Sensory neuron population expansion enhances odor tracking without sensitizing projection neurons

Area of Science:

• Neuroscience
• Evolutionary Biology
• Sensory Biology

Background:

• Widespread evolutionary expansion of sensory neurons is observed but not fully understood.
• Investigating homologous neural pathways in *Drosophila melanogaster* and *Drosophila sechellia* provides insight into this phenomenon.

Approach:

• Compared neural pathways in *D. melanogaster* and *D. sechellia*, a specialist on noni fruit.
• Analyzed species-specific expansions in olfactory sensory neuron (OSN) populations in *D. sechellia*.
• Examined the functional consequences of OSN population increases on behavior and neural processing.

Key Points:

• *D. sechellia* exhibits multigenic, species-specific expansions in noni-detecting OSN populations.
• Increased OSN numbers lead to stronger, more persistent tracking of noni odor.
• Despite more OSNs, projection neuron (PN) sensitivity and reliability do not increase.
• Expanded sensory pathways show reduced PN adaptation, potentially via weakened lateral inhibition.

Conclusions:

• Sensory neuron expansion impacts function unexpectedly, influencing ecologically relevant behaviors.
• Reduced neural adaptation in expanded pathways explains specialized odor-tracking behavior.
• This study reveals a novel mechanism for species-specific sensory adaptations.