Abstract

The evolution of defensive coloration is dependent upon a complex combination of variables related to the prey itself, the environmental context, and predator vision/behavior. Some animals reflect ultraviolet (UV) light, which is visible to predators such as birds. Here, we report the first case of UV reflectance by a tadpole (Ololygon machadoi, Hylidae) and we investigate whether it influences tadpole detection/predation by a bird (Saltator similis, Passeriformes) on backgrounds of three different colors (two blending – yellow and dark – and one not blending – blue – to tadpole colors). We also tested whether a previous experience of the birds with the prey species would influence the search/attack effort. Although many predation attempts were recorded, birds did not consume many tadpoles. Birds attempted to/preyed upon more tadpoles on dark backgrounds in the presence rather than the absence of the UV portion of the spectrum; attempt/predation on the other backgrounds (yellow, blue) did not change between the UV conditions. The differential contrast of dark and yellow tadpole body parts against specific backgrounds may aid to disruptive properties. The interruption of tadpole body contour was probably enough to prevent detection on yellow and blue backgrounds based on low achromatic contrasts of yellow and dark body parts against such backgrounds, respectively. On dark backgrounds, however, an increase in the chromatic contrast of yellow bars caused by UV reflectance may have reached a threshold and increased tadpole detectability. Birds spent more time searching for tadpoles and visited more frequently the trays in the first than in the second trial, and several tadpoles were regurgitated after ingestion, suggesting that the existence of a potential aposematic role of the UV reflectance cannot be disregarded. Birds also spent more time inspecting blue backgrounds, which may relate to their unfamiliarity with such backgrounds. UV reflectance in O. machadoi tadpoles unveals a potential adaptative value of this feature for the larval stage, and our results indicate influence on tadpole detection by birds. The effects of such adaptation in natural habitats and its occurrence in other species deserve further studies.

Significance statement

Defensive colorations that hamper prey detection can play an important role on prey survival, which depends on background matching ability, prey and predator behavior, and predator visual system. Tadpoles are preyed upon by a variety of visually oriented predators and background matching is likely to aid survivorship through decreased detectability. We show for the first time that tadpoles of Ololygon machadoi, although apparently benefited by camouflage, reflect UV wavelenghts, becoming more visible and maybe providing some kind of aversiveness signaling to birds. In natural conditions, however, the water column on deep stream microhabitats usually occupied by the tadpoles is expected to filter UV wavelengths and improve background matching, at least for some specific background colors.

中文翻译：

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旁观者眼中的可检测性-紫外线反射对pass鸟鸟类探测和捕食的作用

摘要

防御性着色的演变取决于与猎物本身，环境环境和捕食者视觉/行为有关的变量的复杂组合。一些动物会反射紫外线（UV），这对于鸟类等天敌来说是可见的。在这里，我们报告first的第一种紫外线反射情况（Ololygon machadoi，Hylidae），并研究它是否会影响鸟类对t的探测/捕食（Salator similis，Passeriformes），背景为三种不同的颜色（两种混合-黄色和深色-一种不混合-蓝色-t颜色）。我们还测试了以前有猎物的鸟类经历是否会影响搜索/攻击工作。尽管记录了许多捕食尝试，但鸟并没有消耗很多t。鸟类试图在黑暗的背景中而不是在不存在紫外线光谱的情况下捕食更多的;；在其他紫外线条件下，其他背景（黄色，蓝色）的尝试/捕食没有改变。深色和黄色t身体部位与特定背景的差异对比可能有助于破坏特性。body体轮廓的中断可能足以阻止分别基于黄色和深色身体部位在这种背景下的低消色差而在黄色和蓝色背景上进行检测。但是，在黑暗的背景下，由紫外线反射引起的黄色条的彩色对比度的增加可能已达到阈值并增加了detect的可检测性。与第二次试验相比，鸟类在第一时间花费了更多的时间寻找and，并且在第二次试验中更频繁地拜访了盘子，并且在摄取后将几只重新灌输，这表明存在潜在的紫外线反射作用。鸟类还花费更多时间检查蓝色背景，这可能与他们对此类背景的陌生感有关。紫外线反射率 由紫外线反射引起的黄色条的彩色对比度的增加可能已经达到阈值，并且增加了t的可检测性。与第二次试验相比，鸟类在第一时间花费了更多的时间寻找and，并且在第二次试验中更频繁地拜访了盘子，并且在摄取后将几只重新灌输，这表明存在潜在的紫外线反射作用。鸟类还花费更多时间检查蓝色背景，这可能与他们对此类背景的陌生感有关。紫外线反射率 由紫外线反射引起的黄色条的彩色对比度的增加可能已经达到阈值，并且增加了t的可检测性。与第二次试验相比，鸟类在第一时间花费了更多的时间寻找and，并且在第二次试验中更频繁地拜访了盘子，并且在摄取后将几只重新灌输，这表明存在潜在的紫外线反射作用。鸟类还花费更多时间检查蓝色背景，这可能与他们对此类背景的陌生感有关。紫外线反射率 这表明不能忽略紫外线反射的潜在定性作用。鸟类还花费更多时间检查蓝色背景，这可能与他们对此类背景的陌生感有关。紫外线反射率 这表明不能忽略紫外线反射的潜在定性作用。鸟类还花费更多时间检查蓝色背景，这可能与他们对此类背景的陌生感有关。紫外线反射率O. machadoi t揭示了该特征在幼体阶段的潜在适应性价值，我们的结果表明对鸟类detection的检测有影响。这种适应在自然栖息地中的影响及其在其他物种中的发生值得进一步研究。

重要性声明

阻碍猎物检测的防御性色彩可能对猎物存活起重要作用，这取决于背景匹配能力，猎物和食肉动物的行为以及食肉动物的视觉系统。by会被各种视觉上的掠食者捕食，背景匹配可能会通过降低可检测性来帮助生存。我们首次显示，虽然明显受益于伪装，但Oachlygon machadoi的reflect却能反射UV波长，变得更明显，并可能向鸟类提供某种厌恶信号。但是，在自然条件下，至少对于某些特定的背景色，通常被the占据的深流微生境上的水柱有望过滤紫外线波长并改善背景匹配。