The saga of the Osedax “bone-eating” worms began 12 years ago, with the first discovery of these deep-sea creatures that feast on the bones of dead animals. The Osedax story grew even stranger when researchers found that the large female worms contained harems of tiny dwarf males.
Examining bone worms collected at 700 meters (2,296 feet) depth by an MBARI remotely operated vehicle, Rouse observed a surprising new type of Osedax species. Females of the new species are roughly the same size as their previously studied relatives, but males are tens of thousands of times larger than those of other Osedax worms, and are roughly the same size as the females.
“This discovery was very unexpected,” said Rouse. “It’s the first known example of such a dramatic evolutionary reversal from dwarf males.”
“Evolutionary reversals to ancestral states are very rare in the animal kingdom,” noted coauthor Vrijenhoek. “This case is exceptional because the genes for producing full-sized adult males should have deteriorated over time due to disuse. But apparently the genes are still there.”
Also surprising was the discovery that males of the new species consume bone on their own, something their dwarf relatives don’t ever do.
Adding even more peculiarity to the discovery is the mating process for the new species. Previously studied Osedax male dwarfs are permanently attached to their female hosts, and therefore do not need mobility to mate, so the scientists wondered how the newly discovered males are able to seek out a mate, given their independence.
“The evolutionary solution (the new species) found was to actually make the male’s body very extendable so he can reach far out to find females to mate with — he can extend his body ten-times its contracted state,” said Rouse.
In essence, Rouse said, the entire worm’s body has evolved as a tool for mating, “and that’s why we named it Osedax ‘priapus,’ the mythological god of fertility,” said Rouse.
The scientists speculate that less competition for space on certain animal bones allowed the evolutionary introduction of Osedax primps.
“This worm was weird enough as it was and now it’s even weirder,” said Rouse. “This shows us that there continue to be mysteries in the sea and there is still so much more to discover, especially since we only found these creatures 12 years ago.”
Scientists have successfully discovered one of modern humans’ ancient lineages through the sequencing of genes of the Southern African Khoisan tribespeople. This is the first time that the history of humankind populations has been analyzed and matched to Earth’s climatic conditions over the last 200,000 years.
A geneticist from NTU, Professor Stephan Christoph Schuster, who led an international research team from Singapore, United States and Brazil, said this is the first time that the history of humankind populations has been analysed and matched to Earth’s climatic conditions over the last 200,000 years.
Their breakthrough findings are published today (4 Dec) in Nature Communications.
The team has sequenced the genome of five living individuals from a hunter/gatherer tribe in Southern Africa, and compared them with 420,000 genetic variants across 1,462 genomes from 48 ethnic groups of the global population.
Through advanced computation analysis, the team found that these Southern African Khoisan tribespeople are genetically distinct not only from Europeans and Asians, but also from all other Africans.
The team also found that there are individuals of the Khoisan population whose ancestors did not interbreed with any of the other ethnic groups for the last 150,000 years and that Khoisan was the majority group of living humans for most of that time until about 20,000 years ago.
Their findings mean it is now possible to use genetic sequencing to reveal the ancestral lineage of any ethnic group even up to 200,000 years ago, if non-admixed individuals are found, like in the case of the Khoisan. This will show when in history there have been important genetic changes to an ancestral lineage due to intermarriages or geographical migrations that may have occurred over the centuries.
“Khoisan hunter/gatherers in Southern Africa have always perceived themselves as the oldest people,” said Prof Schuster, an NTU scientist at the Singapore Centre on Environmental Life Sciences Engineering (SCELSE) and a former Penn State University professor.
“Our study proves that they truly belong to one of mankind’s most ancient lineages, and these high quality genome sequences obtained from the tribesmen will help us better understand human population history, especially the understudied branch of mankind such as the Khoisan.
“The new data gathered will also enable scientists to better understand how the human genome has evolved and hopefully lead to more effective treatment options for certain genetic diseases and illnesses.”
Of the five tribesmen who were the oldest members of the Ju/’hoansi tribe and other tribes living in protected areas of northwest Namibia, two individuals were found to have a genome which had not admixed with other ethnic groups.
The Ju/’hoansi tribe was made famous in the 80s and 90s by the box-office hit movie series “The Gods Must Be Crazy.” The main character of the series was a hunter/gatherer tribesman, played by Nǃxau, a bushman.
The research paper’s first author, Dr Hie Lim Kim, a SCELSE senior research fellow, said “it was very surprising that this group apparently did not intermarry with non-Khoisan neighbours for thousands of years.” This is because the Khoisan peoples and the rest of modern humanity shared their most recent common ancestor around 150,000 years ago.
The current Khoisan culture and tradition, where marriage occurs either among Khoisan groups or results in female members leaving their tribes after marrying non-Khoisan men, appears to be long-standing.
“A key finding from this study is that even today after 150,000 years, single non-admixed individuals or descendants of those who did not interbreed with separate populations can be identified within the Ju/’hoansi population, which means there might be more of such unique individuals in other parts of the world,” added Dr Kim.
Reference: Hie Lim Kim, Aakrosh Ratan, George H. Perry, Alvaro Montenegro, Webb Miller, Stephan C. Schuster. Khoisan hunter-gatherers have been the largest population throughout most of modern-human demographic history. Nature Communications, 2014; 5: 5692 DOI: 10.1038/ncomms6692