Department of Biological Physics, Physical Institute, Eötvös University, 1117 Budapest, Pázmány sétány 1, Hungary.
Proc Biol Sci. 2010 Jun 7;277(1688):1643-50. doi: 10.1098/rspb.2009.2202. Epub 2010 Feb 3.
White horses frequently suffer from malign skin cancer and visual deficiencies owing to their high sensitivity to the ultraviolet solar radiation. Furthermore, in the wild, white horses suffer a larger predation risk than dark individuals because they can more easily be detected. In spite of their greater vulnerability, white horses have been highly appreciated for centuries owing to their natural rarity. Here, we show that blood-sucking tabanid flies, known to transmit disease agents to mammals, are less attracted to white than dark horses. We also demonstrate that tabanids use reflected polarized light from the coat as a signal to find a host. The attraction of tabanids to mainly black and brown fur coats is explained by positive polarotaxis. As the host's colour determines its attractiveness to tabanids, this parameter has a strong influence on the parasite load of the host. Although we have studied only the tabanid-horse interaction, our results can probably be extrapolated to other host animals of polarotactic tabanids, as the reflection-polarization characteristics of the host's body surface are physically the same, and thus not species-dependent.
白马由于对太阳紫外线辐射的高度敏感，常患有恶性皮肤癌和视力缺陷。此外，在野外，白马比深色个体面临更大的捕食风险，因为它们更容易被发现。尽管它们更容易受到伤害，但由于其自然稀有性，白马几个世纪以来一直受到高度赞赏。在这里，我们表明，吸血虻科蝇类，已知会将疾病媒介传染给哺乳动物，对白马的吸引力低于对黑马的吸引力。我们还证明，虻类利用来自外套的反射偏振光作为寻找宿主的信号。虻类对主要是黑色和棕色皮毛的吸引力可以用正趋光性来解释。由于宿主的颜色决定了它对虻类的吸引力，因此这个参数对宿主的寄生虫负荷有很强的影响。虽然我们只研究了虻类与马的相互作用，但我们的结果可能可以推断到其他趋光性虻类的宿主动物，因为宿主体表的反射偏振特征在物理上是相同的，因此不依赖于物种。
