RESUMEN
The genetic structure of Drosophila pseudoobscura populations was inferred from a nucleotide sequence analysis of a 3.4-kb segment of the alcohol dehydrogenase (Adh) region. A total of 99 isochromosomal strains collected from 13 populations in North and South America were used to determine if any population departed from a neutral model and to estimate levels of gene flow between populations. This study also included the nucleotide sequences from two sibling species, D. persimilis and D. miranda. We estimated the neutral mutation parameter, 4N mu, in synonymous and noncoding sites for 17 subregions of Adh in each of nine populations with sample sizes greater than three. The nucleotide diversity data in the nine populations was tested for departures from an equilibrium neutral model with two statistical tests. The Tajima and the Hudson, Kreitman, Aguade tests showed that each population fails to reject a neutral model. Tests for genetic differentiation between populations fail to show any population substructure among the North American populations of D. pseudoobscura. The nucleotide diversity data is consistent with direct and indirect measures of gene flow that show extensive dispersal between populations of D. pseudoobscura.
Asunto(s)
Alcohol Deshidrogenasa/genética , Drosophila/genética , Animales , ADN/genética , Análisis Mutacional de ADN , Drosophila/enzimología , Genética de Población , Heterocigoto , Modelos Genéticos , América del Norte , Análisis de Secuencia de ADN , América del SurRESUMEN
The population of Drosophila pseudoobscura at Bogota, Columbia, is geographically and partially reproductively isolated from populations in the main body of the species in North America. The degree of genetic differentiation and time of divergence between populations at Bogota and Apple Hill, CA, were estimated by comparison of 3388 nucleotides in the alcohol dehydrogenase region (Adh and Adh-Dup genes) of 18 strains. Of the 146 polymorphic nucleotide sites detected, 68 and 31 were unique to the Apple Hill and Bogota samples, respectively, and 53 were shared. On the basis of an observed net divergence per nucleotide site of 0.264% between the two samples, the Bogota and North American populations were estimated to have been separated for at least 155,000 years. This divergence time suggests that D. pseudoobscura extended its range from North America to South America in a period of Pleistocene glaciation, when habitat suitable for the species presumably existed in lowland Central America.