The Red-Shanked Douc Langur – Ryan Deboodt (2019)

The douc langurs are among the most visually striking primates in the world. There three species of douc langurs: the red-shanked douc langur (Pygathrix nemaeus), black-shanked douc langur (Pygathix nigripes) and gray-shanked douc langur (Pygathix cinereus). All are endemic to Indochina.

Here the filmmaker Ryan Deboodt has filmed the Red-Shanked Douc Langur of the Vietnam forests. Habitat loss, disease and trappers are threatening this species.

Doucs are found in a variety of habitats: from lowland to mountainous terrain up to 2,000 m (6,600 feet), semi-deciduous, primary and secondary rainforests, in the mid to upper levels of the canopy with a home range of up to 36 ha. Red-shanked Doucs are diurnal and arboreal, spending their days among the treetops in mixed sex social groups of averaging 18 individuals. The gestation period for the Red-shanked douc is reported to be 183 days. The doucs sleep in large, carefully selected trees with thick canopies. The group occupies the tree from dusk till dawn. They are very rarely seen on the ground but occasionally get down to drink water or eat dirt that contains minerals. The phenomenon of ingesting soil is called geophagy. It is committed by many animals including Humans.

Plants synthesize a staggeringly diverse array of toxic secondary metabolites to protect themselves from herbivores. Potassium containing clay attracts many animals who seek those exposed locations for detoxification of plant toxins such as tannins in their diet. For example, Macaws in Peru have been observed to congregate around clay licks called “Colpa” by indigenous people. Similarly African forest elephants are known to gather around certain clay containing forest openings.

Douc langurs are members of a subfamily of Asian primates called colobines. Evolutionarily, colobines speciated from other Old World monkeys about 15 million years ago. Most monkeys eat a wide variety of food including fruits, vegetables and meat. Colobines however primarily eat leaves, which are more difficult to digest. Their digestive system is similar to that of ruminants where bacteria ferment plant material. Langur guts absorb in the nutrients they release. Then, the animal digests not only the bacteria but also the nucleic acids in the form of RNA providing a rich source for nitrogen.

Comparative genomic studies among primates have identified similarities and differences that help understand how humans including the extinct forms such as the Neandertals and Denisovans have evolved. One example is the comparison of the RNASE1 gene which became duplicated in langurs about four million years ago. The duplicated gene pairs are called RNASE1A and RNASE1B. The latter gene mutated to code for a pancreatic enzyme that made langurs more efficient in extracting nutrients from leaves.

Delacour's Langur from Ryan Deboodt on Vimeo.