Fourth International Bemisia Workshop International Whitefly Genomics Workshop
Cytoplasmic incompatibility phenotypes from reciprocal crosses of three biotypes of the Bemisia Tabaci complex are associated with Cardinium (Bacteroidetes) and Wolbachia, and apparent partial rescue of CI Yyelding sex bias
1 Department of Plant Sciences and
2 Department of Entomology, The University of Arizona, Tucson, AZ, USA. Correspondence: jbrown@ag.arizona.edu
We investigated the effects of two divergent, prospective cytoplasmic incompatibility (CI)-causing bacteria on gene flow among biotypes of the taxonomically confounded B. tabaci species group. We report the detection and identification by PCR, cloning, sequencing, and phylogenetic analysis of several endosymbiotic bacteria associated with three biotypes of B. tabaci: the polyphagous New World (NW) Arizona A (AzA), the polyphagous Old World (OW) Arizona B (AzB), and the monophagous NW Jatropha (Jat). Based on PCR amplification of the 16S rRNA, a Cardinium spp. (phylum Bacteriodetes) was associated with the AzA and three other A biotype isolates (RivA, CulA, SalA lab colonies), whereas a Wolbachia spp. (Rickettsia; Proteobacteria) was consistently associated with the Jat biotype. A Chlamydia spp. and Rickettsia bellii also were detected in certain but not all B. tabaci isolates, and are presumably secondary endosymbionts more likely associated with general fitness traits. To date neither has not been implicated in cytoplasmic incompatibility in the hemiptera, however such involvement cannot be ruled out. In a previous study, we reported partial and complete reproductive compatibility between three biotypes (AzA, B, Jat), respectively. In this follow-up study we have confirmed the association of two putative CI-bacteria, Wolbachia and Cardinium, with the Jat and A biotypes of B. tabaci, corroborating the CI-like phenotype observed in crosses between the AzA, Az B, and Jat biotypes, expressed as unidirectional incompatibility (AzA x B; Jat x B), and surprisingly, bidirectional compatibility (Az A x Jat). Identical results were obtained for A x B crosses when Riverside A was substituted for the AzA. Bidirectional female offspring produced from Jat x AzA crosses may be indicative of a rescue phenomenon by these divergent CI-causing bacteria. Further, results of crosses employing Wolbachia-Jat♀x Cardinium-AzA♂, indicated that fewer female offspring were produced in that cross, compared to AzA-Cardinium♀x Jat-Wolbachia♂. This observation suggested that Cardinium might more ably abate Wolbachia induced female offspring mortality than Wolbachia is able to counter Cardinium-induced CI. These results when taken together provide evidence that two phylogenetically divergent CI-bacteria might contribute operatively to B. tabaci reproductive incompatibility, expressed differentially, and not universally as barriers to gene flow. And, in at least one case this interaction also is seen as sex bias. Herein we report a novel, rescue-like phenomenon between two phylogenetically divergent bacteria, which could possibly have evolved similar CI-inducing mechanisms, making possible the rescue of CI effects induced by the other. Due to the inability to rid B. tabaci of these suspect CI-bacteria using various treatments effective for other insects, an introgression experiment is in progress to explore CI-causality over CI-association.