RESUMO
We describe allelic variation at 28 loci in six Caribbean populations of four sympatric species of Drosophila. Within any one species the allelic frequencies are very similar from population to population, although there is evidence of local as well as regional genetic differentiation. The genetic distance is greater between populations from different islands than between populations of the same island. When the allelic frequencies are compared between different species, a remarkable pattern appears. In any pair of species nearly half of the loci have essentially identical allelic frequencies, while nearly the other half of the loci have different alleles and in different frequencies. The loci with nearly identical allelic frequencies are different when different pairs of species are compared. The patterns of allelic variation within and between species are inconsistent with the hypothesis that the variation is adaptively neutral. Migration or mutation cannot explain the patterns of genetic variation, either. Balancing natural selection is the main process maintaining protein polymorphisms in natural populations.
Assuntos
Drosophila/enzimologia , Frequência do Gene , Genes , Variação Genética , Fosfatase Ácida/biossíntese , Oxirredutases do Álcool/biossíntese , Fosfatase Alcalina/biossíntese , Alelos , Aminopeptidases/biossíntese , Animais , Carboidratos Epimerases/biossíntese , Eletroforese , Esterases/biossíntese , Feminino , Heterozigoto , Masculino , Oxirredutases/biossíntese , Fosfoglucomutase/biossíntese , Fosfotransferases/biossíntese , Polimorfismo Genético , Índias OcidentaisRESUMO
We describe allelic variation at 28 gene loci in natural populations of D. willistoni. Seventy samples were studied from localities extending from Mexico and Florida, through Central America, the West Indies, and tropical South America, down to South Brazil. At least several hundred, and often several thousand, genomes were sampled for each locus. We have discovered a great deal of genetic variation. On the average, 58% loci are polymorphic in a given population. (A locus is considered polymorphic when the frequency of the most common allele is no greater than 0.95). An individual fly is heterozygous, on the average, at 18.4% loci.-Concerning the pattern of the variation, the most remarkable finding is the similarity of the configuration of allelic frequencies from locality to locality throughout the distribution of the species. Our observations support the conclusion that balancing natural selection is the major factor responsible for the considerable genetic variation observed in D. willistoni.