Encarsia gennaroi and E. suzannae (Hymenoptera: Aphelinidae) are sibling species of parasitoids of whiteflies that vary in reproductive mode and infection by endosymbiotic bacteria. The intracellular bacterium Cardinium causes cytoplasmic incompatibility (CI) in E. suzannae, while E. gennaroi is uninfected. The two species are morphologically and genetically differentiated, yet they interbreed and produce hybrid offspring. Here we evaluated the role of unidirectional CI and hybrid incompatibilities (HI) in reproductive isolation by both pre-zygotic (mating preferences) and post-zygotic (crossing) experiments. We found significant assortative mating in choice tests, but no behavioural isolation in no-choice tests. In contrast, post-zygotic isolation was nearly complete, with high levels of hybrid inviability due to CI in the E. gennaroi female x E. suzannae male cross, and to HI in the reciprocal direction. Interestingly, when E. suzannae males are cured from Cardinium by antibiotics, most progeny are viable, indicating that HI are asymmetric. Asymmetry in post-zygotic isolation is a common phenomenon known as “Darwin’s corollary”, and is often caused by negative cytonuclear interactions that can result from differences in nucleotide substitution rates of mitochondrial relative to nuclear DNA. mtDNA evolution can in turn be accelerated by symbiont sweeps, for the spread of a CI symbiont is usually associated with hitchhiking of mitochondrial haplotypes. As mtDNA variation is very reduced in E. suzannae, we argue that Cardinium may have contributed to speciation not only directly, by means of unidirectional CI, but also indirectly by accelerating mtDNA evolution, thus promoting cytonuclear interactions. This novel mechanism differs from the only example available of unidirectional CI promoting speciation, that is, the pair Drosophila recens (infected with CI-Wolbachia) – Drosophila subquinaria (uninfected), where the complementary isolating mechanisms causing speciation are CI and asymmetric mating preferences.
Cardinium contribute to speciation in Encarsia wasps: a novel mechanism based on cytoplasmic incompatibility and Darwin’s corollary / Gebiola, Marco; Hammerstein, Peter; Kelly, Suzanne E.; Giorgini, Massimo; Hunter, Martha S.. - (2016). (Intervento presentato al convegno 9th International Wolbachia meeting tenutosi a Lamington National Park, Australia nel 28 giugno 2016).
Cardinium contribute to speciation in Encarsia wasps: a novel mechanism based on cytoplasmic incompatibility and Darwin’s corollary
Marco Gebiola;Massimo Giorgini;
2016
Abstract
Encarsia gennaroi and E. suzannae (Hymenoptera: Aphelinidae) are sibling species of parasitoids of whiteflies that vary in reproductive mode and infection by endosymbiotic bacteria. The intracellular bacterium Cardinium causes cytoplasmic incompatibility (CI) in E. suzannae, while E. gennaroi is uninfected. The two species are morphologically and genetically differentiated, yet they interbreed and produce hybrid offspring. Here we evaluated the role of unidirectional CI and hybrid incompatibilities (HI) in reproductive isolation by both pre-zygotic (mating preferences) and post-zygotic (crossing) experiments. We found significant assortative mating in choice tests, but no behavioural isolation in no-choice tests. In contrast, post-zygotic isolation was nearly complete, with high levels of hybrid inviability due to CI in the E. gennaroi female x E. suzannae male cross, and to HI in the reciprocal direction. Interestingly, when E. suzannae males are cured from Cardinium by antibiotics, most progeny are viable, indicating that HI are asymmetric. Asymmetry in post-zygotic isolation is a common phenomenon known as “Darwin’s corollary”, and is often caused by negative cytonuclear interactions that can result from differences in nucleotide substitution rates of mitochondrial relative to nuclear DNA. mtDNA evolution can in turn be accelerated by symbiont sweeps, for the spread of a CI symbiont is usually associated with hitchhiking of mitochondrial haplotypes. As mtDNA variation is very reduced in E. suzannae, we argue that Cardinium may have contributed to speciation not only directly, by means of unidirectional CI, but also indirectly by accelerating mtDNA evolution, thus promoting cytonuclear interactions. This novel mechanism differs from the only example available of unidirectional CI promoting speciation, that is, the pair Drosophila recens (infected with CI-Wolbachia) – Drosophila subquinaria (uninfected), where the complementary isolating mechanisms causing speciation are CI and asymmetric mating preferences.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
