Tachyoryctinae
East African mole rats

Tachyoryctinae, the east African mole rats, is a small Old World family of fossorial muroid rodents. There is one mole rat genus, Tachyoryctes, and 13 species. (Musser and Carleton, 2005)

Tachyoryctine mole rats are native to east Africa, from northern Tanzania and the eastern part of the Democratic Republic of the Congo, north to Ethiopia and Somalia. (Carleton and Musser, 1984)

Tachyoryctines inhabit areas that receive more than 500 mm of annual rainfall, including grasslands, woodlands, savannah, and agricultural areas. They have been found at elevations of up to 4,150 meters. (Nowak, 1999)

EXTERNAL CHARACTERISTICS

Tachyoryctines are stocky, mole-like animals. Their head and body length ranges from 160 to 313 mm, tail length ranges from 50 to 95 mm. They weigh 160 to 930 grams. Males tend to be noticeably larger than females. Their tails are about twice the length of the hind feet and are usually covered in fur. The fur on the body is soft and thick and comes in a variety of colors, including black, pale gray, brown, and cinnamon. Albino individuals with white fur are also relatively common. In general, the belly is slightly paler than the upper parts and has a silvery sheen. The eyes are small but visible and functional, and the ears are small as well. There are stiff tactile hairs on the face. East African mole rats have thick, projecting, orange pigmented incisors, with which they dig; small claws; and short, powerful legs.

INTERNAL CHARACTERISTICS

The tachyoryctine dental formula is 1/1, 0/0, 0/0, 3/3 = 16. The molars are hypsodont, hypertrophied, and the alveoli project into the orbit. The molar rows converge anteriorly. The bony palate has posterior furrows and a keel running down its midline. The heavy mandible has prominent coronoid and capsular processes. The incisive foramena are short. Tachyoryctines have flaring zygomatic arches and prominent sagittal and lambdoidal crests, which provide the broad attachment surfaces for the powerful head and neck muscles necessary for digging with their jaws. Due to the reduction of the ventral portion of the infraorbital foramen, the zygomatic plate is poorly demarcated. The infraorbital foramen contains the nasolacrimal canal. The anterior portion of the lateral masseter muscle has a broad origin on the side of the short rostrum, instead of on the zygomatic plate. The area between the orbits is constricted and the frontals are compressed. There are no sphenofrontal, stalacerate, or entepicondylar foramena, and no accessory foramen ovale. The buccinator and masticatory foramena are separate. The pterygoid fossa is deep and well-ossified. The external auditory meatus is tubular in shape, the auditory bullae are moderately inflated, and the malleus is constructed perpendicularly. The interparietal bone is tiny. The tachyoryctine stomach has two chambers, and the cecum has a spiral valve. There is no stapedial artery, and the internal carotid artery provides circulation to the orbits. (Carleton and Musser, 1984; Nevo, 1999; Nowak, 1999)

Male and female tachyoryctines only associate for the short time necessary for mating to take place. Mating is initiated when a male visits a female's burrow at night. (Flynn, 1990)

Tachyoryctines breed year round, but they concentrate most of their reproduction during the wet season. Conflicting information is available on how often females bear litters. Females are either polyestrous and conceive a second litter while they are nursing the first, presumably due to a postpartum estrous (Nowak 1999), or they only breed once every six months (Flynn 1990). Gestation lasts 37 to 49 days and litter sizes range from one to four, although litters of one and two young are most common. The young nurse until they are between 28 and 50 days old, and leave their mother's burrow about a month later, when their black juvenile pelage assumes the adult coloration. The young reach sexual maturity when they are four to six months old. (Flynn, 1990; Nowak, 1999)

Female tachyoryctines build underground nests in which they raise their altricial young. They nurse their young for up to 50 days, and the young stay with their mother for another month, even though they can eat solid food. There is no male parental care known in this group. (Flynn, 1990; Nowak, 1999)

East African mole rats have an average life expectancy of about one year, and their maximum lifespan is about three years. (Flynn, 1990; Nowak, 1999)

