Abstract
In Drosophila, the insulin-signaling pathway controls some life history traits, such as fertility and lifespan, and it is considered to be the main metabolic pathway involved in establishing adult body size. Several observations concerning variation in body size in the Drosophila genus are suggestive of its adaptive character. Genes encoding proteins in this pathway are, therefore, good candidates to have experienced adaptive changes and to reveal the footprint of positive selection. The Drosophila insulin-like peptides (DILPs) are the ligands that trigger the insulin-signaling cascade. In Drosophila melanogaster, there are several peptides that are structurally similar to the single mammalian insulin peptide. The footprint of recent adaptive changes on nucleotide variation can be unveiled through the analysis of polymorphism and divergence. With this aim, we have surveyed nucleotide sequence variation at the dilp1-7 genes in a natural population of D. melanogaster. The comparison of polymorphism in D. melanogaster and divergence from D. simulans at different functional classes of the dilp genes provided no evidence of adaptive protein evolution after the split of the D. melanogaster and D. simulans lineages. However, our survey of polymorphism at the dilp gene regions of D. melanogaster has provided some evidence for the action of positive selection at or near these genes. The regions encompassing the dilp1-4 genes and the dilp6 gene stand out as likely affected by recent adaptive events.
Highlights
In Drosophila, like in all holometabolous insect species, adult body size is mainly determined during the larval stages, as a product of both the growth rate and the duration of the growth period in each larval phase
Drosophila Strains Twelve isochromosomal lines for each the third chromosome (CNIII) and the X chromosome (CNX) that had been extracted from a natural population of Drosophila melanogaster (Sant Sadurnı d’Anoia, Barcelona, Spain) were used to obtain the sequences of the dilp genes located on the third and X chromosomes, respectively
Polymorphism in Drosophila Melanogaster Nucleotide polymorphism was estimated both for the four dilp regions and for each of the seven dilp genes
Summary
In Drosophila, like in all holometabolous insect species, adult body size is mainly determined during the larval stages, as a product of both the growth rate and the duration of the growth period in each larval phase. The insulin-signaling pathway is the main known metabolic pathway involved in establishing adult body size [1,2,3,4]. Life history traits such as fertility and lifespan generally reflect adaptive responses to environmental pressures and, both positive and negative selection might have played an important role in the molecular evolution of the genes underlying such characters [24]. Genes involved in this pathway are, good candidates to have experienced adaptive changes and to reveal the footprint of positive selection. Been recently shown that the insulin-like receptor, which is the first component of the insulin-signaling pathway, has undergone adaptive change in its evolutionary past [25], [26]
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