As noted above, there has been considerable argument over the taxonomy of the genus Arvicanthis. Much of the research conducted prior to the late 1990s on A. niloticus assumed it was the only species of Arvicanthis in existence. This may explain discrepencies in behavioral, circadian, and physical descriptions. Further genetic and morphometric research into the diversity of the genus Arvicanthis may alter the validity of this account.
Arvicanthis niloticus is capable of perceiving touch and scent at birth, and hearing and sight both develop around 6 to 7 days of age. Communication in A. niloticus has not been adequately studied. However, squeaks and distress calls have been observed to begin between 4 and 6 days of age, and vocalization may be involved in its communicative repertoire. Olfaction is a common form of communication in many mammals, including rodents, and may also be utilized by this species. Because these animals are social and diurnal, both visual and tactile communiation likely take place, although details of these forms of communication are not available in current literature.
Communication Channels: visual ; tactile ; acoustic ; chemical
Perception Channels: visual ; tactile ; acoustic ; chemical
This species does not appear to be in any danger. The IUCN red list does not have a data entry for A. niloticus; however, it does list its congener, Arvicanthis blicki as near-threatened. The US Federal list and CITES have no information on A. niloticus.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: least concern
Arvicanthis niloticus is considered an agricultural pest throughout much of Africa, and active pest management programs are currently in effect. Also, this species has been implicated in the transmission of multiple human and crop diseases, including bubonic plague in Egypt, intestinal schistosomiasis, and Rice yellow mottle virus.
Negative Impacts: injures humans (causes disease in humans , carries human disease); crop pest
Given its rapid breeding capabilities, diurnal activity patterns, and small size, A. niloticus has value in laboratory research in medicine, physiology, behavior, and other related fields. Most rodent-based research in these disciplines utilizes either Norway rats, or house mice. However, both of these species are nocturnal, and captive A. niloticus colonies have been validated as diurnal and are thus more similar in certain respects to humans and other diurnal mammals than typical lab rats or mice.
Positive Impacts: research and education
Aside from serving as prey to some African carnivores, A. niloticus also serves other important, though perhaps less desirable, roles in its ecosystem. It is an agricultural pest and competes with other African rodents, primarily natal multimammate mice, and savanna gerbils, for both natural and cultivated resources. Arvicanthis niloticus thus has a strong impact on plant diversity. Senzota (1983) also proposed resource partitioning of grasses by A. niloticus and some African ungulates, including blue wildebeest and Thomson’s gazelles, to reduce competition between the rodents and ungulates.
Arvicanthis niloticus also serves as a host and/or vector for a variety of organisms, including fleas, parasitic worms, and viruses. It has been implicated in many plant and human disease outbreaks as a carrier of a multitude of diseases, such as bubonic plague in ancient Egypt, Rice yellow mottle virus in parts of Africa, and Schistosoma mansoni, which causes intestinal schistosomiasis, a disease that sometimes occurs in severe outbreaks in parts of Africa.
Commensal/Parasitic Species:
A. niloticus is primarily herbivorous, feeding on grasses, leaves and stems of flowering plants, seeds, the bark of some woody plants, and cultivated crops. Arthropods are also eaten by this species. As different food types vary in their availability seasonally, A. niloticus will alter the intake ratio of food types. This flexible, generalist approach may improve its competitive ability. Caching does not appear to be a predominant behavior in this species, but has been observed when larger food items were offered to wild individuals.
Animal Foods: insects
Plant Foods: leaves; wood, bark, or stems; seeds, grains, and nuts
Foraging Behavior: stores or caches food
Primary Diet: herbivore (Folivore )
The range of African grass rats, Arvicanthis niloticus, is traditionally held to extend along the Nile river valley and across most of sub-Saharan Africa, with the exception of the southern and southwestern regions of the continent. However, much debate over the number and range of species within the genus Arvicanthis has yet to be resolved, and the range of A. niloticus may be much more restricted. From genetic analysis, Ducroz, Volobouev, and Granjon (1998) claim this species occurs only in Egypt and northern West Africa, but Musser and Carleton (1993) argue that A. niloticus also inhabits regions including and surrounding Ethiopia.
