Poláček Miroslav, Bartíková Michaela, Hoi Herbert
Slovak Academy of Sciences, Institute of Zoology, Bratislava, Slovakia.
Konrad Lorenz Institute of Ethology, Department of Integrative Biology and Evolution, University of Veterinary Medicine, Vienna, Austria.
PeerJ. 2017 Aug 31;5:e3707. doi: 10.7717/peerj.3707. eCollection 2017.
One possibility suggested regarding female post-mating strategies is differential allocation into offspring investment. Female birds produce not only the largest, but also most colourful eggs of all oviparous taxa. Larger eggs provide space for bigger embryos, or more nutrition for their development, but the question why eggs are more colourful and why there is variation in eggshell colouration remains. In this context, the focus of interest has been to explain inter-clutch variation but in many bird species, eggshell colouration also varies within a clutch. Surprisingly, less attention has been paid to this phenomenon. Therefore, we propose the "female egg recognition" hypothesis, suggesting that mothers use colour characteristics to interpret egg attributes and allocate further investment into each egg accordingly. To evaluate the feasibility of the hypothesis, we tested several underlying predictions and examined their suitability using a dataset from our tree sparrow () study. We predict (i) substantial within-clutch variation in eggshell colouration which, (ii) should be related to laying sequence, (iii) reflect egg quality and, (iv) should stimulate a female response.
Eggshell coloration data were obtained via digital photography under standardized conditions, taken after clutch completion. Lightness (L*), representing the achromatic properties of an egg has been chosen as the most important predictor in dark cavities and was related to egg quality and position in the nest.
In our tree sparrows, first and mainly last eggs were less pigmented, providing information about laying order. Egg volume, which predicts chick quality, positively correlates with eggshell coloration. Finally, we could show that female tree sparrows placed darker, but not bigger, eggs into more central incubation positions.
All basic prerequisites for the "female egg recognition" hypothesis are fulfilled. In this context practicability and feasibility of the hypothesis and alternative explanations are discussed. However future work is necessary to determine a direct effect on offspring condition.
关于雌性鸟类交配后的策略，一种观点认为是在后代投资上的差异分配。在所有卵生类群中，雌性鸟类所产的卵不仅最大，而且颜色最为鲜艳。更大的卵为更大的胚胎提供了空间，或者为其发育提供了更多营养，但卵为何颜色更鲜艳以及蛋壳颜色为何存在差异，这一问题仍然存在。在此背景下，人们关注的焦点一直是解释窝卵之间的差异，但在许多鸟类中，同一窝卵的蛋壳颜色也存在差异。令人惊讶的是，这一现象较少受到关注。因此，我们提出“雌性卵识别”假说，即母亲利用颜色特征来解读卵的属性，并据此对每个卵进行进一步投资。为了评估该假说的可行性，我们测试了几个潜在的预测，并使用我们对树麻雀（）研究的数据来检验它们的适用性。我们预测：（i）同一窝卵的蛋壳颜色存在显著差异，（ii）这种差异应与产卵顺序有关，（iii）反映卵的质量，并且（iv）应能激发雌性的反应。
蛋壳颜色数据是在窝卵完成后，通过在标准化条件下进行数码摄影获得的。明度（L*）代表卵的非彩色属性，在黑暗的巢穴中被选为最重要的预测指标，它与卵的质量和在巢中的位置有关。
在我们研究中的树麻雀里，第一枚卵，主要是最后一枚卵，色素沉着较少，这提供了有关产卵顺序的信息。预测雏鸟质量的卵体积与蛋壳颜色呈正相关。最后，我们发现雌性树麻雀会将颜色较深但并非更大的卵放置在更靠近巢中央的孵化位置。
“雌性卵识别”假说的所有基本前提都得到了满足。在此背景下，讨论了该假说的实用性和可行性以及其他解释。然而，未来还需要开展工作来确定对后代状况的直接影响。
