GENETICAL-DEMOGRAPHIC DATA FROM TWO AMAZONIAN POPULATIONS COMPOSED OF DESCENDANTS OF AFRICAN SLAVES : PACOVAL AND CURIAU

The Amazon region of Brazil includes communities founded by escaped slaves, some of which still remain relatively isolated. We studied two such Afro-Brazilian communities (Pacoval and Curiau), in the rural area of Alenquer, Pará, and in the metropolitan region of Macapá, Amapá, respectively. Among 12 blood loci, alleles considered as markers of African ancestry, such as HBB*S, HBB*C, TF*D1, HP*2M, ABO*B, RH*D-, and CA2*2 were found at frequencies that are expected for populations with a predominantly African origin. Estimates of interethnic admixture indicated that the degree of the African component in Curiau (74%) is higher than that of Pacoval (44%); an Amerindian contribution was not detected in Curiau. Estimated values of African ancestry fit well with the degree of isolation and mobility of the communities. Pacoval exhibited a high proportion of immigrants among the parents and grandparents of the individuals studied, whereas persons living in Curiau exhibited a low level of mobility, despite its location in the metropolitan area of Macapá city, suggesting a relatively strong barrier against the interethnic admixture in this population. In addition, analysis of genetic data in a sub-sample consisting of individuals whose parents and grandparents were born in the study site, and that probably represents the populations two generations ago, indicated that gene flow from non-black people is not a recent event in both populations. Laboratório de Genética Humana e Médica, Universidade Federal do Pará, 66075-970 Belém, Pará, Brasil. Send correspondence to J.F.G. Caixa Postal 8615. Fax: +55-91-249-0373. E-mail: jguerrei@canal13.com.br MCT-PR/CNPq. Museu Paraense Emilio Goeldi, Departamento de Ciências Humanas, Belém, PA, Brasil. 164 Guerreiro et al. immunological tests that have been previously described or referenced (Santos et al., 1983; Schneider et al., 1987; Guerreiro et al., 1989). Allele frequencies were estimated by the maximum likelihood method using the MAXLIK program developed by Reed and Schull (1968), and the degree of racial admixture was estimated through the maximum-likelihood method of Krieger et al. (1965), using the GENIOC program. RESULTS AND DISCUSSION


INTRODUCTION
The slave trade brought at least 53,000 black Africans to the Amazon region.They were imported directly from Africa by the General Company of Great Pará and Maranhão, private individuals, as well as indirectly through internal trade from other Brazilian regions such as Maranhão, Bahia, Pernambuco and Rio de Janeiro (Vergolino-Henry and Figueiredo, 1990).Historical records about the slave trade to the northern region indicate that most Africans were brought from Angola, Mozambique, Kenya and Tanzania, whereas a smaller number was brought from Guine-Bissau and Cape Verde.In addition, there are records of a small number of slaves from French Guyana and Surinam introduced to the region (State of Amapá and Marajó Archipelago).Some were victims of the illegal slave trade, while others came as fugitives (Curtin, 1969;Vergolino-Henry and Figueiredo, 1990).
Following the example of other Brazilian regions and South American countries, several communities named mocambos or quilombos were founded in the Amazon region by escaped slaves, particularly in the State of Pará, a point of entry of African slaves to the region.Many of these communities still remain relatively isolated, and much of their identity is preserved.
Several genetic studies have been performed in populations descended from Africans in the Amazon region of Brazil and Venezuela evaluating the level of isolation and mobility, and quantifying the gene contribution from non-blacks among them.In this study we report genetical (12 blood genetic systems), genetical-demographic (estimates of interethnic admixture) and demographic (migration) data from two populations of predominantly African ancestry in the Brazilian Amazon region.

MATERIAL AND METHODS
The mocambo of Pacoval, formed by fugitive slaves from farms of the neighboring municipality of Santarém, is located in the rural area of the county of Alenquer, along the right margin of the Curuá River, in the northwestern region of the State of Pará, at about 2 o S, 55 o W. Blood samples from 166 individuals were collected (63% females, ages varying from seven to 86 years).
Curiau is located in the metropolitan region of Macapá, capital of the State of Amapá, northern Brazil, at about 0 o , 51 o W. From 1770 Curiau constituted a point of convergence of escaped slaves from the region, including slaves from Suriname and French Guyana (Muggiati, 1971).One hundred and forty-five individuals (49% males, ages varying from four to 84 years) were sampled.
Allele frequencies were estimated by the maximum likelihood method using the MAXLIK program developed by Reed and Schull (1968), and the degree of racial admixture was estimated through the maximum-likelihood method of Krieger et al. (1965), using the GENIOC program.

