CONVERGENT EVOLUTION BETWEEN ENDOSYMBIOTIC BACTERIA IN FEATHER-FEEDING LICE.

Parasitic feather-feeding lice have diets rich in amino acids but deficient in essential B vitamins. Around 22% of feather-feeding louse species are host to vertically inherited endosymbiotic bacteria belonging to the genus Sodalis. These endosymbiotic Sodalis species have undergone genome degeneration, with genes supporting amino acid synthesis being lost, while genes required for B vitamin synthesis are largely retained. However, several species of lice are host to endosymbionts belonging to proteobacteria genera other than Sodalis. It is unknown if these other endosymbionts have undergone a similar degenerative process. Here, we examine the genome of an endosymbiotic Enterobacter species, identified in a feather-feeding wing louse, asking if this endosymbiont arrived at a similar evolutionary outcome as Sodalis species. We find that this endosymbiotic Enterobacter species possesses a reduced genome and, similar to endosymbiotic Sodalis species, retains the genes required for the synthesis of B vitamins, complementing deficiencies in the louse's diet. This endosymbiont also lacks the ability to synthesize amino acids, which are abundant in the louse's diet. The data suggest that both Sodalis and Enterobacter species have independently converged on a common evolutionary solution in response to symbioses with feather-feeding lice. Thus, bacterial endosymbionts in these two different genera appear to be ecological replicates, providing lice with the same metabolic services in support of parasitism.