Post by Admin on Jan 2, 2023 23:33:49 GMT
Assessing temporal and geographic contacts across the Adriatic Sea through the analysis of genome-wide data from Southern Italy
Abstract
Southern Italy was characterised by a complex prehistory that started with different Palaeolithic cultures, later followed by the Neolithization and the demic dispersal from the Pontic-Caspian Steppe during the Bronze Age. Archaeological and historical evidences point to a link between Southern Italians and the Balkans still present in modern times. To shed light on these dynamics, we analysed around 700 South Mediterranean genomes combined with informative ancient DNAs. Our findings revealed high affinities of South-Eastern Italians with modern Eastern Peloponnesians, and a closer affinity of ancient Greek genomes with those from specific regions of South Italy than modern Greek genomes. The higher similarity could be associated with a Bronze Age component ultimately originating from the Caucasus with high Iranian and Anatolian Neolithic ancestries. Furthermore, extremely differentiated allele frequencies among Northern and Southern Italy revealed putatively adapted SNPs in genes involved in alcohol metabolism, nevi features and immunological traits.
1. Introduction
Southern Italy was one of the first European regions to be inhabited by our species. One of the oldest archaeological remains attributed to Homo sapiens, has been in fact excavated in Apulia (Grotta del Cavallo ~ 45 thousand years ago - kya) and recently associated with the Uluzzian culture [1], also reported in the Middle and Upper Palaeolithic in Greece [[2], [3], [4]], although other interpretations have been proposed [5].
At the end of the Last Glacial Maximum, approximately 20 kya, populations from South-Eastern Europe and West Asia partially replaced continental European Hunter Gatherers (HG) [6,7]. Recently, ancient DNA (aDNA) analyses found support of an early arrival of European HG with high affinity to the so-called Villabruna Cluster (or Western Hunter Gatherers - WHG). The earliest evidence of this change has been recorded in the genomes of remains from North-Eastern Italy dated about 17 kya. This shift has been associated with e demographic transition occurring between Early to Late Epigravettian in Southern Europe around 17 kya [8,9] as confirmed by archaeological data [10]. These observations highlighted the existence of a connection between Western and Eastern Europe well before Neolithic times, with Italy playing the role either of a bridge or a refuge [8].
Neolithization revolutionised the culture and the demography of continental Europe, with Southern Italy being the first colonised place West of the Adriatic Sea [[11], [12], [13]]. Recently, the availability of ancient Southern European genomes helped in disentangling the dynamics of the early stages of the Pontic Steppe populations diffusion that occurred in the Bronze Age period [14,15]. Differently from the rest of Europe, Greece and Southern Italy appear to have been less impacted by this demic dispersal, being characterised by an additional Iranian-related ancestry [[16], [17], [18], [19]]. However, the lack of Southern Italian ancient genomes from the Neolithic period keeps open essential questions regarding this major cultural and demographic transition in the region. Starting from 5.5 kya archaeological evidence allows to outline a network of cultural connections interacting along the Adriatic-Ionian axis, operating between two or more different core areas and radiating across trajectories of link and expansion which likely triggered small human groups movements [20,21]. As a matter of fact, from about 4.3 to 4 kya, the well-know Cetina-type cultural elements, also related to the Bell Beaker phenomenon in the North-Western Balkans, played an active role spreading from the Dalmatian core area Southwards across the Adriatic in Northern Apulia and South-Eastern Italy, also influencing the Ionian Islands and Western Greece [22].
Later on, starting from 4 kya, a flourishing and continuous cultural relationship was established between Southern Italy and Aegean communities especially from the Recent Bronze Age (3.3 to 3.2 kya) onward [23,24]. Although the demographic extent of these contacts is not clear, some valuable insights on mobility could be inferred from ceramic crafts. The most recent analytical evidences, relating to the Aegean-type pottery from the core sites of Punta di Zambrone (Tyrrhenian Calabria) and Roca Vecchia (Southern Adriatic Apulia), allow to highlight a strong connection with the Western Greek regions (Ionian Islands, Acarnania, Achaea and Elis) and, to a lesser extent, with Western Crete [25].
