Ancestral complexity and constrained diversification of the ant olfactory system

Communication is a cornerstone of social living, allowing the exchange of
information to align goals and synchronize behaviour. Ants, a group of
highly successful social insects, have heightened olfactory abilities that
are integral to their evolutionary success. Essential for colony cohesion
and cooperation, a female-specific olfactory subsystem processes
information about nestmate recognition cues (cuticular hydrocarbons),
including basiconic sensilla on the antenna and a cluster of specific
glomeruli in the antennal lobe. While it has often been linked to ants’
social lifestyle, the evolutionary origins and phylogenetic distribution
of this system remain unknown. We conducted a comparative exploration of
the ant olfactory system across eight major subfamilies, integrating
neuroanatomical, chemical, and behavioural analyses. Our findings reveal
that sophistication of the ant olfactory system has deep evolutionary
roots. Moreover, antennal lobe investment is not associated with social
traits such as colony size, polygyny, or foraging strategies, but
correlates with cuticular hydrocarbon profile complexity. Despite
neuroanatomical differences, different ant species consistently excel in
nestmate discrimination, indicating adaptation to chemical diversity while
maintaining reliable social recognition. This suggests that cuticular
hydrocarbon profile and neuronal investment in olfactory neuropil have
co-evolved to sustain discrimination performance.