Genetic data on Alghero population (Sardinia): Contrast between biological and cultural evidence

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 93:441453 (1994)

Genetic Data on Alghero Population (Sardinia): Contrast Between Biological and Cultural Evidence P. MORAL, G. MAROGNA, M. SALIS, V. SUCCA, AND G. VONA Laboratorio de Antropologia, Departamento de Biologza Animal, Facultad de Biologia, Uniuersidad de Barcelona, 08028 Barcelona, Spain (P.M.); Centro Trasfusionale USL 2, Alghero (G.M.); Istituto di Scienze Antropologiche, Uniuersita di Sassari, Sassari (M.S.); and Dipartimento Biologia Sperimentale, Sezione Scienze Antropologiche, Uniuersita di Cagliari, 09124 Cagliari (U.S., G.V.), Italy

KEY WORDS Classical Mediterranean populations

polymorphisms,

Genetic

distances,

ABSTRACT

Data on 20 genetic polymorphisms (61 alleles) in the Algehero population on the northwestern coast of Sardinia are presented and discussed in relation to its linguistic peculiarity inside the island. Since the Aragonese (Spain) conquest of Sardinia in the 13th century, the Catalan language, the same as that spoken in Northeastern Spain and certain districts of Southern France, has been used in Alghero even until today. Analysis for heterogeneity of gene frequency distributions indicates that the genetic information obtained on Alghero is adequate to discriminate Sardinians from other neighbouring populations. Genetic variation between populations measured through genetic distances and principal-component analysis shows that the present-day population of Alghero is much closer genetically to Sardinians than to Catalonians. Our genetic results do not support any interpretation of the linguistic affinities between Alghero and Catalonia at present as indicative of biological kinship. o 1994 Wiley-Liss, Inc.

Among European populations, the people of the Mediterranean island of Sardinia constitute an example of genetic isolation, as demonstrated by the well-documented uniqueness of their gene frequencies (Modiano et al., 1986; Piazza et al., 1989a,b; Walter et al., 1991; Vona et al., 1992). Many studies have established numerous genetic, demographic and linguistic peculiarities of Sardinians (Griffo, 1988). Historical and geographical factors have contributed to the genetic differentiation of Sardinians from other Mediterranean populations. Although the earliest human settlements in Sardinia probably go back to the Upper Paleolithic (Sodaar et al., 19861, it is accepted that the substratum of the island’s present population was constituted during the “Nuragic” period (1500-238 B.C.). The series of conquests of the island that followed (Phoenicians, Carthaginians, Greeks, Romans, Vandals, Byzantines, Arabs, etc.) had a 0 1994 WILEY-LISS, INC

quite limited genetic effect except for some specific areas, mainly on the coast (Liliu, 1983; Piazza et al., 1985). This situation has persisted down to the present day; in spite of the immigration following the last World War, census data from 1971 indicate that more than 95% of the inhabitants of Sardinia were born there. Besides this general isolation from the oustide, many local Sardinian populations are isolated to a degree from other Sardinians, especially in some mountainous inland areas. In fact, geographically structured in the form of natural compartments (lowlands and highlands), the island population has been subdivided into “communes,” equiva-

Received June 9, 1993; accepted November 7,1993. Address reprint requests to Dr. Pedro Moral, Dept. Biologia Animal, Facultad de Biologia, Universidad de Barcelona, Ave. Diagonal 645,08028 Barcelona,Spain.

