Nesomyinae
Malagasy rats

The subfamily Nesomyinae is a diverse group of muroid rodents endemic to Madagascar. There are 23 nesomyine species in nine genera. (Musser and Carleton, 2005)

Nesomyine rodents are only found on Madagascar. (Carleton and Musser, 1984; Nowak, 1999)

Nesomyines live in a wide variety of habitats, including grasslands, wet meadows, sandy coastal forests, dry scrublands, and wet or dry inland forests. They range from sea level to 2,400 meters in elevation. (Carleton and Musser, 1984; Nowak, 1999)

Nesomyines are characterized by their morphological and ecological diversity. Typically they are medium to large gerbil-like, vole-like, or rat-like rodents. They measure 80 to 350 mm in head and body length and their tails range from 60 to 250 mm. Nesomyines weigh 21 to 1,500 grams. In some species, females weigh less than males, in other species, there is no sexual dimorphism. Nesomyine tails are short to long, naked to moderately furred, and sometimes tufted. Some have prehensile tails. The hind feet range from wide and short to narrow and long, and most have no hair on the soles. The pelage is long and soft or thick and woolly. It is sandy brown, reddish, or gray on the dorsum and yellowish white, white, or gray on the venter. Most nesomyines have large eyes and prominent ears and whiskers.

The nesomyine dental formula is 1/1, 0/0, 0/0, 3/3 = 16. The incisors are opisthodont. The molars are rooted, have a biserial cusp arrangement, and range from brachydont to hypsodont. In most species, the third molar is equal in size to the first two molars. Nesomyines have strong zygomatic arches with large jugals. Most species have ventrally constricted infraorbital foramina. There is a prominent interparietal bone. The bony palate is wide and smooth and bears one pair of posterior palatine foramina. The pterygoid fossae are flat and level with the bony palate. Most species have a large postglenoid foramen, and all species have an accessory tympanum and malleus of parallel construction. Nesomyines have 13 thoracic and 7 lumbar vertebrae. There are three circumvallate papillae on the tongue, and the stomach consists of a single chamber. The soft palate bears three premolar and five intermolar ridges. (Carleton and Musser, 1984; Nowak, 1999)

The mating system has not been studied for all nesomyine species, but at least one species, the Malagasy giant rat (Hypogeomys antimena), is known to be monogamous and mate for life. (Sommer, 2000)

The reproductive behavior of some nesomyine species is entirely unknown. Therefore, the following may or may not apply to the entire group. Nesomyines reproduce during the wet season, and some species have just a single litter per year. Gestation lasts up to 138 days and there are one to four young per litter. Sexual maturity is not reached until the age of two years in some species. (Nowak, 1999; Sommer, 2000)

Female nesomyines nurse their offspring for up to six weeks in a sheltered spot such as a tree cavity or underground nest chamber. In monogamous species, males may risk predation themselves by keeping watch for danger and protecting their offspring. Also, in those species that live in family groups, such as Hypogeomys antimena, young females remain with their parents for more than a year, not dispersing until after their parents have a new litter. (Sommer, 2000)

The lifespan of nesomyines has not been reported.

Nesomyines are a diverse group, including terrestrial and arboreal rodents. They are modified for cursorial, scansorial, and saltatorial locomotion. They build nests in tree cavities or in underground burrows. These burrows may be quite complex with multiple entrances and chambers. Some nesomyines live in small family groups, with an adult pair and their offspring inhabiting one burrow system. These family groups are territorial, excluding strangers from their home ranges. Other species have permanent home ranges that overlap with one another. Most nesomyines are nocturnal, though a few species are diurnal, crepuscular, or active any time of the night or day. (Carleton and Musser, 1984; Nowak, 1999; Sommer, 2000)

Nesomyines probably sense their environment through vision, hearing, touch, smell, and taste, as do most mammals. Many have large eyes and ears and long vibrissae, suggesting keen visual, auditory, and tactile abilities. Some nesomyine species live in small family groups and give alarm calls to warn their offspring when predators approach. (Nowak, 1999; Sommer, 2000)

These rodents are herbivores that feed on fruit, seeds, berries, roots, and stems. They are not known to cache their food. (Nowak, 1999)

Nesomyines are preyed upon by snakes, raptors, and mammalian carnivores. Some species give alarm calls and quickly retreat into underground burrows when danger threatens. (Sommer, 2000)

Nesomyines are primary consumers that provide food for upper level consumers such as carnivorous mammals and snakes. They are parasitized by nematodes and ticks. (Durette-Desset, et al., 2002; Hoogstraal, et al., 1967; Sommer, 2000)

There are no known positive effects of nesomyines on humans.

There are no known negative effects of nesomyines on humans.

This subfamily consists of endemic species with restricted ranges that are highly vulnerable to habitat loss. As a result, 8 of the 23 species in this group are on the IUCN's Red List of Threatened Species. Two of these species are critically endangered (Eliurus penicillatus and Macrotarsomys ingens), two are endangered (Eliurus majori and Hypogeomys antimena), one is vulnerable (Gymnuromys roberti), and three are lower risk (Brachyuromys betsileoensis, Brachyuromys ramirohitra, and Eliurus webbi). One species, the endangered Malagasy giant rat (Hypogeomys antimena), is being bred and studied in captivity at the Jersey Zoo by the Durrell Wildlife Conservation Trust. (Durrell Wildlife Conservation Trust, 2005; IUCN, 2004)