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III. Discourse: Choose the most appropriate one for each blank withoutconsidering if a capital letter is needed. (2%*5=10%)Phototaxis is the movement of an organism in response to light, whether itgoes towards it or away from it. 21 Nonetheless, this behavior can bemodified. For example, whether light attracts or repels an animal can changeduring its lifetime, especially if the animal occupies different environments as itages: some insects switch from positive to negative phototaxis towards the end oftheir larval stage, as they migrate to a dark refuge (e.g. the soil) to pupate. Youngnurse bees performing indoor tasks are negatively phototactic, while old foragersare attracted to light. At smaller time scales, 22 . Adult Drosophila also shifttheir preference depending on their internal state: they are normally attracted tolight, but will avoid it if their ability to fly is compromised.Phototaxis only requires very simple eyes, but it did not disappear withthe evolution of complex, image-forming eyes such as the honey bees’. There,23 , especially when multiple photoreceptors responding to differentwavelengths are involved. In frogs, grasshoppers, psyllids, Daphnia, andDrosophila, preference for a particular wavelength can override the intensitysignal, in that a specific wavelength can be chosen over a more intense stimulus,either broadband or of another wavelength. Even more strikingly, differentwavelengths can elicit opposite responses: larval zebrafish are attracted towavelengths above 400 nm, but avoid those below. The greenhouse whiteflysimilarly avoids a chamber illuminated by a 400 nm light, but enters oneilluminated with a 550 nm light. Mixing the different wavelengths results in anintermediate response in these two systems, 24 .In this study we ask if the later evolution of more complex visual systemswas accompanied by a sophistication of phototactic behavior. The honey bee is anideal model organism to tackle this question, as it has an elaborate visual system,demonstrates exquisite abilities for visual learning and performs phototaxis. Ourdata suggest that in this insect, phototaxis has wavelength specific properties andis a highly dynamical response including multiple decision steps. In addition, weshow that previous experience with a light (through exposure or classical aversive4conditioning) modulates the phototactic response. This plasticity is dependent onthe wavelength used, with blue being more labile than green or ultraviolet. 25Thus, our results support the idea that complex visual systems allow sophisticatedphototaxis. Future studies could take advantage of these findings to betterunderstand the neuronal circuits underlying this processing of the visualinformation.
(A) suggesting that the lights activated competing mechanisms to produce theoutput behavior.
(B) wavelength, intensity and past experience are integrated into an overallvalence for each light that determines phototactic behavior in honey bees.
(C) individual experience could be integrated to further adapt phototacticresponses to the current environment.
(D) the architecture of the visual system could potentially support moreelaborate forms of phototaxis
(E) it is widespread in the animal kingdom and typically understood as aninnate, stereotyped, relatively simple response to light.(AB) investigating experience-dependent tuning by looking at the modificationof phototaxis after simple exposure or aversive conditioning(AC) phototactic behavior may follow a circadian rhythm, as shown in larvalfruit flies.
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