442

P. MORAL ET AL.

with both parents and all four grandparents born in the same city. Blood specimens were collected in the Centro Transfusionale della USL 2 of Alghero. Several fractions were mailed to the Istituto di Scienze Antropologiche dell'Universita di Sassari, to the Sezione di Scienze Antropologiche dell'universita di Cagliari, and to the Laboratory of Anthropology of the University of Barcelona, where a total of 20 classical polymorphic markers were determined. According to standard methods, the following blood group systems were examined: ABO, RH, LEWIS, KEL, MNS, and LUTHERAN. Red cell isozyme types were analyzed as described by Harris and Hopkinson (1976) with minor modifications. Esterase D (ESD, EC 3.1.1.1), 6-phosphogluconate dehydrogenase (PGC, EC 1.1.1.44), adenylate kinase (AK, EC 2.7.4.3), acid phosphatase (ACP1, EC 3.1.3.2),NADH diaphorase (DIA, EC 1.6.2.2) and phosphoglucomutase type (PGM, EC 2.7.5.1) tests were carried out by cellogel electrophoresis. Glyoxalase I (GLOI, EC 4.4.1.5) types were determined by starch gel electrophoresis, and PGMl subtypes by polyacrylamide gel electrophoresis. The plasma protein orosomucoid types, and transferrin (TF), group-specific component (GC) and alpha-lantitrypsin (PI) subtypes were determined by PAGIF, as described by Montiel et al. (1988) and Constans et al. (1981), respectively. Haptoglobin (HP) phenotypes were obtained by horizontal acrylamide electrophoresis, and the genetic variation of properdin factor B (BF) was observed using agarose gel electrophoresis and subsequent immunofixation with monospecific BF-antiserum from Atlantic Antibodies (Alper et al., 1972). Maximum likelihood estimates of allele frequencies were determined using the MAXLIK program described by Reed and Schull (1968). For each system, genetic differences between Alghero and other populations from Sardinia, continental Italy, and Spain, and the heterogeneity among these population series, were estimated as chiMATERIALS AND METHODS square, on the basis of gene frequency conThe sample of the Alghero population an- tingency tables. F,, values (Wright, 1978) alyzed consisted of 150 unrelated appar- were also computed as a measure of the gene ently healthy individuals, of both sexes, frequency variation, the significance of

lent to isolates, that have been in existence since the 9th century (Modiano et al., 1986; Griffo, 1988). The close negative correlation between altitude and presence of malaria, which was endemic until the eradication of paludism in 1946-1948 (Logan, 19531, is well known (Siniscalcoet al., 1966), and correlations between altitude and endogamy and consanguinity have also been described inside Sardinia (Moroni et al., 1972; Floris and Vona, 1980, 1984). All these factors have contributed to a remarkable local genetic variability as indicated by the heterogeneity found for some genetic markers inside Sardinia (Modiano et al., 1986; Ulizzi et al., 1988; Floris-Masala et al., 1989; Walter et al., 1989). This work deals with the genetic characterization of the Alghero population on the northwestern coast of Sardinia. The city of Alghero was set up by the Doria family at the beginning of the 10th century as a fortified harbour to guarantee overseas trade. Around the middle of the 13th century, the city was conquered by the Kingdom of Aragon in Spain. King Pedro of Aragon ejected the Sardinians from the city and founded a Catalonian colony. Persistent traces of Catalan culture survived the return of the Sardinians at the beginning of the 17th century, after the Aragonese domination (Brigaglia et al., 1982). The Catalan language is used even today in Alghero. This cultural distinctiveness of Alghero led us to ask whether it may be associated with a similar genetic differentiation. The use of a language by a population may be indicative of a common origin when it is associated to a specific genetic identity. But, in other cases, it may simply be a cultural trait imposed by a politically powerful minority without any substantial effect on the genetic structure of the population itself. By analyzing the distribution of twenty gene polymorphisms in the Alghero population, we undertook to evaluate its biological relationships with Sardinians and Catalonians.

CCD.EE CCD.Ee CCD.ee CcD.EE CcD.Ee CcD.ee ccD.EE ccD.Ee ccD.ee CCddEE CCddEe CCddee CcddEE CcddEe Ccddee ccddEE ccddEe ccddee Total

RH system

0 Total

B A1B A2B

A2

A1

ABO system

Phenotvue

7 105

-

1 -

-

15 36 1

-

1 44

34 2 11 3 2 57 109

Obs.

5.74

0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

0.99 46.34 0.12 11.35 34.86 0.65 4.13 0.82

0.01

33.92 3.60 12.44 3.10 0.38 55.56

Exu.