Blood polymorphisms
All phenotype and allele frequencies were in Hardy-Weinberg equilibrium in Curiau, whereas in Pacoval the HP and CP loci showed significant deviations from equilibrium (Tables I and II).Some alleles considered to be markers of African ancestry (HBB*S, HBB*C, TF*D1, HP*2M, ABO*B, RH*D-, and CA2*2) were found at frequencies that are expected for populations with a predominantly African origin.Some unusual findings such as high frequencies of alleles ABO*B and HBB*C in Curiau, and allele RH*D in both populations, which are higher than average frequencies estimated for black African populations, may be attributed to microevolutionary factors (genetic drift and/or founder effect).In addition, the presence of the allele HBB*C in the Curiau sample (0.06) may also be attributed to the contribution of people from French Guyana to the formation of this population, since among the slaves brought to this country about 74% of them were from Senegambia and Guinea in West Africa (Curtin, 1969), where the HBB*C allele is relatively common.HBB*C was not found in Pacoval, nor in Trombetas or Cametá, two other communities of African descent in the Amazon region of Brazil (Schneider et al., 1987;Bortolini et al., 1992), but polymorphic frequencies were found in Curiepe and Panaquire, two Afro-Venezuelan populations (Bortolini et al., 1992;Castro de Guerra et al., 1996), and in various urban populations from the Brazilian Amazon characterized by a white + Amerindian + African contribution (Ayres et al., 1976;Santos et al., 1983Santos et al., , 1996;;Cayres et al., 1991).Thus, these findings indicate that the contribution of people from West Africa to the formation of the Amazonian populations was heterogeneous.

Interethnic admixture
Estimates of interethnic admixture obtained for the two populations (Table III) indicate that the degree of black component in Curiau is significantly higher than in Pacoval.These results fit well with the apparent morphological classification of the individuals sample, which indicated 14% individuals with mixed ancestry in Curiau, and 49% in Pacoval.Interethnic admixture values are also in accordance with the level of isolation and mobility of the two populations.The proportion of immigrants among the parents and grandparents of the individuals sampled in Pacoval is high, whereas Curiau, despite its location in the metropolitan area of Macapá city, exhibits a low level of mobility (Table IV), suggesting a relatively strong barrier against interethnic admixture in this population.The proportion of African ancestry obtained for Curiau is the highest reported among communities composed of descendants of black Africans thus far studied in the Amazon region (Table III).In addition, Curiau is the first Amazonian population where an Amerindian contribution was not detected.
In order to evaluate whether admixture with Caucasians and Amerindians has occurred in the last two generations, a subsample of subjects whose parents and grandparents were born in the study site was analyzed.There where no significant differences (Tables I and II) with respect to the total sample (Pacoval: χ 2 = 5.95, d.f.= 12, P = 0.91; Curiau: χ 2 = 1.00, d.f.= 12, P = 1.00), indicating that admixture with non-blacks is not a recent event in both communities.
In summary, the genetic variability observed in Pacoval and Curiau is consistent with the African origin of the populations, with some degrees of local differentiation and admixture with people of Caucasian and/or Amerindian ancestry.In addition, the presence of people from West Africa among the African slaves brought to the Amazon region was well characterized by the occurrence of the allele HBB*C in Curiau.

AKNOWLEDGMENTS
We are grateful to the communities studied for their collaboration, and to Roberto A.N. Madeiro, Vilson C. Monteiro, Edson S. Abrahim Filho and Hailton O. Monteiro for assistance with the blood sample collection.This work was supported by UFPA and CNPq.

Table I -
Observed phenotype and allele frequencies in Pacoval and its native subsample 1 .

Table II -
Observed phenotype and allele frequencies in Curiau and its native subsample 1 .
1Native subsample: subjects whose parents and grandparents were born in the study site.