Evolutionary rates are correlated between cockroach symbiont and mitochondrial genomes

Bacterial endosymbionts evolve under strong host-driven selection. Factors
influencing host evolution might affect symbionts in similar ways,
potentially leading to correlations between the molecular evolutionary
rates of hosts and symbionts. Although there is evidence of rate
correlations between mitochondrial and nuclear genes, similar
investigations of hosts and symbionts are lacking. Here we demonstrate a
correlation in molecular rates between the genomes of an endosymbiont
(Blattabacterium cuenoti) and the mitochondrial genomes of their hosts
(cockroaches). We used partial genome data for multiple strains
of B. cuenotito compare phylogenetic relationships and
evolutionary rates for 55 cockroach/symbiont pairs. The
phylogenies inferred for B. cuenoti and the
mitochondrial genomes of their hosts were largely congruent, as expected
from their identical maternal and cytoplasmic mode of inheritance. We
found a correlation between evolutionary rates of the two genomes, based
on comparisons of root-to-tip distances and on comparisons of branch
lengths of phylogenetically independent species pairs. Our results
underscore the profound effects that long-term symbiosis can have on the
biology of each symbiotic partner.