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Saturday, April 28, 2018

The extraordinary abilities of the 'Sea Gypsies'

Por Rory

The Bajau, also known as "sea gypsies", who live in Southeast Asia are known for their ability to stay long under water. Now science explains how they achieve it. The Bajau are around one million people living in the southern Philippines, Indonesia and Malaysia. They are nomadic and live on the collection of shellfish from the bottom of the sea.

A group of scientists studied the effects of lifestyle on their biology and discovered that their spleens were larger than those of other people in the same region. The size of the spleen makes them have more oxygen in the blood to be able to dive without masks or tanks. The results of the research were published in the academic journal Cell. "The Bajau have probably been living for thousands of years in boats, traveling from one place to another in Southeast Asian waters, occasionally visiting the land," Melissa Ilardo, researcher at the University of Copenhagen and one of the authors of the report, told the BBC.

"Everything they need is obtained from the sea," she explained. They are known for their extraordinary ability to hold their breath. They appear mentioned in the writings of 1521 of the Venetian explorer Antonio Pigafetta, who was part of the first expedition that went around the world. "When they dive in their traditional way, they do it several times for eight hours a day, from 30 seconds to several minutes and dive to depths of more than 70 meters," Ilardo said. Surprisingly, they dive with improvised wooden goggles and weight belts.

Ilardo detailed what is the role of the spleen in this process: "There is a human response that is triggered by holding your breath and submerging in the water. The heart rate slows down; peripheral vasoconstriction occurs, that is, the blood vessels contract in the extremities to preserve the oxygenated blood for vital organs and the last thing is the contraction of the spleen. "The spleen is the reservoir of oxygenated red blood cells, so when it contracts, it contributes more oxygen, like a biological diving tank," she said. The doctor took a portable ultrasound scanner to Indonesia, where the Bajau live. "I kindly asked them to allow me to examine their spleens," she said. The result was that both divers and non-divers in the community had spleens of similar size. That shows that this enlargement is not a simple consequence of diving regularly.

When the researchers compared the data obtained with another neighbor group called Saluan, traditionally farmers, they discovered that the Bajau spleens were 50% larger than the average. The scientists also found an apparent genetic basis that explains that difference in size. They compared the genomes of the Bajau, the Saluan, and the Chinese ethnic group Han. "We asked if there were genetic mutations at a higher frequency that would have specifically changed that frequency in the case of the Bajau, compared with other populations," said Rasmus Nielsen, a professor at the University of California, Berkeley and co-author of the study.

From the comparison it emerged that there were 25 genome sites that in the case of the Bajau differed significantly from other groups. One of these sites is a gene known as PDE10A that was found to be related to the size of the Bajau spleens, even after taking into account other concurrent factors such as age, sex and height. In mice, the PDE10A gene is known to regulate the thyroid that controls the size of the spleen. This supports the idea that the Bajau could have evolved to develop a spleen of the size necessary for long and frequent dives. "It is not clear how long the Bajau have had this lifestyle or when exactly the adaptation arose," said Ilardo. However, the available information indicates that the Bajau belong to a branch that fell off the Saluan some 15,000 years ago. According to the doctor, that is "enough time" to develop that aquatic adaptation.