Hemmi Jan M, Marshall Justin, Pix Waltraud, Vorobyev Misha, Zeil Jochen
ARC Centre of Excellence in Vision Science, Australian National University, Canberra ACT 2601, Australia.
J Exp Biol. 2006 Oct;209(Pt 20):4140-53. doi: 10.1242/jeb.02483.
Colour changes in fiddler crabs have long been noted, but a functional interpretation is still lacking. Here we report that neighbouring populations of Uca vomeris in Australia exhibit different degrees of carapace colours, which range from dull mottled to brilliant blue and white. We determined the spectral characteristics of the mud substratum and of the carapace colours of U. vomeris and found that the mottled colours of crabs are cryptic against this background, while display colours provide strong colour contrast for both birds and crabs, but luminance contrast only for a crab visual system. We tested whether crab populations may become cryptic under the influence of bird predation by counting birds overflying or feeding on differently coloured colonies. Colonies with cryptically coloured crabs indeed experience a much higher level of bird presence, compared to colourful colonies. We show in addition that colourful crab individuals subjected to dummy bird predation do change their body colouration over a matter of days. The crabs thus appear to modify their social signalling system depending on their assessment of predation risk.
招潮蟹的颜色变化早已为人所知，但仍缺乏功能性的解释。在此我们报告，澳大利亚的相邻种群的呕吐招潮蟹呈现出不同程度的背甲颜色，范围从暗淡的斑驳色到明亮的蓝白色。我们测定了泥质基底和呕吐招潮蟹背甲颜色的光谱特征，发现蟹的斑驳颜色在这种背景下具有隐蔽性，而展示颜色对鸟类和蟹来说都提供了强烈的颜色对比，但亮度对比仅对蟹的视觉系统而言。我们通过统计飞越或以不同颜色群体为食的鸟类数量，测试了蟹种群在鸟类捕食影响下是否会变得具有隐蔽性。与颜色鲜艳的群体相比，具有隐蔽颜色的蟹的群体确实有更高水平的鸟类出现。此外，我们还表明，遭受假鸟捕食的颜色鲜艳的蟹个体确实会在几天内改变它们的体色。因此，蟹似乎会根据它们对捕食风险的评估来改变它们的社会信号系统。
