Chronobiology of odour perception: general or specific modulation?

BODIN A, COUTON L, BARROZO RB, LAZZARI CR.

Tours, Francia

Congreso; 11th International Congress of Behavioural Ecology; 2006

Odour sensitivity in insects changes rhythmically, even in the absence of environmental cycles.  Circadian rhythms of antennal sensitivity were demonstrated in Drosophila and the cockroach Leucophaea.  In both cases, changes affect the reception of different odours and thus a general modulation in chemosensitivity was postulated.  Nevertheless, some questions arise on the adaptive value of these rhythms.  First, in both cases, maximal sensitivity paradoxically occurs during inactivity periods.  Second, a general change in odour sensitivity would be disadvantageous, since different odours can be associated to behaviours allocated in different temporal windows.  It would be much more adaptive to modulate differentially the sensitivity to each odour according to its behavioural context.  Besides, at the behavioural level, maximal responsiveness should occur during active periods and when a given odour becomes biologically relevant.  We tested both hypotheses in Rhodnius prolixus, who exhibits a bimodal activity pattern.  At dusk, they search food following host-emitted odours.  At dawn, they return to refuges guided by assembling pheromones.  We studied the dynamics of responsiveness to carbon dioxide and to aggregation cues.  We show that the sensitivity to these signals does not remain constant along the day, but is restricted to precise temporal windows instead. Responsiveness to CO2 only occurs at dusk and to assembling odours exclusively at dawn.  Thus, our results support a specific modulation of the responsiveness to odours, rather than a general one.  Furthermore, maximal chemosensitivity matches the behavioural context to which each odour is associated with. Supported by Université François Rabelais and the CNRS, France.