Proc. R. Soc. B：白马为何能躲过吸血马蝇

nero1981

Proc. R. Soc. B：白马为何能躲过吸血马蝇
白马在野外的生存很艰难。它们被证明患上了一种皮肤癌，并且更容易遭到食肉动物的攻击。但是白马却有一个优势：与棕马或黑马相比，它们对吸血的马蝇的吸引力要低得多。

据美国《科学》杂志在线新闻报道，这一结果与物理学因素有关。研究人员发现，这些马蝇通过偏振光来追踪猎物——马匹光泽的皮毛会反射大量的偏振光。然而白马苍白的皮毛却会反射大量的非偏振光。这些不规则的信号似乎在告诉饥饿的马蝇：“我不好吃。”研究人员在2月3日的英国《皇家学会学报B卷》（Proceedings of the Royal Society B）网络版上报告了这一发现。

nero1981

Proceedings of the Royal Society B February 3, 2010, doi: 10.1098/rspb.2009.2202

An unexpected advantage of whiteness in horses: the most horsefly-proof horse has a depolarizing white coat

Gábor Horváth1,*, Miklós Blahó1, Gy?rgy Kriska2, Ramón Hegedüs3, Balázs Gerics4, Róbert Farkas5 and Susanne ?kesson6

1Environmental Optics Laboratory, Department of Biological Physics, Physical Institute, E?tv?s University, 1117 Budapest, Pázmány sétány 1, Hungary
2Group for Methodology in Biology Teaching, Biological Institute, E?tv?s University, 1117 Budapest, Pázmány sétány 1, Hungary
3Computer Vision and Robotics Group, University of Girona, Campus de Montilivi, Edifici P4, 17071 Girona, Spain
4Faculty of Veterinary Science, Department of Anatomy and Histology, Szent István University, 1078 Budapest, István u. 2, Hungary
5Faculty of Veterinary Science, Department of Parasitology and Zoology, Szent István University, 1078 Budapest, István u. 2, Hungary
6Department of Animal Ecology, Lund University, Ecology Building, 223 62 Lund, Sweden

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.