DNA sequences and cross-breeding experiments in the hawthorn spider mite Amphitetranychus viennensis reveal high genetic differentiation between Japanese and French populations

Sequence variation of the complete second internal transcribed spacer (ITS2 , 445 bp) of nuclear ribosomal DNA and part of the mitochondrial cytochrome oxidase I gene (COI, 350 bp) was examined in Amphitetranychus viennensis ( Zacher) mites (Acari:Tetranychidae) from four French and four Japanese loca tions. Sequence analysis consistently revealed the separation of the sample s in two major groups: French mites differed from Japanese by 3.8-4.1% of t he nucleotide divergence in COI sequences. These two groups also displayed distinct ITS2 consensus sequences (2.1% nucleotide divergence). A few varia tions, not affecting the diagnostic sites around the consensus sequence, we re revealed among cloned copies of the same individual. Reciprocal crosses and backcrosses between one French and two Japanese populations disclosed s trong reproductive incompatibility. However, fertile hybrid females were ob tained, indicating the conspecificity of the tested mites. Despite the pres ence of Wolbachia in the French strain, but not in the Japanese ones, our c rosses did not display the unidirectional incompatibility typically produce d by this microorganism, but rather a bidirectional - although asymmetrical - incompatibility pattern. The post-zygotic incompatibilities in A. vienne nsis cannot be explained by the presence of Wolbachia but to some extent by mite genome divergence resulting from limited gene exchange between allopa tric populations. Experiments of Wolbachia elimination by antibiotic treatm ent and subsequent crosses with cured strains are still needed to fully und erstand the reproductive incompatibility patterns in this mite species.