Diversity and development of domatia: Symbiotic plant structures to host mutualistic ants or mites

Across the tree of life, specialized structures that offer nesting sites to ants or mites – known as domatia – have evolved independently hundreds of times, facilitating ecologically important defence and/or nutritional mutualisms. Domatia show remarkable diversity in morphology and developmental origin. Here we review the morpho-anatomical diversity of domatia, aiming to unveil the primary mechanisms governing their development. We propose hypotheses to explain the formation of these structures, based on anatomical studies of domatia and developmental genetic analyses in model species. While genes involved in domatium formation are so far unknown, domatia appear to originate via spatiotemporal shifts in the expression of common developmental genetic pathways. Our review paves the way to the genetic dissection of domatium development.