Monito del monte
|Monito del monte|
|Map of Dromiciops gliroides distribution|
The monito del monte (Spanish for "little bush monkey"), Dromiciops gliroides, also called chumaihuén in Mapudungun, is a diminutive marsupial native only to southwestern South America (Chile and Argentina). It is the only extant species in the ancient order Microbiotheria, and the sole New World representative of the superorder Australidelphia (all other New World marsupials are members of Ameridelphia). The species is nocturnal and arboreal, and lives in thickets of South American mountain bamboo in the Valdivian temperate rain forests of the southern Andes, aided by its partially prehensile tail. It eats primarily insects and other small invertebrates, supplemented with fruit.
Phylogeny and biogeography
It has long been suspected that South American marsupials were ancestral to those of Australia, consistent with the fact that the two continents were connected via Antarctica in the early Cenozoic. Australia’s earliest known marsupial is Djarthia, a primitive mouse-like animal that lived about 55 million years ago. Djarthia had been identified as the earliest known australidelphian, and this research suggested that the monito del monte was the last of a clade which included Djarthia. This implied that the ancestors of the Monito del Monte might have reached South America via a back-migration from Australia. The time of divergence between the Monito del Monte and Australian marsupials was estimated to have been 46 million years ago. However, in 2010, analysis of retrotransposon insertion sites in the nuclear DNA of a variety of marsupials, while confirming the placement of the Monito del Monte in Australidelphia, showed that its lineage is the most basal of that superorder. The study also confirmed that the most basal of all marsupial orders are the other two South American lineages (Didelphimorphia and Paucituberculata, with the former probably branching first). This indicates that Australidelphia arose in South America (along with the ancestors of all other living marsupials), and probably reached Australia in a single dispersal event after Microbiotheria split off.
Body length is 11–12.5 cm. Tail length is 9–10 cm.
The monito del monte normally reproduces in the spring and can have a litter size varying anywhere from one to four young. The females have a pseudovagina, and a fur-lined pouch containing four mammae. When the young are mature enough to leave the pouch they are nursed in a nest, and then carried on the mother’s back. The young remain in association with the mother after weaning. Males and females both reach sexual maturity after 2 years. They are known to reproduce aggressively, sometimes leaving blood on the reproductive organs. 
Monitos del monte mainly live in trees, where they construct spherical nests of water resistant colihue leaves. These leaves are then lined with moss or grass, and placed in well protected areas of the tree. The nests are sometimes covered with grey moss as a form of camouflage. These nests provide the monito del monte with some protection from the cold, both when it is active and when it hibernates. It stores fat in the base of its tail for winter hibernation. It lives in the dense, humid forests of highland Chile and Argentina.
Role as a seed disperser
A study performed in the temperate forests of southern Argentina showed a mutualistic seed dispersal relationship between D. gliroides and Tristerix corymbosus, also known as the Loranthacous mistletoe. The monito del monte is the single dispersal agent for this plant, and without it the plant would likely become extinct. The monito del monte eats the fruit of T. corymbosus, and thus disperses the seeds. Scientists speculate that the coevolution of these two species could have begun 60–70 million years ago.
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