NEW YORK – By genetically profiling the population structure in Italy, a team from the University of Pavia, the University of Oxford, the University of Turin, and elsewhere has uncovered genetic variation that reflects both geography and the historical interactions that occurred in different parts of the country.
"The pattern of variation reported across Italian groups appears geographically structured across three main regions in Italy: Southern, Northern, and Sardinia," the authors wrote today in a paper published in Science Advances. "Similarly to Europe, the genetic structure reflects isolation by distance following population movements since prehistoric times and historical admixture from the fringes of the continent."
The researchers brought together data for thousands of present-day and ancient individuals from Italy, comparing population genetics across the country's 20 administrative regions to one another and almost 5,200 more individuals from 140 populations from other parts of Europe and beyond. Their results suggest modern-day Italians carry ancient ancestry related to migrations from steppe and non-steppe populations, though ancestry in Italy varies from one region to the next, due to differences in geography, admixture, and ancestry from incoming populations.
"The analysis of both modern and ancient data suggests that in Italian populations, ancestries related to [Caucasus hunter-gatherers (CHG)] and [Eastern hunter-gatherers (EHG)] derive from at least two sources," the authors reported. "One is the well-characterized steppe signature associated with nomadic groups from the Pontic-Caspian steppes … The other contribution is ultimately associated with CHG ancestry, as previously suggested, and predominantly affected Southern Italy, where it represents a substantial component of the ancestry profile of local modern populations."
The team reasoned that the Italian population genetics might be particularly apt to provide clues to past migrations in Europe, including movement by Anatolian farming groups and Yamnaya pastoralists and their interactions with hunter-gatherers, given the country's geographic location. In an effort to "complement and enrich the information provided by [ancient DNA] studies" the group analyzed new and available genotyping data for individuals in Italy and other parts of the world.
"To characterize the genetic variability of modern-day European populations and their relationship to early European foragers, Neolithic farmers, and Bronze Age nomadic pastoralists," the authors explained, "we investigated the population structure of present-day Italians and other Europeans in terms of their ancestry composition as the result of migration and admixture, both ancient and historical."
Using available ChromoPainter and fineSTRUCTURE pipelines, the researchers analyzed haplotype patterns for 222 modern individuals from Italy and Albania who were newly genotyped with Illumina arrays. They also looked at data for 4,852 individuals from a published modern dataset that includes 1,589 individuals from Italy, and 1,651 individuals from another "high-density dataset" encompassing 524 Italians.
The team analyzed these SNP profiles alongside available ancient samples and modern-day samples representing 5,192 individuals from around the world, identifying genetically distinct population clusters in Sardinia, North and Northcentral Italy, and Southern Italy (including Southcentral Italy and Sicily).
The Sardinian and Northern populations most closely resembled populations in Western Europe, the researchers reported, but populations in Southern Italy and Sicily shared closer genetic ties to populations in the Middle East.
For their subsequent analyses, they took a look at the more subtle ancestral contributions in each region, including ancestry that appears to stem from Neanderthals. Along with relatively pronounced ancestry from Neolithic Anatolians, for example, the Italian populations had ancestry from Eastern, Western, and Caucasus hunter-gatherers.
The authors placed these population movement and mixing events into a broader historical context, when possible, retracing interactions between individuals in Italy, Africa, and Eurasia. For example, they noted that "[h]istorical events, possibly involving continental groups at the end of the Roman Empire and African contributions following the establishment of Arab kingdoms in Southern Europe around 1,300 to 1,200 [years ago], played a role in … shaping the ancestry profiles and population structure of Italians."