Stable coexistence of incompatible Wolbachia along a narrow contact zone in mosquito field populations CE ´ LESTINE M. ATYAME,* †‡ PIERRICK LABBE ´ ,* ‡ FRANC ß OIS ROUSSET,* ‡ MARWA BEJI, § PATRICK MAKOUNDOU,* ‡ OLIVIER DURON,* ‡ 1 EMILIE DUMAS,* ‡ NICOLE PASTEUR,* ‡ ALI BOUATTOUR, § PHILIPPE FORT ‡ ¶ and MYLE ` NE WEILL* ‡ *CNRS, ISEM—UMR 5554, Montpellier, France, †University La Re ´union/CRVOI, Ste Clotilde, Re ´union Island, France, ‡University Montpellier 2, Montpellier, France, §Institut Pasteur Tunis, Laboratory of Epidemiology and Veterinary Microbiology/University Tunis El Manar, Tunis, Tunisia, ¶CNRS, CRBM—UMR 5237, Montpellier, France Abstract In arthropods, the intracellular bacteria Wolbachia often induce cytoplasmic incompati- bility (CI) between sperm and egg, which causes conditional embryonic death and pro- motes the spatial spread of Wolbachia infections into host populations. The ability of Wolbachia to spread in natural populations through CI has attracted attention for using these bacteria in vector-borne disease control. The dynamics of incompatible Wolbachia infections have been deeply investigated theoretically, whereas in natural populations, there are only few examples described, especially among incompatible infected hosts. Here, we have surveyed the distribution of two molecular Wolbachia strains (wPip11 and wPip31) infecting the mosquito Culex pipiens in Tunisia. We delineated a clear spatial structure of both infections, with a sharp contact zone sepa- rating their distribution areas. Crossing experiments with isofemale lines from differ- ent localities showed three crossing types: wPip11-infected males always sterilize wPip31-infected females; however, while most wPip31-infected males were compatible with wPip11-infected females, a few completely sterilize them. The wPip11 strain was thus expected to spread, but temporal dynamics over 7 years of monitoring shows the stability of the contact zone. We examined which factors may contribute to the observed stability, both theoretically and empirically. Population cage experiments, field samples and modelling did not support significant impacts of local adaptation or assortative mating on the stability of wPip infection structure. By contrast, low dis- persal probability and metapopulation dynamics in the host Cx. pipiens probably play major roles. This study highlights the need of understanding CI dynamics in natural populations to design effective and sustainable Wolbachia-based control strategies. Keywords: contact zone, Culex pipiens mosquito, cytoplasmic incompatibility, Wolbachia Received 28 July 2014; revision received 2 December 2014; accepted 3 December 2014 Introduction Wolbachia are maternally inherited intracellular a-prote- obacteria that infect many arthropod species (Werren et al. 2008). Wolbachia are the most frequent bacterial endosymbiont described so far in insects, infecting 20–70% of species (Werren et al. 1995; Jeyaprakash & Hoy 2000; Hilgenboecker et al. 2008; Zug & Hammer- stein 2012). This evolutionary success is mainly attrib- uted to the ability of Wolbachia to manipulate the host reproductive system to its own advantage (Werren et al. 2008). The most common manipulation is cytoplasmic incompatibility (CI), which triggers embryonic mortality when infected males mate with uninfected females, whereas the reciprocal cross remains compatible. Thus, infected females have a reproductive advantage in polymorphic populations which allows the spread of Correspondence: Ce ´lestine M. Atyame, Fax: (262) 262 93 88 01; E-mail: celestine.atyame-nten@univ-reunion.fr 1 Current address: MIVEGEC—UMR 5290-224, CNRS-IRD- UM1-UM2, Montpellier, France © 2014 John Wiley & Sons Ltd Molecular Ecology (2014) doi: 10.1111/mec.13035