«RED-SIDED SHORT-TAILED OPOSSUM Monodelphis sorex (Hensel, 1872) FIGURE 1 - (FPMAM318PH) Adult male specimen head detail, Paraguay (Ulf Drechsel ...»
Number 26 2008
Smith P - Monodelphis sorex - FAUNA Paraguay Handbook of the Mammals of Paraguay
Monodelphis sorex (Hensel, 1872)
FIGURE 1 - (FPMAM318PH) Adult male specimen head detail, Paraguay (Ulf Drechsel www.pybio.org).
FIGURE 2 - (FPMAM315PH) Adult male specimen, Paraguay (Ulf Drechsel www.pybio.org).
Smith P 2008 - RED-SIDED SHORT-TAILED OPOSSUM Monodelphis sorex - Mammals of Paraguay Nº
26 Page 1 Number 26 2008 Smith P - Monodelphis sorex - FAUNA Paraguay Handbook of the Mammals of Paraguay TAXONOMY: Class Mammalia; Subclass Theria; Infraclass Metatheria; Magnorder Ameridelphia; Order Didelphimorphia; Family Didelphidae; Subfamily Marmosinae; Tribe Monodelphini (Myers et al 2006).
Twenty-nine species are recognised in this genus, three are present in Paraguay. Assigned to the The scientific name Monodelphis is from the Greek meaning "single womb" in reference to the lack of a pouch, sorex is Latin meaning “shrew” (Braun & Mares 1995). The species is monotypic.
This species suffers from a complicated taxonomic history. The species was originally described on the basis of immature specimens and as a result many immature specimens referred to in the literature are reliably identified. However adult female and half-grown males have in the past frequently referred to as Hensel´s Short-tailed Opossum Monodelphis henseli (Thomas 1888) and this name has continued to appear in recent works on South American mammals (eg. Redford & Eisenberg 1992, Hershkovitz 1992, Massoia et al 2006) perpetuating the confusion. Furthermore adult males have frequently been confused with M.dimidiata (Wagner 1847), and also attributed to two defunct taxa M.tricolor (Lund 1840) and M.touan (Shaw 1800), both of which are synonyms of the Guianan Short-tailed Opossum M.brevicaudata (Erxleben
1777) a species confined to northern Amazonian South America.
Assigned to the dimidiata species group within Monodelphis by Solari (2010). He questioned the specific distinctness of M.sorex and M.dimidiata, the only two members of the species group, noting that "the taxa do not form reciprocal monophyletic groups" and "show very low internal divergence ( 0.5%), similar to the range found in among populations of a single species of recent divergence". Were they to be synonymised the oldest available name would be M.dimidiata Wagner 1847.
As the only "red-sided" Monodelphis known from Paraguay this species is likely the "Micouré cinquième, ou micouré à queue courte" of de Azara (1801) (Voss et al 2009). If this is the case then the oldest name atrributable to the species is Monodelphis brevicaudis, Olfers 1818 and M.wagneri Matschie, 1916 is a synonym.Hershkovitz (1959) recognised M.brevicaudis as a valid species but assigned no specimens to the taxon and this was followed by Brown (2004) who went so far as to map the species for the Paraguayan Chaco (where M.sorex does not occur), though in her text she notes that the species is based on de Azara´s description and two lost specimens lacking locality data and that the name may require "reassignment". De la Sancha et al (2007) state that Monodelphis brevicaudis has variously been regarded to be a senior synonym of M.domestica or M.brevicaudata, but is now generally considered a synonym of M.sorex.
Voss et al (2009) suggest that suppression of the name M.brevicaudis by the ICZN may be a preferable cause of action, though they caution that the species level taxonomy of this form is far from clear.
The Tawny-headed Short-tailed Opossum Monodelphis scalops was reported erroneously for Paraguay by Contreras & Silveira Avalos (1995), though their written decription clearly refers to M.sorex, a fact confirmed upon examination of the specimen by de la Sancha et al (2007). Synonyms adapted from
Didelphis tricolor Lund 1840:19 not Didelphis tricolor E. Geoffroy St-Hilaire 1803.
Didelphys [Microdelphys] sorex Hensel 1872:122 Type locality "Rio Grande do Sul" restricted to "Taquara" by Cabrera (1958).
Didelphys (Peramys) henseli O.Thomas 1888:159 Type locality "Taquara, Rio Grande do Sul".
Peramys sorex O.Thomas 1888:380 Name combination.
[Didelphis (]Monodelphis [)] henseli Matschie 1916:271 Name combination.
[Didelphis (]Monodelphis [)] lundi Matschie 1916:271 Type locality "Lagoa Santa, Minas Gerais" based on D.tricolor Lund 1840.
[Didelphis (]Monodelphis [)] sorex Matschie 1916:272 Name combination.
Peramys henseli Cabrera 1919:42 Name combination.
P[eramys (Peramys)] sorex A. Mirando-Ribeiro 1936:404 Name combination.
Peramys henselii A. Mirando-Ribeiro 1936:409 Incorrect spelling.
P[eramys]. d.[imidiata]itatiayae A. Mirando-Ribeiro 1936:421 Type locality "Campo Bello, Rio de Janeiro".
