ARC Centre of Excellence in Vision Science and Centre for Visual Sciences, Research School of Biology, The Australian National University, Canberra, Australia.
Proc Biol Sci. 2010 May 22;277(1687):1531-8. doi: 10.1098/rspb.2009.2324. Epub 2010 Feb 3.
Many animals become active during twilight, a narrow time window where the properties of the visual environment are dramatically different from both day and night. Despite the fact that many animals including mammals, reptiles, birds and insects become active in this specific temporal niche, we do not know what cues trigger this activity. To identify the onset of specific temporal niches, animals could anticipate the timing of regular events or directly measure environmental variables. We show that the Australian bull ant, Myrmecia pyriformis, starts foraging only during evening twilight throughout the year. The onset occurs neither at a specific temperature nor at a specific time relative to sunset, but at a specific ambient light intensity. Foraging onset occurs later when light intensities at sunset are brighter than normal or earlier when light intensities at sunset are darker than normal. By modifying ambient light intensity experimentally, we provide clear evidence that ants indeed measure light levels and do not rely on an internal rhythm to begin foraging. We suggest that the reason for restricting the foraging onset to twilight and measuring light intensity to trigger activity is to optimize the trade-off between predation risk and ease of navigation.
许多动物在黄昏时分变得活跃，这是一个狭窄的时间窗口，视觉环境的特性与白天和黑夜有很大的不同。尽管包括哺乳动物、爬行动物、鸟类和昆虫在内的许多动物都在这个特定的时间范围内活跃，但我们不知道是什么提示引发了这种活动。为了确定特定时间窗口的开始，动物可以预测定期事件的时间，或者直接测量环境变量。我们表明，澳大利亚公牛蚁（Myrmecia pyriformis）全年只在傍晚的黄昏时分开始觅食。这种开始既不是在特定的温度下，也不是在相对于日落的特定时间，而是在特定的环境光强度下。当日落时的光强度比正常时亮时，觅食开始的时间会更晚；当日落时的光强度比正常时暗时，觅食开始的时间会更早。通过实验改变环境光强度，我们提供了明确的证据表明，蚂蚁确实在测量光水平，而不是依靠内部节律来开始觅食。我们认为，将觅食开始时间限制在黄昏时分，并测量光强度来触发活动的原因是为了优化捕食风险和导航便利性之间的权衡。