0.209)

0.2332 0.033

0.000 2 0.000 0.000 t 0.000 0.000 -t 0.000

0.007t 0.007 0.665 0.033 0.079 i 0.019 0.0162 0.017

=

0.1872 0.028 0.023i 0.011 0.076i 0.018 0.714i 0.032

(xZ1= 3.73,~ = 0.053)

CDE CDe cDE cDe CdE Cde cdE cde

(xZ1= 1.58,p

ABO*Al ABO*A2 ABO*B ABo*o

Allele frequencies

Lu(a+b Lu(a+ b + Lu(a- b + 1 Total

LUTHERAN system

MS MSs Ms MNS MNSs MNS NS NSs Ns Total

MNSs system

Total

K+kK+k+ K-k+

KELL system

Le(a+b- 1 Le(a- b+ 1 Le(a-b-) Le(a+ b+ Total

LEWIS system

Phenotype

79 86

2

5

13 12 23 2 8 7 103

14

12 12

10 91 101

-

17 66 16 1 100

Obs.'

TABLE 1. Phenotype and allele frequency distribution in Alghero population

0.42 11.17 74.41

7.86 18.26 10.60 7.87 24.20 17.48 1.97 7.54 7.21

0.25 9.50 91.25

Exu.

0.005)

(continued)

0.070f 0.019 0.930i 0.019

=

0.268i 0.035 0.3382 0.038 0.151i 0.029 0.243& 0.035

0.049f 0.015 0.951f 0.015

0.400-C 0.046 0.6002 0.046

( X Z 5 = 16.67, p

LU*A LU*B

MS Ms NS Ns

KEL*k

KEL*K

LE*le LE*Le

Allele frequencies

1 2-1 2 Total

GLOI system

2-1 2 Total

1

PGMl system

2-1 2 Total

1

AK system

A AC C Total

6PGD system

1 2-1 2 3-1' Total

ESD system

Phenotype

23 52 25 100

88 38 5 131

141

-

140 1

138

-

133 5

117 21 2 1 141

Obs.

24.01 49.98 26.01

87.40 39.20 4.40

140.01 0.99 0.00

133.05 4.91 0.04

116.20 22.71 1.11 0.00

Exp.

0.996 t 0.003 0.004 k 0.003

0.982 2 0.008 0.018 t 0.008

0,908 t 0.017 0.089 -t 0.017 0.003 f 0.003 0.84, p = 0.358)

(x2, =

GLOI*1 GLOI*2

0.490 t 0.035 0.510 k 0.035 0 . 1 6 , ~= 0.686)

0.817 t 0.024 0.183 2 0.024 (xZ1 = 0 . 1 2 , ~= 0.725)

PGMl"1 PGM1*2

AK*1 AK*2

PGD*A PGDT

(xZ1 =

ESD"1 ESD"2 ESD*3

Allele frequencies

1F-2F 1s-2F 2F 1F-2S 1s-2s 2s 2F-2S Total

1s

1F 1F-1S

PGMl subtypes

2- 1 2 Total

1

DIA system

A AE3 B AC BC C Total

ACPl system

Phenotype

70

__

3 1 2 20

-

3 6 35

136

-

133 3

1 116

-

1 45 68 1

Obs2

0.70 9.90 35.01 0.50 3.53 0.09 2.20 15.54 1.73 0.79

133.02 2.96 0.02

4.97 37.45 70.61 0.62 2.33 0.02

Exp.

TABLE 1. Phenotype and allele frequency distribution in Alghero population (continued)

0.207 f 0.027 0.780 t 0.027 0.013 f 0.007

PGM"1F PGM"1S PGM"2F PGM*2S

DIA"1 DIA"2

2 5

0.006 0.006

0.100 5 0.025 0.707 f 0.038 0.036 t 0.016 0.157 t 0.031

0.989 0.011

(xZ1 = 5 . 1 0 , ~= 0.024)

ACPI*A ACPI*B ACPI*C

Allele frequencies

148

-

1 8 1

-

18 3 2 7

5

61 42

4 24 43 15 42 16 144

20 62 50 132

~

~~

65.55 37.27 5-30 16.65 4.73 1.06 5.99 1.70 0.76 0.14 5.99 1.70 0.76 0.27 0.14

3.83 24.81 40.11 14.52 46.97 13.75

19.71 62.59 49.70

'Not included for testing Hardy-Weinbergequilibrium. 'Oh. = observed;Exp. = expected.