East African mole rats, like all spalacids, are fossorial creatures. They construct underground nest chambers consisting of food stores, latrines, and nests which they line with grasses. Foraging tunnels 15 to 30 cm deep and up to 52 meters long radiate outward from each mole rat's nest chamber. Mole rats incorporate deep bolt holes into their burrow systems, into which they can make a quick getaway if a predator attacks. They dig with their incisors, pushing back soil with their forefeet, kicking it behind them with their hindfeet, and using their heads to push it out of their tunnels when too much accumulates. Mounds of soil form where mole rats are active; these can be anywhere from 15 cm wide and 7 cm high to 18 m wide and 2 m high near territory centers. Although they are primarily fossorial, tachyoryctines do forage above ground and spend over 5% of the day doing so. They are known to sit just inside their burrow entrances and grab whatever plants they can reach without having to venture too far. Tachyoryctines are diurnal and active year round, but they become less active during the dry season and burrow deeper--up to one meter below the surface. They can survive cold temperatures at high elevations because fermenting feces and nest material in their burrows raises the temperature in their underground chambers. East African mole rats are solitary--just one individual occupies each burrow system--and they are territorial. (Flynn, 1990; Nevo, 1999; Nowak, 1999)

East African mole rats perceive the world using vision, touch, smell, taste, and hearing. Given their small eyes and the fact that they spend most of their lives underground in complete darkness, vision is probably the least important of these senses. On the other hand, the tactile bristles that tachyoryctines have on the sides of the face imply that touch is especially significant. East African mole rats are known to rap on the ground with their upper incisors, which may be a way to communicate territory ownership. Also, males have large sex-pheromone producing glands between each eye and ear and on the penis. (Flynn, 1990)

Tachyoryctines are herbivores that feed on roots, rhizomes, bulbs, tubers, and grass. They store excess food in underground chambers in their burrow systems. (Nowak, 1999)

East African mole rats fall prey to a variety of hawks, owls, and small mammalian carnivores. Their predators include: Simian jackals (Canis simensis), servals (Leptailurus serval), African striped weasels (Poecilogale albinucha), striped polecats (Ictonyx striatus), Abyssinian owls (Asio abyssinicus), Cape eagle-owls (Bubo capensis), Verreaux's eagle-owls (Bubo lacteus), barn owls (Tyto alba), jackal buzzards (Buteo rufofuscus), and lammergeiers (Gypaetus barbatus). They probably avoid predation to some degree by staying hidden underground. Tachyoryctines incorporate bolt holes into their burrow systems into which they can make a quick escape if caught out in the open. If cornered, they can be vicious and do not hesitate to rush at their attacker and attempt to bite. (Flynn, 1990; Nowak, 1999)

Because of their fossorial lifestyle, tachyoryctines probably help to aerate the soil. They are important consumers of a variety of plant species, and they are prey for many avian and mammalian predators. (Flynn, 1990)

Tachyoryctines are hunted for food and their skins are used as charms by native tribes. (Nowak, 1999)

East African mole rats are agricultural pests on peas, beans, corn, sweet potatoes, and various root crops. (Nowak, 1999)

Three tachyoryctine species are on the IUCN's Red List of Threatened Species. Tachyoryctes annectens and Tachyoryctes storeyi are listed as having deficient data, because it is unclear whether they actually are real species, or whether they are subspecies of a tachyoryctine with a wider distribution. Research is needed to clarify their taxonomic relationships with other tachyoryctines and to assess their population status. The third species on the list, T. macrocephalus, is considered vulnerable because it is only known from one location. Fortunately, that location mostly falls within a national park, but illegal grazing still threatens the population there. (IUCN, 2004)

Fossil evidence suggests that the rhizomyine + tachyoryctine clade originated in the early Miocene of south Asia, about 20 million years ago. Tachyoryctines and rhizomyines then diverged about three million years later, and evolved their fossorial lifestyles separate from one another. Tachyoryctines are thought to have evolved their fossorial lifestyle about 7 million years ago. The earliest known tachyoryctine fossils are from the late Miocene of Palestine. Tachyoryctines are thought to have entered Africa via two separate migrations, the first during the Miocene (these taxa then went extinct) and the second during the Pliocene (these taxa gave rise to the modern genus, Tachyoryctes). The earliest known fossils of Tachyoryctes are from the Pliocene of Ethiopia. (Flynn, 1990; Nevo, 1999)