Department of Biological Physics, ELTE Eötvös Loránd University, Pázmány sétány 1, Budapest, 1117, Hungary.
MTA-ELTE Theoretical Physics Research Group, ELTE Eötvös Loránd University, Pázmány sétány 1, Budapest, 1117, Hungary.
Sci Rep. 2022 Aug 4;12(1):10871. doi: 10.1038/s41598-022-14619-7.
Multiple hypotheses have been proposed for possible functions of zebra stripes. The most thoroughly experimentally supported advantage of zebra stripes is their visual unattractiveness to horseflies (tabanids) and tsetse flies. We propose here a plausible hypothesis why biting horseflies avoid host animals with striped pelages: in sunshine the temperature gradients of the skin above the slightly warmer blood vessels are difficult to distinguish from the temperature gradients induced by the hairs at the borderlines of warmer black and cooler white stripes. To test this hypothesis, we performed a field experiment with tabanids walking on a host-imitating grey test target with vessel-mimicking thin black stripes which were slightly warmer than their grey surroundings in sunshine, while under shady conditions both areas had practically the same temperature as demonstrated by thermography. We found that horseflies spend more time walking on thin black stripes than surrounding grey areas as expected by chance, but only when the substrate is sunlit. This is because the black stripes are warmer than the surrounding grey areas in the sun, but not in the shade. This is consistent with the flies' well-documented attraction to warmer temperatures and provides indirect support for the proposed hypothesis. The frequent false vessel locations at the numerous black-white borderlines, the subsequent painful bitings with unsuccessful blood-sucking attempts and the host's fly-repellent reactions enhance considerably the chance that horseflies cannot evade host responses and are swatted by them. To eliminate this risk, a good evolutionary strategy was the avoidance of striped (and spotted) host animals.
已经提出了多种关于斑马条纹可能具有的功能的假设。斑马条纹最受实验支持的优势是它们对马蝇（虻）和采采蝇的视觉不吸引力。我们在这里提出一个合理的假设，即为什么叮咬的马蝇会避开有条纹皮毛的宿主动物：在阳光下，血管上方稍微温暖的皮肤的温度梯度与在温暖的黑色条纹和较冷的白色条纹边界处的毛发引起的温度梯度难以区分。为了验证这一假设，我们在阳光下进行了一项实地实验，让虻在一个模仿宿主的灰色测试目标上行走，该目标上有与血管相似的细黑色条纹，比其周围的灰色环境略温暖，而在阴凉处，两个区域的温度几乎相同，如热成像所示。我们发现，虻在黑色细条纹上行走的时间比周围的灰色区域多，这与预期的机会相符，但前提是基质被阳光照射。这是因为在阳光下，黑色条纹比周围的灰色区域温暖，但在阴凉处则不然。这与苍蝇对较温暖温度的良好记录的吸引力一致，并为所提出的假设提供了间接支持。在许多黑白边界线上经常出现错误的血管位置，随后是疼痛的叮咬和不成功的吸血尝试，以及宿主的驱蝇反应，极大地增加了虻无法逃避宿主反应并被其拍打下来的机会。为了消除这种风险，一个很好的进化策略是避免有条纹（和斑点）的宿主动物。
