The Value of Poop

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The Raffles’ banded langurs (Presbytis femoralis femoralis) are extremely shy. Hence, a good day in the field is when our primatologists are able to see and follow these tree-dwelling primates. But nothing gets our primatologists more excited than the sight of langur faeces! To the uninitiated, a pile of smelly faeces should be nothing exciting or worth bothering about. In fact, langur faeces are a treasure trove of DNA information!

Well, you may wonder why researchers can’t just capture the langurs and extract some blood for analyses, but instead go through the trouble of finding faeces? Firstly, the trapping of shy and rare langurs in the forest poses a great deal of risk for the langurs. As the langurs are shy, it is hard for researchers to come close enough below them to catch them as they fall from the trees after being sedated. Even if researchers manage to be right underneath them as they drop from the trees, the langurs may injure themselves during the fall.

Secondly, collecting faecal sample is non-invasive to the animals. The langurs are not harmed during the process. Thirdly, faeces provide information on the genetic diversity of the langur population, DNA of the plants consumed, and data on gut parasites within the langurs. In short, faeces give our researchers the information needed to take appropriate measures for the conservation of langurs and their forest habitat.

So, what has the DNA told us about our local langurs? Our langur population exhibits very little genetic variation, which is to say that different individuals are actually very closely related to each other. This spells trouble, as low genetic diversity in a population indicates that there may be inbreeding. Just like how inbreeding in humans can result in physical deformities and genetic disorders in babies, inbreeding in langurs can affect infant survivorship. Inbreeding is quite typical of small populations. Over 150 years of development in Singapore has caused our langurs to experience a large degree of habitat loss. While langurs presumably were found in various forests on the island before large-scale development began, by the end of the 1970s and 1980s their population had decreased tremendously. While the current population appears to stabilise at about 40-60 individuals, the langur population has already lost a significant portion of their genetic variation. This makes the long-term future of our langurs an uncertain one. A population that has low genetic variation is not a population that can readily cope with habitat changes and environmental disturbances. Is there anything that we can do to rescue their gene pool? The Raffles’ banded langurs are found not only in Singapore, but also in Johor, Malaysia. The translocation of langurs between Singapore and Johor has the potential to facilitate genetic exchange between the two populations for the long-term survival of the species, but further studies needs to be done before such a serious undertaking is feasible.

Langur DNA is not the only genetic material that can be extracted from langur faecal samples. Chloroplast (the photosynthetic factories of the plant cell) DNA from the remains of plant matter the langurs consumed can also be recovered and identified to plant species! While diet information can also be collected through field observations, this method relies on the observer’s ability to track the langurs over time, which is challenging for elusive primates such as Raffles’ banded langurs. On the other hand, the plant genetic data obtained through faeces is basically a 48-hour sample of the diet which allows for rare components of the langur diet to be detected. Such a 48-hour sample of the diet cannot be achieved on the field because researchers also have to eat and sleep (and also apply for grants for fieldwork!)

Field observations have shown that the langurs consumed 27 species of plants from 24 genera and 20 families. With the help of modern genetic techniques, at least 36 additional species were revealed. The genetic data is broadly consistent with field observations, showing that genetic methods can give reliable biological data to complement traditional field techniques.

What does such dietary data mean for langur conservation? It shows that langurs have a relatively broad diet, which includes a number of non-native plants such as rubber trees. Conserving our langurs means conserving plant diversity in our forests, taking into account some non-native plants which are food plants for our native animals. Food trees of the animals can also be planted during remediation of degraded habitats and reforestation work (such as the Eco link connecting the Central Catchment and Bukit Timah Nature Reserves).

Genetic techniques have allowed our researchers to explore and to understand certain aspects of langur biology and ecology that would have been impractical and time-consuming for fieldwork to uncover. It is thus essential to combine both traditional field work and genetic tools for research and conservation. And with newer molecular techniques constantly being developed, who knows what secrets of the langurs might be uncovered in the future?

Contributed by Sia Sin Wei


Further reads

Ang A, Srivathsan A, Md-Zain BM, Ismail MR, Meier R. Low genetic variability in the recovering urban banded leaf monkey population of Singapore. The Raffles Bulletin of Zoology. 2012 Aug 31;60(2):589-94.

Frankham R, Ballou JD, Briscoe DA. A primer of conservation genetics. Cambridge University Press; 2004 Feb 12.

Srivathsan A, Ang A, Vogler AP, Meier R. Fecal metagenomics for the simultaneous assessment of diet, parasites, and population genetics of an understudied primate. Frontiers in zoology. 2016 Apr 21;13(1):17.

Wich SA, Marshall AJ, editors. An introduction to primate conservation. Oxford University Press; 2016 Jul 7.