M1 M1M2 M2 M1M3 M2M3 M3 M1M4 M2M4 M3M4 M4 M1S M2S M3S M4S S Total

PI system

2-1F 2-1s 2 total

1s

1F 1F-1S

GC system

1 2-1 2 Total

HP system

=

0.551)

0.666 2 0.027 0.189 t 0.023 0.085 ? 0.016 0.030 ? 0.010 0.030 f 0.010

0.765)

(xZz= 1.19, p

PI*M1 PI*M2 PI*M3 PI*M4 PI*S

=

0.163 t 0.022 0.528 ? 0.029 0.309 f 0.027

0.386 t 0.030 0.614 -t 0.030 0.01, p = 0.914)

(xZ3 = 1.15,p

GC*lF GC*lS Gc*2

(xZ1=

HP*1 HP*2

F FS S FF1 SF1 F1 FS0,7 SS0.7 FlS0.7 S0.7 Total

BF system

c1c2 c2 C1C3 C2C3 c3 Total

c1

TF system

F FS S Total

ORMl system

147

-

7 49 33 19 29 7

140

-

73 48 8 9 2

40 58 20 118

11.43 41.00 36.75 12.29 31.00 6.54 0.84 1.50 0.63 0.02

73.59 47.85 7.78 7.98 2.59 0.21

40.35 57.30 20.35

*

0.725 ? 0.077 0.236 2 0.025 0.039 0.012

(xz3

BF*F BF*S BF"F1 BF*SO.7

=

3.99,p

=

0.262)

*

0.279 5 0.026 0.500 ? 0.029 0.211 2 0.024 0.010 0.006

(xZ2 = 0 . 3 7 , ~= 0.831)

TF*C1 TF*C2 TF*C3

ORMl*F 0.585 ? 0.032 ORMl*S = 0 . 0 2 ,0.415 ~= 0.895) i 0.032

446

P. MORAL ET AL

which was determined by Workman and Niswander's (1970) method. To estimate the global genetic differences between populations, an analysis of genetic distances was carried out using a standardised measure of the variance of gene frequencies according to the coancestry coefficient of Reynolds et al. (1983). Standard errors were estimated by the bootstrap resampling technique (Efron, 1982). From genetic distances, a genetic tree relating populations was constructed using the neighborjoining algorithm (Saitou and Nei, 1987). Genetic relationships among populations were also measured through principal-component analysis. RESULTS Data from Alghero

Phenotype and gene frequencies for the 20 polymorphic markers in Alghero population are shown in Table 1. Due to the relatively small number of individuals examined for some systems, expected frequencies were recalculated using Levene's (1949) formula for small samples. However, since the differences between the two estimates were too small, the numbers given in Table 1 are those obtained through standard methods. When possible, the validity of Hardy-Weinberg equilibrium was evaluated by chisquare test. Phenotype distributions were in equilibrium in almost all cases, but two of them showed significant deviations, one at 5% (ACPl system) and one at 1%(MNSs system) level. However 0.7 and 0.1, respectively, of these deviations were expected by pure chance. To rule out the possible effect of small sample sizes on these deviations, the analysis was repeated by calculating exact probabilities (analogous to Fisher's exact test for 2 x 2 contingency tables) with the program BIOSYS (Swofford and Selander, 1981). According to these values, the ACPl phenotype distribution, which shows an excess of AB heterozygotes, does not appear to deviate substantially from the expected H.W. proportions (exact probability: p = 0.275). For the MNSs system, the deviation can be explained by the particular phenotype distribution of Ss blood group (x21 = 13.44, p < 0.01%; exact probability

