Functional adaptation of Wolbachia to novel hosts

Wolbachia is a maternally inherited symbiont of insects, well known for altering host reproduction to select for female offspring. In the fields of vector- and biological control, there is great interest in introducing Wolbachia with particularly favorable phenotypes into a variety of target hosts. Unfortunately, little is known about how Wolbachia adapts to a new host, and experimental attempts at horizontal transfer have proven largely unsuccessful, resulting in the loss of bacterial titers or failure to modify host reproduction. Failure is likely heavily influenced by a lack of co-evolution between host and symbiont. To explore Wolbachia evolution we are using parasitoid wasps of the genus Trichogramma as hosts. We took female wasps from a population infected with Wolbachia for over 50 years and mated them with conspecific males from an uninfected population. Through fertilization, and in the following generation, parthenogenesis, we created a series of genetically unique, recombinant, infected granddaughters. Ten granddaughters were used to initiate experimental, homozygous, iso-female lines. At generations 3 and 29, the Wolbachia performance of each line, relative to the original infected population, was determined by measuring Wolbachia titer and host sex ratio. Initially, recombinant wasps produced fewer female offspring, and a significant proportion of intersexes, a result of incomplete reproductive modification by Wolbachia. Over time, Wolbachia adapted to these new host backgrounds, increasing its fitness through the improved induction of parthenogenesis. This system will be used as a model for studying the evolution of symbiosis, hopefully identifying key genomic changes occurring during this process.