Perception of aversive stimuli of different gustatory modalities in an haematophagous insect,Rhodnius prolixus

Abstract

23 24 25 2 Summary statement 26 27Kissing-bugs use contact chemo-perception to avoid aversive substrates. 28 They can sensory distinguish between salty (sodium chloride) and bitter (caffeine) 29 tastes, but not between different salts (sodium and potassium chloride). Abstract 33Sensory aversion is an essential link for avoiding potential dangers. Here, 34 we studied the chemical perception of aversive compounds of different gustatory 35 modalities (salty and bitter) in the haematophagous kissing bug, Rhodnius prolixus. 36 Over a walking arena, insects preferred a substrate embedded with 0.3 M NaCl or 37 KCl rather than with distilled water. Same salts were avoided when prepared at 1 M. 38When NaCl and KCl were confronted, no preferences were evinced by insects. A 39 pre-exposure to amiloride interfered with the repellency of NaCl and KCl equally, 40 suggesting that amiloride-sensitive receptors are involved in the detection of both 41 salts. Discriminative experiments were then performed to determine if R. prolixus 42 can distinguish between these salts. An aversive operant conditioning involving 43 either NaCl or KCl modulated the repellency of the conditioned salt, but also of the 44 novel salt. A chemical pre-exposure to the salts did not to modify their repellency 45 levels. When we crossed gustatory modalities by confronting NaCl to caffeine (i.e. a 46 bitter stimulus) no innate preferences were evinced. Aversive operant conditionings 47 with either NaCl or Caf rendered unspecific changes in the repellency of both 48 compounds. A chemical pre-exposure to Caf modulated the response to Caf but not 49to NaCl, suggesting the existence of two independent neural pathways for the 50 detection of salts and bitter compounds. Overall results suggest that R. prolixus 51 cannot distinguish between NaCl and KCl but can distinguish between NaCl and Caf 52 and generalizes the response between these two aversive stimuli of different 53 gustatory modality. 54 3 1. Introduction 55 56Innate aversion is a highly adaptive behaviour that plays a key role in the 57 survival of animals, as it can prevent them from suffering critical damages. Aversive 58 stimuli can promote avoidance or escape in an individual by directly provoking pain 59 (e.g. electric shock) or by alerting of the presence of a potential danger (e.g. alarm 60 pheromone). In both cases, the peripheral sensory system is in charge of 61 communicating the presence of a danger to the brain. Among the different sensory 62 modalities, gustatory aversiveness acquires a high relevance, as it can help in 63 preventing the ingestion of large quantities of toxic or harmful compounds that might 64 be present in food. Taste is a quite simple system that allows the detection and 65 differentiation of relative low number of stimuli as compared with the olfactory sense. 66For example, animals can detect more than thousands of different olfactory 67 molecules, but they can only differentiate a dozen or less flavours (Liman et al., 68 2014; McGann, 2017).69 70In insec...