Biogeographic Regions: ethiopian (Native )
As A. niloticus lives in colonial burrows, it requires some degree of ground cover, such as short bushes, trees, rocks, or termite mounds, under which it may nest. A variety of African habitats, including dry savanna, sub-desert, coastal scrub, open woodlands, grasslands, and cultivated areas, provide such protection. Exact altitudinal data are not reported, but A. niloticus is not believed to occur at high altitudes.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: desert or dune ; savanna or grassland ; scrub forest
Other Habitat Features: agricultural
Refinetti (2004) reports an average longevity of 2 years in captivity, with a standard deviation of 1 year for A. niloticus. Nowak (1999) claims that the longest lived individual of this species in captivity died at the age of 6 years and 8 months. Little is known about longevity in the wild; however, Packer (1983) estimates that females in one colony lived for an average of 10.2 months, with a maximum of 20 months.
Range lifespan
Status: wild: 20 (high) months.
Average lifespan
Status: wild: 10.2 months.
Range lifespan
Status: captivity: 6.6 (high) years.
Average lifespan
Status: captivity: 2 years.
Average lifespan
Status: wild: 10.2 months.
Average lifespan
Status: captivity: 2 years.
Average lifespan
Status: captivity: 6.7 years.
Rosevear (1969) described African grass rats as “medium-sized rats with stoutish bodies.” Adults of this species range in head and body length from 106 mm to 204 mm with an average of about 130 mm. Tail lengths range from 85% to 90% of the head and body length and average around 100 mm. Average mass of A. niloticus is 118 g, with a range of 50 g to 183 g. Males are slightly larger than females with reported average masses of 120 g to 123 g for males and 92 to 114 g for females.
Arvicanthis niloticus has a roundish head with large, round ears that are covered with short, fine fur. Incisors are not grooved; the snout is rather short, and the tail is covered in small, barely visible hairs. The hindfoot is well-developed, and the inner three hind toes are longer than the outer two. In contrast, the forefoot is smaller with a relatively short, though usable, thumb.
Variation in the coat color of this species has been reported; however, ambiguity in the boundaries of this species may have resulted in the misidentification of another species of the genus Arvicanthis as a color variant of A. niloticus. According to Rosevear (1969), the dorsal fur of these rats consists mostly of ringed hairs, which are dark black or brown at the base, lighter yellow, reddish-brown, or buff in the middle, and black at the tip. Short underfur, gutter hairs, and all-black guard hairs are also present and, combined with the ringed hairs, produce a "salt and pepper" effect. The ventral coat is shorter and lighter in appearance.
Range mass: 50 to 183 g.
Average mass: 118 g.
Range length: 106 to 204 mm.
Average length: 130 mm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger
Some anti-predatory behaviors have been documented for A. niloticus. Individuals typically retreat immediately down runways back to the communal burrow, possibly stopping to hide under other ground cover from avian predators. Senzota (1990) noted that when no conspecifics were present outside the burrow, individuals of this species spent a substantial amount of time in vigilant behavior at the entrances of the burrow prior to emerging. Movement by predators resulted in retreat into the burrow by A. niloticus, although mere stationary presence would not. If conspecifics were present (foraging, “playing”, or maintaining runways), individuals would readily leave the burrow.
Given the widespread range of this species and the prevalence of predation upon small mammals, particularly rodents, A. niloticus may be preyed upon by a number of carnivorous African animals. It was the primary prey of barn owls, in the Nigerian savanna and accounted for 26.5% of the biomass of these barn owls' diet in one study. Direct predation on A. niloticus by dwarf mongooses, black-backed jackals, spitting cobras, long-crested hawk-eagles, black-shouldered kites, and black-headed herons has been observed in the field.
Known Predators:
Relatively little is known about the mating structure of this species. Packer (1983) studied one colony in Tanzania and reported that the colony averaged 2.6 females and 3.1 males. Only males immigrated into the colony; new females were born in the colony and presumed not to disperse. All females successfully reproduced, and all males had descended testes, indicating the capability of breeding. Therefore, it is most likely that multiple members of an A. niloticus colony are breeding simultaneously.
Senzota (1990) studied two study sites with multiple A. niloticus colonies and indicated that colonies were mainly equally composed of males and females, with females more often outnumbering males than vice-versa. All-female and all-male colonies were also observed, but Senzota found that males were more likely to disperse than females, confirming Packer's findings.
Arvicanthis niloticus is capable of breeding year-round under highly favorable conditions. However, it usually experiences a sexual rest period beginning in March. This is during the hot dry season prior to the rainy season, and the rest period is induced at this time by long days, dry air, and high temperatures, which have an inhibitory effect on the gonads.
