Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Research, Invalidenstr. 43, 10115 Berlin, Germany
School of Earth Sciences, University of Bristol, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
J Exp Biol. 2021 Mar 4;224(Pt 5):jeb230607. doi: 10.1242/jeb.230607.
Extreme phenotypic polymorphism is an oft-cited example of evolutionary theory in practice. Although these morphological variations are assumed to be adaptive, few studies have biomechanically tested such hypotheses. (the African seedcracker finch) shows an intraspecific polymorphism in beak size and shape that is entirely diet driven and allelically determined. Three distinct morphs feed upon soft sedge seeds during times of abundance, but during lean times switch to specializing on three different species of sedge seeds that differ significantly in hardness. Here, we test the hypothesis that beak morphology is directly related to consuming seeds of different hardness. We used a novel experimental analysis to test how beak morphology affects the efficiency of cracking sedge seeds of variable hardness, observing that neither mandibular ramus width nor crushing surface morphology had significant effects on the ability to crack different seed types. It is likely that feeding performance is correlated with other aspects of beak size and shape, such as beak depth and strength, muscle force or gape. Our results highlight how even seemingly straightforward examples of adaptive selection in nature can be complex in practice.
极端表型多态性是进化理论在实践中经常被引用的一个例子。尽管这些形态上的变化被认为是适应性的，但很少有研究从生物力学的角度来检验这些假说。（非洲种子雀）表现出一种完全由饮食驱动和等位基因决定的喙大小和形状的种内多态性。三种不同的形态在丰富时期以软莎草种子为食，但在贫瘠时期则专门以三种不同的莎草种子为食，这三种莎草种子的硬度差异很大。在这里，我们检验了喙形态与食用不同硬度种子之间存在直接关系的假设。我们使用一种新颖的实验分析方法来测试喙形态如何影响对不同硬度莎草种子的开裂效率，结果表明，无论是下颌支宽度还是压碎表面形态都对不同种子类型的开裂能力没有显著影响。很可能是由于其他方面的喙大小和形状，如喙的深度和强度、肌肉力量或张口度与摄食性能相关。我们的结果强调了即使是在自然界中看似简单的适应性选择的例子，在实践中也可能是复杂的。
