Population Dynamics And Genomics Of Rickettsia Infecting The Whitefly Bemisia tabaci

Abstract

Many insects form symbioses with maternally inherited, intracellular bacteria, which can have major effects on the ecology and evolution of the insect host. Here I investigated the interaction between a global agricultural pest, Bemisia tabaci (the sweetpotato whitefly), and a Rickettsia bacterial symbiont. Rickettsia had previously been tracked sweeping through field populations of B. tabaci in the southwestern USA and had been shown to dramatically increase whitefly fitness under laboratory conditions. In contrast, the Rickettsia present in whiteflies in Israel has few observable fitness effects and is declining in frequency in field populations. I explored the population dynamics of Rickettsia in B. tabaci field populations in the USA and Israel, and assessed the genetic diversity of the Rickettsia in these populations. In laboratory experiments, there was no observable effect of Rickettsia on the heat shock or constant temperature tolerance of USA B. tabaci. Instead, whitefly genetic background appears to influence the effects of Rickettsia. Lastly, analysis of the genome sequence of Rickettsia provided insights into the mechanism of the fitness benefit and evolutionary history of the bacterium. Taken together, these integrated ecological, physiological and genomic studies provide some explanation for the contrasting and wide-ranging phenotypes associated with whitefly Rickettsia, and provide support for the hypothesis that the fitness benefit provided by Rickettsia is context dependent. The Rickettsia symbiosis exhibits geographically distinct population dynamics, is affected by whitefly genotype, and may involve manipulation of host plants and/or defense against pathogens rather than nutritional supplementation. Overall, these results highlight the important role that microbial symbionts may play in the adaptation of invasive species to changing environments.