RESUMO
The homeodomain is a DNA binding motif that is usually conserved among diverse taxa. Rapidly evolving homeodomains are thus of interest because their divergence may be associated with speciation. The exact site of the Odysseus (Ods) locus of hybrid male sterility in Drosophila contains such a homeobox gene. In the past half million years, this homeodomain has experienced more amino acid substitutions than it did in the preceding 700 million years; during this period, it has also evolved faster than other parts of the protein or even the introns. Such rapid sequence divergence is driven by positive selection and may contribute to reproductive isolation.
Assuntos
Proteínas de Drosophila , Drosophila/genética , Evolução Molecular , Genes Homeobox , Proteínas de Homeodomínio/genética , Proteínas de Insetos/genética , Sequência de Aminoácidos , Substituição de Aminoácidos , Animais , Clonagem Molecular , Drosophila/fisiologia , Drosophila melanogaster/genética , Genes de Insetos , Proteínas de Homeodomínio/química , Proteínas de Homeodomínio/fisiologia , Hibridização Genética , Infertilidade Masculina , Proteínas de Insetos/química , Proteínas de Insetos/fisiologia , Masculino , Dados de Sequência Molecular , Reprodução , Seleção GenéticaRESUMO
The gene for a male ejaculatory protein, Acp26Aa, in four sibling species of the Drosophila melanogaster subgroup has previously been shown to have a nonsynonymous rate (Ka) of nucleotide substitution that is indistinguishable from the synonymous rate (Ks). By examining this gene in two other species of this subgroup, we found that Ka is generally large and can sometimes be more than twice as large as Ks. This suggests that positive selection may be operating at this locus of male reproduction.
Assuntos
Proteínas de Drosophila , Drosophila/genética , Evolução Molecular , Genes de Insetos , Animais , Sequência de Bases , DNA/genética , Drosophila/classificação , Drosophila melanogaster/genética , Proteínas de Insetos/genética , Peptídeos e Proteínas de Sinalização Intercelular , Masculino , Dados de Sequência Molecular , Peptídeos/genética , Filogenia , Reprodução/genética , Seleção Genética , Especificidade da EspécieRESUMO
Many genes pertaining to male reproductive functions have been shown to evolve rapidly between species, and evidence increasingly suggest the influence of positive Darwinian selection. The accessory gland protein gene (Acp26Aa) of Drosophila is one such example. In order to understand the mechanism of selection, it is often helpful to examine the pattern of polymorphism. We report here that the level of amino acid polymorphism in the N-terminal quarter of Acp26Aa is high in Drosophila melanogaster and is unprecedented in its sibling species Drosophila mauritiana. We postulate that (1) this N-terminal segment may play a role in sperm competition, and (2) D. mauritiana may have been under much more intense sexual selection than other species. Both postulates have important ramifications and deserve to be tested rigorously.
Assuntos
Proteínas de Drosophila , Drosophila/genética , Genes de Insetos , Peptídeos/genética , Polimorfismo Genético , Sequência de Aminoácidos , Animais , Drosophila/crescimento & desenvolvimento , Feminino , Peptídeos e Proteínas de Sinalização Intercelular , Masculino , Dados de Sequência Molecular , Reprodução/genética , Análise de Sequência de DNA , Homologia de Sequência de AminoácidosRESUMO
Molecular differentiation between races or closely related species is often incongruent with the reproductive divergence of the taxa of interest. Shared ancient polymorphism and/or introgression during secondary contact may be responsible for the incongruence. At loci contributing to speciation, these two complications should be minimized (1, 2); hence, their variation may more faithfully reflect the history of the species' reproductive differentiation. In this study, we analyzed DNA polymorphism at the Odysseus (OdsH) locus of hybrid sterility between Drosophila mauritiana and Drosophila simulans and were able to verify such a prediction. Interestingly, DNA variation only a short distance away (1.8 kb) appears not to be influenced by the forces that shape the recent evolution of the OdsH coding region. This locus thus may represent a test case of inferring phylogeny of very closely related species.
Assuntos
Drosophila/classificação , Drosophila/genética , Genes de Insetos , Filogenia , Reprodução/genética , Animais , Drosophila/fisiologia , Infertilidade/genética , Dados de Sequência Molecular , Polimorfismo Genético , Especificidade da EspécieRESUMO
The evolution of the gene for a male ejaculatory protein, Acp26Aa, has been shown to be driven by positive selection when nonsibling species in the Drosophila melanogaster subgroup are compared. To know if selection has been operating in the recent past and to understand the details of its dynamics, we obtained DNA sequences of Acp26Aa and the nearby Acp26Ab gene from 39 D. melanogaster chromosomes. Together with the 10 published sequences, we analyzed 49 sequences from five populations in four continents. The southern African population is somewhat differentiated from all other populations, but its nucleotide diversity is lower at these two loci. We find the following results for Acp26Aa: (1) The R: S (replacement : silent changes) ratio is significantly higher in the between-species comparisons than in the within-species data by the McDonald and Kreitman test. Positive selection is probably responsible for the excess of amino acid replacements between species. (2) However, within-species nucleotide diversity is high. Neither the Tajima test nor the Fu and Li test indicates a reduction in nucleotide diversity due to positive selection in the recent past. (3) The newly derived nucleotides in D. melanogaster are at high frequency significantly more often than predicted by the neutral equilibrium. Since the nearby Acp26Ab gene does not show these patterns, these observations cannot be attributed to the characteristics of this chromosomal region. We suggest that positive selection is active, but may be weak, for each amino acid change in the Acp26Aa gene.
Assuntos
Proteínas de Drosophila , Drosophila/genética , Evolução Molecular , Genes de Insetos , Seleção Genética , Animais , Sequência de Bases , Primers do DNA/genética , Drosophila melanogaster/genética , Variação Genética , Proteínas de Insetos/genética , Peptídeos e Proteínas de Sinalização Intercelular , Desequilíbrio de Ligação , Masculino , Dados de Sequência Molecular , Peptídeos/genética , Polimorfismo Genético , Reprodução/genética , Homologia de Sequência do Ácido NucleicoRESUMO
The cuticular hydrocarbon (CH) pheromones in Drosophila melanogaster exhibit strong geographic variation. African and Caribbean populations have a high ratio of 5,9 heptacosadiene/7,11 heptacosadiene (the "High" CH type), whereas populations from all other areas have a low ratio ("Low" CH type). Based on previous genetic mapping, DNA markers were developed that localized the genetic basis of this CH polymorphism to within a 13-kb region. We then carried out a hierarchical search for diagnostic nucleotide sites starting with four lines, and increasing to 24 and 43 lines from a worldwide collection. Within the 13-kb region, only one variable site shows a complete concordance with the CH phenotype. This is a 16-bp deletion in the 5' region of a desaturase gene (desat2) that was recently suggested to be responsible for the CH polymorphism on the basis of its expression [Dallerac, R., Labeur, C., Jallon, J.-M., Knipple, D. C., Roelofs, W. L. & Wicker-Thomas, C. (2000) Proc. Natl. Acad. Sci. 97, 9449--9454]. The cosmopolitan Low type is derived from the ancestral High type, and DNA sequence variations suggest that the former spread worldwide with the aid of positive selection. Whether this CH variation could be a component of the sexual isolation between Zimbabwe and other cosmopolitan populations remains an interesting and unresolved question.