The bad taste governs feeding decisions in a blood feeder

BARROZO, RB

Bogota

Simposio; Latin American Association of Chemical Ecology; 2014

The ability to discriminate between nutrients from harmful substrates is essential for animal's survival. Though olfaction and vision contribute to find potential food, the taste sense works as a final control system driving food acceptance or rejection. Taste abilities vary in the animal kingdom, humans and most mammals can detect 5 taste modalities: sweet, acid, umami, bitter and salt. Whereas sweet and umami have positive hedonic values, bitter and high salts doses are both related to aversive behaviors in most animals studied so far. In contrast to olfactory sense, the low spectrum of taste modalities that animals recognize is comparable to their low discrimination abilities. For example, humans can fairly distinguish between regular table salt (sodium chloride) and commercial salt substitutes (potassium chloride), though we have troubles to discriminate among bitter substances. Triatomine insects (vectors of Chagas Disease in Latin America) feed on blood from small vessels of vertebrate hosts. As soon as they reach a potential host, they walk over their skin searching for an adequate site to pierce. Then, they insert their stylets and take a first sampling gorge to decide if food is acceptable or not. Our work shows that detection of certain substances such as bitter compounds and certain inorganic salts at high doses inhibits feeding behavior of these bugs. Rejection of food is dependent not only on the chemical nature of tastants but also on the concentration. Aversive behaviors can be triggered during both the assessment of the surface to bite or within the first gorge of food. The sensory organs involved in taste detection are located in the antenna (i.e. external organs) and in the pharynx (i.e. internal organs) of the insects, as show our morphological inspections along with electrophysiological recordings. These two sensory stages work with different avoidance thresholds: antennal input exerts a modulatory rejection signaling at higher doses than internal sensors. Additionally, we study whether bugs are able to discriminate among aversive stimuli, or alternatively they are simply indistinguishable negative input signals that induce feeding inhibition. We use a multiapproach strategy that involves different levels of study. On one hand we target on the putative salt receptors and we study the transduction pathway possibly involved in the aversive detection (nitric oxide pathway); and on the other we use a cognitive approach to gain more insights on the ability of insects to discriminate among aversive taste modalities (i.e. bitter vs. salts) and within a taste modality (i.e. amongst bitter compounds or salts). Our results highlight the relevance of taste perception of aversive and anti-appetitive compounds modulating the feeding behavior of a blood-sucking insect.