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Gymnuromys robertivoalavoanala

By Stephanie Boyle

Geographic Range

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)

Habitat

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)

  • Range elevation
    500 to 1,625 m
    1640.42 to ft

Physical Description

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)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    100 to 155 g
    3.52 to 5.46 oz
  • Range length
    325 to 370 mm
    12.80 to 14.57 in

Reproduction

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)

  • Breeding interval
    Gymnuromys roberti breeds once yearly.
  • Breeding season
    Gymnuromys roberti is thought to breed from October through December.
  • Average number of offspring
    2

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)

  • Parental Investment
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

No information is available on the lifespan of Gymnuromys roberti.

Behavior

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)

Home Range

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

Communication and Perception

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)

Food Habits

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)

  • Plant Foods
  • seeds, grains, and nuts
  • fruit

Predation

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

Ecosystem Roles

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)

Economic Importance for Humans: Positive

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.

Economic Importance for Humans: Negative

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.

Conservation Status

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)

Contributors

Stephanie Boyle (author), University of Michigan-Ann Arbor, Phil Myers (editor), University of Michigan-Ann Arbor, John Berini (editor), Animal Diversity Web Staff.

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

frugivore

an animal that mainly eats fruit

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

island endemic

animals that live only on an island or set of islands.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

soil aeration

digs and breaks up soil so air and water can get in

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

2010. "The IUCN Red List of Threatened Species" (On-line). Accessed March 12, 2011 at http://www.iucnredlist.org/apps/redlist/details/9581/0.

Carleton, M., S. Goodman. 2004. The Natural History of Madagascar. Chicago: The University of Chicago Press.

Carleton, M., S. Goodman. 2000. Rodents of the Parc National de Marojejy, Madagascar. Fieldiana, Zoology, 97: 231-263.

Garbutt, N. 2007. Mammals of Madagascar: A Complete Guide. United States: Yale University Press.

Goodman, S., M. Carleton. 1998. The Rodents of the Reserve Speciale d'Anjanaharibe-Sud, Madagascar. Fieldiana, Zoology, 90: 201-221.

Goodman, S., M. Carleton, M. Pidgeon. 1999. Rodents of the Reserve Naturelle Integrale d'Andohahela, Madagascar. Fieldiana, Zoology, 94: 217-250.

Gunther, A., W. Carruthers, W. Francis. 1896. The Annals and Magazine of Natural History, including Zoology, Botany, and Geology. London: Taylor and Francis.

Musser, G., M. Carleton. 2005. Mammal Species of the World: A Taxonomic and Geographic References. Baltimore: The Johns Hopkins University Press.

Nowak, R. 1999. Walker's Mammals of the World. Baltimore and London: The Johns Hopkins University Press.

Vaughan, T., J. Ryan, N. Czaplewski. 2011. Mammalogy. Sudbury, MA: Jones and Bartlett Publishers, LLC.

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