Evolution of Acid-Sensing Olfactory Circuits in Drosophilids

Area of Science:

• Neuroscience
• Evolutionary Biology
• Genetics

Background:

• Animal behavior is shaped by ecological niches, yet the genetic underpinnings of nervous system evolution remain unclear.
• Understanding the evolution of sensory systems, particularly olfaction, is crucial for explaining species-specific adaptations.

Purpose of the Study:

• To investigate the genetic and cellular basis of olfactory circuit evolution in Drosophila.
• To compare the olfactory system of the specialist fruit fly Drosophila sechellia with its generalist relatives.

Main Methods:

• Comparative analysis of olfactory receptor genes and neural circuits.
• Functional characterization of the ionotropic glutamate receptor IR75b.
• Genetic analysis of regulatory elements influencing gene expression.

Main Results:

• Drosophila sechellia shows a specific attraction to hexanoic acid, a volatile from its exclusive food source, Morinda citrifolia.
• A single amino acid substitution in the IR75b receptor is sufficient to confer hexanoic acid detection.
• Evolution of this sensory pathway involves changes in the IR75b promoter and trans-acting factors, expanding neural representation.

Conclusions:

• Olfactory receptor evolution, driven by ecological pressures, can involve minimal genetic changes with significant functional consequences.
• Adaptations in sensory pathways are key to niche specialization.
• Conserved central processing suggests that higher-order neural circuits may be less prone to rapid evolutionary change compared to peripheral sensory systems.