Gymnuromys roberti
voalavoanala

Gymnuromys roberti, or the voalavoanala, is found in Eastern Madagascar, where it ranges from the Northern Highlands to the southern limits of the Anosyenne Mountains. ("The IUCN Red List of Threatened Species", 2010; Musser and Carleton, 2005)

Gymnuromys roberti occupies lowland and montane humid forests. Its also commonly found in the Reserve Naturelle Integrale d'Andohahela, the Reserve Speciale d'Anjanaharibe-Sud, and the Parc National de Marojejy of Madagascar. Gymnuromys roberti can be found at elevations ranging from 500 m to 1,625 m, but usually resides between 900 m and 1,625 m. It lives in burrows near fallen trees, which can be up to one meter deep and terminate in a food storage chamber. (Carleton and Goodman, 2000; Carleton and Goodman, 2004; Garbutt, 2007; Goodman and Carleton, 1998; Goodman, et al., 1999; Musser and Carleton, 2005; Nowak, 1999)

Gymnuromys roberti is a medium-sized rodent with rat-like features. Head-body length ranges from 149 to 175 mm, and its tail ranges from 176 to 197 mm (approximately 110 to 115% of the head/body length). This species also has long, wide hind feet. Dorsal pelage is typically slate grey, and ventral pelage is greyish white with a slight silvery sheen. The vibrissae are long and dark, ranging in length from 50 to 60 mm. Its tail has little hair on it and is grey on top and lighter grey or white underneath and the tip can be completely white. The ears are ovular and project out from the head. Gymnuromys roberti shows moderate variation in mass, ranging from 100 to 155 g. Sexual dimorphism has not been reported in this species. (Carleton and Goodman, 2004; Garbutt, 2007)

The skull of Gymnuromys roberti (dorsal view, ventral view, lataral view) has a smooth braincase, reduced auditory bullae, a narrow hourglass-shaped interorbital region, short incisive foramina, and no sub-squamosal foramen. They have hypsodont or high crowned molars, and the upper and lower molars increase in size from the front to the posterior of the mouth, unlike most Muroidea. The skull of Gymnuromys roberti is similar to those in the genus Eliurus, except for the lack of a sub-squamosal foramen. (Carleton and Goodman, 2004)

Gymnuromys roberti most closely resembles Eliurus majori with respect to size, tail length, and greyish pelt. These two species can be distinguished by the tuft of hair at the end of E. majori's tail, which is not present in G. roberti. The tail of E. majori (120% of the head/body length) is also significantly longer that that of G. roberti (110 to 115% of the head/body length). (Carleton and Goodman, 2004; Garbutt, 2007)

There is no information available concerning the mating system of Gymnuromys roberti. (Carleton and Goodman, 2004; Garbutt, 2007)

Other than anecdotal accounts of captive animals, relatively little is known about the breeding behavior of Gymnuromys roberti. Females are thought to produce very small litters. Two separate accounts have found female specimens pregnant with two embryos each, and in both accounts the females were discovered between June and July. Males are thought to be sexually active between October and December. (Carleton and Goodman, 2004; Garbutt, 2007; Gunther, et al., 1896; Nowak, 1999)

There is no information available concerning parental investment in Gymnuromys roberti. As a with all mammals, however, mothers nurse their young until weaning. (Carleton and Goodman, 2004; Garbutt, 2007)

No information is available on the lifespan of Gymnuromys roberti.

Perhaps due to its nocturnal lifestyle, there is little information concerning the behavior of Gymnuromys roberti. It lives in burrows near fallen trees, which can be up to one meter deep and terminate in a food storage chamber. (Carleton and Goodman, 2004; Garbutt, 2007)

There is no information available concerning the home range of Gymnuromys roberti.

There is no information available concerning communication and perception in Gymnuromys roberti. It is nocturnal, which may indicate an increased dependence on its auditory, olfactory, and haptic senses. In addition to these, its closest relatives rely on their sense of sight as well. (Vaughan, et al., 2011)

Gymnuromys roberti forages for food in the leaf litter at the base of trees, where it eats fallen seeds and fruits. Also, it stores seeds and fruits in an underground chamber at the end of its burrow. (Carleton and Goodman, 2004; Garbutt, 2007)

There is no information available concerning the major predators of Gymnuromys roberti. ("The IUCN Red List of Threatened Species", 2010)

Gymnuromys roberti is an herbivore that primarily consumes seeds and fruit, which they store in their burrows. Thus, is likely that they play an important role in their local ecosystem as seed dispersers. Food caches may be forgotten, or a cache owner may die before it is depleted. It is also possible that many seeds are lost while individuals are en route to their cache site. There is no information available concerning parasites specific to this species. The burrows of Gymnuromys roberti may help aerate soil and increase water penetration throughout their geographic range. (Carleton and Goodman, 2004; Garbutt, 2007; Nowak, 1999)

There are no known positive effects of Gymnuromys roberti on humans. However, local economies that depend on forest resources may yield indirect economic benefits from seed dispersal and burrowing by G. roberti.

There are no known adverse effects of Gymnuromys roberti on humans. However, as seed predators this species may create a problem for grain farmers throughout its native range.

Based on trapping efforts throughout its range in Madagascar, Gymnuromys roberti has never been particularly common. Previously, G. roberti was listed as vulnerable on the IUCN's Red List of Threatened Species. In 2008, this species was downgraded from vulnerable to least concern and it appears to be somewhat tolerant of habitat change. At present, population trends of G. roberti are unknown. Potential threats include habitat loss due to agricultural expansion and contraction of diseases (e.g., plague) from introduced species such as Rattus rattus. Gymnuromys roberti may also be suffering from increased resource competition with R. rattus. ("The IUCN Red List of Threatened Species", 2010; Musser and Carleton, 2005; Nowak, 1999)