Microevolutionary divergence pattern of the segmentation gene hunchback in Drosophila

Area of Science:

• Evolutionary biology
• Genetics
• Molecular evolution

Background:

• The hunchback (hb) gene is crucial for embryonic segmentation in Drosophila.
• Understanding microevolutionary processes requires examining gene sequence variation and selection pressures.

Purpose of the Study:

• To analyze the microevolution of the hunchback (hb) gene in Drosophila melanogaster and related species.
• To investigate sequence variation, neutrality, and codon usage patterns of the hb gene.

Main Methods:

• Cloning and sequencing of the hunchback gene from 12 isofemale lines of D. melanogaster and related species (D. sechellia, D. orena, D. yakuba).
• Analysis of sequence variation, tests of neutrality, and codon usage patterns.
• Comparison of hb gene expression patterns across sibling species.

Main Results:

• Low sequence variation (theta = 0.0017) was observed in D. melanogaster, correlating with a low-recombination region.
• Neutrality tests did not reject a neutral evolution model for the entire gene region.
• Excess polymorphic sites were detected in the leader and intron regions, suggesting localized selection.
• Highly conserved regions exhibited biased codon usage, supporting selection for translational accuracy.
• Regulatory changes in hb expression were noted in Drosophila yakuba, potentially altering secondary expression domain timing.

Conclusions:

• Microevolutionary processes for the hunchback gene in Drosophila involve a combination of background selection and localized adaptive evolution.
• Selection for translational accuracy likely drives codon usage bias in conserved regions.
• Regulatory evolution in hb may contribute to species-specific developmental patterns.