Genomics and adaptation in Wolbachia, an obligate reproductive parasite in Trichogramma wasps

Wolbachia is a maternally inherited symbiont, known for altering host reproduction to select for female offspring. There is great interest in introducing Wolbachia with favorable phenotypes into myriad target hosts. Unfortunately, little is known about the genomic changes that occur as Wolbachia adapts to new insects. In Trichogramma wasps, infected populations evolve a dependency on Wolbachia-induced parthenogenesis for the production of female offspring. We can use this relationship to identify genomic signatures of adaptation. We present the genome sequence for the obligate Wolbachia strain wTpre, infecting Trichogramma pretiosum. After comparison to 16 other Wolbachia genomes, we show that wTpre has the most unique genes of any arthropod-infecting Wolbachia. Comparisons of genomic sequence show the majority of these unique genes are genes that have been truncated through nonsense and frameshift mutations, representing 20% of the genome. To test whether or not wTpre has maintained adaptive ability after these extensive gene truncations, we have developed a system to challenge wTpre with novel Trichogramma hosts, and track adaptation. Initially, novel hosts produced fewer females, and a significant proportion of intersexes, resulting from incomplete modification by Wolbachia. Over time, Wolbachia adapted to the new hosts, seen as recovery of parthenogenesis. We will employ genome re-sequencing to identify the mutations responsible for adaptation in wTpre and contrast them with the mutations responsible for the aforementioned gene truncations. Knowledge of the genomic changes that occur during Wolbachia adaptation will be used to inform the transfer of Wolbachia to target insects for vector- and biological control.