(CN) — A Portuguese trading ship named the Bon Jesus sank off the southern coast of Africa in 1533, loaded to the gills with gold, silver and ivory — and it’s proven a real treasure trove to scientists.
On its way to India when it went down, and discovered only in 2008, researchers have scoured the ship’s remains to learn what they can about 16th century trade routes and the elephants from whom its ivory was poached.
An international team from Namibia, South Africa, the U.K. and the US collaborated to investigate the remains of the shipwreck. They traced the DNA contained in over 100 raw ivory tusks to determine exactly where the elephants originated, which turned out to be a bit of a surprise. The team released their findings in a study published Thursday in the journal Cell Press.
Ivory was among the main drivers of the trans-continental trading system connecting Europe, Africa and Asia through maritime trade routes in the earlier days of global commerce. European ships would sail around the west coast of Africa, take on some valuable cargo like gold and ivory, then sail around flipping it at Indian ports.
“Our analysis allowed us to connect these trade links more extensively by tracing the origin of the ivory to different habitats in West Africa,” said the study’s co-author, Ashley Coutu, a research fellow at the University of Oxford, in an email.
“We know from archaeological evidence that West African trading centers and networks of exchange flourished for thousands of years before the sailing of the Bom Jesus, so there was an established regional network to move ivory over long distances and eventually to the coast for trade with Portuguese ships.”
Combining paleogenomic, isotopic, archeological and historical methods, it took a true interdisciplinary approach to unravel this nearly 500-year-old puzzle. The team found that the tusks came from African forest elephants, not African savanna elephants, and from West rather than Central Africa as they had expected.
“The isotope analysis determined that tusks were not from elephants in the deep tropical forests, but rather in mixed or savanna habitats, consistent with the locations of trading posts used by the Portuguese in West Africa,” said co-author Alfred Roca, a professor at the University of Illinois, in an email. “Most importantly this combination of DNA and isotope analyses could be used to examine ivory from other historic and archeological sites, to infer trade patterns in the past.”
Roca noted that the team did not find any two tusks from the same herd and said the isotope data indicates that the elephants came from somewhat different habitats and regions.
Certain DNA markers are passed down only along the matrilineal line — from mother to calf — namely mitochondrial DNA. By comparing mDNA sequences from the shipwreck ivory to those of geo-referenced elephants the researchers were able to pinpoint the precise regions and elephant species from which they originated.
The team successfully analyzed DNA from 44 tusks and performed isotope analysis on 97, confirming that the tusks were poached from African forest elephants. They were even able to determine the 17 West African herds the elephants once belonged to.
Because the Portuguese were known to maintain extensive trading routes through the Kongo Kingdom, the expectation was that the ivory had originated there.
Four of the mitochondrial haplotypes uncovered are still found today in elephants from the region, and revealed that the elephants lived in mixed forest habitat, rather than deep in the rainforest.
“We initially analyzed the carbon and nitrogen stable isotope data from the tusks, which revealed that these elephants lived in a range of different habitats, encompassing savanna and woodland, but outside of the deep tropical forest,” Coutu said. “So, we were surprised when the ancient DNA results revealed that genetically, the tusks derived from African forest elephants.”
Coutu said that some West African forest elephants still live outside the tropical rainforest and inhabited both forest and woodland savanna habitats even before the drastic disturbance to the West African ecosystem over the past 500 years.
The team hopes their research and techniques can be applied going forward to help prevent poaching. They even developed software that allows mitochondrial DNA from confiscated ivory to be queried, which produces a map showing where similar sequences have been reported in the past.
By tracking DNA from recovered elephant tusks, others can determine the location of major hotspots to apply scarce anti-poaching resources where they can help most.