| Malagasy mountain mouse | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Rodentia |
| Family: | Nesomyidae |
| Genus: | Monticolomys Carleton &Goodman, 1996 |
| Species: | M. koopmani |
| Binomial name | |
| Monticolomys koopmani Carleton & Goodman, 1996 | |
 | |
| Known collection localities ofMonticolomys koopmani | |
TheMalagasy mountain mouse orKoopman's montane voalavo (Monticolomys koopmani) is a rodent within the subfamilyNesomyinae of the familyNesomyidae. It ismonotypic within thegenusMonticolomys, and is closely related to thebig-footed mouse(Macrotarsomys). It is found in the highlands of easternMadagascar. A small mouse-like rodent, it is dark brown on the upperparts and dark gray below. It has small, rounded, densely haired ears and broad feet with well-developedpads. The long tail lacks a tuft at the tip. The skull is delicate and lacks crests and ridges on its roof.
First collected in 1929, the Malagasy mountain mouse was not formally described until 1996, but it is now known to have a broad distribution. Active during the night, it occurs in bothmontane forest and human-disturbed grasslands and feeds on fruits and seeds. Ascansorial animal, it climbs trees but also lives on the ground. Althoughhabitat destruction may pose a threat, it is classified as "Least Concern" on theIUCN Red List.
Aspecimen was captured in 1929 during the Mission Zoologique Franco-Anglo-Américaine to Madagascar, but the rodents obtained by the expedition were never studied in detail. It was not until the 1970s thatKarl Koopman andGuy Musser recognized that the animal—whose skin had landed at theAmerican Museum of Natural History in New York, while the skull was at theMuséum national d'histoire naturelle in Paris—represented an otherwise unknown species. However, they never published their results. In 1993,Steven Goodman rediscovered the species on Madagascar and in 1996 he and Michael Carleton finally published a formal description.[2] They named the animalMonticolomys koopmani, as the sole member of a newgenus.[3] Thegeneric nameMonticolomys means "mountain-dwelling mouse" and refers to the animal's montane habitat, and thespecific namekoopmani honors Karl Koopman for his many contributions to mammalian systematics.[4]Common names in use for the animal also include "Koopman's montane voalavo"[5] and "Malagasy mountain mouse".[1]
The indigenous rodents of Madagascar, theNesomyinae, prior to the discovery ofMonticolomys comprised seven very distinctive genera—so distinct from each other that some have found it difficult to accept that they are closely related.[6]Monticolomys, however, does not follow this pattern, in that it is similar and closely related to thegerbil-like genusMacrotarsomys of western Madagascar. This relationship was originally proposed by Goodman and Carleton based on morphology,[7] and was strongly supported by aDNA sequence analysis (based on thecytochromeb gene) published in 1999.[8] While this study provided some weak support for a relationship between theMacrotarsomys–Monticolomysclade and the giant jumping rat,Hypogeomys,[9] a later study based on theIRBP gene instead placedMacrotarsomys–Monticolomys sister to a clade containing four other nesomyine genera—Eliurus,Voalavo,Gymnuromys, andBrachytarsomys.[10]
The Malagasy mountain mouse is a small, mouse-like rodent, and quite different in appearance from most other nesomyines.[11] It has a thick, soft fur, which appears dark brown on the upperparts. The cover hairs (which comprise most of the fur) are tricolored: for the basal two-thirds of their length, they areplumbeous gray; the middle isochraceous; and the tip is dark brown to black. The longerguard hairs, which are most common towards the middle of the back, are completely black. The fur of the underparts appears dark gray and is not sharply demarcated from the upperparts. There, the hairs are also plumbeous at the bases, but the tips range from white to yellowish-brown. Themystacial vibrissae—whiskers above the mouth—are medium-sized. The short, rounded ears are densely covered with grayish hairs.[12]Monticolomys has broad hindfeet bearing prominentpads and long outer digits.[13] There are white hairs on the upper sides of themetapodials and digits, and longungual tufts—tufts of hair surrounding the bases of the claws—are present. The thumb of the forefeet bears a nail, but claws are present on the other digits.[14] The long tail[12] is covered with small scales and light brown hairs.[14] The tail lacks a distinct tuft at the tip, as is present inEliurus andMacrotarsomys.[11] Females have sixmammae.[14] Head and body length is 84 to 101 mm (3.3 to 4.0 in), tail length is 116 to 143 mm (4.6 to 5.6 in), hindfoot length is 23 to 25 mm (0.91 to 0.98 in), ear length is 15 to 20 mm (0.59 to 0.79 in), and body mass is 18.5 to 27.5 g (0.65 to 0.97 oz).[15]
