Reproduction and maintenance of all-female triploid hybrids in unique hemiclonal population systems of water frogs, Pelophylax esculentus complex, from eastern Ukraine

Hybridisation impairs fertility in offspring, usually through disrupted gametogenesis. Some hybrids benefit from polyploidisation, while others adopt a clonal strategy. Hemiclonality was described for water frog hybrids from the Pelophylax esculentus complex, including parental P. ridibundus (genotype RR), P. lessonae (LL), and their hybrids, P. esculentus (diploid LR or triploid LLR or LRR), which can transmit one parental genome clonally, eliminating the other. Hybrids coexist with one or both parental species within population systems of various dynamics. Our investigation focuses on clonal diversity and reproductive mechanisms in two unique all-female hybrid population systems in eastern Ukraine. These consist exclusively of triploid hybrid females with the LLR genotype and bisexual P. ridibundus, a combination not observed elsewhere in Europe. Microsatellite analysis showed that L-genomes were less diverse and more clonal, while R-genomes were more diverse, aligning with the presence of parental P. ridibundus but only clonal transmission of L-genomes. Crosses of LLR-females with P. ridibundus males revealed only LR and LLR offspring. Presumably, LLR-females transmit gametes with L-genomes. Selective mortality was observed for LR-hybrids of both sexes and LLR-males during tadpole development, but not LLR-females. Therefore, this selective mortality likely stabilises such population systems and shifts the sex ratio towards LLR-females.