Distribution, diversity and density of wolbachial infections in cladocerans and copepods from Thailand

• First systematic surveys of wolbachial infections in cladoceran and copepods from Thailand.
• Wolbachiae detected in 239 of 1885 crustaceans using wsp and groE primers.
• Wolbachial infection in crustaceans was first found in copepod.
• Sex ratio of natural, artificial infected and uninfected copepods showed wolbachiae cause feminization.
• Wolbachial density in 3 naturally-infected copepods was determined using real time PCR based on wsp gene.

Species of the genus Wolbachia comprise a group of Rickettsia-like, maternally-inherited bacteria that cause several reproductive alterations in arthropod hosts. The best known are cytoplasmic incompatibility and feminization. Here, the first systematic surveys of wolbachial infections in cladocerans and copepods from six geographic regions of Thailand, including Northern, Northeastern, Western, Central, Eastern and Southern are reported. Using gene amplification assays with wsp and groE primers, wolbachiae were detected in 239 (4 spp.) of 1885 (57 spp.) copepods and cladocerans from all regions of Thailand surveyed. Screening results obtained with wsp primers or groE primers were similar in all cases. The presence of wolbachiae was only detected in copepods, not in cladocerans. Sex ratio analyses of the progeny of two species of copepods, Mesocyclops aspericornis and Mesocyclops thermocyclopoides, naturally or artificially infected with wolbachiae showed infection causes feminization (female-bias). The relative density if infection in naturally infected populations of three copepod species, M. thermocyclopoides, Heliodiaptomus elegans and Neodiaptomus blachei, were determined using real-time quantitative PCR assay based on the wsp gene. The density of wolbachiae in M. thermocyclopoides was significantly higher than in the other two species. These results suggest that wolbachial infections are distributed throughout Thailand, and that possibly the natural occurrence of these in copepods may be due to their predation on mosquito larvae. This apparent novel biology may have importance as a genetic drive system for control of vector borne diseases in the future.

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