Who makes dinner? Role reversal of co-obligate symbionts in Adelgidae (Sternorrhyncha: Aphidoidea)

Due to their nutrient poor food source, most sternorrhynchans rely on obligate symbionts to supplement the essential amino acids (EAAs) missing or scarce in their diet. Within this lineage it is common to find two consistent co-obligate symbionts cooperating to produce the EAAs. Typically, the primary (oldest) symbiont produces the majority while the secondary (younger) symbiont fills in the gaps. Adelgidae follow the pattern of supporting two co-obligate symbionts; however, unlike other sternorrhynchans, adelgids have a different pair of symbionts in each major lineage within the family. This pattern implies periodic turnover in symbiont composition. To determine whether the different symbiont pairs of these insects retain similar nutrient-provisioning profiles to more stable symbiont pairs in other sternorrhynchans, we sequenced genomes from symbionts across the family. Preliminary data indicates that these bacteria indeed cooperate to produce the EAAs. However, they take a different approach to division of labor, with the secondary symbiont producing the bulk of the EAAs while the primary symbiont synthesizes relatively few. This role reversal may be a clue to understanding the losses and gains of symbionts in adelgids.