less than 0.01%),whereas the MN group distribution shows an excellent agreement with the expected H.W. proportions (x21 = 0 . 0 8 , ~= 0.78). Allele frequencies found in Alghero are, in general, inside the range of Sardinian variation, sharing those Sardinian peculiarities not matched by any other population in the Mediterranean region (for a comparison with the available frequencies in Western Mediterranean, see Piazza et al., 1989a, Moral, 1986; Ulizzi et al., 1988; Walter et al., 1989; Vona et al., 1992). As to blood groups, Alghero shows low ABO*A and RH*cde frequencies, and high ABO*O, RH*CDe and MN*M values, characteristic of Sardinian populations. The frequency of LUT*A allele in Alghero is higher than both Sardinians and other neighboring groups. For KJ3L and LEWIS systems, no difference was found either from Sardinia or Western Mediterranean. Concerning enzyme frequencies, Alghero is characterized inside Sardinia by high ACP1"B and low ACP1"C values, whereas ESD, PGD, DIA, PGMl, and GLOI frequencies are comparable to those in other Sardinan samples. In comparison with other Western Mediterranean regions, Alghero shows a very high PGM*1 allele frequency, also characteristic of Sardinian populations. As for protein polymorphisms, Alghero, like other Sardinian populations, is characterized by a very high BF*F1 frequency and slightly high GC"1F and TF*C2 gene values. In addition, the Algheran PI*S allele frequency is of the same order of magnitude as that found in Sardinia, but markedly lower than the values characteristic of Spanish populations. The ORMl distribution in Alghero is similar to those described in other Italian and Spanish samples (Sandiumenge et al., 1993). For this marker, data were not available for other Sardinian samples. Comparisons between populations In order to analyze the genetic position of

the Alghero population comparatively, data were collected from other historic and geographically related populations (Table 2). To take into account the possible variation inside the main groups under the scope of this study (Sardinia and Catalonia), we included

GENETIC DATA ON ALGHERO POPULATION

447

TABLE 2. Populations and samples PoDulation Alghero Sardina-North Sardinia-Central Sardinia-South Catalonia-North Catalonia-South Baleares Spain-Northwest Italy-North Italy-Central Italy-South Sicilia

SamDles Alghero city Sassari district Nuoro district Cagliari district France-Catalogne Spain-Catalunya Balearic Islands Galicia Lombardia and Emilia Lazio and Abruzzi Calabria and Puglia Sicily Island

three samples from each one, in representation of the different geographical areas, even though this meant a slight reduction of the genetic information available. Furthermore, to enlarge the population context, we collected samples from Italy and the northwestern part of the Iberian Peninsula. Populations selected are given in Table 2, with a specific population name and references to geographical areas where the samples were collected. Data were obtained for a total of 15 genetic systems and 63 alleles. Information for LEWIS, LUTHERAN, AK, DIA, PGM-subtypes, and ORMl was not available for all populations selected. Most of the data collected come, either as original or as compiled data, from Piazza et al., (1989a,b), Walter et al., (1989), Floris et al. (1986), Moral, (1986), Moral et al. (1986), Miguel and Petitpierre, (1989, 1990), Panadero, (19881, and Aluja (1987). A first approach to the interpopulation heterogeneity was carried out by contingency chi-square test and Wright's F statistics. Table 3 gives the chi-square heterogeneity values both between Alghero and the rest of populations and inside the three main regions considered: Sardinia (SarHET), Catalonia (CatHET)and Italy (ItaHET).These values reemphasize the Alghero population's distinctive similarity to other Sardinian groups in RH, PGM and BF, three markers characteristic of Sardinian populations. It is also remarkable that the Alghero population shows a clear differentiation for PI polymorphism from Catalonian populations where, as in other areas of the Iberian Peninsula, the PI*S allele shows significantly higher frequencies than in other European

