Global mitochondrial and chloroplast genome diversity in the threatened aquatic carnivorous plant Aldrovanda vesiculosa

The submerged aquatic carnivorous plant Aldrovanda vesiculosa (Droseraceae) is threatened by rapid deterioration of wetlands and oligotrophic lake habitats. Its native distribution spans four continents, but many historic populations are now extinct. Previous genetic studies found distinction between populations from Australia and those from the rest of the world, but due to limited genetic markers, neither detailed phylogenetic relationships nor the migration routes of A. vesiculosa populations were revealed. We used a de novo assembly of the A. vesiculosa mitochondrial genome and a previously published plastid genome as references for mapping short DNA sequence reads from 17 globally distributed populations. Phylogenetic trees were constructed based on detected polymorphisms. Genetic diversity of both the mitochondrial and plastid genome was low (Pi 0.55 x 10(-4) and 0.7 x 10(-4), respectively). Greater polymorphisms were found in the mitochondrial compared with the plastid genome, owing to its larger size (1.27 Mb). Australian populations formed a monophyletic clade in both plastid and mitochondrial trees, while the mitochondrial tree also distinguished populations from southern and northern Europe. Aldrovanda vesiculosa likely migrated to Australia and Africa from a southern European refuge during the last interglacial period similar to 100,000 years ago. When the last glaciation started, some populations could have survived in eastern Europe and moved north, when the continental glacier retreated. Aldrovanda vesiculosa experienced repeated population bottlenecks that reduced its genetic diversity.