Precisely, following the Bronze Age, in a period between the so-called Greek “Dark Ages” [26] and the Archaic Greece (2.7 to 2.5 kya), Southern Italy became a hotspot for the foundation of Greek colonies. The first colonies were set in Campania and Sicily, possibly by settlers arriving from Eastern Greece (Euboea island) around 2.8 kya, soon followed by colonies in Calabria, Basilicata and Apulia [[27], [28], [29], [30]], encompassing an area later to be known as Magna Grecia. Between 2.7 to 2.6 kya, some of these settlements, specifically in South-Eastern Sicily (Siracusa and Megara Iblea) and Apulia (Taranto), were attributed to Eastern Peloponnesian founders [31,32].
The nature of the early settlements, the scale of their demographic impact and genetic legacy are still a matter of debate. Some genetic studies [33,34] have tried characterise the demographic impact of these processes in Southern Italy using present-day Italian populations, but none of them had the intent of finely dissecting these ancient components. Furthermore, a recent aDNA study [35] showed that Iron Age Apulians were not yet superimposable to contemporary Southern Italians, pointing to later processes as keys for the understanding of present-day genetic diversity in Italy.
As a consequence of this complex demographic scenario, Italy harbours the largest degree of genetic population structure identified in Europe so far [17], making its population a valuable asset for adaptation studies [[36], [37], [38]].
In this study, we performed a genome-wide analysis, unveiling the contemporary genetic structure of present-day South and Eastern European populations, and highlighting recent and past interactions between Southern Italy and Greece. Furthermore, by integrating available ancient genomes, we finely characterised the genetic similarities between modern-day Southern Italians and different Eurasian ancient groups. Finally, we searched for putatively selected genomic regions by evaluating differences in allele frequencies between Southern and Northern Italians, identifying SNPs potentially under selection that are linked with immunological and dietary traits.
Abstract
Southern Italy was characterised by a complex prehistory that started with different Palaeolithic cultures, later followed by the Neolithization and the demic dispersal from the Pontic-Caspian Steppe during the Bronze Age. Archaeological and historical evidences point to a link between Southern Italians and the Balkans still present in modern times. To shed light on these dynamics, we analysed around 700 South Mediterranean genomes combined with informative ancient DNAs. Our findings revealed high affinities of South-Eastern Italians with modern Eastern Peloponnesians, and a closer affinity of ancient Greek genomes with those from specific regions of South Italy than modern Greek genomes. The higher similarity could be associated with a Bronze Age component ultimately originating from the Caucasus with high Iranian and Anatolian Neolithic ancestries. Furthermore, extremely differentiated allele frequencies among Northern and Southern Italy revealed putatively adapted SNPs in genes involved in alcohol metabolism, nevi features and immunological traits.
1. Introduction
Southern Italy was one of the first European regions to be inhabited by our species. One of the oldest archaeological remains attributed to Homo sapiens, has been in fact excavated in Apulia (Grotta del Cavallo ~ 45 thousand years ago - kya) and recently associated with the Uluzzian culture [1], also reported in the Middle and Upper Palaeolithic in Greece [[2], [3], [4]], although other interpretations have been proposed [5].
At the end of the Last Glacial Maximum, approximately 20 kya, populations from South-Eastern Europe and West Asia partially replaced continental European Hunter Gatherers (HG) [6,7]. Recently, ancient DNA (aDNA) analyses found support of an early arrival of European HG with high affinity to the so-called Villabruna Cluster (or Western Hunter Gatherers - WHG). The earliest evidence of this change has been recorded in the genomes of remains from North-Eastern Italy dated about 17 kya. This shift has been associated with e demographic transition occurring between Early to Late Epigravettian in Southern Europe around 17 kya [8,9] as confirmed by archaeological data [10]. These observations highlighted the existence of a connection between Western and Eastern Europe well before Neolithic times, with Italy playing the role either of a bridge or a refuge [8].
