Voalavo

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This article is about the genus Voalavo. For other Madagascar rodents (also known as "voalavo" in Malagasy), see Nesomyinae.

Voalavo
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Nesomyidae
Subfamily: Nesomyinae
Genus: Voalavo
Carleton & Goodman, 1998
Type species
Voalavo gymnocaudus
, 1998
Species
  • Voalavo antsahabensis
  • Voalavo gymnocaudus
Map of Madagascar showing localities where Voalavo species have been found
Known localities of V. gymnocaudus (red) and
V. antsahabensis
 (green)

Voalavo is a

DNA sequence
data suggest that the current definitions of these two genera need to be changed.

Species of Voalavo are small, gray, mouse-like rodents, among the smallest nesomyines. They lack the distinctive tuft of long hairs on the tail that is characteristic of Eliurus. The tail is long and females have six

braincase is smooth. The incisive foramina (openings in the front part of the palate) are long and the bony palate itself is smooth. The molars are somewhat hypsodont
(high-crowned), though less so than in Eliurus, and the third molars are reduced in size and complexity.

Taxonomy

A specimen of the genus was first collected in 1994 in

sequence of the mitochondrial gene cytochrome b.[4]

Voalavo is part of the subfamily

monophyletic groups;[6] but a 1999 molecular phylogenetic study by Sharon Jansa and colleagues, who compared cytochrome b sequences among nesomyines and other rodents, found that northern voalavo was more closely related to Grandidier's tufted-tailed rat than to other species of Eliurus. This finding called into question the separate generic status of Voalavo. However, tissue samples of Petter's tufted-tailed rat, a species that is thought to be closely related to Grandidier's tufted-tailed rat, were not available, so this species could not be included in the study.[7] Data from nuclear genes also supports the relationship between northern voalavo and Grandidier's tufted-tailed rat, but Petter's tufted-tailed rat remains genetically unstudied and the taxonomic issue has not been resolved.[8]

Molecular phylogenetic analysis of nuclear DNA supports a close relationship between Eliurus, Voalavo, and two other nesomyine genera,

Gymnuromys and Brachytarsomys. These genera are more distantly related to the other nesomyine genera and even more distantly to the other subfamilies of the family Nesomyidae, which occur in mainland Africa.[9]

Description

Measurements of Voalavo[10]
Locality n Head-body Tail Hindfoot Ear Mass
Anjanaharibe-Sud (V. gymnocaudus) 4 86–90 119–120 20–21 – 20.5–23.5
Marojejy (V. gymnocaudus) 5 80–90 113–126 17–20 15–15 17.0–25.5
Anjozorobe (V. antsahabensis) 4 86–91 106–119 19–21 15–16 20.7–22.6
n: Number of specimens measured.
All measurements are in millimeters, except body mass in grams.

Voalavo is a small rodent resembling a mouse with gray fur.[11] Species of the genus are among the smallest known nesomyines, close in size only to Monticolomys koopmani.[12] In terms of external morphology, Voalavo is barely different from Eliurus; fur coloration patterns, general morphology of the feet, and number of mammae (six) are all the same in both genera. However, all species of Eliurus have a pronounced tuft of elongated hairs at the tip of the tail, a feature that is absent in Voalavo, although the latter does have slightly longer hairs near the tip. The tail is longer than the head and body. Relative tail length in northern voalavo (136% of head and body length) is comparable to that of the longest-tailed species of Eliurus, Grandidier's tufted-tailed rat and Petter's tufted-tailed rat,[2] but V. antsahabensis has a somewhat shorter tail.[13] Furthermore, the pads of the feet are larger in Eliurus, and specifically, the thenar pad (located at the middle of the tarsus) is circular and fairly small in Voalavo, but longer and larger in Eliurus.[2] On the chest, Voalavo species have a gland that produces a sweet-swelling musk in breeding males; this gland is absent in Eliurus.[14] Unlike all other nesomyines but Brachyuromys, Voalavo lacks an entepicondylar foramen, an opening on the humerus (upper forelimb bone).[15]

