Department of Biological Physics, ELTE Eötvös Loránd University, H-1117 Budapest, Pázmány sétány 1, Hungary.
Institute of Aquatic Ecology, Centre for Ecological Research, H-1113 Budapest, Karolina út 29-31, Hungary.
Int J Parasitol. 2023 Jan;53(1):1-11. doi: 10.1016/j.ijpara.2022.10.001. Epub 2022 Nov 7.
Several hypotheses tried to explain the advantages of zebra stripes. According to the most recent explanation, since the borderlines of sunlit white and black stripes can hamper thermal vessel detection by blood-seeking female horseflies, striped host animals are unattractive to these parasites which prefer hosts with a homogeneous coat, on which the temperature gradients above blood vessels can be detected more easily. This hypothesis has been tested in a field experiment with horseflies walking on a grey barrel with thin black stripes which were slightly warmer than their grey surroundings in sunshine, while in shade both areas had practically the same temperature. To eliminate the multiple (optical and thermal) cues of this test target, we repeated this experiment with improved test surfaces: we attracted horseflies by water- or host-imitating homogeneous black test surfaces, beneath which a heatable wire ran. When heated, this invisible and mechanically impalpable wire imitated thermally the slightly warmer subsurface blood vessels, otherwise it was thermally imperceptible. We measured the times spent by landed and walking horseflies on the test surface parts with and without underlying heated or unheated wire. We found that walking female and male horseflies had no preference for any (wired or wireless) area of the water-imitating horizontal plane test surface on the ground, independent of the temperature (heated or unheated) of the underlying wire. These horseflies looked for water, rather than a host. On the other hand, in the case of host-imitating test surfaces, female horseflies preferred the thin surface regions above the wire only if it was heated and thus warmer than its surroundings. This behaviour can be explained exclusively with the higher temperature of the wire given the lack of other sensorial cues. Our results prove the thermal vessel recognition of female horseflies and support the idea that sunlit zebra stripes impede the thermal detection of a host's vessels by blood-seeking horseflies, the consequence of which is the visual (non-thermal) unattractiveness of zebras to horseflies.
有几种假说试图解释斑马条纹的优势。根据最近的解释，由于阳光照射下白色和黑色条纹的边界线会干扰吸血雌马蝇对热血管的探测，因此带有条纹的宿主动物对这些寄生虫没有吸引力，这些寄生虫更喜欢具有均匀毛色的宿主，因为在这种宿主的毛色上，血管上方的温度梯度更容易被探测到。这个假说在一个野外实验中得到了检验，实验中让马蝇在一个灰色的桶上行走，桶上有细细的黑色条纹，在阳光照射下，这些条纹比周围的灰色区域稍微暖和一些，而在阴影中，两个区域的温度实际上是相同的。为了消除这个测试目标的多重（光学和热学）线索，我们用改进后的测试表面重复了这个实验：我们用类似水或宿主的均匀黑色测试表面吸引马蝇，在这些表面下有一根可加热的电线。当电线被加热时，这条无形且机械上不可感知的电线会模拟稍暖和的皮下血管，否则它在热学上是不可感知的。我们测量了落在有和没有下面加热或未加热电线的测试表面部分的着陆和行走马蝇的停留时间。我们发现，行走的雌马蝇和雄马蝇在地面上的水平水模拟测试表面的任何（有线或无线）区域都没有偏好，而不管下面电线的温度（加热或未加热）如何。这些马蝇在寻找水，而不是宿主。另一方面，在宿主模拟测试表面的情况下，只有当电线被加热且比周围环境更暖和时，雌马蝇才会更喜欢电线上方的薄表面区域。这种行为只能用电线的较高温度来解释，因为缺乏其他感觉线索。我们的结果证明了雌马蝇对血管的热识别，并支持了这样一种观点，即阳光照射下的斑马条纹会干扰吸血马蝇对宿主血管的热探测，其结果是斑马对马蝇的视觉（非热）吸引力降低。
