Department of Evolution, Ecology, and Behavior, School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
J Exp Biol. 2021 Apr 15;224(8). doi: 10.1242/jeb.238832. Epub 2021 Apr 16.
Some host species of avian obligate brood parasites reject parasitic eggs from their nest whereas others accept them, even though they recognize them as foreign. One hypothesis to explain this seemingly maladaptive behavior is that acceptors are unable to pierce and remove the parasitic eggshell. Previous studies reporting on the force and energy required to break brood parasites' eggshells were typically static tests performed against hard substrate surfaces. Here, we considered host nest as a substrate to simulate this potentially critical aspect of the natural context for egg puncture while testing the energy required to break avian eggshells. Specifically, as a proof of concept, we punctured domestic chicken eggs under a series of conditions: varying tool shape (sharp versus blunt), tool dynamics (static versus dynamic) and the presence of natural bird nests (of three host species). The results show a complex set of statistically significant interactions between tool shapes, puncture dynamics and nest substrates. Specifically, the energy required to break eggs was greater for the static tests than for the dynamic tests, but only when using a nest substrate and a blunt tool. In turn, in the static tests, the addition of a nest significantly increased energy requirements for both tool types, whereas during dynamic tests, the increase in energy associated with the nest presence was significant only when using the sharp tool. Characterizing the process of eggshell puncture in increasingly naturalistic contexts will help in understanding whether and how hosts of brood parasites evolve to reject foreign eggs.
一些禽类专性巢寄生宿主物种会拒绝来自其巢的寄生卵，而另一些则接受它们，尽管它们能识别出这些卵是外来的。有一种假说解释了这种看似适应不良的行为，即接受者无法刺穿并移除寄生卵壳。以前关于打破寄生卵壳所需的力和能量的研究报告通常是针对硬基质表面进行的静态测试。在这里，我们将宿主巢穴视为一种基质，以模拟卵刺穿过程中自然环境的潜在关键方面，同时测试打破禽卵所需的能量。具体来说，作为一个概念验证，我们在一系列条件下对家鸡蛋进行了穿刺：工具形状（锋利与钝）、工具动态（静态与动态）和天然鸟巢（三种宿主物种）的存在。结果显示了工具形状、穿刺动态和巢穴基质之间存在复杂的统计显著相互作用。具体来说，与动态测试相比，静态测试中打破鸡蛋所需的能量更大，但仅当使用鸟巢基质和钝工具时才如此。反过来，在静态测试中，两种工具类型的能量需求都因添加巢穴而显著增加，而在动态测试中，只有使用锋利工具时，与巢穴存在相关的能量增加才具有显著意义。在越来越自然的环境中描述卵壳穿刺过程将有助于理解巢寄生宿主是否以及如何进化以拒绝外来卵。
