Olfaction in dragonflies: electrophysiological evidence

Area of Science:

• Insect neurobiology
• Olfactory system evolution
• Paleoptera sensory mechanisms

Background:

• Dragonflies (Odonata) and mayflies (Ephemeroptera), grouped as Paleoptera, have traditionally been considered anosmic.
• This view stems from the absence of glomerular antennal lobes, key olfactory processing centers in Neoptera.
• The presence and function of olfactory receptors on the antennal flagellum of adult Odonata remained unconfirmed.

Purpose of the Study:

• To investigate the functional status of presumed coeloconic olfactory receptors in adult Odonata.
• To determine if antennae of Odonata possess functioning olfactory capabilities.
• To provide a foundation for further research into Odonata olfaction and its evolutionary implications.

Main Methods:

• Electrophysiological recordings, including electroantennogram (EAG) and single cell recordings (SCR), were performed on the dragonfly Libellula depressa.
• A range of odorants from different chemical classes were tested, including esters, aldehydes, alcohols, carboxylic acids, and amines.
• Responses were analyzed to detect olfactory neuron activity in the antennae.

Main Results:

• Most tested chemicals evoked depolarizing EAG responses in both male and female antennae.
• Single cell recordings provided unambiguous evidence for olfactory neurons within the antennae of L. depressa.
• These results strongly support the olfactory function of coeloconic sensilla on the antennal flagellum.

Conclusions:

• The study demonstrates the presence of functional olfactory neurons in the antennae of dragonflies.
• This electrophysiological evidence challenges the long-held assumption of anosmia in Paleoptera.
• Further behavioral, neuroanatomical, and molecular studies are warranted to elucidate the biological role and evolutionary significance of Odonata olfaction.