In several groups of insects, body structures related to feeding and oviposition are known to have a hardened cuticle by incorporation of transition metals. However, a functional link between metal enrichment and ecological pressures (i.e., adaptation) has been only rarely shown, opening the possibility that in some lineages, the evolutionary history may account for most of the observed variation (i.e., phylogenetic constraint). Here, we addressed this question in the hyper-diverse Hymenoptera (bees, wasps, ants, and sawflies), in which Zn and/or Mn have been found enriching the mandibles of a number of species. Across 87 species spanning most of the extant superfamilies, we found Zn enrichment to be widespread (57 species). Although lacking in the most primitive “Symphyta”, our ancestral state reconstruction was not conclusive in determining whether Zn enrichment was a derived state for the complete order, but it was clearly the ancestral state for the Apocrita, where it was lost in few lineages, notably in Aculeata (where it was then reacquired at least three times). Mn, on the other hand, occurred very rarely in mandibles (10 species). Our comparative analysis revealed a strong phylogenetic effect explaining most Zn % and Mn % variation in mandibles. Additionally, species with herbivorous larvae were less prone to have Zn (but not Mn) than those with carnivorous larvae, although a causal effect of diet on this trait was unlikely. Furthermore, species emerging from concealed vs. unconcealed development sites have similar likelihood to have metal-enriched mandibles. Evolutionary history seems to constrain metal enrichment in hymenopteran mandibles, yet the few observed losses and regains of this trait during evolution claim for deeper investigations on the role of alternative, here untested, ecological pressures.

中文翻译：

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对高度多样化膜翅目（昆虫纲）下颌骨中过渡金属掺入的强系统发育约束

在几组昆虫中，已知与进食和产卵有关的身体结构通过掺入过渡金属而具有硬化的角质层。然而，金属富集和生态压力（即适应）之间的功能联系很少被显示，这开启了在某些谱系中进化历史可能解释了大部分观察到的变异（即系统发育约束）的可能性。在这里，我们在高度多样化的膜翅目（蜜蜂、黄蜂、蚂蚁和锯蝇）中解决了这个问题，其中发现锌和/或锰丰富了许多物种的下颌骨。在跨越大多数现存超科的 87 个物种中，我们发现锌富集很普遍（57 个物种）。虽然缺少最原始的“Symphyta”，我们的祖先状态重建在确定 Zn 富集是否是完整秩序的派生状态方面并不是决定性的，但它显然是 Apocrita 的祖先状态，它在少数谱系中丢失，特别是在 Aculeata（然后在那里重新获得）至少三遍）。另一方面，Mn 很少出现在下颌骨（10 种）中。我们的比较分析揭示了强烈的系统发育效应，解释了下颌骨中大多数 Zn % 和 Mn % 的变化。此外，具有食草幼虫的物种比具有食肉幼虫的物种更不容易含有 Zn（但不是 Mn），尽管饮食对这种性状的因果影响不太可能。此外，从隐蔽和未隐蔽的开发地点出现的物种具有富含金属的下颌骨的可能性相似。