During the breeding season, gestation may take 18 to 25 days, averaging 23 days. Females have two equipotential ovaries and a duplex uterus. Birth weights of pups range from 3 g to 6 g, and litter sizes range from a few to 12 pups, averaging around 5 pups. Females experience a post-partum estrus and thus may be consistently pregnant and lactating, giving birth every 23 to 25 days, during the breeding season (October to March).
Young are weaned at the age of about three weeks and are considered sexually mature at 3 to 4 months. Males were observed to disperse from their natal colonies around 9 to 11 months of age.
Breeding interval: African grass rats breed every 23 to 25 days during the cold dry season in restricted habitats.
Breeding season: Mating occurs throughout the cold dry season (October to March) in restricted habitats and may occur year-round in highly suitable environments.
Range number of offspring: 4 to 12.
Average number of offspring: 5.
Range gestation period: 18 to 25 days.
Average gestation period: 23 days.
Average weaning age: 21 days.
Range time to independence: 1 to 4 months.
Average age at sexual or reproductive maturity (female): 4 months.
Average age at sexual or reproductive maturity (male): 4 months.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous ; post-partum estrous
Average birth mass: 4.15 g.
Average number of offspring: 5.
Average age at sexual or reproductive maturity (male)
Sex: male: 45 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 45 days.
Comprehensive examination of parental care in this species is lacking. However, mothers have been observed to defend their young prior to weaning. Lactation lasts about 21 days, and it is most likely, given preliminary data, that females rarely disperse from their natal nest, whereas males often disperse. Thus, parental care beyond lactation may occur. However, Senzota (1990) noted that wild A. niloticus did not defend their sub-adult offspring in the presence of predators but instead retreated immediately to their burrows.
Male parental care is not well-documented. Males may be kept in captivity with their mates and offspring throughout lactation but have occasionally been observed to commit infanticide, which is not uncommon in captive rodents. However, given the communal social structure of A. niloticus, it is likely that males are at the least indifferent to and at most actively parenting their offspring.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); post-independence association with parents
The Nile rat (Arvicanthis niloticus) is a species of rodent in the family Murinae.[2]
The species is divided into the following six subspecies.
Arvicanthis niloticus is a rodent of medium size, with the length of the head and of the body between 159 and 202 mm, the length of the tail between 125 and 173 mm, the length of the foot between 33 and 42 mm, the length of the ears between 19 and 23 mm and a weight up to 201 g.[4]
The fur is rough. The upper parts of individual hairs are yellowish with blackish tips. Long yellow or orange hairs are present on the bottom. A dorsal dark stripe more or less distinct extends from the head to the base of the tail. The ventral parts are whitish, with the base of the hairs blackish.
Areas where there are the whiskers, the eyes and a small patch behind each ear are orange. The legs are pink. The tail is shorter than the head and body, densely covered with hair, blackish above and white-yellowish below. The karyotype is 2n = 62, FN = 62-64.
It is mainly distributed in the Sahel and the sudano-zambesian Savanna belt, namely Benin, Burkina Faso, Burundi, Central African Republic, Chad, Democratic Republic of the Congo, Ivory Coast, Eritrea, Ethiopia,[5] Gambia, Ghana, Kenya, Malawi, Mauritania, Niger, Nigeria, Senegal, Sierra Leone, Somalia, Sudan, Tanzania, Togo, Uganda, and Zambia. Populations also occur in Algeria, Egypt, and Yemen.
Despite its wide distribution and commonness, little is known about the biology and actual occurrence of the species. It reproduces mainly between June and November. The females give birth to 5-6 small cubs at least 3-4 times a year. Life expectancy in the wild is 2.5–3 years.
Its natural habitats are dry savanna, moist savanna, subtropical or tropical moist shrubland, arable land,[6] pastureland, rural gardens, urban areas, irrigated land, and seasonally flooded agricultural land.
The Nile rat has gained traction as a useful nutritional model to study Type 2 Diabetes (T2DM). The Nile Rat gets Metabolic Syndrome that develops into diet-induced Type 2 Diabetes that is similar to human T2DM: insulin resistance, hyperinsulinemia, increased body fat, hypertension, elevated Triglycerides with decreased High-Density Lipoproteins, and eventually hyperglycemia and beta cell failure resulting in depressed insulin and end-stage diabetes that includes severe ketosis. The beta cell failure follows the same course as the five-stage decline documented in humans with T2DM.[7]
