Temporal modulation of odour perception: does olfactory sensitivity change globally or according to the behavioural context?

BARROZO RB, BODIN A, COUTON L,& LAZZARI C.

Barcelona, Espana

Congreso; 22nd International Congress of Chemical Ecology; 2006

Many biological processes in animals change rhythmically, even in the absence of environmental cycles. The daily variation in odour sensitivity in insects has been demonstrated both, at the sensory level (i.e., receptor cells), and at the behavioural level. It is worthwhile to note that, along the day, a specific modulation (i.e., affecting each odour independently) would be more advantageous than a general change in olfactory responsiveness. The reason is that different odours are associated to behavioural contexts allocated at different temporal windows. As a consequence, maximal responsiveness should be expected to occur 1) during periods of activity and 2) when a given odour becomes biologically relevant. Previous evidence, obtained in Drosophila and Leucophaea does not support however these assumptions. Paradoxically, in both cases maximal sensitivity seems to occur during resting periods, whereas general changes in olfactory sensitivity would occur. The reasons for this paradox are not understood, deserving to be analysed in other species. We chose Rhodnius prolixus, who exhibits a bimodal activity pattern, for testing whether or not olfactory sensitivity to signals relevant at different times of the day, varies in a related way. In nature, bugs normally leave their refuges seeking for food guided by host-emitted cues (e.g. CO2) at the beginning of the night, and they return to shelters following assembling pheromones before sunrise. We studied the daily dynamics of responsiveness to carbon dioxide and to aggregation cues. Our results show that the responsiveness to these two odours does not remain constant along the day, but is restricted to precise temporal windows instead. As predicted for an adaptive response, responsiveness to CO2 only occurs at dusk while assembling pheromones were attractive exclusively at dawn. Thus, our results support a specific modulation of the responsiveness to odours, rather than a general one, as maximal chemosensitivity matches the behavioural context to which each odour is associated with. Supported by Université François Rabelais and the CNRS, France.