The skull is small and delicate. The front part, the rostrum, is narrow and relatively long. Thenasal bones are rounded at the front, but blunt at the back. Thezygomatic plate—a bony plate at the side of the skull—is narrow and extends back to the front margin of the first uppermolar (M1).[14] Thejugal bones constitute much of the thinzygomatic arches (cheekbones). Theinterorbital region, between the eyes, is narrow and hourglass-shaped. There are no crests or ridges on the interorbital region or on thebraincase.[16] Theincisive foramina, openings in the front part of thepalate, extend back to a point between the front roots of the M1s. The bony palate itself is broad and lacks many indentations and protuberances present in other species. Its posterior margin is at the level of the upper third molars (M3s). There is noalisphenoid strut, so that the masticatory-buccinator foramen and the foramen ovale accessorium, two openings on the underside of the skull, are fused.[16] There are 13thoracic (chest), 7lumbar (abdomen), 4sacral (hip), and 38caudal (tail) vertebrae.[17]
The upperincisors have orangeenamel and areopisthodont, with the cutting edge of the tooth inclined backwards. The root of the lower incisors extends though themandible (lower jaw) to a lowcapsular process at the back of the jawbone. The molars arebrachyodont (low-crowned) and bear distinctcusps. The second molars, although decidedly smaller than the first, are similar in their crown morphology, but the much smaller third molars are reduced and more distinct from the first molars in morphology.[17] The molars lack accessory crests and other features. Each of the upper molars is three-rooted, whereas the lowers have two roots.[18] The molars are quite similar to those ofMacrotarsomys, and differ only in minor details.[19]
The species' range is now known to extend across the mountain ranges of eastern Madagascar from theTsaratanana Massif[20] south toAndohahela, at 800 to 2,200 m (2,600 to 7,200 ft) above sea level. It occurs inmontane forest, but also in degraded grassland,[1] where it is among the first species to return after fires.[21] AtAnkaratra, where the species was recorded in 1929, it occurred in such grassland, where the nesomyineBrachyuromys betsileoensis was also found.[18] The animal was again recorded at Ankaratra in 1996, this time in a heavily disturbed forest, where it occurred withEliurus minor and the introducedblack rat (Rattus rattus).[22] AtAndringitra, the animal was recorded in high montane forest together with six other nesomyines—Brachyuromys ramirohitra,Eliurus minor,Eliurus tanala,Eliurus webbi,Gymnuromys roberti, andNesomys rufus—as well as the black rat.[23] At Andohahela,Monticolomys was found at an altitude of 1,875 m (6,152 ft) insclerophyllous forest.[24] Its distribution corresponds to theHigh Mountain Domain, a region defined on the basis of plant distributions. This region is now discontinuous, but the High Mountain Domain habitat was continuous from mountain to mountain as recently as the earlyHolocene.[25]Subfossil remains have been found inMahajanga Province (northwestern Madagascar).[26] Malagasy mountain mouse is morphologically uniform across its wide distribution.[27]
The Malagasy mountain mouse is nocturnal and solitary and produces litters of up to three offspring.[28] It isscansorial, spending time on the ground but also climbing in vegetation.[1] In Andringitra, two specimens were captured on aliana 2 m (6.6 ft) over the ground, and a third was caught on the ground together with two shrew tenrecs (Microgale taiva).[23] All five specimens from Andohahela were trapped on the ground, as was the specimen caught in Ankaratra in 1996.[24] Its diet includes fruits and seeds;[28] in captivity, it eatsAgarista fruits.[29]
As Malagasy mountain mouse is now known to be a widespread, common species occurring in at least oneprotected area (Andringitra National Park; it may also occur inAnkarana Special Reserve), it is listed on theIUCN Red List as "Least Concern". However, fires pose a threat in montane forest and, at lower elevations, its habitat is being converted into agricultural land.[1]