Neolithization revolutionised the culture and the demography of continental Europe, with Southern Italy being the first colonised place West of the Adriatic Sea [[11], [12], [13]]. Recently, the availability of ancient Southern European genomes helped in disentangling the dynamics of the early stages of the Pontic Steppe populations diffusion that occurred in the Bronze Age period [14,15]. Differently from the rest of Europe, Greece and Southern Italy appear to have been less impacted by this demic dispersal, being characterised by an additional Iranian-related ancestry [[16], [17], [18], [19]]. However, the lack of Southern Italian ancient genomes from the Neolithic period keeps open essential questions regarding this major cultural and demographic transition in the region. Starting from 5.5 kya archaeological evidence allows to outline a network of cultural connections interacting along the Adriatic-Ionian axis, operating between two or more different core areas and radiating across trajectories of link and expansion which likely triggered small human groups movements [20,21]. As a matter of fact, from about 4.3 to 4 kya, the well-know Cetina-type cultural elements, also related to the Bell Beaker phenomenon in the North-Western Balkans, played an active role spreading from the Dalmatian core area Southwards across the Adriatic in Northern Apulia and South-Eastern Italy, also influencing the Ionian Islands and Western Greece [22].
Later on, starting from 4 kya, a flourishing and continuous cultural relationship was established between Southern Italy and Aegean communities especially from the Recent Bronze Age (3.3 to 3.2 kya) onward [23,24]. Although the demographic extent of these contacts is not clear, some valuable insights on mobility could be inferred from ceramic crafts. The most recent analytical evidences, relating to the Aegean-type pottery from the core sites of Punta di Zambrone (Tyrrhenian Calabria) and Roca Vecchia (Southern Adriatic Apulia), allow to highlight a strong connection with the Western Greek regions (Ionian Islands, Acarnania, Achaea and Elis) and, to a lesser extent, with Western Crete [25].
Precisely, following the Bronze Age, in a period between the so-called Greek “Dark Ages” [26] and the Archaic Greece (2.7 to 2.5 kya), Southern Italy became a hotspot for the foundation of Greek colonies. The first colonies were set in Campania and Sicily, possibly by settlers arriving from Eastern Greece (Euboea island) around 2.8 kya, soon followed by colonies in Calabria, Basilicata and Apulia [[27], [28], [29], [30]], encompassing an area later to be known as Magna Grecia. Between 2.7 to 2.6 kya, some of these settlements, specifically in South-Eastern Sicily (Siracusa and Megara Iblea) and Apulia (Taranto), were attributed to Eastern Peloponnesian founders [31,32].
The nature of the early settlements, the scale of their demographic impact and genetic legacy are still a matter of debate. Some genetic studies [33,34] have tried characterise the demographic impact of these processes in Southern Italy using present-day Italian populations, but none of them had the intent of finely dissecting these ancient components. Furthermore, a recent aDNA study [35] showed that Iron Age Apulians were not yet superimposable to contemporary Southern Italians, pointing to later processes as keys for the understanding of present-day genetic diversity in Italy.
As a consequence of this complex demographic scenario, Italy harbours the largest degree of genetic population structure identified in Europe so far [17], making its population a valuable asset for adaptation studies [[36], [37], [38]].
In this study, we performed a genome-wide analysis, unveiling the contemporary genetic structure of present-day South and Eastern European populations, and highlighting recent and past interactions between Southern Italy and Greece. Furthermore, by integrating available ancient genomes, we finely characterised the genetic similarities between modern-day Southern Italians and different Eurasian ancient groups. Finally, we searched for putatively selected genomic regions by evaluating differences in allele frequencies between Southern and Northern Italians, identifying SNPs potentially under selection that are linked with immunological and dietary traits.
