They are ecologically dominant herbivores in the New World tropics 20, 21 and serve important roles in carbon and nitrogen cycling 22. Leaf-cutting ants (genera Acromyrmex and Atta), a phylogenetically derived lineage that arose within the fungus-growing ants around 20 million years ago, harvest fresh vegetation as the substrate on which they grow their fungal mutualists. Fungus farming, which has been described as a major transition in evolution 20, evolved only once in ants around 60 million years ago 20. Here we report the discovery of a dense layer of biogenic high-magnesium calcite in the leaf-cutter ant Acromyrmex echinatior.įungus-growing attine ants (tribe Attini, subtribe Attina) engage in an ancient and obligate mutualism with coevolved fungi (order Agaricales), which they cultivate for food. It is also surprising that despite the near ubiquity of biogenic mineralization across metazoan phyla and the widespread presence of calcium carbonate in the Crustacea, biomineralized calcium carbonate has so far remained unknown in the most diverse group of animals, the insects, which arose from within the Crustacea 19. Given the importance of calcareous anatomical structures across metazoan phyla and given that magnesium significantly strengthens such structures 17, it is surprising that high-magnesium calcite appears to be rare in animals 18. Magnesium-enriched calcite (CaCO 3) has been discovered in the central part of the sea urchin tooth, where the increased hardness imparted by magnesium is thought to aid in the grinding of limestone 14, 15, 16. Calcium carbonate biomineralization is particularly widespread among metazoans 1, 7: the hard parts of corals 8, mollusk shells 9, stomatopod dactyl club 10, and sea urchin spines 11 contain calcium carbonate, as do the light-focusing eye lenses of chitons and brittlestars 12, 13. The minerals involved, as well as the biogenic structures they form, are diverse. The discovery of biogenic high-magnesium calcite in the relatively well-studied leaf-cutting ants suggests that calcareous biominerals enriched in magnesium may be more common in metazoans than previously recognized.īiomineral skeletons first appeared more than 550 million years ago 1, 2, 3, 4, 5, and by the early Cambrian biomineral-based defensive structures had evolved in most extant metazoan phyla, apparently in response to increasing predation pressure 6. Increased survival of ant workers with biomineralized exoskeletons during aggressive encounters with other ants and reduced infection by entomopathogenic fungi demonstrate the protective role of the biomineral layer. In situ nanoindentation demonstrates that the biomineral layer significantly hardens the exoskeleton. Live-rearing and in vitro synthesis experiments indicate that the biomineral layer accumulates rapidly as ant workers mature, that the layer is continuously distributed, covering nearly the entire integument, and that the ant epicuticle catalyzes biomineral nucleation and growth.
Here, we report the discovery of high-magnesium calcite armor overlaying the exoskeletons of major workers of the leaf-cutter ant Acromyrmex echinatior. University of Strathclyde Virtual Organ Bath 2.Although calcareous anatomical structures have evolved in diverse animal groups, such structures have been unknown in insects.Turning Technologies Turning Point 8.9.4.26.
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