# Adaptive Evolution of Odorant-Binding and Chemosensory Protein Gene Families in Genus Drosophila Fallén, 1823 (Diptera, Drosophilidae)

## TL;DR

This study explores how odorant-binding and chemosensory proteins in fruit flies evolved, helping them adapt to different diets and environments.

## Contribution

The study reveals adaptive gene expansion and functional diversification in the OBP family of Drosophila, linked to dietary shifts and environmental adaptation.

## Key findings

- OBP gene numbers varied widely (37–66 genes) across Drosophila species, while CSP genes were conserved.
- Positive selection in Obp22a, Obp57e, and Obp83ef led to changes in binding affinity for plant odors and insecticides.
- Gene expansion in the OBP family is associated with dietary diversity and adaptation to toxic substances.

## Abstract

Odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) serve as carriers for signal molecules within the insect olfactory system, playing a crucial role in detecting chemical cues related to feeding and reproduction. However, their roles in host shift and environmental adaptation remain poorly understood. This study identified the OBP and CSP gene families across 32 Drosophila species, revealing their adaptive evolutionary trajectory. It was found that the gene number of the OBP family varied widely between species, ranging from 37 to 66 genes, while the gene number of the CSP family was conserved. The OBP family experienced two major gene expansion events on the ancestral branches of the diet-diverse melanogaster lineage, leading to an increased number. Positive selection occurred during evolution in the orthologous groups of Obp22a, Obp57e and Obp83ef. Homology modeling and molecular docking revealed that variation in the positively selected sites across different Drosophila species resulted in significant changes to free binding energy and affinity for plant odors and insecticides. Our findings highlight gene expansion and functional diversification within the Drosophila OBP family may contribute to shaping the dietary spectrum and promoting adaptation to toxic substances.