Monodelphis henseli Cabrera & Yepes 1940:32 Name combination.
Monodelphis henseli Cabrera & Yepes 1940:32 First use of current name combination.
Monodelphis tricolor paulensis COC Vieira 1950:359 Type locality "Pirituba, subúrbio da cidade de Sao Paulo".
Monodelphis touan paulensis Cabrera 1958:9 Name combination.
Monodelphis henseley Tálice, Laffite de Mosera & Machado 1960:151 Incorrect spelling.
Smith P 2008 - RED-SIDED SHORT-TAILED OPOSSUM Monodelphis sorex - Mammals of Paraguay Nº 26 Page 2 Number 26 2008 Smith P - Monodelphis sorex - FAUNA Paraguay Handbook of the Mammals of Paraguay Monodelphis touan Olrog & Lucero 1981:68 Not Mustela touan Bechstein 1800.
Monodelphis henseli Ávila-Pires 1994:369 Name combination.
Microdelphis sorex Ávila-Pires 1994:369 Name combination.
Monodelphis brevicaudatus Chebez & Massoia 1996: 199 Not Didelphis brevicaudatus Erxleben 1777.
ENGLISH COMMON NAMES: Red-sided Short-tailed Opossum, Southern Red-sided Opossum (Gardner 2007), Hensel´s Short-tailed Opossum (Redford & Eisenberg 1992), Shrewish Short-tailed Opossum (Wilson & Cole 2000, Canevari & Vaccaro 2007).
SPANISH COMMON NAMES: Colicorto rojizo (Canevari & Vaccaro 2007, Massoia et al 2000), Colicorto selvático (Canevari & Vaccaro 2007, Massoia et al 2000), Colicorto musaraña (Canevari & Vaccaro 2007, Emmons 1999), Musaraña (Massoia et al 2000), Colicorto de Hensel, Colicorto Misionero (Massoia et al 2006).
GUARANÍ COMMON NAMES: Guaiquiaca-aña (Canevari & Vaccaro 2007), Anguja (Massoia et al 2000), Mbicuré-í (Massoia et al 2000, Canevari & Vaccaro 2007).
DESCRIPTION: A small to medium-sized Monodelphis with short, rounded ears and tail approximately 50% of head and body length. Pelage short and smooth, lying flat against the body. Forehead, crown and dorsum dark brown, somewhat greyer on the head and reddish-orange on the rump. Sides of head to just above the eye orange-rufous. Flanks and sides reddish-orange, sometimes with slight greyish tinge but always clearly demarcated from the dorsal and ventral colouration. Venter creamy-yellow to pale reddish.
Feet reddish. Tail dark brown above and pale reddish below. Great sexual dimorphism in size with males up to 50% larger than females. Females lack a pouch and possess more mammae than any other mammal (25-27) arranged with five central nipples and the remainder in lateral lines. Juvenile with similar pattern to adults but much darker, reddish-chestnut on flanks and sides.
CRANIAL CHARACTERISTICS: The following cranial measurements are those provided by Contreras & Silviera Avalos (1995) for their male Paraguayan specimen: Greatest Length: 35.4mm; Minimum
Postorbital Constriction: 5.6mm; Width of Brain Case: 13.9; Greatest Zygomatic Width: 20.5mm; Mandible Length:
27mm; Length of Nasals: 15.5mm; Palate Length: 17.4mm.
DENTAL CHARACTERISTICS: I5/4 C1/1 P 3/3 M 4/4 = 50. The following dental measurements are those provided by Contreras & Silviera Avalos (1995) for their male Paraguayan specimen: Length of Upper Tooth Row 16.9mm; Length of Upper Molar Row 9.9mm; Length of Lower Tooth Row 14.1mm; Distance across M3 10.1mm; Distance M1-M4 on Upper Tooth Row 5.7mm; Distance M1-M4 on Lower Tooth Row 7.2mm.
GENETIC CHARACTERISTICS: 2n=18 (Svartman & Vianna-Morgante 1999).
TRACKS AND SIGNS: No information.
EXTERNAL MEASUREMENTS: A medium-sized Short-tailed Opossum. There is marked sexual dimorphism in size, with males up to twice the size and weight of females. TL: 14.48cm (11.9-21.5cm);
HB: 9.38cm (7.8-13cm); TA: 5.1cm (3.6-8.5cm) approximately 50% of body length; FT: 1.52cm (1.5cm); EA: 0.88cm (0.53-1.1cm); WT: 48g; (Massoia et al 2000, Redford & Eisenberg1992, Emmons 1999).
Contreras & Silveira Avalos (1995) gave the following measurements for a single male specimen wrongly identified by them as M.scalops: TL: 21cm; HB: 14.5cm; TA: 6.5cm; FT: 1.7cm not including claw, 1.9cm including claw; EA: 1.5cm; WT: 68g.
SIMILAR SPECIES: Intermediate in size amongst the three Monodelphis species currently documented for Paraguay, this is the only species that occurs in the Atlantic Forest. This species can be instantly separated from the other two species on account of its distinctive pelage colouration with reddish flanks contrasting with a grey-brown dorsal surface. Other Paraguayan species are uniformly coloured. Note however that juveniles are much darker than adults and were once considered a separate species.
