First Cophylogenetic Reconstruction of Hemipteran Insect-Phytoplasma Associations Reveals Eco-Evolutionary Dynamics.

Vector-borne plant pathogens exhibit a remarkable capacity to colonize distantly related hosts, reflecting long-term ecological and evolutionary interactions among pathogens, plants, and insect vectors. Phytoplasmas, which are obligate bacterial parasites transmitted by hemipteran insects, represent a model system for investigating how host-pathogen associations diversify across ecological and evolutionary timescales. Despite extensive knowledge of phytoplasma diversity and vector relationships, the historical processes shaping these associations remain poorly understood. Here, we investigated the eco-evolutionary dynamics of global phytoplasma-hemipteran associations using complementary cophylogenetic approaches that integrate phylogenetic relationships, divergence time estimates, and host association data. We tested the hypothesis that community assembly of phytoplasma-vector networks over the last ~300 million years has been driven by multiple processes, including host switching, lineage duplication, and cospeciation, with additional influences from environmental change and historical biogeography. Our analyses revealed limited evidence for cospeciation across the evolution of the associations. Instead, duplication, host switching, and lineage losses were the predominant processes shaping current associations, with more than 90 inferred incongruent links between phytoplasmas and their insect hosts. A significant cophylogenetic signal was detected only between Psyllidae and phytoplasma group 16SrX, suggesting a history of relative ecological stability or specialization following their concurrent emergence in the Late Cretaceous. Reconstruction of the origins of phytoplasma associations with particular families of insect vectors indicates that the common ancestor of modern Cicadellidae may have already acquired an association with phytoplasmas, but that associations with other vector families were acquired more recently. These findings indicate that phytoplasma-vector associations are largely dynamic and shaped by ecological opportunity rather than strict codiversification. Integrating evolutionary history with ecological interactions provides a framework to better understand the emergence, persistence, and potential future spread of vector-borne plant diseases.