betsileoensis, Brachyuromys ramirohitra, and Eliurus webbi), and five as having deficient data (Dendromus vernayi, Dendroprionomys rousseloti, Leimacomys büttneri, Prionomys batesi, and Megadendromus nikolausi). The major threat to most of these species is habitat destruction and fragmentation caused by human activities such as agriculture and logging. Although the range of the family as a whole is broad, many of the individual species in the family are endemic to particular locations, which makes them especially vulnerable to habitat loss. This is especially true of the Malagasy rodents, the nesomyines, as they are all endemic and all subjected to extreme habitat pressures. Research on the ecology of many nesomyid species is ongoing, in the hopes of preserving suitable habitat where these rodents can persist. (IUCN, 2004; Kingdon, 1974; Nowak, 1999)