Evolutionary rates are correlated betweenBuchneraendosymbionts and mitochondrial genomes of their aphid hosts

The evolution of bacterial endosymbiont genomes is strongly influenced by host-driven selection. Factors affecting host genome evolution will potentially affect endosymbiont genomes in similar ways. One potential outcome is correlations in molecular rates between the genomes of the symbiotic partners. Recently, we presented the first evidence of such a correlation between the mitochondrial genomes of cockroaches and the genome of their endosymbiont ( Blattabacterium cuenoti ). Here we investigate whether similar patterns are found in additional host-symbiont partners. We use partial genome data from multiple strains of bacterial endosymbionts, B. aphidicola and Sulcia mulleri , and the mitochondrial genomes of their sap-feeding insect hosts. Both endosymbionts show phylogenetic congruence with the mitochondria of their hosts, a result that is expected due to their identical mode of inheritance. We compared root-to-tip distances and branch lengths of phylogenetically independent species pairs. Both analyses show a highly significant correlation of molecular rates between genomes of Buchnera and mitochondrial genomes of their hosts. A similar correlation was detected between Sulcia and their hosts, but was not statistically significant. Our results indicate that evolutionary rate correlations between hosts and long-term symbionts may be a widespread phenomenon.