Abstract

A diversity of defence colourations that shift over time provides protection against natural enemies. Adaptations for camouflage depend on an organism’s interactions with the natural environment (predators, habitat), which can change ontogenetically. Wallace’s flying frogs (Rhacophorus nigropalmatus) are cryptic emerald green in their adult life stage, but juveniles are bright red and develop white spots on their back 1 month after metamorphosis. This latter conspicuous visual appearance might function as antipredator strategy, where frogs masquerade as bird or bat droppings so that predators misidentified them as inedible objects. To test this idea, we created different paraffin wax frog models—red with white spots, red without white spots, green, and unpainted—and placed them in equal numbers within a > 800 m² rainforest house at the Vienna Zoo. This environment closely resembles the Bornean rainforest and includes several free-living avian predators of frogs. We observed an overall hit rate of 15.5%. A visual model showed that the contrast of red, green and control models against the background colouration could be discriminated by avian predators, whereas green models had less chromatic difference than red morphs. The attack rate was significantly greater for red but was reduced by half when red models had white spots. The data therefore supports the hypothesis that the juvenile colouration likely acts as a masquerade strategy, disguising frogs as animal droppings which provides similar protection as the cryptic green adult colour. We discuss the ontogenetic colour change as a possible antipredator strategy in relation to the different habitats used at different life stages.

Significance statement

Predation pressure and the evolution of antipredator strategies site at the cornerstone of animal-behaviour research. Effective antipredator strategies can change in response to different habitats that animals use during different life stages. We study ontogenetic shifts in colour change as dynamic antipredator strategy in juvenile and adult Wallace’s flying frogs. We show that the unusual colour pattern of juveniles (bright red with small white spots) likely functions as a masquerade of animal droppings. Specifically, we show that white dotting, which can be associated with animal faeces, acts as the main visual feature that turns an otherwise highly conspicuous individual into a surprisingly camouflaged one. To our knowledge, this is the first experimental exploration of a vertebrate masquerading as animal droppings.

中文翻译：

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从伪装到融入：华莱士飞蛙反捕食者伪装的个体发生变化

摘要

随着时间的推移，防御颜色的多样性会发生变化，提供针对天敌的保护。对伪装的适应取决于生物体与自然环境（捕食者、栖息地）的相互作用，这种相互作用可以在个体发生上发生变化。华莱士飞蛙 ( Rhacophorus nigropalmatus)）在成虫阶段呈隐秘的翠绿色，但幼虫呈鲜红色，并在变态后1个月后在背部出现白斑。后一种显眼的视觉外观可能起到反捕食者策略的作用，青蛙伪装成鸟类或蝙蝠的粪便，以便捕食者将它们误认为是不可食用的物体。为了测试这个想法，我们创建了不同的石蜡青蛙模型——红色有白点、红色无白点、绿色和未上漆——并将它们以相同数量放置在 > 800 m 2 的范围内^。维也纳动物园的雨林屋。这种环境与婆罗洲雨林非常相似，并且包括几种自由生活的青蛙鸟类捕食者。我们观察到总体命中率为 15.5%。视觉模型表明，鸟类捕食者可以区分红色、绿色和对照模型与背景颜色的对比，而绿色模型的色差比红色模型的色差小。红色模型的攻击率明显更高，但当红色模型有白点时攻击率降低一半。因此，这些数据支持了这样的假设：幼年青蛙的颜色可能是一种伪装策略，将青蛙伪装成动物粪便，从而提供与成年青蛙的神秘绿色类似的保护作用。

意义陈述

捕食压力和反捕食策略的演变是动物行为研究的基石。有效的反捕食者策略可以根据动物在不同生命阶段使用的不同栖息地而改变。我们研究颜色变化的个体发育变化作为幼年和成年华莱士飞蛙的动态反捕食策略。我们发现，幼鱼不寻常的颜色图案（亮红色带有小白点）很可能是动物粪便的伪装。具体来说，我们表明，与动物粪便相关的白色点是主要的视觉特征，它将原本非常显眼的个体变成了令人惊讶的伪装个体。据我们所知，这是对伪装成动物粪便的脊椎动物的首次实验探索。