A new study reveals how millennia of human migration across Pacific islands led to the introduction of invasive pig species all over the Asia-Pacific region.
The new research has revealed new information about the spread of animals across the islands of Indonesia, which has not always happened naturally.
Dr David Stanton, evolutionary geneticist from Cardiff University School of Biosciences, said: "The Wallace line, proposed by naturalist Alfred Russel Wallace, is a biological boundary in the Malay Archipelago – wildlife on either side of that line rarely crossed. For example, leopards and monkeys are found on the Asian side, and marsupials are found on the Australasian side. An exception is pigs."
Pig populations occur on both sides of the Wallace Line. We wanted to understand the role people played in their spread.
The study - led by Laurent Frantz from Queen Mary University of London and the Ludwig Maximilians University of Munich, David Stanton from Cardiff University, and Greger Larson from the University of Oxford - looked at the genome of over 700 pigs, including those from living and archaeological specimens.
This genetic analysis allowed the reconstruction of their movement across Southeast Asia and identified when they arrived on certain islands and how they might have interbred with various native pig species.
The researchers found that people of different cultures have moved pig species in the region for millennia. The earliest evidence points to people living in Sulawesi perhaps as early as 50,000 years ago, known to be the earliest cave painters, who both depicted and transported warty pig species as far away as Timor, possibly to establish future hunting stock.
The introduction of pigs in Island Southeast Asia dramatically accelerated, around 4,000 years ago, when early agricultural communities transported domestic pigs in the region. Their journey began from Taiwan, extending across the Philippines, northern Indonesia (Maluku), into Papua New Guinea, and on to the outlying islands as far as Vanuatu, and remote Polynesia.
The authors also found evidence for the introduction of pigs from Europe during the colonial period.
Many of these domestic pigs escaped, and became feral, in some cases, like on the Komodo islands, hybridising with the warty pigs brought by people from Sulawesi thousands of years earlier. These hybrid pigs are now a major source of food for the endangered Komodo dragons.
The findings of this study highlight the dramatic impact of human activity on local ecosystems in the Pacific.
Professor Laurent Frantz, senior author of the study, said: "It is very exciting that we can use ancient DNA from pigs to peel back layers of human activity across this megabiodiverse region."
This research reveals what happens when people transport animals enormous distances, across one of the world's most fundamental natural boundaries. These movements led to pigs with a melting pot of ancestries. These patterns were technically very difficult to disentangle, but have ultimately helped us understand how and why animals came to be distributed across the Pacific islands.
Professor Greger Larson, University of Oxford, said: "Wild boar dispersed across all of Eurasia and North Africa and certainly don't need people to help them disperse into new areas. When people have landed a hand, pigs were all too willing to spread out on newly colonised islands in South East Asia and into the Pacific. By sequencing the genomes of ancient and more recent populations we've been able to link those human-assisted dispersals to specific human populations in both space and time."
