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Invited presentation, 9th Ancient DNA Conference, Pompeii 2008 (www.ancientdna9.it)
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Nuragic Sardinians are still among us, the Etruscans aren’t. Two genealogical studies
Guido Barbujani
Dip. Biologia ed Evoluzione Università di [email protected]
Nuragic Sardinians resemble some modern Sardinians
Genetic map of Europe (Menozzi, Piazza, Cavalli-Sforza 1978)
53 tooth samples from 6 nuragic sites
Elimination of samples that do not comply with the strictest quality standards
10 different sequences in 23 nuragic individuals
h, haplotype diversity=0.83
Etruscans: 0.95Tuscans: 0.96Basques: 0.96Greeks: 0.98Sicilians: 0.96
Ogliastra 0.78Gallura 0.93
North Africa: 13.9 4
Near East: 10.7 6
Europe: 18.3 8
Iberians: 29.4 2Etruscans: 22.2 4
Shared sequences among Nuragic people and other modern and ancient populations
Gallura: 18.5 1Ogliastra: 54.6 4
The Etruscans do not resemble modern Tuscans
A bit of history
Etruscan a non-Indo-European languageDocumented from the end of VIII century BCEtruscan cities independent statesCommon culture and language, but never a political unitMaximum territory expansion: VI century BCMilitary defeats, Roman assimilation in the II century BC
Dionysius of Halicarnassus: the Etruscans an Italic populationHerodotus: the Etruscans seamen from Lydia, escaping famine
V
A
S
PM
T
C
R o m e
Adria (17, 5), Volterra (6, 3),Castelfranco di Sotto (2, 1),Castelluccio di Pienza (1, 1),Magliano and Marsiliana (25, 6)Tarquinia (18, 5), Capua (8, 6)
80 bone samples from 8 Etruscan necropoleis
27 individuals, 22 different haplotypes, h=0.946
Shared sequences between the Etruscans and modern populations
23 3
35
2
1
31
52
22
33
1
3
7
4
2
2
2
4
Genetic distances (Fst x 1000) between the Etruscans and
modern populations
3680 90
7048
74
118
5550
37
47
4176
6051
57
261
69
65
41
62
73
71
Testing hypotheses by serial coalescent simulation
Reconstructing (proceeding backwards in time) the maternal genealogy of a sample
Two possibilities: either each individual has a different mum
Or two individuals have the same mum (coalesence)
Coalescence probability a function of population size N and sample size n
Past
Present
GenealogiesMRCA
N = 10N constantn = 69 generations
Mutation
Mutation
1
CAATG
CAATA
CAGTG
TAATA
CAATG CAGTG CAGTGCGGTG TAACA TAATA
TAACA1 2 3 3 4 5
Il Modello: Serial Simcoal
Serial coalescence
N=20Modern sample (n=5)0
100
Time(generations)
Ancient sample (n=2)
Anderson C.N.K., Ramakrishnan U., Chan Y.L. e Hadly E.A. (2005) Bioinformatics
INPUT Population size Population growth rate Migration matrix Mutation model and rate Sample sizes and ages
OUTPUT N haplotypes Haplotype diversity Nucleotide diversity Mismatch distribution Haplotype sharing
Etruscans Tuscans Murlo
Sample size 27 49 86
Haplotype n 22 40 60
Haplotype diversity 0.946 0.949 0.960
Nucleotide diversity 0.011 0.014 0.012
Avg. mismatch 3.91 5.03 4.50
Haplotype sharing 0.09 0.14
Fst 0.024 0.028
Observed population statistics
Consistency criterion: overlap between the 95% confidence intervals of observed and simulated statistics
Etruscans and Tuscans a single population?
Nf=25,000
Nf=25,000
r = 0
Model 1: Small population, constant size
• Allele sharing: 4.2% (1.4-8.1) OK
• Hapl. diversity:
- Etruscans: > Obs.
- Tuscans: > Obs.
0
100
Generations
Tuscans
Etruscans
Mutation rate: 1 per million years per nucleotide × 360 nucleotides, × 25 years per generation, ÷2 → 0.0045
Etruscans and Tuscans a single population?
Nf=300,000
Nf=25,000
r = -0.025
Model 3: Expanding population
• Allele sharing: 5.0% (1.3-9.1) OK• Hapl. diversity:
- Etruscans: > Obs.
- Tuscans: > Obs
0
100
Generations
Tuscans
Etruscans
Only models in which modern Tuscans and Etruscans belong to distinct genealogies are consistent with the data (χ2<31)
Interpretations, doubts
• Unless mutation rate is much higher than currently believed, the Etruscans left very few modern mitochondrial descendants in Tuscany (Belle et al. 2006)
• Did they all go extinct?• Did massive immigration dilute a component of Etruscan origin
in the Tuscans’ mtDNA gene pool?
• Postmortem DNA modifications and/or technical problems affected the Etruscan mtDNA sequences (Achilli et al. 2007)
No evidence of sequence errors in the Etruscan dataset
61 tooth samples from Middle-Age Tuscany Guimaraes et al., in preparation
Joint analysis of11 Etruscan sequences27 Medieval sequences (900-1300 A.D.), from 6 cemeteries
322 (Achilli et al.) and 49 (Francalacci et al.) modern Tuscan sequences
Model 1χ2=110
0 C
E
M
Model 4χ2=142
C
E
M
Only the model in which medieval Tuscans and Etruscans belong to the same genealogy and modern Tuscans don’t is consistent
with the data (χ2<49)
Model 2χ2=122
C
E
M
Model 3χ2=145
C
E
M
Model 5χ2=66
C
E
M
Model 6 χ2=40
E
M
C
Model 7χ2=63
E
M
C
What happened to the Etruscans but not to Nuragic Sardinians?
1. Perhaps the Etruscan we studied represent more a social elite than the entire population
2. Major demographic changes in the last few centuries in the Netherlands (Manni et al. 2002) and in the British Isles Töpf et al. (2007)
Relatively recent immigration has deeply changed the genetic structure of the population in Tuscany and in Gallura, but not in the Iberian peninsula and in Ogliastra
David Caramelli
Giorgio Bertorelle
Andrea Benazzo, Silvia Ghirotto Loredana Castrì
Elise Belle
Many thanks to
Enza Colonna
Simulation parameters
• Population sizes: Etruscans: 292,000÷12 = 25,000 Tuscans: 3,500,000÷12 = 300,000
• Growth rate: Nt=N0ert → r=1/100 ln 300,000/25,000 = 0.025
• Mutation rate: 1 mutation per million years per nucleotide × 360 nucleotides, × 25 years per generation, ÷2 → 0.0045
• 360 nucleotides
• Transition bias: 0.94
Only the model in which medieval Tuscans and Etruscans belong to the same genealogy and modern Tuscans don’t is consistent
with the data (χ2<49)