Jia W. Pan and Pelin Cayirlioglu Volkan
To increase detection of a complex chemical environment, vertebrates and insects express an extraordinary number of distinct olfactory receptor neuron (ORN) classes, each functionally specialized to detect a set of odorants. This is achieved as the olfactory system develops and each of these ORN classes makes developmental decisions defining the olfactory receptor genes they will express and their class-specific connections in the brain. In addition to this high level of ORN diversity, olfactory systems are also very dynamic evolutionarily, with both the number and functionality of olfactory receptor genes as well as the requirement for certain ORN circuits being under ecological constraints. In this review, we will discuss molecular and developmental strategies underlying ORN diversity and evolutionary plasticity as well as present the insect olfactory system as a model for evo-devo research in light of recent findings.