Month: September 2022

FRAGMENT FROM NATURE continues from last weekend and concludes this weekend on the evolutionary strategy of Wolbachia bacteria to control their host zygote survival by cytoplasmic compatability. This extreme strategy has made them a very successful parasite. View in LinkedIn

RECOMBINATION. “Despite this, clear evidence of recombination has been observed among cif genes from wPip, which infects C. pipiens mosquitoes. wPip strains can carry multiple copies of Type I cif genes, and recombination between closely related paralogs correlates with different CI crossing types.” (CI = cytoplasmic incompatibility). https://lnkd.in/dXjWp9f View in LinkedIn

ROLE OF RECOMBINATION. “Whether recombination itself created these incompatibilities or whether crossing types arose due to sequence divergence following recombination is unknown. We found that recombination is frequent across the cif gene phylogeny, but it almost exclusively occurs between related syntenic cifA–cifB gene pairs within the same Type.” https://lnkd.in/dXjWp9f View in LinkedIn

COEVOLUTION. “As Wolbachia genomes often carry divergent cif homologs, the absence of recombination between these genes is compatible with recombination being constrained by selection. This can be explained by the coevolution of binding affinities between the proteins encoded by cifA and their cognate cifB gene.” https://lnkd.in/dXjWp9f View in LinkedIn

THE CONUNDRUM. “The evolution of sperm modification by Wolbachia poses an evolutionary puzzle—the trait is only expressed in males and yet symbionts in males are not passed on to the next generation. In randomly mating populations, it will be at best selectively neutral.” https://lnkd.in/dXjWp9f View in LinkedIn

FOLLOWING THE BREADCRUMBS. “In the absence of other phenotypic effects on the host, theory predicts that the loss-of-sperm modification will lead to the loss of Wolbachia from the host population. We found that the majority of loss-of-function mutations appears to have occurred recently.” https://lnkd.in/dXjWp9f View in LinkedIn

LOSS OF FUNCTION GENES. “Firstly, these mutations tend to be on terminal branches of the gene tree. Secondly, pseudogenes rarely accumulate many loss-of-function mutations. Although this suggests that cifA and cifB pseudogenes rarely codiverge with the Wolbachia genome for long periods, it is unclear whether this results from the loss of the Wolbachia infection or through the genes being deleted from the genome, for instance, by phage excision.” https://lnkd.in/dXjWp9f View in LinkedIn

POSITIVE SYMBIOSIS. “Since the publication of theoretical studies on CI evolution, it has become increasingly clear that many Wolbachia strains can persist in host populations without inducing any reproductive manipulation by providing fitness benefits.” (CI = cytoplasmic incompatibility). https://lnkd.in/dXjWp9f View in LinkedIn

OPEN ISSUE. “Therefore, it remains to be demonstrated whether the degeneration of cif genes causes the loss of Wolbachia from populations.” https://lnkd.in/dXjWp9f View in LinkedIn

HORIZONTAL TRANSFER. “The frequent loss of cif genes raises a paradox when trying to explain the high prevalence of CI across Wolbachia strains. Hurst and McVean (1996) argued that CI-inducing Wolbachia infections were more likely to transfer horizontally between host species, so symbiont strains that induce CI are more likely to persist over an evolutionary timescale.” (CI = cytoplasmic incompatibility). https://lnkd.in/dXjWp9f View in LinkedIn