Dynamics of an Ongoing Wolbachia Spread in the European Cherry Fruit Fly, Rhagoletis cerasi (Diptera: Tephritidae)

Abstract

Numerous terrestrial arthropods are infected with the alphaproteobacterium Wolbachia. This endosymbiont is usually transmitted vertically from infected females to their offspring and can alter the reproduction of hosts through various manipulations, like cytoplasmic incompatibility (CI), enhancing its spread in new host populations. Studies on the spatial and temporal dynamics of Wolbachia under natural conditions are scarce. Here, we analyzed Wolbachia infection frequencies in populations of the European cherry fruit fly, Rhagoletis cerasi (L.), in central Germany-an area of an ongoing spread of the CI-inducing strain wCer2. In total, 295 individuals from 19 populations were PCR-screened for the presence of wCer2 and their mitochondrial haplotype. Results were compared with historic data to understand the infection dynamics of the ongoing wCer2 invasion. An overall wCer2 infection frequency of about 30% was found, ranging from 0% to 100% per population. In contrast to an expected smooth transition from wCer2-infected to completely wCer2-uninfected populations, a relatively scattered infection pattern across geography was observed. Moreover, a strong Wolbachia-haplotype association was detected, with only a few rare misassociations. Our results show a complex dynamic of an ongoing Wolbachia spread in natural field populations of R. cerasi.

Keywords: agricultural pest; bacterial spread; cytoplasmic incompatibility; endosymbiont; horizontal transfer; maternal transmission; reproductive manipulation.

Figure 1

Geographic distribution of Wolbachia of R. cerasi: (a) Schematic overview of Wolbachia infections across Germany. Distribution of wCer2-uninfected (grey dots), wCer2-infected (red dots), and transitional populations with wCer2-infected and wCer2-uninfected flies (orange dots) sampled between 2000–2008, modified from [16]. Black-filled state represents Hesse, the central study site; (b) wCer2 infection frequencies between 2001 and 2014 and (c) in 2016. Grey = proportion of wCer2-uninfected flies, red = proportion of wCer2- infected flies, black numbers represent flies collected from Prunus and red numbers represent flies collected from Lonicera.

Figure 2

(a) Prevalence of haplotypes between 2001 and 2014 and (b) in 2016. White = proportion of individuals associated with HT1, black = proportion of individuals with HT2. Asterisks represent number of wCer2-infected individuals associated with HT1, whereas the pound represents the only individual that was wCer2-uninfected but associated with HT2.