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Freediving people have evolved to stay underwater longer

21 April, 2018, 10:30 | Author: Sylvester Abbott
  • Ms Ilardo spent several months in Jaya Bakti Indonesia, taking genetic samples and conducting ultrasound scans of people from the Bajau and Saluan tribes

This nomadic people live in waters along the Philippines, Malaysia, and Indonesia and dive to hunt for fish but, without access to advanced diving gear, their livelihood relies on the ability to hold their breath for long periods of time as they dive to new depths.

"This suggests that it is Bajau lineage, rather than the actual activity of diving, which is responsible for a larger spleen", the study said.

Among them was one site on a gene known as PDE10A, which was determined to be linked to the Bajau's larger spleen size.

Intrigued by the work on genes that had helped Tibetans, Ethiopians and South Americans adapt to chronic high altitude oxygen deprivation, Melissa Ilardo, now a postdoc at the University of Utah in Salt Lake City, proposed to her colleagues to do similar studies on the Indonesian Bajau people.

The spleen acts as a biological "scuba tank" during long dives, and a larger spleen makes more oxygen available in their blood for diving.

The tribe described as sea nomads are now settled in Indonesia and are known for their ability to hold their breath for a long time. She traveled to seaside villages in the Central Sulawesi peninsula near Indonesia, where both the Bajau and an unrelated population, the Saluan people, live, and recruited 43 Bajau and 33 Saluan individuals to participate. Members of the Bajau can dive up to 70 meters with nothing more than a set of weights and a pair of wooden goggles. Finally, the contraction of the spleen (or spleno- contraction) makes it possible to inject a surplus of oxygenated red blood cells into the circulation.

The goal of Melissa Ilardo was to check if the size of their spleen was correlated with their breathing capacity, and to check if it was a genetic adaptation.

The scans showed that the spleens of the Bajau, whether from divers or nondivers, are 50% larger than those of the Saluan. Thus, diving leads to a slowing of the heartbeat (bradycardia), which reduces oxygen consumption, as well as a narrowing of the peripheral blood vessels (vasoconstriction), which selectively redistributes the blood flow to the organs most sensitive to hypoxia.

A University of Hawaii anthropologist, Rodney C. Jubilado, who's not involved in the study, said that the Bajau "are simply a stranger to the land".

"This study is a wonderful example of the value of studying these small populations living under extreme conditions", said Professor Eske Willerslev of the University of Copenhagen, who carried out the genetic study. It is thought that the PDE10A gene controls the levels of thyroid hormone T4.

For more than 1,000 years, the Bajau - known as "Sea Nomads" - have crossed the seas of southern Asia in house boats, catching fish by free-diving with spears.

"We think the way it works is that the expression of this variant gene changes thyroid hormone release, which then has an effect on spleen size", Nielsen said. "I had a portable ultrasound machine". Researcher Melissa Ilardo explains that they never dive competitively so the duration they can spend under water at one-go has never been measured.

"There we saw this hugely significant difference", she said.

The Bajau having larger spleens than their non-diving neighbors suggested that their diving culture had shaped their physiology. By making their data freely available to other researchers, she and her co-authors hope that some of what they've learned from the Bajau can be applied in medical contexts. "This is the first time that we really have a system like that in humans to study", said Dr Rasmus Nielsen.

For the Bajau, Ilardo believes that the decision to participate in this research is about better understanding themselves.



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