RESUMO
Pigmentation is a model trait for evolutionary and developmental analysis that is particularly amenable to molecular investigation in the genus Drosophila. To better understand how this phenotype evolves, we examined divergent pigmentation and gene expression over developmental time in the dark-bodied D. americana and its light-bodied sister species D. novamexicana. Prior genetic analysis implicated two enzyme-encoding genes, tan and ebony, in pigmentation divergence between these species, but questions remain about the underlying molecular mechanisms. Here, we describe stages of pupal development in both species and use this staging to determine when pigmentation develops and diverges between D. americana and D. novamexicana. For the developmental stages encompassing pigment divergence, we compare mRNA expression of tan and ebony over time and between species. Finally, we use allele-specific expression assays to determine whether interspecific differences in mRNA abundance have a cis-regulatory basis and find evidence of cis-regulatory divergence for both tan and ebony. cis-regulatory divergence affecting tan had a small effect on mRNA abundance and was limited to a few developmental stages, yet previous data suggests that this divergence is likely to be biologically meaningful. Our study suggests that small and developmentally transient expression changes may contribute to phenotypic diversification more often than commonly appreciated. Recognizing the potential phenotypic impact of such changes is important for a scientific community increasingly focused on dissecting quantitative variation, but detecting these types of changes will be a major challenge to elucidating the molecular basis of complex traits.
Assuntos
Proteínas de Ligação a DNA/genética , Proteínas de Drosophila/genética , Drosophila/genética , Evolução Molecular , Regulação da Expressão Gênica/genética , Pigmentação/genética , RNA Mensageiro/genética , Alelos , Animais , Proteínas de Ligação a DNA/biossíntese , Drosophila/metabolismo , Proteínas de Drosophila/biossíntese , Fenótipo , Locos de Características Quantitativas , RNA Mensageiro/biossíntese , Especificidade da EspécieRESUMO
Genetic changes contributing to phenotypic differences within or between species have been identified for a handful of traits, but the relationship between alleles underlying intraspecific polymorphism and interspecific divergence is largely unknown. We found that noncoding changes in the tan gene, as well as changes linked to the ebony gene, contribute to pigmentation divergence between closely related Drosophila species. Moreover, we found that alleles linked to tan and ebony fixed in one Drosophila species also contribute to variation within another species, and that multiple genotypes underlie similar phenotypes even within the same population. These alleles appear to predate speciation, which suggests that standing genetic variation present in the common ancestor gave rise to both intraspecific polymorphism and interspecific divergence.
