Metachirus nudicaudatus (E. Geoffroy Saint-Hilaire, 1803)

PATTON, JAMES L., DA SILVA, MARIA NAZARETH F. & MALCOLM, JAY R., 2000, Mammals Of The Rio Juruá And The Evolutionary And Ecological Diversification Of Amazonia, Bulletin of the American Museum of Natural History 2000 (244), pp. 1-306 : 63-66

Metachirus nudicaudatus

(Desmarest, 1817)

TYPE LOCALITY: ‘‘Cayenne,’’ French Guiana.

DESCRIPTION: This is a terrestrial species that is readily distinguishable from all other sympatric marsupials by a combination of its moderate size, light yellow­ to reddishbrown dorsal coloration with creamy­white spots over the eyes, venter from chin to tail a uniform pinkish yellow, naked tail with only a very minimally furred base, long and rather narrow hind feet, lack of a pouch in adult females, and skull with rounded interorbital region without supraorbital ledges or postorbital processes. Sexual dimorphism is slight to nonexistent within our limited sam­ ple, but it is present in six of 19 characters (TOL, HF, CIL, ZB, RW, and CD; all at p <0.05, based on one­way ANOVA; table 11). Selected external and cranial measurements for adult individuals of both sexes are given in table 11.

DISTRIBUTION AND HABITAT: We took M. nudicaudatus only in the middle and lower reaches of the Rio Jurua´, and always on the ground in terra firme forest. However, in the Headwaters localities we found individuals in terra firme as well as in ‘‘várzea’’ forest which in this region is narrowly distributed along parts of the river and is probably only inundated in extreme years.

REPRODUCTION: The species appears to breed throughout the year as parous females with attached young were collected during the rainy season months of February, March, April, and May and during the dry season months of August and September. Very young aged individuals (age class 1 and 2 for Didelphis, Gardner, 1982 ) were taken at nearly all localities during the months from February to November. The modal number of attached young was 8 (range 6–9, n = 7)

KARYOTYPE: 2n = 14, FN = 20 (fig. 47D) The autosomal complement consists of four pairs of large metacentric and submetacentric

elements and two pairs of medium acrocentrics. The X­chromosome is a small acrocentric and the Y is an even smaller acrocentric. This karyotype has been described and figured by Reig et al. (1977), Palma and Yates (1996), and Svartman (1998). Chromosomal preparations are available from four individuals (MNFS 366, 380, 1038, and 1104).

SPECIMENS EXAMINED (n = 44): (1) 1m, 3f — MNFS 1068, 1104, 1117, 1234; (2) 1f — MNFS 1394; (a) 1m — MNFS 1006; (c) 1m — MNFS 1038; (3) 1f — MNFS 1578; (4) 2m, 5f — MNFS 1479, 1529, 1659, JUR 211, 220 225, 244; (6) 2m, 3f — JLP 15542, 15567, 15569, 15620, 15661; (7) 2m, 9f — MNFS 366, 370, 380, 393­395, 400, 474, JLP 15305, 15340, 15359; (9) 2f — JLP 16042–16043; (12) 1m, 1f — MNFS 757– 758; (13) 1m — JUR 292; (14) 4m, 2f — JUR 433, 466, 470, 495–496, 505; (15) 1m, 1f — JUR 352, 399.

MICOUREUS LESSON, 1842

Woolly mouse opossums

The woolly mouse opossums are arboreal, omnivorous, and common members of the

Neotropical forest marsupial assemblage The genus is widely distributed, ranging from Belize to northern Argentina, and from the lowland Amazonian to middle elevation elfin forests on both Andean slopes (Emmons and Feer, 1997). The number of species recognized in the genus is in flux, as adequate geographic analyses that can identify species boundaries have yet to be performed. For example, Gardner (1993) recognizes four species and Emmons and Feer (1997) five. Both sets of authors record three species within Amazonia: constantinae Thomas, 1904 , from western Brazil and southeastern Bolivia, regina Thomas, 1898 , in extreme western Amazonia, and demerarae Thomas, 1905 , throughout Amazonia from western Brazil to the Guianan region and south to the Mata Atlântica of coastal Brazil. The widespread M. demerarae , however, exhibits considerable variation in coloration and other pelage characteristics, especially in the degree of the furred tail­base, and is likely to be composite (see immediately below). Its relationship to M. constantinae , for example, needs clarification (contrast map in Emmons and Feer

[1997] with area assignments by Anderson [1997]). Finally, populations from the middle elevations of the eastern Andean slopes in Perú (e.g., rapposa Thomas) and Bolivia (e.g., mapiriensis Tate) need critical evaluation in relation to those from lowland forests.

We examined 401 base pairs of cytochrome­b sequence for 23 individual woolly mouse opossums from the Rio Jurua´. These comprise 17 separate haplotypes that form two deeply divergent clades that differ by more than 16% (fig. 50). Each of these clades is internally uniform with average divergences of less than 4%. We have placed these two clades in a broader set of geographic comparisons with specimens from Middle America, elsewhere throughout much of Amazonia, and the Mata Atlântica of coastal Brazil (fig. 51; table 12). For this larger data set the 630 base pairs of sequence available identify four clades that differ by an average of 10 to 15% (fig. 52). Both taxa found along the Rio Juruá have broader distributions outside of that river basin, one linking to samples from northern Peru´, and the other to a series of localities scattered throughout central, northeastern, and eastern Amazonia. The two additional clades are represented by a single individual of M. alstoni from Panamá and a series of specimens from the Mata Atlântica of coastal Brazil. The significance of the latter is discussed below under the account of M. demerarae .

Representatives of the two haplotype clades that occur within the Rio Juruá basin occupy generally separate habitats, although they are truly sympatric at some localities and broadly overlap in the middle and headwaters sections of the river. The two forms possess the morphological characteristics usually accorded to the western Amazonian regina and the eastern Amazonian demerarae (Tate, 1933; updated by Gardner 1993). Micoureus regina occupies only the upper reaches of the Rio Juruá basin, while M. demerarae is found throughout the Rio Juruá basin.