Unlocking the mystery of the dugong through tissue and bone

Views : 3007 | 23 Sep 2021

“When I was a child I visited the Phuket Marine Biological Centre, by the Department of Marine and Coastal Resources under the Ministry of Natural Resources and Environment, remembering that there were many large aquariums filled with dugongs where I got to stroke the head of a live dugong” recalled Professor Dr. Korakot Nganvongpanit, director of the Excellence Centre in Veterinary Biosciences, Chiang Mai University. “Sadly, that was the last time that I ever touched a live dugong. Since then I have only stroked bones and carcasses.”

Professor Dr. Korakot has a passion for collecting carcasses of animals for study; in fact, he has collected so many that he can open an anatomy pathology museum.

Amongst his international peers in the biosciences world (amongst which he is ranked 27th of 228 amongst global dugong experts), his work is highly acclaimed. Dugongs are a unique mammal which, to date, researchers and conservationists have had no success in breeding or even keeping alive in captivity - the longest a dugong has survived in captivity has been a mere 2-3 years, and that was in Japan. The dugong DNA cannot be studied unless the mammal is dead, and since they are now so close to extinct, it is a great challenge to find a carcass fresh enough to extract necessary tissues for study.

Professor Dr. Korakot Nganvongpanit, director of the Excellence Centre in Veterinary Biosciences,
Chiang Mai University

Veterinary Anatomy and Pathology Museum

With close cooperation between Chiang Mai University's Faculty of Veterinary and the Phuket Marine Biological Centre, molecular biology has been used to study the sex of dugongs, whales and dolphins, extracted from skeletons, which provides critical information in studying sea mammals. The length of the telomere at the end of a chromosome is used by bio scientists to determine the age of a sea mammal as well as revealing a wealth of genetic information. The team of researchers have since discovered that the genetic makeup of Thailand's dugongs is very different from other sub-species around the world.

internationally peer-reviewed research published by Professor Dr. Korakot Nganvongpanit, director of the Excellence Centre
in Veterinary Biosciences, Chiang Mai University

Demystifying the Sea Mammal via Molecular Biology
Determining the sex of dugongs, whales and dolphins

Professor Dr. Korakot began his studies into the dugong in earnest 5-6 years ago when he studied the bones of a dugong, using x-ray fluorescence (XRF) to study the teeth of dugongs, eventually expanding his studies into the sex of the dugongs.

It is estimated that there are only 250 dugongs left in the waters of Thailand's Andaman Sea, with the number dwindling at an alarming rate due in large part to accidents caused by encounters with man - boating or fishing accidents. When marine mammals are found dead the protocol is to record all the details such as where they were found, species, sex, size and other important data. The challenge for those working specifically on the dugong population is that it is rare to come across a fresh carcass, most being so decomposed it is impossible to determine the sex, let alone extract any other useful tissue for study. That is why a project between Chiang Mai University and the Phuket Marine Biological Centre is focusing on the collection and analysis of data through the lens of molecular biology.

To date, 48 sea mammal’s data have been collected, which include three dugongs and the remainder being whales and dolphins. This data is critical for researchers to draw upon to find scientific solutions to help conserve the dwindling numbers of these sea mammals.

Skeleton of a dugong on display at the Veterinary Anatomy and Pathology Museum, Faculty of Veterinary Medicine,
Chiang Mai University

Predicting the Age of the Dugong
New Knowledge to Advance the study of Sea Mammals

Tragically, teeth are the first to disappear when a dugong carcass is found - extracted and sold into the illegal wildlife market where one incisor can reach upwards of 70,000 baht. Without the tooth there is no way to determine the age of a dugong since the usual technique of measuring the dentinal growth layers in the incisor cannot be applied.

To circumvent this problem, Professor Dr. Korakot and his team have studied and developed a method which can closely predict the age of a sea mammal by using tissue extracted from the tooth or other parts of the body. Once extracted, molecular biology techniques are used to measure the length of telomere, which is the end of a chromosome and which diminishes in length with age. Age can be determined to an 86% accuracy.

“It is always tragic when we come across the carcass of a dugong,” explained Professor Dr. Korakot, adding, “especially when they are young, as they have so many breeding years left in them. In the past we would have to extract a tooth, cut it in half and dentinal growth layers (similar to rings in a tree trunk) can be counted to determine age : 45 layers equal 45 years old. Not only do we often only gain access to a carcass long after the teeth have been extracted, but if we are fortunate enough to find one which has yet to have been harvested for trade they can sometimes be too old, their teeth too worn down to read. We may be able to count 45, but in actual fact the dugong is 60 years old, the teeth just simply being too ground down to offer an accurate reading. Some teeth which are deformed are also of no use in determining age. It was because of these challenges that we thought to find a new solution to the problem.”

The findings of Professor Dr. Korakot have been peer reviewed in international publications, revealing new findings previously unknown, such as the age of maturity for a dugong being 20 years of age.

Genetically Unique The Thai Andaman Dugong

Dugongs, while few in numbers, are found all over the world; Gulf of Thailand, Andaman Sea, South China Sea, Japan, Malaysia, Philippines, India as well as along the Eastern coast of Africa.

With such genetic variables, the team of researchers have studied tissue from 110 Andaman Sea dugongs and eight Gulf of Thailand dugongs with the aim of understanding the special characteristics and genetic makeup of our unique sea mammals. This has been the study of the largest number of dugongs ever conducted anywhere and at any time.

The findings of Professor Dr. Korakot and his team, published as ‘Genetic diversity in a unique population of dugong along the sea coasts of Thailand’, found that there are a total of 60 sub-species of dugong worldwide. One finding that has generated much attention is that Thailand’s dugong population have two very distinct families; one belongs to the same group as those found in the South China Sea, Malaysia, Indonesia, Australia and Japan while the second group which lives in the Andaman is unique to Thailand, a sub-species which branched off from other sub-species over 1.2 million years ago.

Dugong development by genetics (a)
speciation process from ancestral population groups evolving over millions of years (b)
and the speciation of the six Thai dugong groups (Clade A) which separated 1.2 million years ago (c)

Genetic diversity in a unique population of dugong along the sea coasts of Thailand

This remarkable finding, it is hoped, will energise conservation efforts in Thailand for the remaining dugong population with authorities turning to stricter measures to ensure the species’ survival. It is clear that research is crucial in shedding light, creating understanding and developing tools to be used in sea mammal conservation.

“I am addicted to research,” added Professor Dr. Korakot. “I like doing what I am doing. I feel as though it is often a matter of timing and opportunity which create results. No one in the world has had the opportunity I have had to study over 100 dugongs across the span of 30 years. It has worked out very well.”

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