Abstract:
Tetranychus urticae Koch (two-spotted spider mite) is an arachnid species that infests and damages several economically valuable crops. Wolbachia pipientis is an intracellular endosymbiont alpha-proteobacterium. These bacteria cause a unidirectional reproductive mismatch between uninfected females and infected males, though Tetranychus urticae females are capable of producing male offspring via arrhenotokous parthenogenesis (laying haploid male bearing eggs without copulation). Also, another natural unidirectional reproductive barrier was found among two populations of Tetranychus urticae, namely green and red morphs. Wolbachia causes embryonic mortality, while population based incompatibility causes excessive male offspring production. In this study, we investigated whether these population-based reproductive barriers were behavioural (i.e. due to prezygotic reasons) or not, through observations and tests on the frequency, latency and duration of matings. We found no differences before and during copulation, therefore we consider this incompatibility to be postzygotic. As our second experiment, we took records of all the crosses between the populations and compared our results using statistical techniques. We measured the fitness and sex ratio of the offsprings by including Wolbachia infected males in our experimental design. We also tested the cytoplasmic incompatibility that was either Wolbachia-based or population-based, and tested the incompatibility of the individuals that have the natural barrier and were infected by Wolbachia. Our results showed that when the copulation possesses two types of incompatibilities, though a slight effect of embryonic mortality can be observed, population-based excess in male production surpasses Wolbachia-based incompatibility.