The skull of Voalavo also resembles that of Eliurus, with a long facial skeleton, an hourglass-shaped interorbital region (between the eyes), and a smooth interorbital region and braincase, without ridges or shelves.[2] Other shared characteristics include an essentially featureless bony palate, without many pits and ridges, and a broad mesopterygoid fossa (the opening behind the palate). In other characteristics, Voalavo resembles some but not all species of Eliurus. For example, the length of the incisive foramina matches the maximum seen in Eliurus species (in this case, in Major's tufted-tailed rat and White-tipped tufted-tailed rat).[16] The back margin of the incisive foramen is rounded in eastern voalavo, but angular in northern voalavo.[17] The two species also differ in the shape of the suture (dividing line) between the maxillary and palatine bones, which is straight in eastern voalavo, but more curved in northern voalavo.[18] The capsular process, a projection at the back of the mandible (lower jaw) that houses the root of the lower incisor, is indistinct in Voalavo, a feature it shares with Grandidier's tufted-tailed rat, Major's tufted-tailed rat, and Petter's tufted-tailed rat, but not the other species of Eliurus.[16]

Other features of the skull distinguish the two genera. The

zygomatic notch (a notch formed by a projection at the front of the zygomatic plate), which is present in Eliurus.[16] Among nesomyines, only Brachytarsomys has a more reduced zygomatic notch.[19]

Like Eliurus, Voalavo has moderately high-crowned (

cusps, but of transverse laminae (plates) that generally lack longitudinal connections.[21] However, Eliurus molars are slightly more hypsodont than those of Voalavo. The third upper and lower molars are smaller relative to the second molars in Voalavo than in Eliurus. Perhaps as a consequence, the upper third molar lacks discrete laminae in Voalavo, and the lower third molar has only two laminae (three in Eliurus).[22] There are three roots under each upper molar and two under each lower.[21]

Distribution and ecology

Both species of Voalavo occur in

Subfossil remains of Voalavo have been found in the former Mahajanga Province (northwestern Madagascar).[26]

Very little is known of the ecology of eastern voalavo,

parasites have been recorded on northern voalavo, including mites and Eimeria.[29]

Conservation status

Because eastern voalavo has a small range that is threatened by the practice of

Least Concern".[30]

References

  1. ^ Carleton & Goodman 1998, pp. 164, 182.
  2. ^ a b c d Carleton & Goodman 1998, p. 189.
  3. ^ Goodman et al. 2005, p. 168.
  4. ^ Goodman et al. 2005, pp. 870–872.
  5. ^ Carleton & Goodman 1998, p. 193.
  6. ^ Carleton & Goodman 1998, pp. 193–195.
  7. ^ Jansa, Goodman & Tucker 1999, p. 262.
  8. ^ Jansa & Carleton 2003, pp. 1263–1264; Carleton & Goodman 2007, p. 17.
  9. ^ Jansa & Weksler 2004, pp. 268–269, fig. 1; Musser & Carleton 2005, p. 930.
  10. ^ Carleton & Goodman 1998, table 11-7; Carleton & Goodman 2000, table 12-5; Goodman et al. 2005, table 1.
  11. ^ Carleton & Goodman 1998, p. 182.
  12. ^ Carleton & Goodman 1998, pp. 182, 189; Goodman et al. 2005, p. 865.
  13. ^ Goodman et al. 2005, p. 868.
  14. ^ Goodman et al. 2005, p. 866.
  15. ^ Carleton & Goodman 1998, p. 20.
  16. ^ a b c Carleton & Goodman 1998, p. 190.
  17. ^ Goodman et al. 2005, p. 869.
  18. ^ a b Goodman et al. 2005, p. 870.
  19. ^ Carleton & Goodman 1998, pp. 190–191.
  20. ^ Carleton & Goodman 1998, p. 191.
  21. ^ a b Carleton & Goodman 1998, p. 192.
  22. ^ Carleton & Goodman 1998, pp. 192–193.
  23. ^ Musser & Carleton 2005, p. 953.
  24. ^ a b Goodman 2009.
  25. ^ Goodman et al. 2005, p. 872.
  26. ^ Mein et al. 2010, p. 105.
  27. ^ Carleton & Goodman 2000, p. 251.
  28. ^ Goodman, Ganzhorn & Rakotondravony 2003, table 13.4.
  29. ^ OConnor 1998, p. 76; OConnor 2000, p. 140; Laakkonen & Goodman 2003, p. 1196.
  30. ^ Goodman 2009b.

Literature cited

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