Repeated evolution of multi-partner nutrional symbioses in aphids

Summary

Aphids are a large group of animals comprising 4,000+ currently described species. As many animals with nutrient-restricted diet, they depend on obligate symbiotic bacteria for the provision of several essential nutrients. This group of sap-sucking insects depend on the Gammaproteobacteria Buchnera aphidicola for the provision of essential amino acids and some B vitamins. However, recent evidence has demonstrated that in some cases, the typical aphid-Buchnera association has evolved to incorporate yet another obligate symbiotic partner. This new associate complements its Buchnera partner, which has lost the capacity to synthesise compounds essential for its nutritional complementation role. These multi-partner associations occur not only in aphids, but also in several other insect taxa. However, we still know little about the way these associations evolve and which role, if any, they might play in the adaptation of their hosts to new environments. Through the use of high throughput next-generation sequencing, we have explored the existence of such multi-partner associations across aphids, identifying not only the identity but also the potential nutritional roles of the involved parties. We have explored the tissue tropism of selected species and revealed repeated patterns of symbiont localisation across species. In addition, these explorations have revealed that these associations are more common than previously thought, and that they have evolved not once, but multiple times throughout the evolutionary history of aphids. These studies are improving our understanding of these associations and revealing important principles of the origin and diversity of these complex associations.

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