Experimental evidence of Wolbachia introgressive acquisition between terrestrial isopod subspecies

Abstract

Wolbachia are the most widespread endosymbiotic bacteria in animals. In many arthropod host species, they manipulate reproduction via several mechanisms that favour their maternal transmission to offspring. Among them, cytoplasmic incompatibility (CI) promotes the spread of the symbiont by specifically decreasing the fertility of crosses involving infected males and uninfected females, via embryo mortality. These differences in reproductive efficiency may select for the avoidance of incompatible mating, a process called reinforcement, and thus contribute to population divergence. In the terrestrial isopod Porcellio dilatatus, the Wolbachia wPet strain infecting the subspecies P. d. petiti induces unidirectional CI with uninfected individuals of the subspecies P. d. dilatatus. To study the consequences of CI on P. d. dilatatus and P. d. petiti hybridization, mitochondrial haplotypes and Wolbachia infection dynamics, we used population cages seeded with different proportions of the two subspecies in which we monitored these genetic parameters five and seven years after the initial set up. Analysis of microsatellite markers allowed evaluating the degree of hybridization between individuals of the two subspecies. These markers revealed an increase in P. d. dilatatus nuclear genetic signature in all mixed cages, reflecting an asymmetry in hybridization. Hybridization led to the introgressive acquisition of Wolbachia and mitochondrial haplotype from P. d. petiti into nuclear genomes dominated by microsatellite markers of P. d. dilatatus. We discuss these results with regards to Wolbachia effects on their host (CI and putative fitness cost), and to a possible reinforcement that may have led to assortative mating, as possible factors contributing to the observed results.

Wolbachiaas agents of extensive mtDNA lineage sharing between species through multiple infection

“…This sharing of mtDNA genomes in a background of nuclear genomic segregation can be explained by rare hybridisation events followed by indirect selection for a single mtDNA haplotype via Wolbachia (Hurst & Jiggins 2005). Even if F 1 progeny are of low fitness, any successful backcrossing with an uninfected parental species may open the door to the spread of the mtDNA from the infected parental species through symbiont drive and hitchhiking (Bech et al . 2021).…”