Little Monkey(s) of the Forest

Most people are familiar with the true monkeys of South America, which include acrobatic spider monkeys, clever capuchins, and colorful tamarins, just to name a few. But in terms of evolutionary distinctiveness, none of these primates comes close to southern South America’s “little monkey of the forest,” the monito del monte (Dromiciops gliroides).

A monito del monte (Dromiciops sp.) from the region near Valdivia, Chile. Photo courtesy of Mark A. Chappell.
A monito del monte (probably Dromiciops gliroides) from near Valdivia, Chile. Photo courtesy of Mark A. Chappell.

Despite its common name, the monito del monte is not a monkey, nor is it a close relative of monkeys. It isn’t even a placental mammal like the vast majority of living mammals. It is a marsupial, meaning that it is more closely related to kangaroos, koalas, and wombats than to deer, squirrels, raccoons and most familiar mammals. Interestingly, even among marsupials, the monito del monte is more closely related to Australian species than to New World world ones like opossums and shrew-opossums. But that is a story for another post…

Until recently, the monito del monte’s primary claim to fame – albeit an inauspicious one – was that it was the sole living species of its taxonomic order.* (Orders are the 29 or so main groups into which living mammals are divided.) In other words, the monito del monte was thought to have no close living relatives. A more appropriate moniker would be huerfanito del monte (little orphan of the forest). But that is no longer the case. A study recently published in the Journal of Mammalogy says that there are three species of monito del monte living in South America today, not just one.

The approximate distribution of monitos del Monte in southern Chile and Argentina, with localities where the three species have been identified. From D'Elia et al. (2016).
The approximate distribution of monitos del monte in southern Chile and Argentina. Points on the map indicate sources of specimens included in recent genetic and anatomical studies. From D’Elia et al. (2016:fig. 1).

How did scientists reach this conclusion? By carefully studying the genetics and anatomy of monito del monte specimens from throughout their geographic range. The first hint of this hidden diversity came from a genetic study by Christopher Himes and colleagues published in 2008. It showed that there were three distinct populations of monitos del monte: a northern one spanning 36-39° S latitude, a southern one spanning 40-43° S latitude (including Chiloé Island), and a third one squeezed in between the other two. In other words, these three groups of monitos del monte were not breeding with one another equally, a key prerequisite of speciation.

The more recent study by Guillermo D’Elía and colleagues tested whether the genetically different groups could be recognized based on skull shape and other anatomical features traditionally used by mammalogists to distinguish living species. The found that monito del monto anatomy reflected their genetics, and on that basis, the scientists named two new species: Pancho’s monito del monte (Dromiciops bozinovici) in the north and Mondaca’s monito del monte (Dromiciops mondaca) in between it and the southern species, which retained the scientific name Dromiciops gliroides.

Why does it matter whether there are three monitos del monte or just one? Perhaps most importantly, it affects species conservation efforts. Monitos del monte are listed as vulnerable by the IUCN and have the smallest geographic distribution by far of any order of mammals (another ignoble claim to fame), roughly 150,000 km2 (less than 60,000 miles2). Within this tiny area of the globe, the range of Mondaca’s monito del monte is less than 5,000 km2 (2,000 miles2), about one-third the size of Connecticut. If this newfound species is to persist, preserving native habitat in this region must be a high priority.

*The monito del monte shared this distinction with the aardvark (Orycteropus afer), the only extant member of the order Tubulidentata.

References Cited:

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