Using mitochondrial and nuclear markers to evaluate the degree of genetic cohesion among Echinococcus populations.
Based on the distinctiveness of their mitochondrial haplotypes and other biological features, several recent publications have proposed that some Echinococcus granulosus strains should be regarded as separate species. However, the genetic cohesion of these species has not been extensively evaluated using nuclear markers. We assess the degree of polymorphism of the partial mitochondrial cox1 (366bp), the nuclear mdh (214bp) and EgAgB4 (281-283bp) genes of E. granulosus sensu lato isolates collected from areas where different strains occur sympatrically. Five distinct mitochondrial haplotypes were determined by direct sequencing (G1, G2, G5, G6 and G7). The mdh genotypes were first screened by SSCP: three alleles were identified (Md1-Md3), which were further confirmed by nucleotide sequencing. For EgAgB4, which was analysed by direct sequencing the PCR products, two groups of sequences were found: EgAgB4-1 and EgAgB4-2. No haplotype-specific mdh or EgAgB4 sequences occur. Nevertheless, alleles Md1 and Md2 and type 1 sequences of EgAgB4 showed a higher frequency within the group of haplotypes G1-G2, while allele Md3 and EgAgB4-2 are most frequent in the G5-G7 cluster. By AMOVA it is shown that 79% of the total genetic variability is found among haplotype groups. These findings are compatible with two not mutually exclusive evolutionary hypotheses: (a) that haplotypes share an ancestral polymorphism, or (b) that the reproductive isolation between parasites with distinct haplotypes is not complete, leading to gene introgression. The biologic and epidemiologic consequences of our findings are discussed.
Badaraco
J L
JL
Programa de Pós Graduação em Genética e Biologia Molecular, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, CEP 91501-970, Brazil.
Ayala
F J
FJ
Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, USA.
Bart
J-M
JM
Laboratoire de Parasitologie, Faculté de Sciences Médicales et Pharmaceutiques de Besançon, Université de Franche-Comté, Besançon, France.
Gottstein
B
B
Institute of Parasitology, Faculty of Medicine and Veterinary Medicine, University of Berne, Berne CH-3001, Switzerland.
Haag
K L
KL
Programa de Pós Graduação em Genética e Biologia Molecular, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, CEP 91501-970, Brazil; Departamento de Genética, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, 91501-970 RS, Brazil.
D000462:Algeria / Q000453:epidemiology; D000818:Animals; D001118:Argentina / Q000453:epidemiology; D001938:Brazil / Q000453:epidemiology; D002162:Camelus; D002417:Cattle; D004443:Echinococcosis / Q000453:epidemiology / Q000469:parasitology*; D048209:Echinococcus granulosus / Q000145:classification / Q000201:enzymology / Q000235:genetics* / Q000276:immunology; D005787:Gene Frequency; D014644:Genetic Variation; D005838:Genotype; D006239:Haplotypes; D006801:Humans; D008074:Lipoproteins / Q000235:genetics*; D008291:Malate Dehydrogenase / Q000235:genetics*; D018807:Polymorphism, Single-Stranded Conformational; D012383:Romania / Q000453:epidemiology; D012756:Sheep; D013552:Swine
D008074:Lipoproteins; C514022:antigen B, Echinococcus granulosus; D008291:Malate Dehydrogenase