Thylamys elegans

79. Elegant Fat-tailed Opossum Thylamys elegans French: Opossum élégant / German: Elegante Fettschwanzbeutelratte / Spanish: Marmosa coligruesa elegante Other common names: Elegant Fat-tailed Mouse Opossum, Chilean Mouse Opossum Taxonomy. Didelphis elegans Waterhouse, 1839, “Valparaiso,” Valparaiso, Chile. This species is monotypic. Distribution. N & C Chile (from Coquimbo S to Los Lagos). Descriptive notes. Head-body 9-13.7 cm, tail 10.5-14.6 cm. No specific data are available for body weight. Dorsal fur of the Elegant Fat-tailed Opossum is dark brown, with tricolored pattern sometimes slightly indistinct; body sides are pale grayishbrown. Top of f headis colored as QT, but facial and mid-rostral fur is markedly paler, with a distinct dark mid-rostral stripe and slightly developed black eye-rings that extend toward nose. Tail length is ¢.110% of head-body length, and tail is markedly and uniformly bicolored (fuscous dorsally and grayish-white ventrally). When tail is heavily incrassated, it can reach c¢.10 mm in diameter. Ventral fur is whitish or yellowish in a narrow stripe from chin to anus, flanked with broad lateral bands of gray-based hairs, or entirely gray-based buffy hairs, sometimes with whitish fur on chest. Throat gland is present. Furis dense,velvety, and long. Ears are large, broad, naked, and pale fuscous, and feet are small and whitish. Females lack a pouch and have 15 mammae, seven on each side and a medial mamma, although often only 11-13 are functional. The Elegant Fat-tailed Opossum has a 2n = 14, FN = 22 karyotype, with five pairs of biarmed and one pair of acrocentric autosomes, and with a biarmed X-chromosome and a very small acrocentric Y-chromosome. An FN = 20 karyotype with four pairs of biarmed and two pairs of acrocentric chromosomes has also been reported. The Ychromosome has sometimes been reported as missing from somatic cells. Skull shape is sexually dimorphic. Habitat. Habitats as varied as cloud forests, brushlands, and riverbank thickets from sea level to 1000 m. The Elegant Fat-tailed Opossum prefers undisturbed, more closed, and shrubby microhabitats than open areas. Food and Feeding. The Elegant Fat-tailed Opossum is considered mainly insectivorous, with a high proportion of arthropods and larvae in its diet, amounting to up to 90% in volume of samples analyzed. Fruit, small vertebrates, and carrion may also be consumed occasionally. Breeding. Female Elegant Fat-tailed Opossums build nests with hair and leaves between rocks, in trees, in abandoned birds’ nests, and in galleries dug by guinea pigs (Cavia). Up to 17 embryos have been recorded, although not all would survive given number of functional mammae. Only 11-13 young usually survive until weaning. Breeding is seasonal, with 1-2 litters/breeding season, and occurs in September—March. Activity patterns. Some Elegant Fat-tailed Opossums have been captured in the morning, although almost 90% of captures have been during the night, most close to dawn. They have daily fluctuations in body temperature, with higher temperatures occurring during the night. Captive Elegant Fat-tailed Opossums entered daily torpor; they aroused spontaneously only when food was absent, and they did not enter torpor when food was available. Frequency of torpor varies with food availability; if food availability exceeds daily energy requirements, torpor does not occur. Food availability similarly influences length of torpor. Movements, Home range and Social organization. The Elegant Fat-tailed Opossum can occur on the ground and in shrubs. It climbs well and has been seen using stems of 3-300 mm in diameter while on bushes, even using its tail as a climbing aid. In southern Chile, its home range varied from 0-14 ha in July to 0-08 ha in December. In a site with semi-desert vegetation dominated by low thorn scrub, density of the Elegant Fattailed Opossum over three years was 100-1360 ind/km?, with an average of 410 ind/ km? Maximal values occurred at the time of a population explosion in the whole small mammal community. In a bushy area, average density was 550 ind/km?, with a maximum of 2290 ind/km?*. In a longer study in another site dominated by thorn scrub, densities of the Elegant Fat-tailed Opossum fluctuated from 100 ind/km? to more than 2200 ind/km?* over twelve years. Status and Conservation. Classified as Least Concern on The IUCN Red List. The Elegant Fat-tailed Opossum has a wide distribution and presumably a large overall population. It occurs in several protected areas. There are no major conservation threats to the Elegant Fat-tailed Opossum, but several populations are likely facing declines due to high rates of deforestation for logging and agriculture in central Chile. Bibliography. Astua (2010), Bozinovic et al. (2005), Braun et al. (2005), Creighton & Gardner (2007c), Gallardo-Santis et al. (2005), Geiser (1994), Giarla et al. (2010), Iriarte et al. (1989), Jaksic, Jiménez et al. (1992), Jaksic, Yanez & Fuentes (1981), Lima et al. (2001), Mann (1951, 1953, 1956), McNab (2005), Meserve (1981), Meserve et al. (1995), Meynard et al. (2002), Milstead et al. (2007), Palma, A.R.T. & Vieira (2012), Palma, R.E. (1997), Palma, R.E., Boric-Bargetto et al. (2014), Palma, R.E., Rivera-Milla et al. (2002), Reig et al. (1977), Silva-Duran & Bozinovic (1999), Simonetti (1989), Solari (2003), Spotorno et al. (1997), Svartman (2009), Tate (1933).Published as part of Russell A. Mittermeier & Don E. Wilson, 2015, Didelphidae, pp. 129-186 in Handbook of the Mammals of the World – Volume 5 Monotremes and Marsupials, Barcelona :Lynx Edicions on page 176, DOI: 10.5281/zenodo.668533