Poláček Miroslav, Griggio Matteo, Bartíková Michaela, Hoi Herbert
Institute of Zoology, Slovak Academy of Sciences, Bratislava, Slovakia ; Konrad Lorenz Institute of Ethology, Department of Integrative Biology and Evolution, University of Veterinary Medicine, Vienna, Austria.
PLoS One. 2013 Nov 6;8(11):e78771. doi: 10.1371/journal.pone.0078771. eCollection 2013.
Higher interclutch colour variation can evolve under the pressure of brood parasitism to increase the detection of parasitic eggs. Nest sanitation could be a prerequisite for the evolution of anti-parasite defence in terms of egg ejection. In this respect, we used nest sanitation behaviour as a tool to identify: i) motivation and its underlying function and, ii) which features provoke ejection behaviour. Therefore, we experimentally tested whether size, colour or shape may influence ejection behaviour using artificial flat objects. We found a high interclutch variation in egg colouration and egg size in our tree sparrow (Passer montanus) population. Using colour and size we were in fact able to predict clutch affiliation for each egg. Our experiments further revealed the existence of direct anti-parasite behaviours and birds are able to recognise conspecific eggs, since only experimentally-deposited eggs have been removed. Moreover, experiments with different objects revealed that the motivation of tree sparrows to remove experimental objects from their nests was highest during egg laying for objects of varying size, most likely because of parasitism risk at this breeding stage. In contrary, motivation to remove white objects and objects with edges was higher during incubation stage as behavioural patterns connected to hatching started to emerge. The fact that rejection rate of our flat objects was higher than real egg ejection, suggests that egg ejection in tree sparrows and probably more general in small passerines, to be limited by elevated costs to eject eggs with their beaks. The presence of anti-parasite behaviour supports our suggestion that brood parasitism causes variation in egg features, as we have found that tree sparrows can recognise and reject conspecific eggs in their clutch. In conclusion, in tree sparrows it seems that nest sanitation plays a key role in the evolution of the removal of parasitic eggs.
在巢寄生的压力下，窝卵间更高的颜色差异可能会进化，以增加对寄生卵的检测。就卵的排出而言，巢清洁可能是抗寄生虫防御进化的一个先决条件。在这方面，我们将巢清洁行为作为一种工具来确定：i）动机及其潜在功能，以及ii）哪些特征会引发排出行为。因此，我们使用人工扁平物体通过实验测试了大小、颜色或形状是否会影响排出行为。我们发现我们研究的树麻雀（Passer montanus）种群中窝卵的颜色和大小存在很大的窝间差异。实际上，利用颜色和大小我们能够预测每个卵所属的窝。我们的实验进一步揭示了直接的抗寄生虫行为的存在，并且鸟类能够识别同种卵，因为只有实验放置的卵被移除了。此外，用不同物体进行的实验表明，对于大小不同的物体，树麻雀在产卵期间将实验物体从巢中移除的动机最高，这很可能是因为在这个繁殖阶段存在寄生风险。相反，在孵化阶段，移除白色物体和有边缘物体的动机更高，因为与孵化相关的行为模式开始出现。我们的扁平物体的排斥率高于实际卵的排出率，这一事实表明，树麻雀以及可能更普遍地在小型雀形目中，用喙排出卵会受到成本升高的限制。抗寄生虫行为的存在支持了我们的观点，即巢寄生会导致卵的特征发生变化，因为我们发现树麻雀能够识别并排斥它们窝中的同种卵。总之，在树麻雀中，巢清洁似乎在寄生卵移除的进化中起着关键作用。