Abbreviation

ALG SAS NU0 CAG CTN CTS BAL GAL ITN ITC ITS SIC

areas. On the other hand, Alghero differs significantly from both Sardinian and nonSardinian groups for MNSs and ACPl frequency distributions. Within the three geographical regions, significant heterogeneity is found for more than half the markers considered. We examined the extent of inter- and intraregion genetic diversity using Wright's FSTstatistics tested by chi-square. A hierarchical analysis of population differentiation was performed grouping the populations in Table 2 into three regions: Sardinia, the Iberian Peninsula, and Italy. F values for ABO and RH systems can only be considered as approximate, since the gene numbers were roughly estimated from gene frequencies. Some of the markers have very small negative F values because the sampling variance (Wright, 1978) was subtracted to correct for sampling bias. Table 4 gives F p R , FRT, and F, values, which distinguish the total interpopulation differentiation (F,) into two components: the gene diversity among populations within regions ( F p R ) and the diversity among regions (FRT). All markers are significantly heterogenous across populations at the 1%level, except TF at the 5% level (see F, values in Table 4). The markers with the highest F, values (>0.010) are BF, MN, MNSs, RH, KEL and PGM, whereas GC and TF show the lowest. It is worth mentioning that most markers (ten out of fifteen) show higher interregion than intraregion heterogeneities ( F R T > FpR). Further, the average F-statistics combined across loci show that most genetic differentiation among the populations considered here can be explained as diversity among

448

P. MORAL ET A L

regions rather than as heterogeneity within regions. Genetic distances Once the usefulness of these markers in distinguishing among Sardinians, Catalonians and Italians was established, we carried out a genetic distance analysis in order to investigate the genetic relationships between Alghero and these populations. Table 5 shows the pairwise genetic distances and the bootstrap errors of the estimates. The lowest genetic distances correspond to Spanish-Spanish and Italian-Italian comparisons, whereas the highest ones appear between Nuoro (Central Sardinia) and the rest of the populations. In general, these distance values may be grouped into three main classes. The first consists of the lowest values, where all non-Sardinian vs. nonSardinian comparisons were included. The highest distance group comprises the nonSardinian vs. Sardinian genetic distances, and a third group of intermediate values includes the distances between the four Sardinian populations. In other words, from the genetic distances, it clearly appears that the main genetic differentiation is between Sardinians and non-Sardinians, reflecting within Sardinia a high variability, especially reflected in the outlying position of the Nuoro district sample. Inside Sardinia, Alghero shows the smallest genetic distances from Sassari and Cagliari, whereas the differentiation from Nuoro is some three to four times greater. The distances between Alghero and both Spanish and Italian populations are approximately of the same order of magnitude, and equivalent t o those shown by the other two Sardinian coastal samples (Cagliari and Sassari) from those populations. As a graphical description of the distance matrix in Table 5, a neighbor-joining tree was constructed, as presented in Figure 1. This method, which does not assume a constant evolutionary rate, finds the shortest tree representing the genetic distances among populations. The tree indicates that the greatest degree of divergence is between Sardinians and non-Sardinians, providing support for the hypothesis that today, the Alghero population is much closer geneti-

GENETIC DATA ON ALGHERO POPULATION

449

TABLE 4. F-statistics for interpopulation and inter-region variability Locus

FW'

FRTZ

Fm3

Chi-sauare

d.f.*

ABO ACPl BF ESD GC GLOI HP KELL MN MNSs PGD PGM PI RH TF Average

,002 .007

.004 -.001 ,032 ,000 .001 ,001 ,002

,006 .006 .040 ,003 ,001

639.4*** 245.4*** 1080.96*** 154.0*** 71.7.k"" 137.6*** 47.7*** 750.8*** 1156.8*** 1542.0*** 45.5*** 265.7*** 634.8*** 13415.8*** 61.4*

33 22 33 22 33 11 11

.008

,003 ,000 ,006 ,001 .015 ,008 ,009 ,005 .002 ,003 ,003 ,000 .005

,007

.003 .015 ,027 ,023 ,003 ,010

.ooo

.019 ,014 -.001 ,008 ,005 .a20 ,001

,008

,022 ,001 ,013

,008

11

11 33 11 11

55 77 44

***,and * indicate ,001 and .05 significance, respectively. Fpn. gene diversity among populations ( P ) within regions (R). 'FRT:gene diversity among regions. Fm: total gene diversity among populations. 4d.f. = degree of freedom.

