Supplementary material from "Heavy Metal Predators: Diverse Elemental Enrichment Across the Weapons of Scorpions"

Scorpions diverged from their closest relatives around the Ordovician Period, and since then, environmental interactions have shaped the evolution of the material properties of their exoskeletons. Hardening of this structure via the incorporation of transition metals has enabled biomechanical advancements in weapon development. Scorpion weapons consist of the stinger (telson) and claws (chelae), and contain diverse metals such as zinc, manganese, and iron, though little is known about comparative patterns of incorporation across the wider clade. In this study, we harness X-ray driven microanalytical techniques to characterise the different elemental enrichment patterns within the weapons of eighteen species from a range of scorpion families. We hypothesised that enrichment by metal would be inversely correlated between weapons, tied to their functional roles and morphological diversity. We identified cryptic enrichment strategies, including weapon selective elemental replacement and an inverse enrichment of Zn between weapons. Chela enrichment by Zn was found to positively correlate with a morphological indicator of chelae pinch strength, wherein Zn enrichment was greater in specimens with reduced crushing power. This study supports a growing body of research into the evolution of metal enrichment amongst invertebrates and provides greater understanding of the material properties of the exoskeleton within weapon development.