From hybrid to hemiclone: the genetic basis and evolutionary significance of clonal reproduction in Pelophylax esculentus

Meiosis typically generates genetic diversity but can be disrupted, leading to alternative reproductive modes such as hybridogenesis. Interspecific hybridization is often associated with such transitions, yet the underlying mechanisms in vertebrate systems remain poorly understood. We investigated this process by crossing Pelophylax ridibundus and P. lessonae, producing hybrid P. esculentus. Using low-coverage genome sequencing and repeat analysis, we developed a novel minisatellite marker (PlesSat01-48) specific to the P. lessonae genome and combined it with the previously described RrS1 marker of P. ridibundus to cytogenetically track both parental genomes. Fluorescent in situ hybridization revealed that newly formed P. esculentus hybrids undergo rapid modifications of gametogenesis. These include chromosome misalignment, lagging chromosomes, and micronucleus formation leading to premeiotic genome elimination of the P. lessonae genome, while the remaining genome is clonally propagated. This process establishes hemiclonal reproduction via hybridogenesis. Our findings support the recurrent origin of P. esculentus and provide direct cytogenetic insight into the evolution of hybridogenetic reproduction in water frogs.