'

TABLE 5. Genetic distances and bootstrap standard errors (X1000)

CAGLIARI NUORO SASSARI BALEARES N CATAL.

S CATAL. GALICIA C ITALY N ITALY S ITALY

SICILY

ALG.

CAG.

6.88 (.196)' 20.19 (.557) 5.12 (.127) 12.97 (.394) 16.76 (506) 17.51 (517) 21.73 (.599) 15.12 (.427) 21.65 (.647) 16.54 (.503) 16.32 (.442)

15.35 (568) 5.25 (.154) 19.39 (.547) 17.98 (.500) 21.46 (.641) 24.99 (.570) 17.38 (.488) 21.74 (.587) 17.87 (511) 16.37 (.414)

NU0

SAS.

BAL.

9.28 (.234) 36.02 (.986) 40.35 (.986) 35.41 (.918) 47.59 (1.117) 29.41 (373) 35.74 (.946) 36.23 (1.162) 30.76 (.945)

20.51 (.520) 23.29 (.584) 22.76 c.568) 33.21 (.859) 17.97 (.561) 27.32 (.906) 22.66 (.730) 20.81 (.663)

2.77 (.093) 2.08 (.063) 5.45 (.175) 3.83 (.065) 7.07 (.239) 9.64 (.176) 5.76 (.lo81

N CT.

S CT.

GAL.

C IT.

NIT.

SIT.

6.03 (.189) 2.27 (.957)

3.84 (.146)

1.99 (.080)

3.77 (.112) 4.19 (.140) 5.71 (.174) 6.56 (.171) 5.81 (.129)

5.66 (.197) 3.00 (.060) 5.10 (.231) 8.49 (207)

5.02 (.lo41

8.74 (.229) 6.17 (.197) 12.05 (.273) 7.28 (.197)

3.23 (.122) 3.52 (.120) 1.42 (.040)

Figures in parentheses indicate the S.E. of the distance estimates.

cally to Sardinians than to Catalan or Italian populations. The branch length leading to the Nuoro population emphasizes the outlying genetic position of this Central Sardinian sample. Principal components

Genetic variation among populations was also measured through principal-component analysis. The first three components explain 31.3%, 20.3% and 13.5%, respectively

(65.1% accumulated) of the total variance. Although they include information from all genes, the gene contribution to these components is different, as shown by the correlations of the original gene frequencies with the factors. In particular, the alleles BF*Fl, RH*CDe, RH*cde, Al30*0,MN*M, GC*lF, BF*F, PGM1*1 and PI*M2 are highly correlated ( r > 0.8) to the first component; ACPl*B, ESD"2, RH*Cde, GLOI"1, and GC*lS gene frequencies are particularly as-

