NEW YORK – By analyzing ancient DNA from sites across several Canary Islands, members of an international research team have untangled ancestry patterns in the North African ancestors of indigenous populations found some 500 to 1,800 years ago, while digging into the population genetic effects of population isolation and migrations in the region.
"For the first time, we have generated paleogenomic data from the seven islands with the aim of exploring how isolation and insularity affected the genetic makeup of the Canarian indigenous people," co-senior author Rosa Fregel, an evolution, paleogenomics, and population genetics researcher affiliated with the University of La Laguna (ULL) in Spain and Stanford University, and first author Javier Serrano of the ULL, said in an email.
For a paper appearing in Nature Communications on Tuesday, the researchers used shotgun sequencing and/or in-solution capture sequencing to assess DNA isolated from bone or tooth samples from 40 individuals from nearly two dozen 3rd to 16th century archaeological sites on seven Canary Islands, generating low- to medium-coverage genome sequences for nine ancient individuals and genome-wide profiles for the remaining 31 individuals.
Though past archaeological, linguistic, and genetic studies have linked Canary Island's indigenous populations to North African origins, more precise details on these populations and the colonization events that brought them to the islands remain murky, Fregel and Serrano explained.
In addition, they explained, the ancestry patterns present in indigenous individuals on the islands can provide a peek at ancestral populations from North Africa, where ancient DNA preservation has been adversely affected by hot, humid climate conditions.
"Until now, only hunter-gatherers and early farmers from Morocco have been studied using paleogenomic techniques and no other information had been obtained for the Western North African region, making it difficult to understand its genomic history from the Late Neolithic to the Antiquity," Fregel and Serrano explained.
They noted that a "window into the past of North Africa can be accessed through the study of the indigenous people from the Canary Islands, being a population of North African origin that was most probably isolated from the mainland before the arrival of the Islamic invasions."
Together with whole-genome sequence data for nine more Canary Island representatives sequenced for prior studies, the new sequence and SNP data made it possible to tease out genetic ties between indigenous Canarians and Neolithic populations found in Morocco roughly 5,000 years ago, which carried North Africa ancestry and ancestry from early European farmers who migrated back to North Africa.
But the populations also carried ancestry linked to Bronze and Iron Age populations in the Mediterranean, along with ancestry from a previously unappreciated migration across the Sahara, the authors explained, highlighting still other migrations into North Africa.
"Along with components already present in Moroccan Neolithic populations, the Canarian natives show signatures related to Bronze Age expansions in Eurasia and trans-Saharan migrations," the authors reported.
Even so, the investigators saw a range of ancestry proportions from one island to the next. While ancient European ancestry tended to be higher in individuals from the Gran Canaria, Lanzarote, and Fuerteventura islands closest to the continent, the El Hierro, La Palma, La Gomera, and Tenerife islands further to the west had enhanced levels of North African ancestry.
"When both ancient DNA and radiocarbon data are analyzed together, it is observed that the differences between the eastern and western islands appear to have existed from the beginning of the indigenous colonization period and that they remained unchanged," Fregel and Serrano noted. "This is important because it determines that, if there were asymmetric migrations between the two regions, they must have occurred at the beginning of the indigenous colonization period."
In contrast to ancestry patterns, diversity patterns tended to differ with the size of a given island and the resources available there, the team reported, with populations on more minute, resource-poor Canary Islands showing signs of long-term isolation and diminished population size. That pattern was particularly pronounced on the small island of El Hierro, where climate instability in the 9th century coincided with a strong population bottleneck.
"Overall, this dataset has allowed us to better understand the prehistory of North Africa and to start producing a more detailed picture of the complex colonization process of the Canary Islands, where human resilience, isolation, and diverse insular environments led to the differentiation of their genetic landscape," the authors concluded.