Data from: Honeybees (Apis mellifera) learn color discriminations via differential conditioning independent of long wavelength (green) photoreceptor modulation

BACKGROUND: Recent studies on colour discrimination suggest that experience is an important factor in how a visual system processes spectral signals. In insects it has been shown that differential conditioning is important for processing fine colour discriminations. However, the visual system of many insects, including the honeybee, has a complex set of neural pathways, in which input from the long wavelength sensitive (‘green’) photoreceptor may be processed either as an independent achromatic signal or as part of a trichromatic opponent-colour system. Thus, a potential confound of colour learning in insects is the possibility that modulation of the ‘green’ photoreceptor could underlie observations. METHODOLOGY/PRINCIPAL FINDINGS: We tested honeybee vision using light emitting diodes centered on 414 and 424 nm wavelengths, which limit activation to the short-wavelength-sensitive (‘UV’) and medium-wavelength-sensitive (‘blue’) photoreceptors. The absolute irradiance spectra of stimuli was measured and modelled at both receptor and colour processing levels, and stimuli were then presented to the bees in a Y-maze at a large visual angle (26°), to ensure chromatic processing. Sixteen bees were trained over 50 trials, using either appetitive differential conditioning (N = 8), or aversive-appetitive differential conditioning (N = 8). In both cases the bees slowly learned to discriminate between the target and distractor with significantly better accuracy than would be expected by chance. Control experiments confirmed that changing stimulus intensity in transfers tests does not significantly affect bee performance, and it was possible to replicate previous findings that bees do not learn similar colour stimuli with absolute conditioning. CONCLUSION: Our data indicate that honeybee colour vision can be tuned to relatively small spectral differences, independent of ‘green’ photoreceptor contrast and brightness cues. We thus show that colour vision is at least partly experience dependent, and behavioural plasticity plays an important role in how bees exploit colour information.

研究背景：近年来有关颜色辨别的研究表明，感知经验是视觉系统处理光谱信号的关键影响因素。在昆虫中已有研究证实，差别条件作用对精细颜色辨别的加工至关重要。然而，包括蜜蜂在内的多数昆虫的视觉系统拥有复杂的神经通路：长波敏感（‘绿’）光感受器（long wavelength sensitive (‘green’) photoreceptor）的输入信号，既可以作为独立的无彩色信号进行加工，也可作为三色对立颜色系统的一部分进行处理。因此，昆虫颜色学习研究中存在一个潜在混淆变量：‘绿’光感受器的调制可能是观测结果的成因。

研究方法/主要结果：本研究采用中心波长为414 nm与424 nm的发光二极管（light emitting diodes，LED）作为刺激源，该刺激源仅能激活短波敏感（‘紫外’）光感受器（short-wavelength-sensitive (‘UV’) photoreceptor）与中波敏感（‘蓝’）光感受器（medium-wavelength-sensitive (‘blue’) photoreceptor）。研究人员分别在光感受器与颜色加工两个层面，对刺激物的绝对辐照度光谱进行了测量与建模；随后以26°的大视角将刺激呈现在Y型迷宫中，以确保实验仅涉及颜色加工过程。共训练16只蜜蜂，完成50个试次，其中8只采用奖赏性差别条件作用训练，另外8只采用厌恶性-奖赏性差别条件作用训练。两种训练方式下，蜜蜂均能逐步学会区分目标刺激与干扰刺激，其辨别准确率显著高于随机水平。对照实验证实，在迁移测试中改变刺激强度不会对蜜蜂的行为表现产生显著影响；同时本研究成功复现了此前的研究结论：蜜蜂无法通过绝对条件作用学习相似的颜色刺激。

研究结论：本研究数据表明，蜜蜂的颜色视觉能够适配相对微小的光谱差异，且该过程不依赖于‘绿’光感受器的对比度与亮度线索。由此证实，蜜蜂的颜色视觉至少在一定程度上依赖于感知经验，而行为可塑性在蜜蜂利用颜色信息的过程中发挥着重要作用。