Ripples on the surface. Surnames and genes in Sicily and Southern Italy

[Tacitus]

https://www.tandfonline.com/doi/full/10.1080/03014460.2017.1411525?src=recsys&

Abstract

Background: Southern Italy and Sicily played a key role in the peopling history of the Mediterranean. While genetic research showed the remarkable homogeneity of these regions, surname-based studies instead suggested low population mobility, hence potential structuring.

Aim: In order to better understand these different patterns, this study (1) thoroughly analysed the surname structure of Sicily and Southern Italy and (2) tested its relationships with a wide set of molecular markers.

Subjects and methods: Surname data were collected from 1213 municipalities and compared to uniparental and autosomal genetic markers typed in ∼300 individuals from 8–10 populations. Surname analyses were performed using different multivariate methods, while comparisons with genetic data relied on correlation tests.

Results: Surnames were clearly structured according to regional geographic patterns, which likely emerged because of recent isolation-by-distance-like population dynamics. In general, genetic markers, hinting at a pervasive homogeneity, did not correlate with surname distribution. However, long autosomal haplotypes (>5 cM) that compared to genotypic (SNPs) data identify more “recent” relatedness, showing a clear association with surname patterns.

Conclusion: The apparent contradiction between surname structure and genetic homogeneity was resolved by figuring surnames as recent “ripples” deposited on a vast and ancient homogeneous genetic “surface”.

RTWT

[Tacitus]

Some parts that stood out to me:


While the contribution of the pre-Neolithic European hunter-gatherers—which is relevant in other European countries (Skoglund et al., 2012 Skoglund P, Malmström H, Raghavan M, Storå J, Hall P, Willerslev E, Gilbert MT, et al. 2012. Origins and genetic legacy of Neolithic farmers and hunter-gatherers in Europe. Science 336:466–469.[Crossref], [PubMed], [Web of Science ®], [Google Scholar])—is only moderate in Southern Italy and Sicily, the most important layers of the ‘continuum’ seem to refer to later events. They are (1) a huge Neolithic-like genetic component (∼50%) and (2) a Bronze Age component incorporating a significant Caucasus-related ancestry (∼24%). If the former is obviously related to migrations that spread Neolithic technologies towards the West, the second one suggests a less known net of Bronze-Age population movements along the Eastern Mediterranean shores through Anatolia.


The same studies suggested that this peculiar genetic background (‘Mediterranean continuum’) was already in place at least at the end of the Bronze Age. Subsequent major population movements, such as the Greek colonisation of ‘Magna Graecia’, mostly reinforced this peculiar pattern, while some minor differences emerged only in more recent times, most notably as a by-product of the Early Middle Ages Slavic migrations and of later migrations prompted by the Turkish-Ottoman invasion of the Balkan Peninsula (such as in the case of the Arbereshe; Fiorini et al., 2007 Fiorini S, Tagarelli G, Boattini A, Luiselli D, Piro A, Tagarelli A, Pettener D. 2007. Ethnicity and Evolution of the Biodemographic Structure of Arbëreshe and Italian Populations of the Pollino Area, Southern Italy (1820–1984). American Anthropol. 109:735–746.[Crossref], [Web of Science ®], [Google Scholar]).


At the same time, population clusters found in Southern Italy (CalS, CalC, CalN, Bas, ApuS, ApuN), despite some overlapping, show a remarkable geographic specificity, suggesting that the observed structure likely resulted from isolation-by-distance phenomena (Figures 3 and 4). Interestingly, the areas occupied by these clusters do not coincide with administrative units (provinces), instead suggesting similarities with those highlighted by linguistic maps (see for example, Pellegrini, 1977 Pellegrini GB. 1977. Carta dei dialetti d’Italia. Pisa: Pacini. [Google Scholar]). On the contrary, the four identified Sicilian clusters (SicW1, SicW2, SicE1, SicE2) show pervasive geographic overlapping and, in most cases, clear evidence of admixture/introgression from other clusters (Figure 3). Consequently, Sicily maintained a more homogeneous surname composition compared to Southern Italy, showing only a moderate East–West polarity.


However, in this study we could observe the ‘meeting place’ between DNA and surnames when introducing autosomal haplotype-based markers (IBD tracts), which in fact are particularly apt at exploring the recent layers of genetic variation (‘fine-scale structuring’). It is worth noting that the different inheritance modalities (patrilineal for surnames and bi-parental for autosomes) did not prevent the association between IBD-tracts and surnames, which on the contrary was not observed when considering Y-chromosomal markers, neither slow- nor fast-evolving. Therefore, we may speculate that surnames reflect the most recent events of human population history, not only at a micro-geographic scale but also at a regional/macro-geographic one. This fact may be of great help for designing criteria for DNA sampling campaigns, not only for detecting ‘local’ surnames, but also and most importantly for identifying the most useful sampling locations.


The ‘Mediterranean genetic continuum’, shared between Sicily, Southern Italy and a wider Mediterranean area, traces its origins to Neolithic and Bronze Age layers. It took shape along thousands of years of East–West migrations, of which the Greek conquest of the area (Magna Graecia) was probably only the last of a long series. On the other hand, the differentiation identified by surnames took place later, probably starting from the late Middle Ages and continuing until recent times, without erasing the underlying genetic homogeneity. Since the surname structure is clearly shaped by geography, we may hypothesise that it mainly originated from low-rate, short-distance population mobility, which finally resulted in an isolation-by-distance-like pattern.