Does a parthenogenesis-inducing Wolbachia induce vestigial cytoplasmic incompatibility?

Abstract

Wolbachia is a maternally inherited bacterium that manipulates the reproduction of its host. Recent studies have shown that male-killing strains can induce cytoplasmic incompatibility (CI) when introgressed into a resistant host. Phylogenetic studies suggest that transitions between CI and other Wolbachia phenotypes have also occurred frequently, raising the possibility that latent CI may be widespread among Wolbachia. Here, we investigate whether a parthenogenesis-inducing Wolbachia strain can also induce CI. Parthenogenetic females of the parasitoid wasp Asobara japonica regularly produce a small number of males that may be either infected or not. Uninfected males were further obtained through removal of the Wolbachia using antibiotics and from a naturally uninfected strain. Uninfected females that had mated with infected males produced a slightly, but significantly more male-biased sex ratio than uninfected females that had mated with uninfected males. This effect was strongest in females that mated with males that had a relatively high Wolbachia titer. Quantitative PCR indicated that infected males did not show higher ratios of nuclear versus mitochondrial DNA content. Wolbachia therefore does not cause diploidization of cells in infected males. While these results are consistent with CI, other alternatives such as production of abnormal sperm by infected males cannot be completely ruled out. Overall, the effect was very small (9%), suggesting that if CI is involved it may have degenerated through the accumulation of mutations.

Occasional males in parthenogenetic populations of Asobara japonica (Hymenoptera: Braconidae): low Wolbachia titer or incomplete coadaptation?

“…There was also very little mitochondrial variation between Amami and the other three thelytokous strains. Moreover, there is no variation between the Wolbachia strains in the five thelytokous A. japonica strains (Kraaijeveld et al, 2011b). This suggests that the Wolbachia infection in A. japonica is relatively young.…”

“…To optimize the qPCRs, we designed new primers for all three genes. Primer sequences for wsp and gatB were based on the sequences for wAjap described in Kraaijeveld et al (2011b), while the primer sequences for ITS2 were based on the sequence for A. japonica described in Kremer et al (2009). The following primers were used: wsp-wAjap-F: 5¢-GAG GCA AAA TTT ACG CCA GA-3¢ and wsp-wAjap-R: 5¢-AAC TAG CCC TGA AAT TGC TGT TA-3¢, producing a 60-bp amplicon; gatB-wAjap-F: 5¢-GAA GCA AAG AGG ATG CAA GC-3¢ and gatB-wAjap-R: 5¢-TCC TGG CTT ACC TCA ACA GG-3¢, producing a 73-bp amplicon; ITS2-Ajap-F: 5¢-GGC AAG CAC AAT CAA GGT CT-3¢ and ITS2-Ajap-R: 5¢-ACA AAA ACA AAT TTT GCG GC-3¢, producing a 93-bp amplicon.…”

“…Fertile crosses between males and females from Iriomote and Amami, and between (natural and cured) males from Kagoshima and females from Amami indicate that individuals from these strains belong to the same species (Murata et al, 2009;Kraaijeveld et al, 2011b). However, Murata et al (2009) also found indications for weak asymmetrical sexual isolation, suggesting that Iriomote and Amami have been geographically isolated for a long time.…”

Genetic conflict, kin and the origins of novel genetic systems

“…The clearest case of genetic conflict leading to the evolution of a novel genetic system is that of feminizing bacteria converting arrhenotoky (figure 1) to thelytokous parthenogenesis (parthenogenetic production of females), which has been documented in several species of wasps and thrips [42][43][44][45]55]. Origins of obligate thelytokous parthenogenesis are probably the most frequently occurring evolutionary transition between genetic systems in nature.…”

Manipulation of Arthropod Sex Determination by Endosymbionts: Diversity and Molecular Mechanisms

“…The most prevalent of these host manipulators are the alpha-proteobacteria Wolbachia pipientis and Rickettsia sp ., the bacteroidetes Cardinium hertigii , the gamma-proteobacterium Arsenophonus, and the mollicutes Spiroplasma poulsonii and S. ixodetis which belong to very distantly related bacterial clades [Duron et al, 2008]. Four broad categories of host reproductive manipulation are distinguished: induction of cytoplasmic incompatibility between egg and sperm, thelytokous parthenogenetic reproduction, killing of male offspring, and feminization of genotypic males [Hurst et al, 2002;Werren et al, 2008;Kraaijeveld et al, 2011]. The molecular genetic details of the mechanisms by which these endosymbionts exert the effects on their hosts are not yet well known.…”