Two additional species of possible occurrence in Paraguay are confusable with this species. The Tawny-headed Short-tailed Opossum Monodelphis scalops is clearly distinguishable by its uniformly tawny head, which lacks the brownish-grey crown and forehead of this species, and has grey rather than reddishorange flanks.
The Yellow-sided Short-tailed Opossum Monodelphis dimidiata is of similar general patternation and size to this species. However the dorsal area is distinctly grey, not grey-brown as in this species and the flanks and side of the face are pale tawny-yellow, not reddish-orange. Note that in M.sorex the lateral Smith P 2008 - RED-SIDED SHORT-TAILED OPOSSUM Monodelphis sorex - Mammals of Paraguay Nº 26 Page 3 Number 26 2008 Smith P - Monodelphis sorex - FAUNA Paraguay Handbook of the Mammals of Paraguay reddish colouration is sharply demarcated from the pale mid-venter whereas in M.dimidiata there is a gradual shading from the sides to the mid-venter. M.dimidiata has long, lax fur (except in old males), compared to the short, smooth fur of this species, and the feet are whitish or buffy as opposed to reddish in M.sorex. Furthermore M.dimidiata occurs in open, grassy habitats, not humid forests.
DISTRIBUTION: An Atlantic Forest endemic species occurring in southern Brazil, south-eastern Paraguay and Misiones Province in Argentina (Departamentos Cainguas, Guaraní, Iguazú, Oberá, General Belgrano and Montecarlo and likely San Pedro - Massoia et al 2006). In Brazil the records are clustered in Minas Gerais, Sao Paulo and Rio Grande do Sul, though the species likely occurs more or less continuously between those points where suitable habitat occurs. In Paraguay there are specimen records from PN San Rafael, Departamento Itapúa and 12km W of Ciudad del Este area, Departamento Alto Paraná (Contreras & Silveira Avalos 1995).
HABITAT: Occurs in humid Atlantic forest in eastern Paraguay where it is the only Monodelphis so far reported. In Misiones it apparently tolerate considerable disturbance being found in capuera and cultivated areas close to forest (Massoia et al 2006).
ALIMENTATION: Considered to be insectivorous by Canevari & Vaccaro (2007) and "principally carnivorous" by Massoia et al (2000).
Foraging Behaviour and Diet Casella & Cáceres (2006) published the first specifics on the diet of this species after studying stomach contents of animals (n=26) captured in western Paraná State, Brazil.
They considered the species to be an opportunistic generalist feeder with a principally insectivorous diet supplemented with meat and fruit. Arthropods were the principal item in the diet with Coleoptera the single most prevalent group found in 92% of stomachs. Other animal items found in stomachs in order of prevalence were: Hymenoptera 80%, Blattaria 31%, Mammalia 31%, Orthoptera 30%, Decapoda 15%, Opiliones 15%, Acari 8%, other Crustacea 8%, Myriapoda 4%, Aves 4% and insect larvae 4%. Seeds were found in 8% of stomachs (Cecropia sp. and Rubus sp.) and unidentified plant material in 30% of stomachs.
Of the 57 seeds found, 54 were intact and only 3 had been predated, suggesting that it was the fruit that had been consumed and indicating that the species may play a role in seed dispersal.
REPRODUCTIVE BIOLOGY: No published information. Pregnancy The species has the largest number of mammae of any mammal (25-27) and in view of this Gardner (2007) suggested that the species may prove to be semelparous - a possibility supported by the high number of young individuals when compared to adults in specimen collections.
GENERAL BEHAVIOUR: Activity Levels The species is terrestrial and crepuscular (IUCN 2008). No other published information.
Mortality Ávila-Pires & Gouvêa (1977) mentioned a specimen of M.dimidiata taken from the oesophagus of a Elanus leucurus, but Gardner (2007) considers it more likely that it was this species however White-tailed Kite is an open-country species that does not occur in Atlantic Forest and M.dimidiata is typical of grassland habitats (P.Smith pers.obs.). Massoia et al (2006) note that it is regular in pellets of Tyto alba in Misiones, Argentina.
Parasites The tick Ixodes loricatus (Ixodidae) has been recorded on this species (Barros-Battesti & Knysak 1999).
Notman (1923) described an ectoparasitic Staphylinid beetle Omaloxenus bequarti found on a Monodelphis collected at "Alto Itatiaya, Setto (sic) do Itatiaya, Brazil" which may have been this species.
Fain (1979) reported M.dimidiata as the host of a Listrophid mite Didelphoecius paranensis, but Gardner (2007) believes that the correct identification of the host may actually be M.sorex.
VOCALISATIONS: No information.
HUMAN IMPACT: This rarely-encountered forest species has little impact on humans within its range.
CONSERVATION STATUS: Globally considered to be Low Risk, Least Concern by the IUCN on account of a supposedly wide distibution and its occurrence in a number of protected areas. See
http://www.iucnredlist.org/details/13701 for the latest assessment of the species. The species has recently been downgraded from its previous designation as vulnerable.