Ctenomys rionegrensis
Rio Negro tuco-tuco

Rio Negro tuco-tucos are found in four populations: one occupies a small region of western Uruguay in the Department of Rio Negro, and the remaining three are found in the Entre Rios Province in eastern Argentina. (Bidau, et al., 2008; Wlasiuk, et al., 2003)

Rio Negro tuco-tucos generally inhabit sand dunes and areas with sandy soils near the mouth of the Rio Uruguay, along the Rio Parana, and near the Rio Negro. (Bidau, et al., 2008; D'Anatro and Lessa, 2006)

Rio Negro tuco-tucos are rodents with short necks, large heads with reduced ears, and short forelimbs with large claws. They are well suited for a fossorial lifestyle. Adults generally weigh between 100 and 700 grams and grow to 15 to 25 centimeters from snout to tail. The tail is hairless and stiff. Three distinct fur colors are found among these tuco-tucos: melanic (black), agouti (light and dark banded hairs with black tips), and dark-backed. How this variation arose genetically is being investigated. The robust incisors are orange on the anterior surface and are ever-growing. Rio Negro tuco-tucos can be distinguished from other tuco-tucos by the male phallus which has a “trilobed bacular tip and a pair of spikes within the intromittent sac.” Resting metabolic rates have not been calculated, but the basal metabolic rate of a similar species (Ctenomys australis) is around 0.343±0.053 liters of oxygen per hour. (Altuna and Lessa, 1985; Lacey, et al., 2000; Wlasiuk, et al., 2003)

Little is known about the mating system of Rio Negro tuco-tucos. Presumably, it is similar to Pearson's tuco-tucos, Ctenomys pearsoni, which have been better studied. Courtship rituals involve aggressive displays between males and chemical and auditory stimulation. Rio Negro tuco-tucos sing during courtship. Males spend time with females before copulating, as females are induced ovulators. ("Gabriel Francescoli", 2005; Altuna, et al., 1991; Francescoli, 1999; Lacey, et al., 2000)

The breeding season of Rio Negro tuco-tucos occurs during the late austral autumn. In a study by Tassino and Passos (2009), pregnant females were observed during the beginning of austral winter and lactating females were observed during the austral spring. Females generally bear 2 to 4 offspring after gestating for 100 days and lactate for about two months. Average time to weaning and average birth mass is unknown. In Ctenomys talarum average time to weaning is around 30 days from birth and the birth mass is 46.0 ± 16.43g. ("Tuco-Tucos: Ctenomyidae - Behavior And Reproduction", 2010; Tassino and Passos, 2010; Zenuto, et al., 2002)

After copulation, males and females separate, with females taking care of the young until they become independent.

Little is known about the lifespan of Rio Negro tuco-tucos in captivity, but the expected lifespan in the wild is about 3 years.

Rio Negro tuco-tucos are solitary and territorial, socializing only to mate. They are semi-fossorial, residing in burrows which they dig with their incisors. (Francescoli, 1999; Lacey, et al., 2000; "Tuco-Tucos: Ctenomyidae - Behavior And Reproduction", 2010)

Little is known regarding the home range of Rio Negro tuco-tucos. Because these are fossorial animals, they presumably do not venture far from their burrows.

Rio Negro tuco-tucos signal to each other over long distances by "singing." The name "tuco-tuco" comes from the sound these animals make. A recording of their vocalizations can be found here: http://eto.fcien.edu.uy/gaboeng.htm. These animals communicate to demarcate territory and to find each other during the mating season. ("Gabriel Francescoli", 2005; Francescoli, 1999)

Rio Negro tuco-tucos are herbivorous, primarily eating grasses, roots, and shoots. Like rabbits, they are coprophagous. ("Tuco-Tucos: Ctenomyidae - Behavior And Reproduction", 2010)

The dull coat color of Rio Negro tuco-tucos is an example of cryptic coloration, as it would make them difficult to spot on a riverbank. Some predators include owls, foxes, armadillos, grison, and some snakes. (Wlasiuk, et al., 2003)

Little is known about the subtleties of the ecological role of Rio Negro tuco-tucos. Birds of prey, large snakes, and several carnivorous mammals prey on this rodent, and presumably some parasites would use them as hosts, although this is not well-studied. Rio Negro tuco-tucos are shy and solitary and are not commensals with humans. (Lacey, et al., 2000; Lacey, et al., 2000)

Rio Negro tuco-tucos are not known to benefit humans, but because three fur phenotypes exist within relatively small isolated populations and because of profound differentiation within the species, they are currently being intensely studied by evolutionary biologists.

There are no known adverse effects of Rio Negro tuco-tucos on humans.

Rio Negro tuco-tucos are listed as an endangered species on the IUCN Red List because "its extent of occurrence is less than 5,000 km², its area of occupancy is less than 500 km², its distribution is severely fragmented, there are only four populations and there is continuing decline in the extent and quality of its habitat. It may be locally abundant if habitat is available but habitat is being quickly destroyed." (Bidau, et al., 2008)