Gene Change May Have Helped Indonesia's Deep-Sea Divers

Gene Change May Have Helped Indonesia's Deep-Sea Divers

Gene Change May Have Helped Indonesia's Deep-Sea Divers

The evidence showed that Bajau spleens were permanently enlarged, and did not get bigger simply as a response to diving.

Melissa Ilardo, who was a graduate student at the University of Copenhagen when she did the work, sought to understand whether the Bajau had evolved their own strategies to cope with hypoxia while swimming. She suspected this involved the spleen, since contraction of the spleen is a key part of the mammalian diving reflex, and some deep-diving seals, such as the Weddell, have enlarged spleens. Now researchers have found that they have developed extra large spleens over the years which enable them to dive to a depth of 200 feet.

The Bajau, who are spread among the islands of Indonesia, Malaysia and the Philippines, have been living on houseboats for thousands of years and depend on the sea for most of their needs. Members of the Bajau can dive up to 70 meters with nothing more than a set of weights and a pair of wooden goggles.

To test the theory, they looked in-depth at 59 Bajau, and 34 of their land-dwelling neighbors, the Saluan. The heart rate slows down, blood vessels in the extremities shrink to preserve blood for vital organs, and the spleen contracts. This genetic variant upregulates thyroid hormone, which in mice has been linked to larger spleen size.

The scans showed that the spleens of the Bajau, whether from divers or nondivers, are 50% larger than those of the Saluan. The same works when a person is facing a situation of acute oxygen deprivation called acute hypoxia. So while the adoption of advantageous new traits is the result of mutation and natural selection (as was likely the case among the Bajau), new traits can also be introduced by interbreeding, and the subsequent retention (still via natural selection) of a beneficial new characteristic.

They spend 60 percent of their daily working time underwater and can stay underwater for up to 13 minutes at a time, the study said.

Prior to her travels, Ilardo spent months learning the Indonesian language, Bahasa Indonesia, which the Bajau people speak in addition to their native language, so that she could communicate with them directly, and convey to them the research findings.

"We show that natural selection on genetic variants in the PDE10A gene have increased spleen size in the Bajau, providing them with a larger reservoir of oxygenated red blood cells", the researchers wrote in their study.

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The Bajau, a group of "Sea Nomads" who live on houseboats traveling the waters of Southeast Asia, rely on incredible diving prowess to survive.

The spleen plays a key role in the "human dive response" that puts the body in survival mode when it is submerged under cold water for even brief amounts of time. "I had a portable ultrasound machine".

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

The researchers also stumbled across a gene called PDE10A, which is thought to control a certain thyroid hormone, in the Bajau but not the Saluan.

The findings have implications for other areas of medical research, the study authors said.

What makes the Bajau different, Ilardo said, is that their historically seafaring lifestyle and fishing practices may have driven the evolutionary process. Finally, Edward Gilbert-Kawai, physician-physiologist at the University of London, also notes that "it is highly unlikely that the size of the spleen is controlled by a single gene". "This is the first time that we really have a system like that in humans to study", said Dr Rasmus Nielsen.

Willerslev admitted he initially urged Ilardo not to pursue the research for her PhD thesis, believing it was too risky and that she may find nothing.

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