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tion of the Alghero population through the frequencies of the 61 alleles identified, and supplies new genetic data on Sardinian genetic variation. All phenotype distributions showed good agreement with Hardy-Weinberg expectations except the MNSs system. There is no reason to think that the deviation of the MNSs polymorphism from Hardy-Weinberg equilibrium is due t o anything other than chance. Algheran allele frequencies showed some of the distinctive features that set Sardinians apart from other Mediterranean and world populations: very high frequencies of RH*CDe, MN*M, PGM1*1 and BF*Fl alleles, and a very low value of RH*cde haplotype. However, remarkable differences from other Sardinian groups have been detected, especially for MNSs and ACPl systems, due mainly to high MNS*MS and ACPl*B, and low ACPl*C values in Alghero. These differences could be explained taking into account the high variability of these markers in Sardinia (Ulizzi et al., 1988; Vona et al., 1992). GAL The ACPl*C allele frequency in Alghero, Fig. 1. Neighbor-joining tree relating populations. one of the lowest in Sardinia, is in agreeAbbreviations as in Table 2. ment with the positive correlation described between this gene and altitude (Palmarino sociated ( r > 0.7) with the second, while the et al., 1975). Comparisons with other populations third component is mainly correlated (r > 0.7) with AJ3O*B, HP*l and PGD*A al- based on most of the markers examined and leles. Figure 2 shows component-l scores measured through genetic distances and plotted against scores for components 2 and principal-component analysis mainly show 3. The distribution due to the first compo- the clear separation of Alghero together nent underlines the main population subdi- with other Sardinian populations from Catvision between Sardinians and the rest, alonian and Italian groups. Within the patwhereas the second shows the separation tern of genetic variability in Sardinia, our between Spanish and Italians as well as the results on Alghero fit very well to a Sardinremarkable genetic differentiation inside ian coastal population, as indicated by geSardinia. This second component also re- netic distances. This could be attributed to veals a particular position for Alghero, similar environmental conditions in the Sarwhich tends to detach itself both from the dinian coast. However, although it was diffiSardinian samples of Cagliari and Sassari cult to exclude the influence of selection and from Catalonian populations. The third completely, the data on the possible adapcomponent contributes to the separation be- tive role of several genetic traits in Sardinia tween Italian samples, showing a greater (Piazza et al., 1985; Ulizzi et al., 1988) and proximity between Alghero and these popu- the number of genetic systems involved seem to guarantee that the population relalations than from Catalonian groups. tionships mainly reflect the genetic history DISCUSSION of the populations, in terms of migrations The analysis of the twenty classical poly- and local population diversifications rather morphisms presented here constitutes the than adaptative effects. In this way, the sinfirst approach to the genetic characteriza- gular position of the Nuoro district popula-

NU0

GENETIC DATA ON ALGHERO POPULATION

45 1

Second Principal Component NU0

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T

GAL

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Fig. 2. Principal-component analysis. a: First component plotted against the second one. b: First component plotted against the third. Abbreviations as in Table 2.

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tion, as displayed especially by the neighbor-joining tree, could be explained by a higher geographical and historical isolation than in the peripheral areas of the island. As for the relationships with Catalonian groups, the fact that genetic distances between Alghero and these groups are slightly smaller than those between Catalonians and other Sardinian samples, and the particular separation of Alghero both from Sardinia and Catalonia in the two first-principal-component displays, could indicate that Alghero is slightly closer to Catalonia than other Sardinian groups. This could be explained by a possible gene flow during the Aragonese domination, which should be tested by further studies. However, the closer genetic affinities (three to four times greater) with Sardinian populations indicate that the possible Catalan gene flow into Alghero was probably quite limited. In summary, the genetic markers examined in the present paper do not support any interpretation of the cultural affinities a t present between Alghero and Catalonia, in terms of genetic proximity. This lack of fit between the linguistic evidence and the genetic evidence makes Alghero an exception to the usually important parallelism between linguistics and genetics as it has been shown in current debates about language, genes, and human history (Cavalli-Sforza et al., 1992, 1993; Barbujani and Sokal, 1990). The Catalan language in the Alghero population would thus be interpreted rather as an example of language replacement due to the colonialism of the Kingdom of Aragon in the 13th century than as indication of genetic influence. ACKNOWLEDGMENTS We thank Robin Rycroft for correcting the English manuscript. LITERATURE CITED Alper CA, Boenisch T, and Watson L (1972) Genetic polymorphism in human glycine-rich-beta-glycoprotein. J. Exp. Med. 135:68-80. Aluja MP (1987) Estudi de diversos polimorfismes bioquimics a la comarca de la Cerdanya. PhD Thesis, Universitat Autonoma Barcelona, Barcelona. Barbujani G, and Sokal RR (1990) Zones of sharp genetic change in Europe are also linguistic boundaries. Proc. Natl. Acad. Sci. USA87:181f%1819.

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