Thylamys pallidior (Thomas, 1902)

Russell A. Mittermeier & Don E. Wilson, 2015, Didelphidae, Handbook of the Mammals of the World – Volume 5 Monotremes and Marsupials, Barcelona: Lynx Edicions, pp. 129-186 : 176-177

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Thylamys pallidior


80. View Plate 9: Didelphidae

Pallid Fat-tailed Opossum

Thylamys pallidior

French: Opossum a ventre blanc / German: Fahle Fettschwanzbeutelratte / Spanish: Marmosa coligruesa pélida

Other common names: \White-bellied Fat-tailed Mouse Opossum, White-bellied Thylamys

Taxonomy. Marmosa elegans pallidior Thomas, 1902 ,

” Challapata , Bolivia.”

Recent phylogenetic analyses have revealed two clades that might represent two species. As treated here, this species includes 71. fenestrae as a synonym. Some specimens from Huancavelica and Lima provinces in central Peru previously identified as 7. pallidior are actually an unnamed taxon more closely related to T. tatei . Monotypic.

Distribution. S Peru, SE Bolivia, N Chile, and Argentina. View Figure

Descriptive notes. Head-body 7.3-10.5 cm,tail 9-11.8 cm; weight 13-38-5 g. The Pallid Fat-tailed Opossum has grayish-brown dorsal fur, darker mid-dorsally and markedly paler on body sides, thus showing typical tricolored pattern of species of Thylamys . Head is same color as mid-dorsum; fur on face, around eyes and cheeks, and at bases of ears is paler, with narrow but conspicuous black eye-rings that extend toward nose. Tail length is ¢.115% of head-body length, and tail is bicolored, gray or drab dorsally and whitish to yellowish-white ventrally, without a pale tip. When tail is incrassated (enlarged with stored fat), it reaches 45 mm or more in diameter. Ventral fur is entirely white, with narrow lateral bands of gray-based hairs often present. Fur is long (11-13 mm mid-dorsally) and lax. Feet are small and whitish; ears are grayish with pale gray fur at their bases. Females lack a pouch, and nine mammaeare present, four on each side and a medial mamma, but 15 have also been reported, with seven on each side and a medial mamma. The Pallid Fat-tailed Opossum has a 2n = 14, FN = 20 karyotype, with four pairs of biarmed and two pairs of acrocentric autosomes, and with a small acrocentric X-chromosome. The Y-chromosome is absent in somatic cells. Skull shape is sexually dimorphic.

Habitat. Mostly arid and semi-arid habitats, including highand low-elevation deserts, semi-deserts, and steppes, from sea level to ¢.4500 m. These habitats occur in the Coastal Desert, Andes, Puna, Prepuna, Monte Desert, and Patagonian steppe. Although Pallid Fat-tailed Opossums frequently occur in areas with little vegetation, which may be rocky or associated with water, they also occurs in Polylepis ( Rosaceae ) woodlands in Bolivia; Larrea ( Zygophyllaceae ) shrublands, Prosopis ( Fabaceae ) woodlands, dry thorn scrub in the Monte Desert; and scrubby steppe vegetation in Patagonia. Studies assessing habitat preference of the Pallid Fat-tailed Opossum showed that it prefers less complex habitats but always associated with high vegetation cover on the ground, possibly to avoid predation. Vegetation structure is more strongly correlated with its presence than habitat type. Some Pallid Fat-tailed Opossums have been collected in buildings.

Food and Feeding. The Pallid Fat-tailed Opossum feeds mainly on small arthropods, mostly insects, but leaves, fruits, and seeds may also represent important components of its diet. Small vertebrates are not regular itemsin its diet but have occasionally been reported; it seems to prey on vertebrates opportunistically. Among these vertebrates, small lizards, rodents, and birds have been recorded, and it also preys occasionally on bird eggs, occupying the attacked nest after emptying it. Among invertebrates observed in stomach contents, Coleoptera is most frequently present, followed by Arachnida, Chilopoda, Hymenoptera, Lepidoptera, and Diptera . In the Monte Desert, there seems to be no seasonal variation in use of different diet categories on some occasions, but a diet composed primarily of leaves of Prosopisflexuosa and no animal items was also observed in the rainy season in the Monte Desert. Diet of the Pallid Fat-tailed Opossum is independent of presence of drinking water because it is can lowerits urine volume and increase its concentration if water availability decreases. As with many other species of Thylamys , the Pallid Fat-tailed Opossum is able to store fat in its tail (incrassation), which is able to increase its thickness up to 4-5 times its normal diameter. Fat is used during periods of resource shortage or during torpor. Tail incrassation usually starts in autumn, and incrassated individuals have been captured in February—July and December.

Breeding. Pallid Fat-tailed Opossums build nests in tree holes, under or in between rocks, or under shrubs. Nests are made with grass, feathers, and other items. Although nine or 15 mammae have been reported, much smaller litters have been observed, with 3-4 young, based either on direct count of young or counts of uterine scars. They breed two times a year. Lactating females have been found in December and February in Argentina, and juveniles and young individuals have been found in February—June.

Activity patterns. The Pallid Fat-tailed Opossum is nocturnal, showing higher body temperatures at night and lower temperatures during daytime. When ambient or body temperatures drop below specific thresholds (15°C for ambient temperature or 29°C for body temperature), they enter torpor.

Movements, Home range and Social organization. The Pallid Fat-tailed Opossum has been reported as ground dwelling, but it climbs and jumps well and uses bushes occasionally, so it can be considered more scansorial than strictly ground dwelling. Studies show thatit actively uses the vertical dimension of the habitat, with almost threefourths of captures, in some studies, occurring in an upper stratum rather than on the ground.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Pallid Fat-tailed Opossum has a wide distribution, with presumably large overall populations, and it also occurs in several protected areas throughout its distribution.

Bibliography. Abdala et al. (2006), Albanese & Ojeda (2012), Albanese, Dacar & Ojeda (2012), Albanese, Rodriguez & Ojeda (2011), Asta (2010), Birney, Sikes et al. (1996), Braun, Mares & Stafira (2004), Braun, Pratt & Mares (2010), Braun, Van Den Bussche et al. (2005), Creighton & Gardner (2007c), Diaz et al. (2001), Fernandez, FJ. et al. (2012), Flores et al. (2000), Formoso et al. (2011), Giarla et al. (2010), Mares & Braun (2000), Meynard et al. (2002), Ojeda & Tabeni (2009), Palma (1995), Palma & Yates (1996), Palma, Boric-Bargetto et al. (2014), Palma, Rivera-Milla et al. (2002), Solari (2003), Tate (1933), Teta, D’Elia et al. (2009).














Thylamys pallidior

Russell A. Mittermeier & Don E. Wilson 2015

Marmosa elegans pallidior

Thomas 1902