Two recent papers have explained how Wolbachia, a bacterium that infects parasitic wasps, ensures that most of the wasps' offspring are parthenogenetically-inclined females. This pleases me very much because it means that maybe the virus on Jeep—the all-female planet of Ammonite1—could do what some of what I said it could do, in terms of enabling human parthenogenesis. I mean, okay, people aren't wasps, and a virus is very different to a bacterium—but, hey, it's now been established that infectious agents can so too encourage parthenogenetic reproduction! There's proof of concept: an all-women planet could sustain itself! So, ha, this is where I dance around singing 🎶 Let a bug bite your eye—it's a parasite, my!—that's me laughing...🎶 That is, laughing at all those who rolled their eyes at Ammonite and, in a get-this-turd-off-my-shoe tone, labelled it 'science fantasy'. Amd, well, yes, okay, it absolutely is fantasy, in the sense that faster-than-light travel is fantasy—which makes 95% of all SF ever written fantasy—but, in other senses, no, it is fucking not. Chortle.
Anyway, I've linked to both papers so that those so inclined can read for themselves. If you don't want to struggle through the whole papers I've pasted in the abstracts below—but life is short, so tl;dr: At some point in the Wolbachia bacterium's distant past, long before it started focusing on parasitic wasps, it infected a different insect and from that beastie borrowed some genes that code for a protein that plays a key role in sex determination. When it infects the wasps that lay eggs in flies, the baby wasps that munch their way out of those flies tend to be overwhelmingly—100 to 1—females that can reproduce parthenogenetically. (I do recommend reading the second paper, if only because they provide a nifty graphical abstract as well as the written one. I wish more papers would do that.)
The first paper is "Identification of Parthenogenesis-Inducing Effector Proteins in Wolbachia" in Genome Biology and Evolution:
Bacteria in the genus Wolbachia have evolved numerous strategies to manipulate arthropod sex, including the conversion of would-be male offspring to asexually reproducing females. This so-called "parthenogenesis induction" phenotype can be found in a number of Wolbachia strains that infect arthropods with haplodiploid sex determination systems, including parasitoid wasps. Despite the discovery of microbe-mediated parthenogenesis more than 30 yr ago, the underlying genetic mechanisms have remained elusive. We used a suite of genomic, computational, and molecular tools to identify and characterize two proteins that are uniquely found in parthenogenesis-inducing Wolbachia and have strong signatures of host-associated bacterial effector proteins. These putative parthenogenesis-inducing proteins have structural homology to eukaryotic protein domains including nucleoporins, the key insect sex determining factor Transformer, and a eukaryotic-like serine–threonine kinase with leucine-rich repeats. Furthermore, these proteins significantly impact eukaryotic cell biology in the model Saccharomyces cerevisiae. We suggest that these proteins are parthenogenesis-inducing factors and our results indicate that this would be made possible by a novel mechanism of bacterial-host interaction
And the second is "Wolbachia symbionts control sex in a parasitoid wasp using a horizontally acquired gene" in Current Biology.
Host reproduction can be manipulated by bacterial symbionts in various ways. Parthenogenesis induction is the most effective type of reproduction manipulation by symbionts for their transmission. Insect sex is determined by regulation of doublesex (dsx) splicing through transformer2 (tra2) and transformer (tra) interaction. Although parthenogenesis induction by symbionts has been studied since the 1970s, its underlying molecular mechanism is unknown. Here we identify a Wolbachia parthenogenesis-induction feminization factor gene (piff) that targets sex-determining genes and causes female-producing parthenogenesis in the haplodiploid parasitoid Encarsia formosa. We found that Wolbachia elimination repressed expression of female-specific dsx and enhanced expression of male-specific dsx, which led to the production of wasp haploid male offspring. Furthermore, we found that E. formosa tra is truncated and non-functional, and Wolbachia has a functional tra homolog, termed piff, with an insect origin. Wolbachia PIFF can colocalize and interact with wasp TRA2. Moreover, Wolbachia piff has coordinated expression with tra2 and dsx of E. formosa. Our results demonstrate the bacterial symbiont Wolbachia has acquired an insect gene to manipulate the host sex determination cascade and induce parthenogenesis in wasps. This study reveals insect-to-bacteria horizontal gene transfer drives the evolution of animal sex determination systems, elucidating a striking mechanism of insect-microbe symbiosis.
Enjoy!
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