Monito del monte
|Monito del monte|
|Map of Dromiciops gliroides distribution|
The monito del monte (Spanish for "little monkey of the mountain"), 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.
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, such as underbrush, tree cavities, or fallen timber. 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 lives in the dense, humid forests of highland Chile and Argentina.
Monitos del monte are small marsupials that look like mice. Dromiciops have the same dental formula as Didelphids: 18.104.22.168, total of 50 teeth. Their size ranges from 16–42 g (0.56–1.48 oz). They have short and dense fur that is primarily brown-gray with patches of white at their shoulders and back, and their underside is more of a cream or light gray color. Monitos del monte also have distinct black rings around their eyes. Their small furred ears are well-rounded and their rostrums are short. The head to body length is around 8–13 cm (3.1–5.1 in), and their tail length is between 9 and 13 cm (3.5 and 5.1 in). Their tails are somewhat prehensile and mostly furred with the exception of 25–30 cm (9.8–11.8 in) of the underside. The naked underside of their tails may contribute to increasing friction when the mammal is on a tree. The base of their tails also functions as a fat storage organ which they utilize during winter hibernation. In a week, monitos del monte can store enough fat that their body size may double.
- Sexual dimorphism
It has been observed that at the end of the summer season female Monitos del monte tend to be larger and heavier than male ones. Their tails also vary in size during this time; females have a thicker tail, which suggests that they may need more energy during hibernation. The sexual dimorphism is only seen during this time and not year-round, so this may be a seasonal variation.
Monitos del monte have a monogamous mating system. The females have well-formed, fur-lined marsupia containing four mammae. They normally reproduce in the spring once a year and can have a litter size varying from one to five. They can feed a maximum of four offspring, so if there are five young, one will not survive. When the young are mature enough to leave the pouch, approximately 5 months, are nursed in a distinctive nest. They are 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.
This marsupial is nocturnal and arboreal; using its prehensile tail, hands, and feet to climb. It experiences short shift /daily or prolonged torpor depending on the ambient and internal temperature, food availability, and metabolic rate. This behavior allows it to survive in extreme weather and when there is food shortage (allows for energy to be conserved instead of spent on food foraging). It'll also covers its nest with moss for protection and warmth.
Monitos del monte are carnivorous, primarily insectivores. They eat insects and other invertebrates they find on the branches of trees and cracks in barks. During the summer, they eat large quantities of fruits, specially mistletoe fruit.
- Seed-dispersing role
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 sole 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 then germination takes place in the gut. Scientists speculate that the coevolution of these two species could have begun 60–70 million years ago.
For the past few years there has been a decline in the number of Dromiciops, which is now classified as 'near threatened'. There are many contribution factors of the decline:
- its already limited habitat is constantly faced with deforestation and fragmentation;
- The introduction of the domestic cat, Felis catus, has also added to the reduction of Dromiciops numbers;
- it is considered bad luck by natives – there have been events in which houses were burned down when monitos del monte were seen inside;
- other people believe this marsupial is venomous or causes disease, but in reality they do not affect humans negatively.
The monito del monte will not be the only organism which will be affected if it becomes endangered. Dromiciops illustrate parasite-host specificity with the tick, Ixodes neuquenensis. This tick can only be found on the monito del monte, so its survival depends on the survival of this nearly endangered mammal. T. corymbosus also depends on the survival of this species, because without the seed dispersal agency of monitor del monte, it would not be able to reproduce.
Not much conservation efforts are being undertaken at the moment, but there are ecological studies being conducted in the Chiloé Island that may help find future conservation efforts. Dromiciops has been found in the Los Ruiles National Reserve and the Valdivian Coastal Reserve, which are protected areas in Chile.
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