Abstract
The bacterial endosymbiont Wolbachia has been used to control insect pests owing to its ability to manipulate their life history and suppress infectious diseases. Therefore, knowledge on Wolbachia dynamics in natural populations is fundamental. The European cherry fruit fly, Rhagoletis cerasi, is infected with the Wolbachia strain wCer2, mainly present in southern and central European populations, and is currently spreading into wCer2-uninfected populations driven by high unidirectional cytoplasmic incompatibility. Here, we describe the distribution of wCer2 along two transition zones where the infection is spreading into wCer2-uninfected R. cerasi populations. Fine-scale sampling of 19 populations in the Czech Republic showed a smooth decrease of wCer2 frequency from south to north within a distance of less than 20 km. Sampling of 12 Hungarian populations, however, showed a sharp decline of wCer2 infection frequency within a few kilometres. We fitted a standard wave equation to our empirical data and estimated a Wolbachia wave speed of 1.9 km yr−1 in the Czech Republic and 1.0 km yr−1 in Hungary. Considering the univoltine life cycle and limited dispersal ability of R. cerasi, our study highlights a rapid Wolbachia spread in natural host populations.
Highlights
Wolbachia is an endosymbiotic bacterium that is present in a wide range of arthropod and nematode species and can alter the reproduction of its host [1]
The most efficient way is the induction of cytoplasmic incompatibility (CI) which results in embryonic mortality when the sperm of an infected male fertilizes the egg of a female that is not infected or is infected with a different Wolbachia strain [2]
The classical textbook examples of Wolbachia spread in nature are the invasion of wRi in D. simulans populations in California [3] and Australia [8], and the release of artificially Wolbachia-infected Ae. aegypti mosquitos in Australia [10,17]
Summary
Wolbachia is an endosymbiotic bacterium that is present in a wide range of arthropod and nematode species and can alter the reproduction of its host [1]. The European cherry fruit fly, Rhagoletis cerasi, is an important agricultural pest of cherries that is distributed throughout Europe [11] This tephritid is infected with at least five different Wolbachia strains [12,13]. All populations share one common strain, wCer, whereas a second strain, wCer, is mainly present in southern and central European populations [12] This strain causes a high degree of CI between wCer2-infected males and wCer2-uninfected females, with egg mortality rates of up to 98% [14], and is currently spreading in central Europe [15]. Using the standard wave model, we estimated the adult fly dispersal potential and the Wolbachia wave width and speed in the Czech Republic and in Hungary (see details in electronic supplementary material, S2)
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