DNA research on Papua New Guinea’s lowlanders and highlanders shows how populations facing unique challenges have distinct genetic adaptations.
New data collected by the Papuan Past project presents whole-genome sequences from highlanders and lowlanders on Papua New Guinea (PNG). The findings are presented in a paper published in Nature Communications.
PNG has a wide range of environments despite being in a tropical region.
Its lowlands are a labyrinth of swamps, lowland forest and tall-grass savannahs. Average maximum temperatures are more than 30°C.
In the highland rainforests, night frost is common above 2,100 metres.
Humans, along with other animal and plant life, have adapted to the different environments and ecologies. But these adaptations are not well understood, and the new research shows how deep they go.
Highlanders have to contend with low oxygen due to altitude. Lowlanders are exposed to pathogens like malaria which are absent in the highlands.
“We explored the signatures of selection in newly sequenced whole genomes of 54 PNG highlanders from Mt Wilhelm (Chimbu Province) and 74 PNG lowlanders from Daru Island (Western Province),” explains project leader and corresponding author Dr François-Xavier Ricaut from the University of Toulouse, France.
“We hypothesised that the genomes of both populations have been shaped differently to mitigate the detrimental effects of their respective environments,” Ricaut adds.
“The genetic variants under selection identified in our study show associations with blood-related phenotypes,” says lead author Dr Mathilde André from Estonia’s University of Tartu.
For example, the authors found a higher red blood cell count in highlanders to help adapt to lower oxygen availability. On the other hand, lowlanders show a higher white blood cell count.
“This supports the idea that hypoxia [low oxygen] might have been the main driving force of selection that has acted on Papua New Guinean highlanders. However, specific pathogens might have shaped the genome of lowlanders through selection,” André adds.
The authors suggest an origin for the lowlanders’ adaptation outside Homo sapiens.
Denisovans are a now extinct ancient human discovered in 2010 who lived in Asia until about 30,000 years ago.
Previous research has shown that up to 4% of Papua New Guineans’ DNA is of Denisovan origin. It has also been established that Denisovan DNA likely helped in the evolution of modern Papuan immune systems.
The new study points to a genetic mutation in Denisova that impacts a specific protein structure.
“It looks like the altered protein is beneficial for the lowlanders to survive in their environment,” says co-lead of the project Dr Mayukh Mondal, also from the University of Tartu. “Although we do not know the exact cause of this selection, this mutation might help the lowlanders overcome malaria.”
