Arthropods commonly carry maternally-inherited intracellular bacterial symbionts that may profoundly influence host biology and evolution. The intracellular symbiont Rickettsia sp. nr. bellii swept rapidly into populations of the sweetpotato whitefly Bemisia tabaci in the southwestern USA. Previous laboratory experiments showed female-bias and fitness benefits were associated with Rickettsia infection, potentially explaining the high frequencies of infection observed in field populations, but the effects varied with whitefly genetic line. Here we explored whether host extranuclear or nuclear genes influenced the variation in the Rickettsia-host phenotype in two genetic lines of the whitefly host, each with Rickettsia-infected and uninfected sublines. Introgression between the Rickettsia-infected subline of one genetic line and the Rickettsia-uninfected subline of the other was used to create two new sublines, each with the maternally-inherited extranuclear genetic lineages of one line (Rickettsia, two other symbionts and the mitochondria) and the nuclear genotype of the other. Performance assays comparing the original and new lines showed that in addition to Rickettsia, the interaction of Rickettsia infection with host nuclear genotype influenced development time and the sex ratio of the progeny, while the extranuclear genotype did not. Host nuclear genotype, but not extranuclear genotype, also influenced the titer of Rickettsia. Our results support the hypothesis that differences in host nuclear genotype alone may explain considerable within-population variation in host-symbiont phenotype, and may contribute to the observed variation in Rickettsia-whitefly interactions worldwide.

Hunter_JEB_2016_Hostgenotype_TotalprogenyThese are the data used for the total progeny analysis presented in figure 2.Hunter_JEB_2016_Hostgenotype_Sex_ratiosThese are the sex ratio data used for figure 4. Refer to the manuscript text for descriptions of treatments etc.Hunter_JEB_2016_Hostgenotype_Develop_timeThese are the data used for the development time analysis (Fig. 3 a and b).Hunter_JEB_2016_Hostgenotype_RickettsiatiterThese are the estimates of Rickettsia titer relative to actin titer among the 4 Rickettsia-infected treatments. (Fig. 5)