Genetic characterization of the Cayapa Indians of Ecuador and their genetic relationships to other Native American populations

Human Biology, Apr 1994 by Rickards, O, Tartaglia, M, Martinez-Labarga, C, De Stefano, G F

The Cayapa, who define themselves as Chachi, live in the tropical forest area of Esmeraldas Province (northwestern Ecuador), along the Cayapas River and its tributaries, and in the towns of Muisne and Quininde (Figure 1). (Figure 1 omitted). According to the latest census of the population (1978), the Cayapa number about 3600 individuals, with 64% settled in the Cayapas River area (Carrasco 1988).

The Cayapa speak a language that was included by Loukotka (1968) in the Chibcha linguistic group of the northern division of the Andean tribe languages. Greenberg (1987) classified the Cayapa language as belonging to the Paezan linguistic group of the Chibchan-Paezan branch of the Amerind family, which is one of the three major groups in which native American languages are subdivided. This tripartite subdivision (Amerind, Na-Dene, and Eskimo-Aleut) potentially corresponds to the three waves of migration of Asiatic people, who are supposed to have populated the Americas (Williams et al. 1985; Greenberg et al. 1986), even though Schanfield (1992) and Horai et al. (1993) recently proposed at least two distinct migrations of Amerind-speaking groups.

The origin of the Cayapa, who very likely first inhabited Ecuador (Barriga Lopez 1987), is extremely controversial. Some researchers, on the basis of both oral traditions and archeological, ethnic, and historical clues, state that the Cayapa migrated from Ibarra, situated in the Andean Highlands in northern Ecuador (see Figure 1), to the forest area, where they live nowadays, because of the Incas' expansion (fifteenth century) and, later, the Spanish invasion (sixteenth century) (Barrett 1925; DeBoer 1987). Other researchers suggest, on the basis of linguistic evidence, an Amazonian origin of the Cayapa and of other Ecuadorian Indian populations, namely, the Colorado and the Caranqui. More precisely, the Cayapa seem to have migrated along the Napo River to the Andean Highlands and from there to the coast (Barriga Lopez 1987; Carrasco 1988). This hypothesis is also supported by the high adaptation of the Cayapa to the tropical forest environment (Moreno Navarro 1979).

The Cayapa's subsistence economy is based on agriculture, hunting, and fishing. The Cayapa are severely stressed by various infectious diseases, such as malaria, tuberculosis, intestinal parasitosis, and onchocerciasis (Guderian et al. 1983; Stinson 1989; De Stefano, unpublished data, 1990). The matrimonial pattern is exogamous within the Cayapa community, and marriages with the neighboring black population, which also lives along the Cayapas River, are highly discouraged. No genetic admixture between the two groups seems to occur, nor is there admixture between the Cayapa and other Indian groups of Ecuador (Erickson et al. 1966; Stinson 1989).

At present, the only genetic data on the Cayapa population is the work of Matson et al. (1966a) on haptoglobin (HP), transferrin (TF), hemoglobin, and some blood group systems. Significant advances in protein electrophoresis and questions about the origin and relationships between indigenous peoples of the Americas have arisen since then. Therefore the objectives of the present study are (1) to analyze the distribution of some red cell enzyme polymorphisms in the Cayapa population and to verify the degree of their genetic isolation, (2) to study the genetic relationships among the Cayapa and other Amerind tribes of South and Central America, taking into account their linguistic subdivision and geographic position, and (3) to extend this analysis to other native populations.

MATERIALS AND METHODS

One-hundred sixty-four adult individuals of both sexes, healthy, and apparently not related, who listed their ancestry as Cayapa, were sampled along the Cayapas River. Blood specimens were drawn by G.F. De Stefano by venipuncture, put into sterile tubes containing ACD (acid-citrate-dextrose) as an anticoagulant, and kept at 4degC until they were transported to Rome, within one week. Hemolysates were prepared after three washes with cold PBS (phosphate-buffered saline) solution, divided into small aliquots, and stored at -80degC until analyzed.

We performed electrophoretic typings on cellulose acetate strips (Cellogel, Chemetron Labometrics, Milan, Italy) according to the method of Harris and Hopkinson (1976) and modified by Chemetron Labometrics; this procedure was used to type for acid phosphatase 1 (ACP1), adenosine deaminase (ADA), esterase D (ESD), phosphogluconate dehydrogenase (PGD), phosphoglucomutase 2 (PGM2), and superoxide dismutase A (SODA). We used the method of Spielmann and Kuhnl (1982) to type for adenylate kinase 1 (AK1), the method of Noppinger and Morrison (1981) to type for carbonic anhydrase II (CA2), and the method of Meera Khan and Doppert (1976) to type for glyoxalase

(GLO1). Glucose-6-phosphate dehydrogenase (G6PD) phenotypes were determined in both tris-EDTA-borate (TBE; Betke et al. 1967) and phosphate (Fildes and Parr 1963) buffer systems, and hemoglobin (HB) was typed together with G6PD using TBE buffer. Phosphoglucomutase 1 (PGM1) subtyping was carried out by isoelectric focusing (IEF) on thin-layer polyacrylamide gel (0.3 mm thick) according to the method of Kuhnl and Spielmann (1978) with minor modifications. PGM1 thermostability phenotypes were determined by combining the IEF procedure with the heat denaturation technique described by Scozzari et al. (1981).